300 THE BONE & JOINT JOURNAL

HIP

Early surveillance of ceramic-on-metal total hip arthroplasty

J. C. Hill,O. J. Diamond,S. O’Brien,J. G. Boldt,M. Stevenson,D. E. Beverland

From Musgrave Park Hospital, Belfast, United Kingdom

J. C. Hill, MEng, MSc, PhD, Primary Joint Research Manager, Outcomes Unit O. J. Diamond, MB, BCh BAO, MSc, MD, MRCS (Ed), DipSEM, Registrar in Trauma and Orthopaedic Surgery, Outcomes Unit S. O’Brien, RGN, Dip/N (Lond), BSc(Hons), PhD, Outcomes Unit Manager, Outcomes Unit D. E. Beverland, MD, FRCS, Consultant Orthopaedic Surgeon, Outcomes UnitMusgrave Park Hospital, Stockman’s Lane, Belfast, BT9 7JB, UK.

J. G. Boldt, MD, Consultant Orthopaedic and Trauma Surgeon, Head of Orthopaedic Department Klinik SiloahPrivate Hospital Worbstrasse, 324 CH 3073 Guemligen, Switzerland.

M. Stevenson, BSc. FSS, Senior Lecturer, Medical StatisticsInstitute of Clinical Science 'B' , Grosvenor Road, Belfast BT12 6BJ, UK.

Correspondence should be sent to Dr J. C. Hill; e-mail: janet.hill@belfasttrust.hscni.net

©2015 The British Editorial Society of Bone & Joint Surgerydoi:10.1302/0301-620X.97B3. 33242 $2.00

Bone Joint J2015;97-B:300–5. Received 24 September 2013; Accepted after revision 27 October 2014

Ceramic-on-metal (CoM) is a relatively new bearing combination for total hip arthroplasty (THA) with few reported outcomes. A total of 287 CoM THAs were carried out in 271 patients (mean age 55.6 years (20 to 77), 150 THAs in female patients, 137 in male) under the care of a single surgeon between October 2007 and October 2009. With the issues surrounding metal-on-metal bearings the decision was taken to review these patients between March and November 2011, at a mean follow-up of 34 months (23 to 45) and to record pain, outcome scores, radiological analysis and blood ion levels. The mean Oxford Hip Score was 19.2 (12 to 53), 254 patients with 268 hips (95%) had mild/very mild/no pain, the mean angle of inclination of the acetabular component was 44.8o (28o to 63o), 82 stems (29%) had evidence of radiolucent lines of > 1 mm in at least one Gruen zone and the median levels of cobalt and chromium ions in the blood were 0.83 μg/L (0.24 μg/L to 27.56 μg/L) and 0.78 μg/L (0.21 μg/L to 8.84 μg/L), respectively. The five-year survival rate is 96.9% (95% confidence interval 94.7% to 99%).

Due to the presence of radiolucent lines and the higher than expected levels of metal ions in the blood, we would not recommend the use of CoM THA without further long-term follow-up. We plan to monitor all these patients regularly.

Cite this article: Bone Joint J 2015;97-B:300–5.

Traditionally, most total hip arthroplasties(THAs) have used metal-on-polyethylene (MoP)articulations.1 However, particulate debrisresulting from wear of the polyethylene bearingsurface can lead to failure due to osteolysis andsubsequent loosening.2 As a result, alternativearticulations such as ceramic-on-ceramic (CoC)and metal-on-metal (MoM) have been intro-duced in an endeavour to reduce wear and oste-olysis, and to extend the life of the implant.3,4

Both of these bearing surfaces have been shownto produce less wear than MoP.5 However, withthe recent problems observed with MoM THA,CoC is now considered to be the safer choicewith low rates of wear and excellent survival,which in some studies is greater than that ofMoP, at ten years and beyond, even in young,high demand patients.6-9

In spite of the low rates of wear of both CoCand MoM bearings, there are theoreticaladvantages to the use of ceramic-on-metal(CoM) bearings. The use of bearing surfaceswith different levels of hardness may result inlower rates of wear.10 In CoM, the harderceramic head may be more resistant to damageand stripe wear under edge loading than ametal head, and the use of a metal acetabularliner avoids the problems associated with

ceramic liners, which may chip or crack duringseating.7,11 In theory, blood metal ion levelsshould be lower than with MoM bearings andthere are also unsubstantiated claims ofreduced squeaking compared with CoC.12

Finally, metal liners can be made less thick thanceramic liners, allowing larger head sizes to beused; for instance, with the Pinnacle system(DePuy Synthes, Leeds, United Kingdom) it ispossible to use a 36 mm head with a 50 mmacetabular component, whereas with a ceramicliner it is only available with a 52 mm implant.It was these theoretical advantages thatprompted us to start using a CoM bearing in2007.

