alloplastic reconstruction of the tmj.pdf

SROMS 1 VOLUME 7.5

Autogenous tissues provide several advan-tages for use in TMJ reconstruction. The ramus-condyle unit can be fashioned to include a carti-laginous articulating surface, and an autogenousgraft will not to elicit a foreign body reaction.In addition, the autogenous materials can forma permanent bony union with the mandibularramus and undergo biologic remodeling inresponse to function. Most importantly, autog-enous TMJ grafts retain their growth potentialwhen used in the skeletally immature patient.Although several long-term follow-ups of au-togenous grafting reported acceptable results,4-8

there are also documented disadvantages asso-ciated with autogenous grafts, including donorsite morbidity and the variability of the bio-logic behavior of the graft (i.e., resorption, anky-losis, or excessive growth). Theoretically, areliable autogenous joint replacement would bethe procedure of choice, both for skeletally

ALLOPLASTIC RECONSTRUCTION OF THETEMPOROMANDIBULAR JOINT

Peter D. Quinn, DMD, MD

INTRODUCTION

John Nobel once said, The purpose of medicine is to prevent significant disease, to decreasepain, and to postpone death when it is meaningful to do so. Technology has to support these goals, ifnot, it may even be counterproductive. The history of alloplastic temporomandibular joint reconstruc-tion has, unfortunately, been characterized by multiple highly publicized failures based on inappropri-ate design, lack of attention to biomechanical principles, and ignorance of what already had beendocumented in the orthopedic literature.1-3 In addition, because the temporomandibular joint (TMJ) isthe only ginglymoarthrodial joint in the body, and because its function is intimately related to occlusalharmony, a prosthetic TMJ necessitates characteristics not considered in orthopedic implant design.

immature and skeletally mature patients becauseit would obviate the inevitable revision surger-ies that alloplastic joint implants require.

Currently accepted indications andcontraindications for alloplastic joint reconstruc-tion are summarized in Table 1 and their rela-tive advantages and disadvantages are listed inTable 2. Types of alloplastic joint implantsinclude interpositional material after a gaparthroplasty, alloplastic fossa and eminence,condylar prostheses, and total joint prostheses.The focus of this monograph will be to discusscurrently available total joint alloplastic implantsin systems currently in clinical studies. Whereappropriate, we will reference experience withsystems that are no longer marketed. However,the basic assumption of this review will be thatall non-surgical, conservative treatment has beenexhausted, and that all conservative surgical

Alloplastic Reconstruction of the TMJ Peter D. Quinn, DMD, MD

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43. Elves MW, Wilson JN, Scales JT, et al:Incidence of metal sensitivity in patientswith total replacements, BMJ IV:376. 1975.

44. Black J: Biological Performance of Mate-rials: Fundamentals of Biocompatibility.Marcel Dekker, Inc., New York, 1992.

45. Lippincott A, Chase D and Christensen R:Alternative total TMJ arthroplasty: Metal-on-metal for longevity in implant survivor-ship and patient satisfaction. Surgical Tech-nology International VII, 1998.

46. Sonnenburg M and Sonnenburg I: Develop-ment and clinical application of the totaltemporomandibular joint endoprosthesis.Rev Stomatol Chir Maxillofac 91:165, 1990.

47. McBride KL: Total temporomandibular jointreconstruction, IN: Controversies in Oraland Maxillofacial Surgery, Worthington Pand Evans JR (eds) Philadelphia, PA,Saunders, 1994, p 381.

48. Sedel L and Cabanela M: Hip Surgery Ma-terials and Development. Mosby 1998, p48.

49. Charnley J: An artificial bearing in the hipjoint: implications in biological lubrication.Lubrication and Biomechanics 25:1079,1966.

50. Estok D and Harris WH: Factors affectingcement strains near the tip of a cementedfemoral component. J Arthroplasty 12:40,1997.

51. Lee IY, Skinner HB and Keyak JH: Effectsof variation of prosthesis size on cementstress tip of a femoral implant. J BiomedMater Res 28:1055, 1994.

52. Wolford LM, Cottrell DA and Henry CH:Temporomandibular joint reconstruction ofthe complex patient with the Tech Medicacustom-made total joint prosthesis. J OralMaxillofac Surg 52:2, 1994.

53. Mercuri LG, Wolford LM, Sanders B, et al:Custom CAD-CAM total temporomandibu-lar joint reconstruction system: preliminarymulticenter report. J Oral Maxillofac Surg53:106, 1995.

54. Wolford LM, Riechel O and Franco PF:Five-year follow-up study on Tech Medicacustom-made total joint prostheses. AAOMSAnnual Meeting: Abstract Session 15, 1997.

55. Falkenstrom CA: Biomedical Design of aTotal Temporomandibular Joint Replace-ment. Thesis, University of Groningen,1993.

56. Wilkes CH: Internal derangements of thetemporomandibular joint: Pathologicalvariations. Arch Otolaryngol Head NeckSurg 115:469, 1989.


SROMS 2 VOLUME 7.5

TABLE 1: Indications and Contraindications for Alloplastic Joint Reconstruction.

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methodologies have been employed beforealloplastic joint replacement is ever consideredfor a patient.

HISTORY OF ALLOPLASTIC TMJRECONSTRUCTION

According to Mercuri, John MurrayCarnochan, a New York surgeon, attempted thefirst interposition of a prosthetic materialbetween joint surfaces in 1840. He treated anankylosed TMJ by placing a small block of woodbetween the base of the skull and theosteotomized condyle.9 Risdon, in 1933, usedgold foil as an interpositional material after gaparthroplasty.10 Eggers,11 in 1946, and Goodsell,12

in 1947 used tantalum foil as an interpositionalimplant after ankylosis surgery. In 1960,Robinson13 used a stainless steel glenoid fossaimplant for the correction of ankylosis. It cov-

ered both the glenoid fossa and the articulareminence and was secured by two screws in thezygomatic arch.

During the years 1963 through 1971,Christensen expanded on the use of these fossaliners and fabricated twenty different sizes ofa chrome-cobalt glenoid fossa.14,15 Morganmodified Christensens TMJ fossa eminenceprosthesis.16 The Morgan prosthesis covered thearticular eminence only and came in five differ-ent standard shapes. In 1965, Christensen beganusing a condylar prosthesis, which consisted ofan acrylic head fixed to a Vitallium plate. In1972, Homsy et al. published a pilot study of aProplast coated chrome-cobalt condylar pros-thesis.17

In 1973, Morgan reported on a condylarreplacement composed of an acrylic head


SROMS 19 VOLUME 7.5

23. Kiehn CL, DesPrez JD and Converse CF:Total prosthetic replacement of the temporo-mandibular joint. Ann Plast Surg 2:5, 1979.

24. Recommendations for management of tem-poromandibular joint (TMJ) implants.Workshop on TMJ implant surgery. Nov.1992.

25. Charnley J: Tissue reaction of poly-tetrafluorethylene, Lancet (1963): 1379.

26. Leidholt JD and Gorman HA: Teflon hipprostheses in dogs. J Bone Joint Surg47(A):1414, 1965.

27. Fontenot MG and Kent JN: In vitro wearperformance of Proplast TMJ disc implants.J Oral Maxillofac Surg 50:133, 1992.

28. Henry CH and Wolford LM: Treatment out-comes for temporomandibular reconstruc-tion after Proplast-Teflon implant failure. JOral Maxillofac Surg, 51:352, 1993.

29. Kearns GJ, Perrott D and Kaban L: A proto-col for the management of failed alloplastictemporomandibular joint disc implants. JOral Maxillofac Surg, 53:1240, 1995.

30. Chase DC, et al.: The Christensen prosthe-sisA retrospective clinical study. OralSurg Oral Med Oral Path 80:273, 1995.

31. Ryan DE: Alloplastic implants in the tem-poromandibular joint. Oral and Maxillofa-cial Surgery Clinics of North America 1:429,1989.

32. Ryan DE: The Proplast-Teflon dilemma. JOral Maxillofac Surg 47:319, 1989.

33. Ryan DE: Alloplastic disc replacement. Oraland Maxillofacial Surgery Clinics of NorthAmerica, 6:307, 1994.

34. Pandy R, Quinn J, Joyner C, et al: Arthro-plasty implant biomaterial particle associ-ated macrophages differentiate into lacunarbone resorbing cells. Annals of the Rheu-matic Diseases 55:388, 1996.

35. Willert HG, Bertram H and Buchorn GH:Osteolysis in alloarthroplasty of the hip: therole of ultra-high molecular weight polyeth-ylene wear particles. Clin Orthop 258:95,1990.

36. Wagner M and Wagner H: Preliminary re-sults of uncemented metal on metal stemmedand resurfacing hip replacement arthroplasty.Clin Orthop 329 (Suppl):78, 1996.

37. McKee GK and Chen SC: The statistics ofthe McKee-Farrar method of total hip re-placement, Clin Orthop 95:26, 1973.

38. Breck LW: Metal to metal total hip joint re-placement using the Urist socket. An endresult study. Clin Orthop 95:38, 1973.

