radiographic demarcation of the acetabular bone-cement interface

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Radiographic Demarcation of the Acetabular Bone-Cement Interface The Effect of Femoral Head Size Andrew Frankel, M_D,* Richard A. Balderston, MD,-I- Robert E. Booth, Jr., MD,-]- and Richard H. Rothman, MD, PhD-]- Abstract: Between 1983 and 1988, 182 total hip anhroplasties were inserted using modern cement techniques including metal-backed acetabular compo- nents. Femoral head size was 32 mm in 84, 22 mm in 98. Radiographic analysis revealed three-zone demarcation of acetabular bone-cement interface in 56% of the 32 mm group as compared to 5% of the 22 mm group at 19 and 24 months mean follow-up period, respectively. When a subgroup of women under 60 years of age was created to control variables, the high-grade demarcation rates were 67% and 18%, respectively. Although Charnley hip scores remain similar between the two groups, these results emphasize the adverse effects of large femoral head prostheses on cement-bone interface and underline the need for alternative methods of fixation. Key words: hip anhroplasty, primary ce- mented. The major complication of conventional cemented total hip arthroplasty has been late aseptic loosening. Acetabular loosening rates as diagnosed by demar- cation in the three zones of DeLee and Charnley (5) have ranged between 7.9% and 20.9% at 10-year follow-up evaluation for Charnley prostheses (1, 7, 10, 11). Muller prostheses, with their larger femoral head sizes, have had acetabular demarcation rates of 41.7% at 10 years (10). Morrey and Ilstrup reviewed the Mayo Clinic experience with acetabular loos- ening, noting the highest rate of loosening with 32 mm components. Twenty-two mm components had * From the Program of Orthopaedic Surgery, Thomas Jefferson Uni- versity, Philadelphia, Pennsylvania. From Thomas Jefferson University, Philadelphia, Pennsylvania, and Pennsylvania Hospital. Philadelphia, Pennsylvania. Reprint requests: Richard H. Rothman, MD, PhD, Department of Orthopaedic Surgery, Thomas Jefferson University, 1051 Wal- nut Street, Philadelphia, PA 19107. a significantly lower revision rate, and 28 mm the lowest (9). As a direct result of the frequency of aseptic loos- ening, improvements in both cement techniques and prosthetic design have evolved. Pressurization and centrifugation of polymethylmethacrylate and pul- satile lavage were introduced in the late 1970s in an effort to improve fixation, and early 5-year results have been encouraging (3). In the early 1980s metal backing was added to acetabular components to re- duce peak stresses in bone and cement. Neck profiles have been modified and designed in both the tem- porary Charnley systems and T-28 systems to reduce impingement and cup loosening. In an effort to evaluate the effect of femoral head size on acetabular loosening, the authors examined the clinical and radiographic results of patients undergoing total hip arthroplasty with two different sizes of femoral head prostheses. Modern cement

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Page 1: Radiographic demarcation of the acetabular bone-cement interface

Radiographic Demarcat ion of the Acetabular B o n e - C e m e n t Interface

The Effect of Femoral Head Size

A n d r e w F r a n k e l , M_D,* R i c h a r d A. B a l d e r s t o n , MD,-I-

R o b e r t E. B o o t h , Jr . , MD,-]- a n d R i c h a r d H. R o t h m a n , M D , PhD-]-

Abstract: Between 1983 and 1988, 182 total hip anhroplasties were inserted using modern cement techniques including metal-backed acetabular compo- nents. Femoral head size was 32 mm in 84, 22 mm in 98. Radiographic analysis revealed three-zone demarcation of acetabular bone-cement interface in 56% of the 32 mm group as compared to 5% of the 22 mm group at 19 and 24 months mean follow-up period, respectively. When a subgroup of women under 60 years of age was created to control variables, the high-grade demarcation rates were 67% and 18%, respectively. Although Charnley hip scores remain similar between the two groups, these results emphasize the adverse effects of large femoral head prostheses on cement-bone interface and underline the need for alternative methods of fixation. Key words: hip anhroplasty, primary ce- mented.

The major complication of conventional cemented total hip arthroplasty has been late aseptic loosening. Acetabular loosening rates as diagnosed by demar- cation in the three zones of DeLee and Charnley (5) have ranged between 7.9% and 20.9% at 10-year follow-up evaluation for Charnley prostheses (1, 7, 10, 11). Muller prostheses, with their larger femoral head sizes, have had acetabular demarcation rates of 41.7% at 10 years (10). Morrey and Ilstrup reviewed the Mayo Clinic experience with acetabular loos- ening, noting the highest rate of loosening with 32 mm components. Twenty- two m m components had

* From the Program of Orthopaedic Surgery, Thomas Jefferson Uni- versity, Philadelphia, Pennsylvania.

From Thomas Jefferson University, Philadelphia, Pennsylvania, and Pennsylvania Hospital. Philadelphia, Pennsylvania.

Reprint requests: Richard H. Rothman, MD, PhD, Department of Orthopaedic Surgery, Thomas Jefferson University, 1051 Wal- nut Street, Philadelphia, PA 19107.

a significantly lower revision rate, and 28 m m the lowest (9).

As a direct result of the frequency of aseptic loos- ening, improvements in both cement techniques and prosthetic design have evolved. Pressurization and centrifugation of polymethylmethacrylate and pul- satile lavage were introduced in the late 1970s in an effort to improve fixation, and early 5-year results have been encouraging (3). In the early 1980s metal backing was added to acetabular components to re- duce peak stresses in bone and cement. Neck profiles have been modified and designed in both the tem- porary Charnley systems and T-28 systems to reduce impingement and cup loosening.