Ceramic-on-metal (CoM) articulations arenot widely used in THA. In the 2013 reportfrom the National Joint Registry for England,Wales and Northern Ireland (NJR) only 2017CoM THAs are recorded, with up to four yearsof follow-up data;13 in the Australian Ortho-paedic Association Joint Replacement Registry(AOANJRR), there are only 316 such THAs.14

In the NJR, the four-year rate of revision forCoM is 4.15% (95% confidence interval (CI)3.06 to 5.62),13 compared with 2.20% (95%CI 2.06 to 2.34) and 5.24% (95% CI 4.97 to5.52) for cementless THA using CoC and

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MoM bearings, respectively. The AOANJRR reports athree-year rate of revision of 3.6%.14

Due to the recent concern with the early failure of MoMTHAs15 and the lack of clinical data available on the use ofCoM THA, a surgeon-initiated surveillance programmewas carried out at our hospital. This study reports a single-surgeon series of CoM THAs, with outcomes includingimplant survival, radiological outcomes, blood ion levels,and clinical outcomes including pain and patient-reportedoutcome measures (PROMs).

Patients and MethodsA total of 287 CoM THAs (271 patients) were performedunder the care of the senior author (DEB) between October2007 and October 2009. CoM was our bearing of choicefor younger patients, and the mean age of patients in thiscohort was 55.6 years (20 to 77). Of the 271 patients, 141were women (150 hips, 52%) and 152 (53%) were right-sided. In all cases, a Corail femoral stem was used with aBiolox Delta ceramic head, and a Pinnacle metal liner (allDePuy Synthes, Leeds, United Kingdom). The Corail stemis available with three configurations of neck: standard(available with and without a collar), coxa vara (which hasa collar) and high offset (which is collarless); 28 mm, 32mm and 36 mm diameter modular heads were used; allwere available with three lengths of neck (1.5 mm, 5 mm,8.5 mm). The operations were undertaken with the patientin a lateral decubitus position using the posterior approach.

In our institution, patients are routinely reviewed at sixweeks, one year and ten years by an arthroplasty nurse spe-cialist. An additional review was carried out for this cohortbetween March and November 2011. Unfortunately, thepaper was not submitted until now due to the volume ofwork and low staffing levels within the unit. At each visit,outcomes were assessed using the Oxford hip Score(OHS)16 in its original format (scoring from 12 (best) to 60(worst)), Harris hip score (HHS)17 and a visual analoguescore (VAS) for pain, with 1 being no pain and 5 severepain. Anteroposterior (AP) pelvic and lateral hipradiographs were taken at one year and at the time of the

review. At the review, blood was taken to measure cobaltand chromium whole blood ion levels. Samples were ana-lysed in an approved laboratory using inductively coupledplasma mass spectrometry (Element2, Thermo Finnigan,Bremen, Germany). In order to give up to date data, sur-vival is reported at the time of the submission of the paper,rather than at the time of the surveillance review. Patientswere contacted via telephone, and the two that were lost tofollow-up at the time of review were later verified as stillhaving their THA by a relative.

Radiographs were analysed by an independent expert(JB). The angle of inclination of the acetabular componentwas measured using the teardrop method on the immediatepost-operative AP radiograph.18 The presence and size ofradiolucent lines (RLLs) were assessed and classified inGruen19 zones (1 to 14, for the femoral component) andDeLee and Charnley20 zones (1 to 3, for the acetabular com-ponent). THAs were classified into one of five groups basedon the width of radiolucency around the femoral compo-nent (0 mm, 1 mm, 2 mm, 3 mm to 4 mm or > 5 mm).Statistical analysis. This was performed using SPSS v. 17 forWindows (SPSS Inc., Chicago, Illinois). Chi-squared testingfor trend was performed to determine which factors affectedthe presence of radiolucency around the femoral stem. Out-comes included the rate of revision, pain score, OHS andHHS (one year and at most recent review) and metal ion lev-els (cobalt and chromium). Independent variables used inthe analysis were age, gender, component sizes (head, ace-tabular component and stem), length of the neck and radio-logical inclination of the acetabular component. Pairedsamples t-tests were used to determine any significancebetween OHS, HHS and pain scores at different time points.Independent samples t-tests were used to establish whetherthe levels of cobalt and chromium in patients’ blood was dif-ferent for males and females. Product moment correlationswere used to determine correlations between blood metalions and acetabular component inclination angle. A lifetable analysis was undertaken for 95% CI at five years. Themedian censor point was five years and ten months.