39. Muller ME: The benefits of the metal-on-metal total hip replacements, Clin Orthop311:54, 1995.

40. Wilson JN and Scales JT: The Stanmoremetal on metal total hip prosthesis using athree pin type cup: A follow-up of 100 ar-throplasties over nine years. Clin Orthop95:239, 1973.

41. Sieber HP, Rieker CB and Kottig P: Analy-sis of 118 second-generation metal-on-metalretrieved hip implants. J Bone & Joint Surg81-B:46, 1999.

42. Haynes DR, Rogers SD, Hay S, et al: Thedifferences in toxicity and release of bone-resorbing mediators induced by titanium andcobalt-chromium alloy wear particles, JBone Joint Surg 75A:825, 1993.


SROMS 3 VOLUME 7.5

TABLE 2: Advantages and Disadvantages of Alloplastic Joint Reconstruction.

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mechanically bonded to a Vitallium ramalmesh. During the late 70s and 80s, condylarprostheses by Spiessl, Raveh, Flot, Momma,Kummoona, and Sonnenburg were reported insmall series. Recently van Loon et al. summa-rized the alloplastic design, methods of fixation,and clinical results with fossa, condylar, and totaljoint prostheses up to 1995.18

TOTAL JOINT PROSTHESES

We will review the total joint systemsthat were extensively used in the United States.These include the Kent-Vitek, Christensen, andTech-Medica (TMJ Concepts) prostheses.

Kent-Vitek Prosthesis

Prosthesis Design:

The first total joint system widely usedin this country was the Kent-Vitek prosthesis.(Fig. 1) The system consisted initially of abilaminate glenoid fossa implant (VK I). Itsarticulating surface was a Teflon-coatedfluorethylpolyethylene (FEP) and the surfacefacing the fossa was polytetraflouroethylene(PTFE, Proplast) which could be carved to fitthe variable anatomy in the glenoid fossa. Thislayer originally came in thicknesses of 2.5 mmand 4.5 mm, allowing the surgeon to adjust thearticulating surface inferiorly if the naturalcondyle had lost vertical height secondary to


SROMS 18 VOLUME 7.5

4. Perrott DH, Vargevik K, Kaban LB: Costo-chondral reconstruction of mandibularcondyles in non-growing primates. JCraniofac Surg 6:227, 1995.

5. MacIntosh RB: Current spectrum of costo-chondral grafting. IN: Surgical Correctionof Dentofacial Deformities. Bell, WH andEpker B (eds) Philadelphia, WB Saunders1985, 51-73.

6. MacIntosh RB: Current spectrum of costo-chondral grafting. IN: Modern Practice ofOrthognathic and Reconstructive Surgery,Vol 2, Bell WH (ed.) Philadelphia, 1992.WB Saunders.

7. Lindquist C, et al.: Adaptation of autogenouscostochondral grafts used for temporoman-dibular joint reconstruction: a long-termclinical and radiologic follow-up, J OralMaxillofac Surg 46:465, 1988.

8. Lindquist C, et al.: Autogenous costochon-dral grafts in temporomandibular joint ar-throplasty: a survey of 66 arthroplasties in60 patients, J Maxillofac Surg 14:143, 1986.

9. Carnochan JM: Mobilizing a patientsankylosed jaw by placing a block of woodbetween the raw bony surfaces after resec-tion. Archiv de Medicin 1860:284, 1860.

10. Risdon F: Ankylosis of the temporoman-dibular joint. J Am Dent Assoc 21:1933,1933.

11. Eggers GWN: Arthroplasty of the temporo-mandibular joint in children withinterpositional tantalum foil. J Bone JointSurg 28:603, 1946.

12. Goodsell JO: Tantalum in temporomandibu-lar joint arthroplasty: report of a case. J OralSurg 5:41, 1947.

13. Robinson M: Temporomandibular ankylo-sis corrected by creating a false stainlesssteel fossa. JS Calif S Dent Assoc 28:186,1960.

14. Christensen RW: The correction of mandibu-lar ankylosis by arthroplasty and the inser-tion of a cast Vitallium glenoid fossa. JSCalif S Dent Assoc 31:117, 1963.

15. Christensen RW: The temporomandibularjoint prosthesis eleven years later. OralImplantol 2:125, 1971.

16. Morgan DH: Dysfunction, pain, tinnitus,vertigo corrected by mandibular joint sur-gery. JS Calif S Dent Assoc 39:505, 1971.

17. Homsy CA, Cain TE, Kessler FB, et al.:Porous implant systems for prosthesis sta-bilization. Clin Orthop 89:220, 1972.

18. van Loon J, et al.: Evaluation of temporo-mandibular joint prostheses. J OralMaxillofac Surg 53:984, 1995.

19. Kent JN, Block MS, Homsy CA, et al.: Ex-perience with a polymer glenoid fossa pros-thesis for partial or total TMJ reconstruc-tion. J Oral Maxillofac Surg 44:520, 1986.

20. Kent JN and Misiek DJ: Biomaterials forcranial, facial, mandible and TMJ recon-struction. IN: Fonseca RJ and Walker RV(eds): Maxillofacial Trauma. Philadelphia,WB Saunders, 1991.

21. Kent JN, Block MS, Halper J, et al.: Updateon the Vitek partial and total temporoman-dibular joint systems. J Oral Maxillofac Surg51:408, 1983.

22. Spagnoli D and Kent J: Alloplasts. OMFSKnowledge Update, Vol 1, 1994.


SROMS 4 VOLUME 7.5

Table 3: Early Alloplastic TMJ Prostheses

degenerative disease, pathology, or previoussurgery. Homsy simulated a 12-kg total load onthe tested joint prostheses, and demonstratedacceptable wear rates for both the Teflon FEPand the PTFE. The condylar prosthesis wasconstructed of chrome-cobalt with a layer ofProplast on the inner surface of the ramalflange to encourage rapid ingrowth in both hardand soft tissues. The condylar prosthesis alsohad an L-shaped groove on the medial surface,and a template was used to drill a channelthrough the cortical bone on the medial ramusof the mandible, allowing the anti-rotationalflange to fit securely against the surface of theramus. The prosthesis was then fitted with twoor three bolt-and-nut type fasteners. In 1986,the fossa was modified (VK II) with its uppersurface of Proplast-hydroxyapatite and its

articulating surface made of ultra-high-molecu-lar-weight polyethylene (UHMWPE).19

Clinical Outcomes

Kent and Misiek reported a series of 170patients who had received 182 joints for partialor total joint reconstruction between 1982 and1988.20 There was a higher success rate forpatients reconstructed with the VK II fossa(94%) as opposed to the VK I fossa (75%). In1993, Kent et al, published a ten-year follow-up for the VK I fossa and a six-year follow-up,for the VK II fossa.21 Some 248 of the 262 jointswere available for long-term follow-up and thecumulative success rate for the VK I total jointswas approximately 20%. The success rate of theVK II total joints was approximately 80%.

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SROMS 17 VOLUME 7.5

ment Conference on the management of TMJdisorders. Judith Albino, Ph.D., the chairpersonof that panel, stated, The use of certainalloplastic implants in surgery for TMD hasresulted in disastrous consequences for manypatients who have undergone such treatment.Consequently, the utmost caution must be uti-lized in considering the use of any implants. Atthe same time, it is recognized that certainpatients are in need of implants, and newerimplant designs need to be fully assessed asquickly as possible. There clearly is a need fora safe, effective, and functional total jointalloplastic implant with a reasonable life span.Past failures should be guideposts to future suc-cesses. It is extremely important not to aban-don the efforts to improve our alloplasticimplants but rather to follow a standard proto-col for artificial device development such as theone suggested by Fontenot and Kent. (Fig. 5)

McBride recently wrote, As approvedbiomaterials in new total joint implant systemsbecome available, and additional experience isgained with total joint implants, the quality ofresults obtained will continue to improve to thepoint where total joint reconstruction willbecome the treatment of choice for severe tem-poromandibular joint degeneration.3 Butclearly, it is our responsibility to exhaust allnonsurgical modes of treatment before proceed-ing with any surgical option. In those selectpatients where a total joint prosthesis is ulti-mately indicated, sound biomechanical prin-ciples with well- designed clinical studies willbe the sine qua non of alloplastic joint replace-ment.

Dr. Peter Quinn received his dentaldegree from the University of Pennsylvania,School of Dental Medicine, and his medicaldegree from the Medical College of Pennsylva-nia. He completed postgraduate training in oraland maxillofacial surgery at the Hospital of theUniversity of Pennsylvania. Currently, he isChairman of the Department of Oral and Max-illofacial Surgery and Pharmacology at the Uni-versity of Pennsylvania, School of Dental Medi-cine; and Chairman of the Department of Oraland Maxillofacial Surgery at the Hospital of theUniversity of Pennsylvania.

Dr. Quinns main areas of surgicalinterest are artificial joint replacement for thetemporomandibular joint, bone grafting for themaxillofacial skeleton, and maxillofacial trauma.In addition to his academic and clinical areas ofinterest, he currently serves as chair of the Uni-versity of Pennsylvania Medical Center Medi-cal Board.