ResultsThe mean follow-up time for the surveillance review was34 months (standard deviation (SD) 5.1; 23 to 45). At thistime, three patients (four hips) had died, and two (two hips)had been lost to follow-up. Three patients (three hips) wereunable to attend and were reviewed by telephone; these didnot have radiographs or metal ion measurements. As aresult, 281 hips (266 patients) were reviewed, of which 278hips (263 patients) had radiographs and metal ion measure-ments. Since the surveillance review, a further three patientshave died (Fig. 1).

The mean OHS was 19.2 (SD 8.8) and the mean HHS was92.8 (SD 10.5). 254 patients (268 hips; 95%) reported mild,very mild or no pain (Fig. 2). The mean OHS and HHS painscores improved significantly between pre-operative scoreand latest follow-up (p < 0.001 in all cases) (Table I). Six

Assessed for eligibility(n* = 287)

Excluded (n = 6)- Deceased (n = 4)- Lost to follow-up (n = 2)

Full review(n = 278)

Telephone review only(n = 3)

Reviewed(n = 281)

Fig. 1

CONSORT flow diagram (n* = number of THAs, not number ofpatients).

302 J. C. HILL, O. J. DIAMOND, S. O’BRIEN, J. G. BOLDT, M. STEVENSON, D. E. BEVERLAND

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patients (2%) complained of noise (clicking, grinding orjuddering) from the hip, although patients were not askedabout this routinely.

As of August 2014, eight patients (eight THAs) haveundergone a revision due to pain (Table II) and six patients(seven THAs) have died. The rate of survival for all patientsat five years is 96.9% (95% CI 94.7 to 99) (Fig. 3). Two

further patients were offered revision as the first had apseudotumour surrounding the greater trochanter and thesecond showed radiographic changes in zones 1, 7, 8 and14, as well as experiencing pain. Neither, however, under-went the procedure. One was considered too high risk foranaesthesia and the other refused surgery as his symptomswere tolerable despite the identification of a pseudotumour

Nu

mb

er o

f TH

As

Pre-op

No painVery mildMildModerateSevere

One yr 34 mths

200

150

100

50

0

Fig. 2

Histogram showing pre- and post-operative pain scores at one year and34 months.

Table I. Oxford hip score (OHS) and Harris hip score (HHS) of patients

OHS HHS

Mean (range) Absolute p-value* Mean (range) Absolute p-value*

Pre-operative 47.1 (28 to 58) - 37.6 (10 to 71) -1 year 21.8 (12 to 53) < 0.001 88.1 (30 to 100) < 0.001Surveillance review 19.2 (12 to 53) < 0.001 92.8 (29 to 100) < 0.001

* compared with pre-operative score

Table II. Reasons for revision surgery in eight patients (eight hips)

Revisionnumber

Time to revision (mths) Symptoms

Metal ion levels (μg/L) at surveillance review

Metal ion levels (μg/L) prior to revision MRI findings

1 36 Anterior thigh pain, radiological changes in zones 1, 7 and 8

Not done – revised before review took place

Not done No evidence of soft-tissue mass or fluid collection

2 34 Thigh pain, restricted move-ment, periosteal reaction, radiological changes in zones 1 and 7, suggestive of infection

Co: 0.2; Cr: 0.5 Not repeated Not done

3 49 On-going pain and progressive radiolucency on radiographs

Co: 1.1; Cr: 1.1 Co: 1.1; Cr: 1.3 No evidence of soft-tissue mass or fluid collection

4 61 Ongoing pain increasing in severity

Co: 2.4; Cr: 2.2 Co: 5.8; Cr: 1.6 Pseudotumour formation

5 55 Pain and noise reported as ‘juddering’ by the patient

Co: 5.1; Cr: 2.3 Co: 5.4; Cr: 2.6 Fluid collection around hip

6 55 Lateral thigh pain, sticking and grinding sensation

Co: 14.8; Cr: 4.0 Co: 57.3, Cr: 6.0 No evidence of pseudotumour

7 54 Sudden pain for six weeks prior to revision, unable to bear weight on hip

Co: 0.83; Cr: 0.5 Co: 2.3; Cr: 0.3 No evidence of pseudotumour

8 72 Developed start-up pain and difficulty walking

Co: 10.2; Cr: 5.6 Co: 12.6; Cr: 11.5 No evidence of pseudotumour

Co, cobolt; Cr, chromium

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on MRI. If these patients had been revised, the overall fiveyear survival would have been 96.2% (95% CI 93.8 to98.5).

The median blood levels of cobalt and chromium in all263 patients (278 THAs) were 0.83μg/L (0.24 to 27.56) and0.78μg/L (0.21 to 8.84), respectively. A total of 31 patients(12.5%, 35 THAs) had blood cobalt levels of > 2 μg/L, andsix patients had levels of > 7 μg/L (2.5%, seven THAs). Forchromium, 26 patients (11.1%, 31 THAs) had levels of> 2 μg/L, and one patient (0.4%, one THA) had levels of> 7μg/L (Fig. 4) Chromium levels were significantly higher inwomen than in men (p = 0.024, t-test, but there was nosignificant difference between genders in cobalt levels(p = 0.20, t-test). It should be noted that three patients hadan ASR THA and two patients had MoM resurfacing hiparthroplasty on the contralateral side.

The mean angle of inclination of the acetabular compo-nent was 44.8o (28o to 63o) (Fig. 5). There was no signifi-cant correlation between this angle and the levels of cobalt

or chromium ions (product moment correlation, p = 0.14and p = 0.25, respectively). The angle of inclination was> 45o in 135 THAs (132 patients; 47.7%) and it was > 50o

in 46 hips (45 patients; 16.3%).At the surveillance appointment, 84 stems in 82 patients

(30%) had RRLs of > 1 mm in at least one Gruen zone.Overall, 22 stems in 22 patients (8%) had radiolucent linesof > 5mm. There was no correlation between any of thepredictors studied and the extent of radiolucent lines.Patients receiving a stem without a collar (high offset orstandard) were more likely to have radiolucency comparedwith those with a collar (standard or coxa vara; chi squaredtest for trend p < 0.001). Of the collared stems, 101 stemsin 98 patients (73%) had no radiolucency compared with63 stems in 63 patients (47%) of those with no collar; 15%of collarless stems had radiolucent lines of > 5 mm (Fig. 6).

DiscussionThis study has shown acceptable PROMS in predominantlyyoung patients receiving CoM THA. However, there was ahigher that expected rate of revision and a high proportionof surviving patients with high metal ion levels in the bloodand RLLs on radiographs. CoM is a relatively new articu-lation in THA and there are little data to support its use.Such studies that do exist report small numbers of patientswith short follow-up.11,21-24 There is one prospective ran-domised controlled trial comparing CoM (n = 42, with onelost to follow-up) to MoM (n = 39, three lost to follow-up)which concluded that the rise in serum cobalt and chro-mium levels was similar in both articulations with similarclinical outcomes and no revisions in either group one yearpost-operatively.21

Joyce et al22 presented a cohort of 56 patients with amean age of 64 years, at a mean of 1.5 years followingsurgery. They reported a revision rate of 10.7% withrevisions being largely for pain and femoral loosening;

1.10

Cu

mu

lati

ve s

urv

ival 1

0.99

0.98

0.97

0.96

0.95

0.94

Follow-up (yrs)0 1 2 3 4 5 6 7

95% CI lower limit95% CI upper limitSurvival

Fig. 3

Life table analysis for 95% confidence intervals (CI) at five years.

200

160

120

80

40

00 to 0.99 1 to 1.99 2 to 3.99 4 to 6.99 7 +

Blood metal ion level (µg/L)

Cobalt Chromium

Nu

mb

er o

f T

HA

s

Fig. 4

Graph showing distribution of blood ion levels of cobalt and chromiummeasured at 34 month follow-up. (THA, total hip arthroplasty).

100

80

60

40

20

026 to 30 31 to 35 36 to 40 41 to 45 46 to 50 51 to 55 56 to 60 61 to 65

Cup inclination angle (º)

Nu

mb

er o

f T

HA

s

Fig. 5

Histogram showing the distribution of acetabular inclination anglesmeasured on post-operative anteroposterior radiographs. (THA, totalhip arthroplasty).