______________________________________

REFERENCES

1. Braun T, Kent J: Temporomandibular jointsurgery Part II - Partial and total joint re-construction and osseous procedures.Selected Readings in Oral and Maxillofa-cial Surgery Vol. 1, No. 4.

2. Mercuri LG: Alloplastic temporomandibu-lar joint reconstruction. Oral Surg Oral MedOral Path 85: 631, 1998.

3. McBride KL: Total temporomandibular jointreconstruction. IN: Controversies in OMFS:Worthington P and Evans JR (eds.) Phila-delphia, WB Saunders 1994, 381-396.

Figure 5. On previous page from Oral and MaxillofacialSurgery Knowledge Update, Volume 1, 1994, p. 221.


SROMS 5 VOLUME 7.5

Figure 1. Kent-Vitek Prosthesis mounted on a driedskull.

_____________________________________

(Table 4) All of the failures in the VK I fossawere due to wear of the Teflon-polymerarticular surface. In retrospect, it is apparentthat the loads in pathological TMJs were con-siderably higher than the 12-kg total load placedon the test prosthesis. It should be noted thatsuccess rates were significantly higher if no sur-gery had been performed before the placementof either total joint prosthesis.

The PTFE was clearly the problematicmaterial in the Kent-Vitek prosthesis. TheProplast-Teflon inter-positional implant(PTIPI) was used between 1983 and 1988 as a

meniscal replacement. In 1986, several authorsreported condylar resorption even though manyof the patients were initially asymptomatic. Insymptomatic patients who had PTIPIs removed,there was evidence of: 1) wear and fragmenta-tion of the Teflon-FEP surface, 2) erosion ofboth the condylar head and fossa, and 3) sig-nificant foreign body reaction characterized bymacrophage and giant cell infiltrates.

Spagnoli and Kent performed a retrospec-tive multi-center evaluation of PTIPIs.22 In 465patients (680 joints), the average follow-up was32 months with a range of 6 months to 76months. At the time of the study, only 96(14.1%) had been removed, and of the remain-ing 584 implants, 540 (92.4%) were asymptom-atic. In that group, however, 224 of the asymp-tomatic and 25 symptomatic joints showed somedegree of condylar resorption which included45 with malocclusion.

One reported complication with the Kent-Vitek total joint replacement (Table 5) was gle-noid fossa resorption, especially for patients whohad the VK I and had undergone lengthening ofa foreshortened ramus. This, theoretically,resulted in increased loading on the prosthesis.

Kiehn reported successful joint reconstruc-tion with a VK fossa and a Synthes condyle.23

The Synthes condylar element consisted of areconstruction plate with a spherical head. Itmay have provided better mating for the condy-lar-fossa components, decreasing the occurrenceof variable point loading that could, over along of period of time, induce mobility of thefossa prosthesis and loosening and fragmenta-tion of the PTFE.

Determine TMJ Environmental Conditions:Biomechanics

Anatomic Boundary ConditionsSurgical Technique

Determine Properties ofCandidate Materials

Material Criteria:Physical PropertiesBiocompatability

Mechanical Testing

Artificial TMJ Device Design:Design Iteration andEngineering Analysis

Testing and Evaluation ofProposed/Existing Artificial

TMJ Device:TMJ Simulation Studies

Stess Analysis

Animal Studies

Controlled Clinical Trials

General Clinical Use

Postmarket Surveillance:Artificial TMJ Device Retrieval

Patient Follow-up

Complications

Phase 1

Phase 2

Phase 3

Phase 4

Phase 5

Figure 5: Recommended Protocol forArtificial TMJ Device Development

and Evaluation


SROMS 6 VOLUME 7.5

Table 4: VK-I and VK-II Total Joint Follow-up Data

Table 4: VK-I (Vitek, Inc. Houston, Tex.) placed 1986-90, FEP indicates fluorinated ethylene propylene; andUHMWPE, ultra-high-molecular-weight polyethylene. The cumulative success rates were calculated using theKaplan-Mier analysis employed by the National Institutes of Health. From Kent et al., 1993.

_________________________________________________________________________________

We have followed 16 patients after totaljoint reconstruction using either Kent VK I orKent VK II fossae and Synthes condylarimplants. The mean follow-up for these patientswas 12.2 years and 12 of the prostheses are stillfunctioning. The four that had to be revised allhad VK I fossae.

In December of 1990, the FDA issuedan alert urging oral and maxillofacial surgeonsto reexamine all of their patients who hadreceived PTIPIs. The consensus of the 1992AAOMS workshop on TMJ implant surgery24

was that the use of Teflon-Proplastinterpositional implants should be discontinuedsince it is an inappropriate material for this pur-pose. They further recommended removal ofthe implant and affected soft tissues, with advice

to follow postoperatively with MRI or CT onceper year for two years and then discontinue ifasymptomatic. They also advised that If thepatient refuses implant removal, follow everysix months with clinical examination and MRI.

In November of 1992, AAOMS con-vened a workshop on TMJ implant surgery.Although the majority of the discussion at thisconference was centered on the TeflonProplast interpositional meniscal implant, thepanel also recommended following patients withtotal joint prostheses that had PTFE elements.If baseline tomographic imaging revealed anyevidence of foreign body reaction, the recom-mendation was to Remove total joint, dbridethe area, and replace with a costochondral graftor a total joint prosthesis for which safety andefficacy has been established.

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SROMS 15 VOLUME 7.5

medium. Once we have achieved the initialfit, a small amount of doughy cement (1.5 cc to2.0 cc) is placed on the prosthesis and it is fittedto the base of the skull. Before final polymer-ization, the prosthesis is removed and any flash-ing is cut away with a surgical blade andsmoothed with an acrylic bur outside of the body.The cobalt-chromium-molybdenum condylarprosthesis is available in lengths of 45 mm, 50mm and 55 mm, and sizers are available to selectthe proper length after the patient has beenplaced in intermaxillary fixation. The sphericalsurface of the condylar head maximizes condyleto fossa mating, and the swan neck design onthe condylar neck avoids the inherent fittingproblems of the right angle design found in mostmetallic condylar prostheses.

Falkenstrom proposed that moving thepoint of rotation (condylion) inferior to the levelof the natural joint would result in an imitationof translation when the mouth opens.55 Thispseudo-translation is achieved in the Lorenz-Biomet prosthesis because the thickness of thepolyethylene fossa displaces the point of rota-tion inferiorly.

Clinical Outcomes

To date, we have placed a total of 59implants in 42 patients (25 unilateral and 17 bi-lateral). The gender breakdown is, predictably,91% female and 9% male. According to theWilkes classification, 6% of the patients wereClass III, 44% were Class IV, and 50% wereClass V.56 The mean number of prior surgeriesfor patients enrolled in the study was 5.7 (range,0 to 13).

To date, 22 of the patients have had thejoints in function for longer than three years. Inthat group, the mean preoperative opening was17.1 mm, and the mean postoperative openingat 36 months was 29.2 mm. The pain intensityvisual analog scale showed a mean score preop-eratively of 8.6 with a score of 1.9 at 36 months.Interference with eating (0 = no interference,10 = liquids only) showed a mean preoperativescore of 8.9 and a postoperative mean of 1.9.

Of the 59 joints, we have had one com-plication of a staph scalp infection, necessitat-ing the removal of a fossa prosthesis. Thispatient had had bilateral prosthetic joints forapproximately 10 months before the complica-tion occurred. Even after removal of the fossaprosthesis, she continued to function well, withthe only result being a 3-mm to 4-mm deviationtoward the side where the fossa prosthesis hadbeen removed on terminal opening. The clini-cal study will continue until the majority of thepatients have been followed for five years.

CONCLUSIONS

The American Association of Oral andMaxillofacial Surgeons 1992 workshop on themanagement of patients with TMJ alloplasticimplants recommended that Alloplastic totaljoint replacement is an option in patients withextensive TMJ disease. However, because long-term outcomes with currently available totaljoints have yet to be determined, their applica-tion must be considered as a compassionate useat this time.

In September of 1996, the NationalInstitute of Health convened a panel at theNational Institutes of Health Technology Assess-


SROMS 7 VOLUME 7.5

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Table 5: Analysis of VK Total Joint Failures

Material failure = observable wear; biologic failure =reankylosis; and patient failure = unexplained pain,no decrease in interincisal opening, and occlusionwas satisfactory. From Kent et al., 1993._____________________________________

It is important to note that Sir JohnCharnley, an orthopedic surgeon, stopped usingPTFE in orthopedic implants in 1963 becauseof tissue reaction to wear debris that resulted inloosening of the acetabular component second-ary to bony erosion.25 These findings were con-firmed by Leidholt and Gorman in 1965, whohad placed hip prostheses with PTFE in dogs.26

They reported both an acute and a chronicinflammatory reaction (characterized by giantcells) to PTFE particles.