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however, the mean serum cobalt and chromium levels were< 2 μg/L. Kazi et al23 reported a prospective study of 94CoM THAs at two years, again finding low mean levels ofmetal ions (cobalt 1.37 μg/L; 0.12 to 10.68; chromium1.09 μg/L; 0.00 to 5.51). Only one hip in that series wasrevised, and the authors concluded that CoM THA is safeand efficacious. However, they expressed concerns aboutthe potential for chromosomal aberrations secondary tohigh levels of metal ions. Isaac et al11 reported on 30 CoMTHAs at a follow-up of 12 months, reporting a revisionrate of 3.3% and median blood metal ion measurements of0.72 μg/L and 0.43 μg/L for cobalt and chromium, respec-tively. There is one case report of a CoM THA failure asso-ciated with massive metallosis and pseudotumour in a 51-year-old female.24

The five-year revision rate for CoM THAs in this series is3.1%, but if all patients suitable for revision had beenrevised, it would be 3.8% (95% CI 1.5% to 6.2%). Of theeight revised THAs, six were revised after > four years. Thecurrent revision rate is slightly lower than CoM THAs inthe tenth NJR report (4.15% at four years).13

In well-functioning MoM THAs, the serum chromiumlevel should be approximately 2 μg/L; this figure doubles inthose which do not function well.25,26 One of the theoreticaladvantages of CoM is the potential reduction in blood metalion levels when compared with MoM and our results wouldappear to concur as mean and median cobalt and chromiumlevels were much less than the suggested threshold of 2 μg/Lfor a well-functioning hip.26 The United Kingdom Medicinesand Healthcare products Regulatory Agency (MHRA)27

considers levels of cobalt or chromium > 7 ug/L to be a con-cern, however, others have suggested that a level of 4 ug/Lmay be more appropriate.28 In our study, 11.4% had ion

levels > 2 μg/L, 4.0% were > 4 μg/L and 2.2% were > 7 μg/Lfor either cobalt or chromium. Although these are relativelysmall numbers of patients, we consider this to be worrying.Despite the theoretical advantages, given the present con-cerns and our lack of understanding about the local and sys-temic effects of raised whole blood or serum metal ion levels,coupled with the availability of other satisfactory options forTHA, we feel that CoM articulations should be avoided, atleast until we have the data from follow-up studies at a min-imum of ten years.

In this study, RLLs were more frequent in hips without acollar. We suggest that the collar may provide a barrier.Vidalain29 reviewed a series of 347 THAs (320 patients)who had undergone THA with a Corail stem and a polyeth-ylene acetabular component using the standard neck type,with and without a collar. In 127 THAs they found, at amean follow-up of 20.9±1.9 years, that while 89% of thosewith a collared stem had no radiolucency, this figure wasonly 81% for hips without a collar. RLLs were observedmore frequently in our series (71% of collared stems had noradiolucency and 47% of uncollared stems had no radiolu-cency) after a much shorter follow-up. Previous authorshave suggested that high offset stems may create highstresses at the stem/femur interface but none have shown adefinite link.30

We have reported poor survival with a worrying level ofblood metal ions and radiological changes in CoM THAs.We have not demonstrated CoM to be superior to the alter-natives in terms of noise or ion levels and we would not rec-ommend the use of this bearing couple in THA. We plan tomonitor all our CoM patients regularly.

Author contributionsJ. C. Hill: Writing and editing paper, Analysis and interpretation of data.O. J. Diamond: Writing and editing paper.S. O’Brien: Data acquisition, Editing paper.J. G. Boldt: Analysis and interpretation of data.M. Stevenson: Statistical analysis.D. E. Beverland: Designing and editing paper.

The author or one or more of the authors have received or will receive benefitsfor personal or professional use from a commercial party related directly orindirectly to the subject of this article. In addition, benefits have been or will bedirected to a research fund, foundation, educational institution, or other non-profit organisation with which one or more of the authors are associated.

This article was primary edited by A.D. Liddle and first proof edited by G. Scott.

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80

60

40

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0

100

Perc

enta

ge

of

TH

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(%)

Standard with collar

Standard no collar

High offset Coxa vara

Neck type

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Fig. 6

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