In 1992, Fonteneau and Kent investi-gated the in-vitro wear performance of 1.3 mmPTIPI implants.27 The joints were loaded in amechanical TMJ simulator with 20 pounds offorce. Implant failure was categorized at threephases: 1) thinning, 2) deformation, and 3) coldflow with thinning, leading to fracture andaccelerated wear with fracture fragmentationand particulation of the underlying Proplast.They predicted an in-vivo service life of 757days, and suggested that parafunctional habits

and overuse of the jaw could further reduce thisshort service life. They recommended removalof all PTIPIs.

In 1993, Henry and Wolford conducted aretrospective study on 107 patients with 163joints previously treated with PTIPI. 28 Theaverage follow-up was 84.6 months (range 59to 126 months) and 88% of the joints showedsignificant osseous changes radiographically.Based on their symptoms and clinical andradiographic examination, the authors predictedthat all of these TMJ implants will eventuallyfail.

Their results indicated that for patientswho had the Proplast implants removed, andhad further reconstructive surgery, the suc-cess rate of TMJ reconstruction using autolo-gous tissues approaches zero. In the complexmultiply-operated TMJ patient, and those withpreviously failed alloplasts, a total joint pros-thesis using materials with proven safety andefficacy in orthopedic use may be the only optionavailable to predictably improve the quality oflife.

Kearns, et al. recently reported on themanagement of failed alloplastic TMJ diskimplants.29 They looked at a group of 27 patients(42 joints) in which they removed 24 Proplast-Teflon implants, 11 Silastic implants, and 7Christensen fossa implants. The mean follow-up period after implant removal was 38.3months. They used a pedicled temporalismuscle-fascia flap for joint lining after aggres-sive joint dbridement and arch bars withmaxillomandibular guiding elastics for condy-lar recontouring. They concluded that this treat-ment was an effective means of controlling painand improving jaw motion.


SROMS 14 VOLUME 7.5

have poorer outcomes.

In 1995, Mercuri et al. reported resultsfrom placement of 363 joints (296 bilateral and67 unilateral).53 In this group, there was a meannumber of 5.4 prior unsuccessful surgeries.There was also the predictable predominanceof females in the patient study group (202females versus 13 males). Nineteen patientswere defined as failures. At two years postop-eratively, there was a 49% improvement in themean pain score, a 43% improvement in themean function score, and a 50% improvementin the mean diet score. At the two year mark,there was also a 31% improvement ininterincisal opening and a predictable loss oflateral excursion because the lateral pterygoidmuscle is detached during condylectomy priorto implant placement. The authors concluded:Preliminary analysis of the data reveals a sta-tistically significant decrease in pain, an increasein function, and improvement in diet from thepreoperative measurements to one to two yearspostoperatively. Wolford, in 1997, presentedfurther follow-up of his initial 1994 study group,showing an overall success rate for stability ofthe Tech-Medica prosthesis of 90% and painreduction in 89% of the patients.54

Lorenz-Biomet Prosthesis

Prosthesis Design

We are currently involved in an FDAapproved clinical study of the TMJ prosthesisthat was developed by Lorenz-Biomet. (Fig. 4)The fossa prosthesis is constructed of UHMWPEwith a minimum of 4-mm of thickness in themid-point of the fossa itself. The fossa isdesigned with a zygomatic extension that haspre-drilled holes for fixation to the zygomatic

Figure 4. Biomet-Lorenz prosthesis mounted on adried skull.

______________________________________

arch with four 2.0 mm self-tapping screws. Itwas also designed with an exaggerated circum-ferential lipping to protect the condyle from het-erotopic bone formation and to avoid mechani-cal dislocation of the condyle from the fossa.The fossa is available in three stock sizes.

Because it is a stock prosthesis, it must beprepared to achieve tripod bony stability. First,the articular eminence is flattened, removing agreat deal of the inherent anatomic variabilityin the fossa anatomy itself. A small dowel witha retention groove is placed on the superior sur-face of the fossa prosthesis if the surgeon electsto use PMMA orthopedic cement as a void filler.We have used an orthopedic bone cement rein-forced with methylmethacrylate-styrene co-polymers (Simpelex P). Again, the orthopediccement is not intended to be used as a loading


SROMS 8 VOLUME 7.5

Christensen Fossa Prosthesis

Prosthesis Design

At the present time, the most widely usedsystem for alloplastic total joint reconstructionin this country is the Christensen prosthesismarketed by TMJ, Incorporated. (Fig. 2) In theearly 1960s, Christensen used a cast Vitalliumglenoid fossa against the natural condyle fortreatment of mandibular ankylosis.14 The 0.5 mmthick cast chromium-cobalt prosthesis was avail-able in approximately 20 different sizes, eachbased on anatomic variations in human adultskulls. There are now over 40 preshaped sizesfor both the right and the left fossae. Templatesizers were used to select the proper fossa size.The prosthesis is secured to the zygomatic archwith a minimum of four self-tapping 2.0-mmscrews. According to TMJ, Inc., the TMJ fossa-eminence prosthesis may be indicated in casesof internal derangement, meniscal perforation,adhesions, or ankylosis of the TMJ where con-servative therapies and treatment plans are nolonger indicated. The TMJ fossa-eminence pros-thesis is designed to provide a smooth surfacefor articulation with either the natural condylein a partial joint replacement or with a matchedChristensen TMJ condylar prosthesis in a totaljoint replacement.

Clinical Outcomes

Chase et al. recently used the fossa pros-thesis alone in hemiarthroplasties in 40 joints(22 patients) where the disk was retained.30

Although the majority of the patients did exhibitan increase in range of motion and a decrease inpain, 36% of the joints underwent another sur-gical procedure (an average of 13 months later)to remove the disk. In another group of patients(26 patients and 49 joints), Chase et al. placed a

Figure 2. Isolated Christensen cast Vitallium glenoidfossa with Type I condylar prosthesis.

______________________________________

fossa prosthesis at the time of meniscectomy.30

In this group, only two patients requiredreoperation during the mean follow-up time of5.1 years.

In our experience, it is extremely impor-tant to place the fossa prosthesis in a way thatgains maximum extended coverage of thearticular eminence, so that the condylar head(either the natural or the prosthetic) does nottraverse the actual edge of the fossa prosthesisduring the full range of motion. Condylar move-ment beyond the edge of the prosthetic fossacan result in lipping of a natural condyle orpotential mechanical obstruction of a prostheticcondyle with either subluxation, dislocation orboth.

In our own series of hemiarthro-plasties, where the fossa prosthesis was placed


SROMS 13 VOLUME 7.5

Sonnenburg and Sonnenburg, and Osteomed.46,47

UHMWPE is a linear (unbranched) chain dis-tinguished by having a molecular weight ofgreater than one million. Most commerciallyavailable UHMWPE orthopedic implants havean average molecular weight of three to six mil-lion. UHMWPE is the gold standard in hipprostheses even though polyethylene still is thepredominant wear particle found in failed totalhip joint arthroplasties.48

Polyethylene appears to be a potent stimu-lator of macrophage activation. Polyethylenewear in vivo is multifactorial with a complexinteraction among various factors, and it is notsurprising that wear rates are highly variable.Nonetheless, the wear rate for UHMWPE isconsiderably lower than other polymers used inorthopedic implants.47 The current strategies toimprove UHMWPE include polymer cross-link-ing, fiber reinforcement, and alternative steril-ization techniques.

It is difficult to make comparisons of thewear characteristics of hip prostheses and TMJprostheses because the functional loads are sodifferent. In vitro testing of both the TMJ Con-cepts and the Lorenz-Biomet prosthesesshowed acceptable wear characteristics. Thisultimately will be supported by adequate in vivoperformance.

Prior to surgery, the patient undergoes aCT scan while in occlusion, according to adefined protocol. A CAD-CAM model is thenforwarded to the surgeon to make surgical modi-fications such as coronoidectomy or occlusaladjustments. The prosthesis is designed, and awax-up stage is approved by the surgeon priorto final fabrication.

Theoretically, there is a clear advantage tocustom design because of the variations in theglenoid fossa and articular eminence. Severalattempts have been made in the past to use astock UHMWPE prosthesis that was fitted tothe base of the skull with a PMMA cement(Sonnenburg and Sonneburg, and Osteo-med).46,47 PMMA was introduced by Charnley49

and has been used for fixation of total joint pros-theses for more than thirty years. However, therehave been extensive reports of osteolysis at thecement bone interface, causing the aseptic loos-ening of the cemented hip prosthesis. It is diffi-cult to draw exact analogies to this situation inthe TMJ because it is a ginglymoarthroidial jointwith very different load characteristics. Fromthe orthopedic experience, it has been suggestedthat the small loose edges of polymerized cement(a thin cement mantle) is potentially more prob-lematic than a solid immobile core of cement.50,51

Ideally, PMMA cement should not be used as aloaded interface or medium but only as a voidfiller to avoid potential dead space when cus-tom fitting a stock prosthesis.

Clinical Outcomes

In 1994, Wolford et al. reported a study of56 patients with 100 joint reconstructions uti-lizing the Tech-Medica (TMJ Concepts)prosthesis.52 The average follow-up was 30months. Sixty-three percent of the patients hada good outcome, 23% had a fair outcome, and14% had a poor outcome. Five ramus prosthe-ses were removed or revised in this group. Sev-enteen patients received further operationsbecause of heterotopic bone formation, fibro-sis, calcification, inflammation, and/or pain.Complications occurred most often in patientswith previous Proplast-Teflon implants. Ingeneral, multiply-operated patients tended to


SROMS 9 VOLUME 7.5

against a natural condyle after meniscectomy,53% of the patients (27 of 51 joints) ultimatelyrequired revision surgery for the placement ofChristensen condylar prostheses. In a retrospec-tive analysis, 41 of these patients (mean follow-up of 6.3 years), the parameter that was mostpredictive of failure was the degree of degen-erative joint disease at the time of the placementof the glenoid fossa. Coronal CT scans showedsignificant sclerosis, and T2 weighted MRIimages revealed changes suggestive of avascu-lar necrosis, requiring further surgery. The meantime for placement of a condylar prosthesis afterthe initial fossa placement was 3.6 years.

It is our feeling that this should not beconstrued as a failure of the implant, but ratherindication that placement of a metallic fossa wasthe wrong choice. This confirms the globalexperience in the orthopedic literature wherehemiarthroplasty is generally not advised. Wealso feel that the fossa prosthesis is contraindi-cated in the face of severe vertical bone loss fromcondylar degeneration, previous surgery, or trau-matic osteoarthritis because the fossa alone can-not restore the proper ramal height required tocorrect mandibular asymmetry.

Christensen Condylar Prosthesis

Prosthesis Design

In 1965, Christensen produced a condylarprosthesis consisting of a cobalt-chrome ramalprosthesis with a polymethylmethacrylate(PMMA) head. (Fig. 2) We will refer to thisChristensen prosthesis as a Type I Christensen.Methylmethacrylate is a high molecular weight,acrylic material that can either polymerize atroom temperature (cold cure) or with the appli-cation of heat (heat cure). In its solid form,PMMA is relatively biocompatible and normallybecomes encapsulated in a thin, non-inflamma-

tory fibrous tissue envelope. Unfortunately,particulate PMMA has been implicated inimplant loosening and failure. Foreign-bodyreactions lead to osteolysis at the implant boneinterface.

Ryan has extensively studied the patho-logic response to alloplastic implants andrecently noted that Pandey, et al. evaluated thetissue responses to particulates of titanium, stain-less steel, chrome-cobalt, high density polyeth-ylene (HDP), and PMMA.31-34 Subcutaneouslesions from these particles were partially orcompletely surrounded by fibrous tissue that wasthicker around implanted PMMA and HDP par-ticles than around the metal particles. The heavi-est macrophage and giant cell response was seenin granulomas formed in response to implantedPMMA and HDP.

Resorption associated with PMMAgranuloma-derived macrophages was signifi-cantly greater than that of macrophages associ-ated with HDP, titanium, chrome-cobalt, orstainless steel granulomas. Irrespective of thetype of biomaterial implanted, the mononuclearphagocytes elicited in this foreign-bodyresponse were all capable of differentiating intobone resorbing cells. Thus, wear particles shedfrom the biomaterials commonly used in jointreplacement surgery must be all regarded aspotentially becoming the focus of a macroph-age response, resulting in aseptic loosening ofthe prosthesis. Osteolysis due to particulate weardebris is mainly responsible for long-term fail-ure of total hip replacements.35-36

It should be noted that all alloplastic mate-rials produce some wear debris. It is not knownwhether aseptic loosening of TMJ prostheses is


SROMS 12 VOLUME 7.5

In-vitro testing of the chromium metal-on-metal prosthesis showed No adverse wear, nofatigue failure of the test devices, no looseningof the implants from the synthetic bone substi-tute, no gross material removal or device fail-uredeformation is shownonly a slight blem-ish on the condylar head. Analysis of this cyclicfatigue test under these extreme test conditionsat 5,000,000 cycles shows a survivorship calcu-lation of this implant device well over sixty yearsof duration.45 Long-term in-vivo testing isneeded to substantiate these in vitro result, andthere are no clinical studies to support this con-clusion. In our own series of 9 patients withChristensen metal-on-metal prostheses (meanfollow-up of 4.9 years) we have had no overtimplant failures to date.

In addition to the standard metal-on-metal stock prostheses, TMJ, Incorporated alsoconstructs custom cobalt-chromium metal-on-metal joints from CT generated data. A three-dimensional CAD-CAM model is producedaccording to a defined scanning protocol. Thesemodels are especially helpful in designing pros-theses in anatomically mutilated joints. Forjoints where the fossa anatomy is relatively nor-mal but there is a lack of adequate bone in theramus to support the 2.7-mm screws, the stockTMJ Incorporated prosthesis comes in a Chasemodification (a slanted L-shape) that extends theramal strut to take advantage of bone in the areaof the angle of the mandible.

Tech-Medica (TMJ Concepts) Prosthesis

Prosthesis Design

The mandibular component of the Tech-Medica system is a condylar head made ofcobalt-chromium-molybdenum alloy attached toa mandibular body made of titanium 6AL-4V

Figure 3. Custom Tech-Medica prothesis on a CAD-CAM model.

______________________________________

alloy. (Fig. 3) The glenoid fossa component iscomprised of an articular surface made ofUHMWPE attached to a mesh backing made ofunalloyed titanium. Both the glenoid prosthe-sis and the condylar prosthesis are secured withtitanium 6AL-4V alloy screws. These prosthe-ses are now marketed as the TMJ Conceptspatient-fitted prosthesis.

The TMJ Concepts prosthesis is customfitted with a titanium mesh backing to the baseof skull. TMJ Concepts and the Lorenz-Biomet prosthesis both utilize UHMWPE forthe articulating surface of the fossa. UHMWPEwas also used in fossa prostheses designed by


SROMS 10 VOLUME 7.5

based on the same mechanisms that producesloosening of hip prostheses, but prudencerequires the use of materials with minimal wearpotential. Therefore, one area of concern in theType I Christensen prosthesis was the PMMAhead. Explanted joints showed significant wearon the anterior superior surface of the condylarhead. In two patients, the wear extended to thetip of the superior surface of the central metalpost within the condylar head itself. Tissuesamples taken at the time of explantation clearlyshowed particulate debris that was, in large part,encapsulated with minimal inflammation.

Currently, the Christensen prosthesis is nolonger manufactured with a PMMA head but iscompletely metallic (cobalt-chrome). In addi-tion to the PMMA head, the original Type Icondylar prosthesis was structurally weaker thanthe current Type II prosthesis. The width of theramal flange has been increased and its screwplacement has been optimized so that all thescrew holes are offset.

The recommended surgical technique is tocomplete the condylectomy with aggressivedbridement of the joint to remove all foreignbody reaction and heterotopic bone. An ostec-tomy is performed approximately at the level ofthe base of the sigmoid notch. A coronoidectomyshould also be performed when there is signifi-cant foreshortening of the temporalis muscle andpersistent decreased range of motion even afterthe condylectomy has been performed. The gle-noid fossa prosthesis is placed and secured tothe zygomatic arch with 2.0-mm screws and thepatient is placed in intermaxillary fixation.Condylar sizers can be used to select the propervertical length of the prosthesis and the condyleis secured with the self-tapping 2.7-mm

bicortical screws. Two screws are placed tosecure the prosthesis and then the intermaxil-lary fixation is removed to visually observe thecondyle/fossa mechanical interface. One mustensure that there is at least 35 mm of interincisalopening without any evidence of subluxation,dislocation, or obstruction. If the mechanicalfunction is acceptable, the rest of the ramalscrews can be placed.

In placing the screws, it is important to onlydrill initially through the buccal cortical plateand then look for bleeding in the area of theneurovascular bundle. Condylar sizers can behelpful in taking advantage of available bonewhile, at the same time, avoiding damage to theinferior alveolar nerve. Since there is no lateralpterygoid function with an alloplastic condylarprosthesis, 30-35 mm of pure rotational move-ment would be a reasonable expectation.Angling the condylar prosthesis, so that the headis positioned in the posterior portion of the fossa,maximizes condylar rotation. In cases whereablative surgery or previous autogenous and/oralloplastic grafting has resulted in significantloss of ramal bone, both the Type I and Type IIChristensen prostheses, with an L-shapedextension (Chase modification) are available,allowing screw fixation at the angle of the man-dible.

Clinical Outcomes

Chase et al. retrospectively examined 21patients (34 joints) with a mean follow-up of2.4 years (range, 1 to 10 years).30 In this group,95% percent had a significant decrease in painand 86% percent had a significant improvementin their functional ability (diet). The authorsstated that, All prostheses in this group were


SROMS 11 VOLUME 7.5

functioning to patient satisfaction. Theyreported no failures.

We have followed a series of 90 patients(109 joints) which were reconstructed with aChristensen prosthesis. There were 19 bilateraland 71 unilateral cases with a mean follow-upof 73.1 months (range, 36 to 108 months). Wehave had 9 fractures of the condylar prostheses,but these occurred at an average of 5.8 yearsafter placement. It is extremely important to alsonote that all of the fractures occurred in the TypeI prostheses. There also was a strong correla-tion with uncorrected parafunctional habits, suchas bruxing, in the patients in which fracturesoccurred. The fractures tended to occur at a pointsuperior to the most superior ramal screw, andin areas where the screw holes were not opti-mally offset at a forty-five degree angle. Theo-retically, metal fatigue occurred at the junctionof the screw fixated component and the non-fixated component (superior to the last screw inthe condylar prosthesis). We have not encoun-tered any fractures in the Type II reinforced pros-theses.

Metal on Metal Prostheses

Prosthesis Design

There has been renewed interest recentlyin the orthopedic literature in the use of metal-on-metal hip implants. Early studies on metal-on-metal hips were reported by McKee in 1973and consequently by Breck, Muller and Wil-son.37-40 Sieber et al, in 1999, reported on a seriesof over 60,000 hips where second generationcobalt-chrome molybdenum alloy metal-on-metal implants had been used.41 An analysis of118 retrieved specimens of the head or cup

showed that the metal surfaces had a self-pol-ishing capacity and that volumetric wear was60 times less than that of metal-on-polyethyl-ene implants.

The orthopedic literature reports poten-tial problems with metal-on-metal prostheses,including high frictional torque that could resultin loosening. Wear debris could potentially bemore toxic than polyethylene.42 In addition towear volume, the wear particles are smaller andmore numerous for a given wear volume. Also,the incidence of metal sensitivity is greater inmetal-on-metal joint prostheses with high wearrates.43

Many orthopedic researchers feel that thepoor clinical results in the 60s and 70s withmetal-on-metal prostheses resulted from poorstem and cup design and inconsistent manufac-turing of the materials themselves.44 Becausethe load on hip prostheses is much greater thanthat in the TMJ, the amount of wear may not beanalogous.

Lippincott et al. prospectively followed23 patients with metal-on-metal Christensenprostheses.45 The pain score on a 0 to 10 visualanalog scale averaged 8.88 preoperatively and2.6 at 36 months postoperatively. Preoperatively,the average interincisal opening was 22 mm andthe average postoperative interincisal openingwas 27 mm. Four implant sets were removedfrom two patients because of excessive hetero-topic bone, and SEM microscopic analysisrevealed that the dominant wear mechanism wasabrasion, with no unique wear scars on eitherthe condylar head or the fossa eminence.


SROMS 9 VOLUME 7.5

against a natural condyle after meniscectomy,53% of the patients (27 of 51 joints) ultimatelyrequired revision surgery for the placement ofChristensen condylar prostheses. In a retrospec-tive analysis, 41 of these patients (mean follow-up of 6.3 years), the parameter that was mostpredictive of failure was the degree of degen-erative joint disease at the time of the placementof the glenoid fossa. Coronal CT scans showedsignificant sclerosis, and T2 weighted MRIimages revealed changes suggestive of avascu-lar necrosis, requiring further surgery. The meantime for placement of a condylar prosthesis afterthe initial fossa placement was 3.6 years.

It is our feeling that this should not beconstrued as a failure of the implant, but ratherindication that placement of a metallic fossa wasthe wrong choice. This confirms the globalexperience in the orthopedic literature wherehemiarthroplasty is generally not advised. Wealso feel that the fossa prosthesis is contraindi-cated in the face of severe vertical bone loss fromcondylar degeneration, previous surgery, or trau-matic osteoarthritis because the fossa alone can-not restore the proper ramal height required tocorrect mandibular asymmetry.

Christensen Condylar Prosthesis

Prosthesis Design

In 1965, Christensen produced a condylarprosthesis consisting of a cobalt-chrome ramalprosthesis with a polymethylmethacrylate(PMMA) head. (Fig. 2) We will refer to thisChristensen prosthesis as a Type I Christensen.Methylmethacrylate is a high molecular weight,acrylic material that can either polymerize atroom temperature (cold cure) or with the appli-cation of heat (heat cure). In its solid form,PMMA is relatively biocompatible and normallybecomes encapsulated in a thin, non-inflamma-

tory fibrous tissue envelope. Unfortunately,particulate PMMA has been implicated inimplant loosening and failure. Foreign-bodyreactions lead to osteolysis at the implant boneinterface.

Ryan has extensively studied the patho-logic response to alloplastic implants andrecently noted that Pandey, et al. evaluated thetissue responses to particulates of titanium, stain-less steel, chrome-cobalt, high density polyeth-ylene (HDP), and PMMA.31-34 Subcutaneouslesions from these particles were partially orcompletely surrounded by fibrous tissue that wasthicker around implanted PMMA and HDP par-ticles than around the metal particles. The heavi-est macrophage and giant cell response was seenin granulomas formed in response to implantedPMMA and HDP.

Resorption associated with PMMAgranuloma-derived macrophages was signifi-cantly greater than that of macrophages associ-ated with HDP, titanium, chrome-cobalt, orstainless steel granulomas. Irrespective of thetype of biomaterial implanted, the mononuclearphagocytes elicited in this foreign-bodyresponse were all capable of differentiating intobone resorbing cells. Thus, wear particles shedfrom the biomaterials commonly used in jointreplacement surgery must be all regarded aspotentially becoming the focus of a macroph-age response, resulting in aseptic loosening ofthe prosthesis. Osteolysis due to particulate weardebris is mainly responsible for long-term fail-ure of total hip replacements.35-36

It should be noted that all alloplastic mate-rials produce some wear debris. It is not knownwhether aseptic loosening of TMJ prostheses is


SROMS 12 VOLUME 7.5

In-vitro testing of the chromium metal-on-metal prosthesis showed No adverse wear, nofatigue failure of the test devices, no looseningof the implants from the synthetic bone substi-tute, no gross material removal or device fail-uredeformation is shownonly a slight blem-ish on the condylar head. Analysis of this cyclicfatigue test under these extreme test conditionsat 5,000,000 cycles shows a survivorship calcu-lation of this implant device well over sixty yearsof duration.45 Long-term in-vivo testing isneeded to substantiate these in vitro result, andthere are no clinical studies to support this con-clusion. In our own series of 9 patients withChristensen metal-on-metal prostheses (meanfollow-up of 4.9 years) we have had no overtimplant failures to date.

In addition to the standard metal-on-metal stock prostheses, TMJ, Incorporated alsoconstructs custom cobalt-chromium metal-on-metal joints from CT generated data. A three-dimensional CAD-CAM model is producedaccording to a defined scanning protocol. Thesemodels are especially helpful in designing pros-theses in anatomically mutilated joints. Forjoints where the fossa anatomy is relatively nor-mal but there is a lack of adequate bone in theramus to support the 2.7-mm screws, the stockTMJ Incorporated prosthesis comes in a Chasemodification (a slanted L-shape) that extends theramal strut to take advantage of bone in the areaof the angle of the mandible.

Tech-Medica (TMJ Concepts) Prosthesis

Prosthesis Design

The mandibular component of the Tech-Medica system is a condylar head made ofcobalt-chromium-molybdenum alloy attached toa mandibular body made of titanium 6AL-4V

Figure 3. Custom Tech-Medica prothesis on a CAD-CAM model.

______________________________________

alloy. (Fig. 3) The glenoid fossa component iscomprised of an articular surface made ofUHMWPE attached to a mesh backing made ofunalloyed titanium. Both the glenoid prosthe-sis and the condylar prosthesis are secured withtitanium 6AL-4V alloy screws. These prosthe-ses are now marketed as the TMJ Conceptspatient-fitted prosthesis.

The TMJ Concepts prosthesis is customfitted with a titanium mesh backing to the baseof skull. TMJ Concepts and the Lorenz-Biomet prosthesis both utilize UHMWPE forthe articulating surface of the fossa. UHMWPEwas also used in fossa prostheses designed by


SROMS 8 VOLUME 7.5

Christensen Fossa Prosthesis

Prosthesis Design

At the present time, the most widely usedsystem for alloplastic total joint reconstructionin this country is the Christensen prosthesismarketed by TMJ, Incorporated. (Fig. 2) In theearly 1960s, Christensen used a cast Vitalliumglenoid fossa against the natural condyle fortreatment of mandibular ankylosis.14 The 0.5 mmthick cast chromium-cobalt prosthesis was avail-able in approximately 20 different sizes, eachbased on anatomic variations in human adultskulls. There are now over 40 preshaped sizesfor both the right and the left fossae. Templatesizers were used to select the proper fossa size.The prosthesis is secured to the zygomatic archwith a minimum of four self-tapping 2.0-mmscrews. According to TMJ, Inc., the TMJ fossa-eminence prosthesis may be indicated in casesof internal derangement, meniscal perforation,adhesions, or ankylosis of the TMJ where con-servative therapies and treatment plans are nolonger indicated. The TMJ fossa-eminence pros-thesis is designed to provide a smooth surfacefor articulation with either the natural condylein a partial joint replacement or with a matchedChristensen TMJ condylar prosthesis in a totaljoint replacement.

Clinical Outcomes

Chase et al. recently used the fossa pros-thesis alone in hemiarthroplasties in 40 joints(22 patients) where the disk was retained.30

Although the majority of the patients did exhibitan increase in range of motion and a decrease inpain, 36% of the joints underwent another sur-gical procedure (an average of 13 months later)to remove the disk. In another group of patients(26 patients and 49 joints), Chase et al. placed a

Figure 2. Isolated Christensen cast Vitallium glenoidfossa with Type I condylar prosthesis.

______________________________________

fossa prosthesis at the time of meniscectomy.30

In this group, only two patients requiredreoperation during the mean follow-up time of5.1 years.

In our experience, it is extremely impor-tant to place the fossa prosthesis in a way thatgains maximum extended coverage of thearticular eminence, so that the condylar head(either the natural or the prosthetic) does nottraverse the actual edge of the fossa prosthesisduring the full range of motion. Condylar move-ment beyond the edge of the prosthetic fossacan result in lipping of a natural condyle orpotential mechanical obstruction of a prostheticcondyle with either subluxation, dislocation orboth.

In our own series of hemiarthro-plasties, where the fossa prosthesis was placed


SROMS 13 VOLUME 7.5

Sonnenburg and Sonnenburg, and Osteomed.46,47

UHMWPE is a linear (unbranched) chain dis-tinguished by having a molecular weight ofgreater than one million. Most commerciallyavailable UHMWPE orthopedic implants havean average molecular weight of three to six mil-lion. UHMWPE is the gold standard in hipprostheses even though polyethylene still is thepredominant wear particle found in failed totalhip joint arthroplasties.48

Polyethylene appears to be a potent stimu-lator of macrophage activation. Polyethylenewear in vivo is multifactorial with a complexinteraction among various factors, and it is notsurprising that wear rates are highly variable.Nonetheless, the wear rate for UHMWPE isconsiderably lower than other polymers used inorthopedic implants.47 The current strategies toimprove UHMWPE include polymer cross-link-ing, fiber reinforcement, and alternative steril-ization techniques.

It is difficult to make comparisons of thewear characteristics of hip prostheses and TMJprostheses because the functional loads are sodifferent. In vitro testing of both the TMJ Con-cepts and the Lorenz-Biomet prosthesesshowed acceptable wear characteristics. Thisultimately will be supported by adequate in vivoperformance.

Prior to surgery, the patient undergoes aCT scan while in occlusion, according to adefined protocol. A CAD-CAM model is thenforwarded to the surgeon to make surgical modi-fications such as coronoidectomy or occlusaladjustments. The prosthesis is designed, and awax-up stage is approved by the surgeon priorto final fabrication.

Theoretically, there is a clear advantage tocustom design because of the variations in theglenoid fossa and articular eminence. Severalattempts have been made in the past to use astock UHMWPE prosthesis that was fitted tothe base of the skull with a PMMA cement(Sonnenburg and Sonneburg, and Osteo-med).46,47 PMMA was introduced by Charnley49

and has been used for fixation of total joint pros-theses for more than thirty years. However, therehave been extensive reports of osteolysis at thecement bone interface, causing the aseptic loos-ening of the cemented hip prosthesis. It is diffi-cult to draw exact analogies to this situation inthe TMJ because it is a ginglymoarthroidial jointwith very different load characteristics. Fromthe orthopedic experience, it has been suggestedthat the small loose edges of polymerized cement(a thin cement mantle) is potentially more prob-lematic than a solid immobile core of cement.50,51

Ideally, PMMA cement should not be used as aloaded interface or medium but only as a voidfiller to avoid potential dead space when cus-tom fitting a stock prosthesis.

Clinical Outcomes

In 1994, Wolford et al. reported a study of56 patients with 100 joint reconstructions uti-lizing the Tech-Medica (TMJ Concepts)prosthesis.52 The average follow-up was 30months. Sixty-three percent of the patients hada good outcome, 23% had a fair outcome, and14% had a poor outcome. Five ramus prosthe-ses were removed or revised in this group. Sev-enteen patients received further operationsbecause of heterotopic bone formation, fibro-sis, calcification, inflammation, and/or pain.Complications occurred most often in patientswith previous Proplast-Teflon implants. Ingeneral, multiply-operated patients tended to


SROMS 7 VOLUME 7.5

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Table 5: Analysis of VK Total Joint Failures

Material failure = observable wear; biologic failure =reankylosis; and patient failure = unexplained pain,no decrease in interincisal opening, and occlusionwas satisfactory. From Kent et al., 1993._____________________________________

It is important to note that Sir JohnCharnley, an orthopedic surgeon, stopped usingPTFE in orthopedic implants in 1963 becauseof tissue reaction to wear debris that resulted inloosening of the acetabular component second-ary to bony erosion.25 These findings were con-firmed by Leidholt and Gorman in 1965, whohad placed hip prostheses with PTFE in dogs.26

They reported both an acute and a chronicinflammatory reaction (characterized by giantcells) to PTFE particles.

In 1992, Fonteneau and Kent investi-gated the in-vitro wear performance of 1.3 mmPTIPI implants.27 The joints were loaded in amechanical TMJ simulator with 20 pounds offorce. Implant failure was categorized at threephases: 1) thinning, 2) deformation, and 3) coldflow with thinning, leading to fracture andaccelerated wear with fracture fragmentationand particulation of the underlying Proplast.They predicted an in-vivo service life of 757days, and suggested that parafunctional habits

and overuse of the jaw could further reduce thisshort service life. They recommended removalof all PTIPIs.

In 1993, Henry and Wolford conducted aretrospective study on 107 patients with 163joints previously treated with PTIPI. 28 Theaverage follow-up was 84.6 months (range 59to 126 months) and 88% of the joints showedsignificant osseous changes radiographically.Based on their symptoms and clinical andradiographic examination, the authors predictedthat all of these TMJ implants will eventuallyfail.

Their results indicated that for patientswho had the Proplast implants removed, andhad further reconstructive surgery, the suc-cess rate of TMJ reconstruction using autolo-gous tissues approaches zero. In the complexmultiply-operated TMJ patient, and those withpreviously failed alloplasts, a total joint pros-thesis using materials with proven safety andefficacy in orthopedic use may be the only optionavailable to predictably improve the quality oflife.

Kearns, et al. recently reported on themanagement of failed alloplastic TMJ diskimplants.29 They looked at a group of 27 patients(42 joints) in which they removed 24 Proplast-Teflon implants, 11 Silastic implants, and 7Christensen fossa implants. The mean follow-up period after implant removal was 38.3months. They used a pedicled temporalismuscle-fascia flap for joint lining after aggres-sive joint dbridement and arch bars withmaxillomandibular guiding elastics for condy-lar recontouring. They concluded that this treat-ment was an effective means of controlling painand improving jaw motion.


SROMS 14 VOLUME 7.5

have poorer outcomes.

In 1995, Mercuri et al. reported resultsfrom placement of 363 joints (296 bilateral and67 unilateral).53 In this group, there was a meannumber of 5.4 prior unsuccessful surgeries.There was also the predictable predominanceof females in the patient study group (202females versus 13 males). Nineteen patientswere defined as failures. At two years postop-eratively, there was a 49% improvement in themean pain score, a 43% improvement in themean function score, and a 50% improvementin the mean diet score. At the two year mark,there was also a 31% improvement ininterincisal opening and a predictable loss oflateral excursion because the lateral pterygoidmuscle is detached during condylectomy priorto implant placement. The authors concluded:Preliminary analysis of the data reveals a sta-tistically significant decrease in pain, an increasein function, and improvement in diet from thepreoperative measurements to one to two yearspostoperatively. Wolford, in 1997, presentedfurther follow-up of his initial 1994 study group,showing an overall success rate for stability ofthe Tech-Medica prosthesis of 90% and painreduction in 89% of the patients.54

Lorenz-Biomet Prosthesis

Prosthesis Design

We are currently involved in an FDAapproved clinical study of the TMJ prosthesisthat was developed by Lorenz-Biomet. (Fig. 4)The fossa prosthesis is constructed of UHMWPEwith a minimum of 4-mm of thickness in themid-point of the fossa itself. The fossa isdesigned with a zygomatic extension that haspre-drilled holes for fixation to the zygomatic

Figure 4. Biomet-Lorenz prosthesis mounted on adried skull.

______________________________________

arch with four 2.0 mm self-tapping screws. Itwas also designed with an exaggerated circum-ferential lipping to protect the condyle from het-erotopic bone formation and to avoid mechani-cal dislocation of the condyle from the fossa.The fossa is available in three stock sizes.

Because it is a stock prosthesis, it must beprepared to achieve tripod bony stability. First,the articular eminence is flattened, removing agreat deal of the inherent anatomic variabilityin the fossa anatomy itself. A small dowel witha retention groove is placed on the superior sur-face of the fossa prosthesis if the surgeon electsto use PMMA orthopedic cement as a void filler.We have used an orthopedic bone cement rein-forced with methylmethacrylate-styrene co-polymers (Simpelex P). Again, the orthopediccement is not intended to be used as a loading


SROMS 6 VOLUME 7.5

Table 4: VK-I and VK-II Total Joint Follow-up Data

Table 4: VK-I (Vitek, Inc. Houston, Tex.) placed 1986-90, FEP indicates fluorinated ethylene propylene; andUHMWPE, ultra-high-molecular-weight polyethylene. The cumulative success rates were calculated using theKaplan-Mier analysis employed by the National Institutes of Health. From Kent et al., 1993.

_________________________________________________________________________________

We have followed 16 patients after totaljoint reconstruction using either Kent VK I orKent VK II fossae and Synthes condylarimplants. The mean follow-up for these patientswas 12.2 years and 12 of the prostheses are stillfunctioning. The four that had to be revised allhad VK I fossae.

In December of 1990, the FDA issuedan alert urging oral and maxillofacial surgeonsto reexamine all of their patients who hadreceived PTIPIs. The consensus of the 1992AAOMS workshop on TMJ implant surgery24

was that the use of Teflon-Proplastinterpositional implants should be discontinuedsince it is an inappropriate material for this pur-pose. They further recommended removal ofthe implant and affected soft tissues, with advice

to follow postoperatively with MRI or CT onceper year for two years and then discontinue ifasymptomatic. They also advised that If thepatient refuses implant removal, follow everysix months with clinical examination and MRI.

In November of 1992, AAOMS con-vened a workshop on TMJ implant surgery.Although the majority of the discussion at thisconference was centered on the TeflonProplast interpositional meniscal implant, thepanel also recommended following patients withtotal joint prostheses that had PTFE elements.If baseline tomographic imaging revealed anyevidence of foreign body reaction, the recom-mendation was to Remove total joint, dbridethe area, and replace with a costochondral graftor a total joint prosthesis for which safety andefficacy has been established.

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SROMS 15 VOLUME 7.5

medium. Once we have achieved the initialfit, a small amount of doughy cement (1.5 cc to2.0 cc) is placed on the prosthesis and it is fittedto the base of the skull. Before final polymer-ization, the prosthesis is removed and any flash-ing is cut away with a surgical blade andsmoothed with an acrylic bur outside of the body.The cobalt-chromium-molybdenum condylarprosthesis is available in lengths of 45 mm, 50mm and 55 mm, and sizers are available to selectthe proper length after the patient has beenplaced in intermaxillary fixation. The sphericalsurface of the condylar head maximizes condyleto fossa mating, and the swan neck design onthe condylar neck avoids the inherent fittingproblems of the right angle design found in mostmetallic condylar prostheses.

Falkenstrom proposed that moving thepoint of rotation (condylion) inferior to the levelof the natural joint would result in an imitationof translation when the mouth opens.55 Thispseudo-translation is achieved in the Lorenz-Biomet prosthesis because the thickness of thepolyethylene fossa displaces the point of rota-tion inferiorly.

Clinical Outcomes

To date, we have placed a total of 59implants in 42 patients (25 unilateral and 17 bi-lateral). The gender breakdown is, predictably,91% female and 9% male. According to theWilkes classification, 6% of the patients wereClass III, 44% were Class IV, and 50% wereClass V.56 The mean number of prior surgeriesfor patients enrolled in the study was 5.7 (range,0 to 13).

To date, 22 of the patients have had thejoints in function for longer than three years. Inthat group, the mean preoperative opening was17.1 mm, and the mean postoperative openingat 36 months was 29.2 mm. The pain intensityvisual analog scale showed a mean score preop-eratively of 8.6 with a score of 1.9 at 36 months.Interference with eating (0 = no interference,10 = liquids only) showed a mean preoperativescore of 8.9 and a postoperative mean of 1.9.

Of the 59 joints, we have had one com-plication of a staph scalp infection, necessitat-ing the removal of a fossa prosthesis. Thispatient had had bilateral prosthetic joints forapproximately 10 months before the complica-tion occurred. Even after removal of the fossaprosthesis, she continued to function well, withthe only result being a 3-mm to 4-mm deviationtoward the side where the fossa prosthesis hadbeen removed on terminal opening. The clini-cal study will continue until the majority of thepatients have been followed for five years.

CONCLUSIONS

The American Association of Oral andMaxillofacial Surgeons 1992 workshop on themanagement of patients with TMJ alloplasticimplants recommended that Alloplastic totaljoint replacement is an option in patients withextensive TMJ disease. However, because long-term outcomes with currently available totaljoints have yet to be determined, their applica-tion must be considered as a compassionate useat this time.

In September of 1996, the NationalInstitute of Health convened a panel at theNational Institutes of Health Technology Assess-


SROMS 5 VOLUME 7.5

Figure 1. Kent-Vitek Prosthesis mounted on a driedskull.

_____________________________________

(Table 4) All of the failures in the VK I fossawere due to wear of the Teflon-polymerarticular surface. In retrospect, it is apparentthat the loads in pathological TMJs were con-siderably higher than the 12-kg total load placedon the test prosthesis. It should be noted thatsuccess rates were significantly higher if no sur-gery had been performed before the placementof either total joint prosthesis.

The PTFE was clearly the problematicmaterial in the Kent-Vitek prosthesis. TheProplast-Teflon inter-positional implant(PTIPI) was used between 1983 and 1988 as a

meniscal replacement. In 1986, several authorsreported condylar resorption even though manyof the patients were initially asymptomatic. Insymptomatic patients who had PTIPIs removed,there was evidence of: 1) wear and fragmenta-tion of the Teflon-FEP surface, 2) erosion ofboth the condylar head and fossa, and 3) sig-nificant foreign body reaction characterized bymacrophage and giant cell infiltrates.

Spagnoli and Kent performed a retrospec-tive multi-center evaluation of PTIPIs.22 In 465patients (680 joints), the average follow-up was32 months with a range of 6 months to 76months. At the time of the study, only 96(14.1%) had been removed, and of the remain-ing 584 implants, 540 (92.4%) were asymptom-atic. In that group, however, 224 of the asymp-tomatic and 25 symptomatic joints showed somedegree of condylar resorption which included45 with malocclusion.

One reported complication with the Kent-Vitek total joint replacement (Table 5) was gle-noid fossa resorption, especially for patients whohad the VK I and had undergone lengthening ofa foreshortened ramus. This, theoretically,resulted in increased loading on the prosthesis.

Kiehn reported successful joint reconstruc-tion with a VK fossa and a Synthes condyle.23

The Synthes condylar element consisted of areconstruction plate with a spherical head. Itmay have provided better mating for the condy-lar-fossa components, decreasing the occurrenceof variable point loading that could, over along of period of time, induce mobility of thefossa prosthesis and loosening and fragmenta-tion of the PTFE.

Determine TMJ Environmental Conditions:Biomechanics

Anatomic Boundary ConditionsSurgical Technique

Determine Properties ofCandidate Materials

Material Criteria:Physical PropertiesBiocompatability

Mechanical Testing

Artificial TMJ Device Design:Design Iteration andEngineering Analysis

Testing and Evaluation ofProposed/Existing Artificial

TMJ Device:TMJ Simulation Studies

Stess Analysis

Animal Studies

Controlled Clinical Trials

General Clinical Use

Postmarket Surveillance:Artificial TMJ Device Retrieval

Patient Follow-up

Complications

Phase 1

Phase 2

Phase 3

Phase 4

Phase 5

Figure 5: Recommended Protocol forArtificial TMJ Device Development

and Evaluation


SROMS 4 VOLUME 7.5

Table 3: Early Alloplastic TMJ Prostheses

degenerative disease, pathology, or previoussurgery. Homsy simulated a 12-kg total load onthe tested joint prostheses, and demonstratedacceptable wear rates for both the Teflon FEPand the PTFE. The condylar prosthesis wasconstructed of chrome-cobalt with a layer ofProplast on the inner surface of the ramalflange to encourage rapid ingrowth in both hardand soft tissues. The condylar prosthesis alsohad an L-shaped groove on the medial surface,and a template was used to drill a channelthrough the cortical bone on the medial ramusof the mandible, allowing the anti-rotationalflange to fit securely against the surface of theramus. The prosthesis was then fitted with twoor three bolt-and-nut type fasteners. In 1986,the fossa was modified (VK II) with its uppersurface of Proplast-hydroxyapatite and its

articulating surface made of ultra-high-molecu-lar-weight polyethylene (UHMWPE).19

Clinical Outcomes

Kent and Misiek reported a series of 170patients who had received 182 joints for partialor total joint reconstruction between 1982 and1988.20 There was a higher success rate forpatients reconstructed with the VK II fossa(94%) as opposed to the VK I fossa (75%). In1993, Kent et al, published a ten-year follow-up for the VK I fossa and a six-year follow-up,for the VK II fossa.21 Some 248 of the 262 jointswere available for long-term follow-up and thecumulative success rate for the VK I total jointswas approximately 20%. The success

alloplastic reconstruction of the tmj.pdf

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