In an effort to evaluate the effect of femoral head size on acetabular loosening, the authors examined the clinical and radiographic results of patients undergoing total hip arthroplasty with two different sizes of femoral head prostheses. Modern cement

Page 2: Radiographic demarcation of the acetabular bone-cement interface

$2 The Journal of Arthroplasty Vol. 5 Supplement October 1990

techniques and metal-backed acetabular compo- nents were utilized in all cases.

T a b l e 2. M e a n Charn ley Scores

32 m m 2 2 m m P Value

Materials and Methods

Between 1983 and 1986, 84 cementless Trilock femoral components with a femoral-head diameter of 32 mm were inserted with cemented metal-backed acetabular components. Sixty-eight were inserted in men, 16 in women. During the same time interval, 98 cemented 22 nun femoral-head diameter prostheses were inserted with cemented metal- backed acetabular components. Twenty-two were inserted in men, 76 in women. Only patients undergoing primary arthroplasty for degenerative ar- thritis or avascular necrosis were included in the study. Pressurization, cement configuration, and pulsatile lavage were routinely employed.

Patients were evaluated by an independent ex- aminer and a hip data form and hip score of D'Au- bigne-Postel (4), as modified by Charnley (2), prior to operation and yearly after operation. Radiographs were taken at each visit and analysis was performed by measuring the width of radiolucent lines at the acetabular b o n e - c e m e n t interface in each of the three zones of DeLee and Charnley (5). Evidence of acetabular component motion was also evaluated by radiographs by looking for cephalad migration and/ or orientation angle shift. All results were entered on a computer. Statistical analysis was performed by F statistics, Kruskal-Wallis, and Chi square analyses where appropriate.

Results

The mean age, height, and weight of the two groups, presented in Table 1, demonstrated signifi- cant differences. The preoperative Charnley hip scores and classifications were nearly identical in both groups (Tables 2, 3). The clinical and radio- graphic follow-up period averaged 29 months for the

Preoperative pain 2.99 3.01 NS Postoperative pain 5.78 5.77 NS Preoperative function 2.62 2.64 NS Postoperative function 5.72 5.33 P = .016 Preoperative ROM 3.09 3.11 NS Postoperative ROM 5.60 5.30 P < .005

NS, not significant; ROM, range of motion.

Table 3. Charnley Classifications

3 2 m m 2 2 m m

Charnley A 40% 40% Chamley B 13% 10% Charnley C 8% 18% Charnley BB 38% 32% 3-Zone demarcation (47) 56% (5) 5% Acetabular movement (13) 15% (2) 2%

32 mm group (range, 4 - 5 3 months) and 24 months for the 22 m m group (range, 6 - 4 0 months) .

At the most recent follow-up examination, mean hip scores for pain, function, and range of mot ion had improved markedly (Table 2). There was no, sig- nificant difference between the two groups' m e a n postoperative pain scores. The 22 m m group had sig- nificantly lower mean function and range of mot ion scores. To date, there have been no dislocations, in- fections, or revisions in either group.

Radiographic analysis revealed high-grade de- marcation of all three zones of DeLee and Charnley (as indicated by a continuous 1 mm or greater ra- diolucent line at the b o n e - c e m e n t interface) in 47 (56%) of the 32 m m group. Only five (5%) patients in the 22 m m group demonstrated three-zone de- marcation (P = .001). Thirteen of the 32 m m group exhibited radiographic signs of acetabular move- ment, as evidenced by either greater than 3 nun of cephalad migration of the component in relation to the transischial line or more than 3 degrees of an- gular shift of the intersection of the long axis o f the component and the transischial line. None of the 22 mm group exhibited radiographic signs of acetabular movement .

T a b l e 1. D e m o g r a p h i c Data

32 mm 22 mm P Value

Women 16 76 P < .00 l Men 68 22 P < .001 Age 53 yrs. 68 yrs. P < .001 Height 69 inches 64 inches P < .001 Weight 182 lbs. 145 lbs. P < .00l

Discussion

The results presented show the significant differ- ence (over tenfold) between aseptic loosening rates of the 32 m m group and the 22 rnm group. This difference was clearly multifactorial. The 32 nun

Page 3: Radiographic demarcation of the acetabular bone-cement interface

Acetabular Bone-Cement Interface = Frankel et al. $3

group, besides having the larger femoral head size, also had a greater percentage of men, heavier pa- tients, younger patients, a smaller percentage of Charnley class C patients, and patients with longer follow-up periods.

In an effort to control m a n y of these variables, a subgroup was created to look at only w o m e n under 60 years of age. The new populat ion 's characteristics are listed in Table 4. The three-zone demarcat ion rates remained significantly different. Two of the 32 m m w o m e n exhibited radiographic signs of acetab- ular motion. Differences still existed be tween the subgroups ' mean ages and mean fol low-up periods. Nonetheless, the significantly higher acetabular loos- ening rate of the larger femoral heads illustrate the necessity to avoid their use w h e n also using cement. It also illustrates that m ode rn cement techniques and metal-backed acetabular c o m p o n e n t s do not nec- essarily improve the long- term fixation of acetabular implants with large femoral heads.

Theoretical reasons for the significant differences in loosening rates be tween the different sized prostheses are multiple also. The larger circumfer- ence femoral heads have been shown to have greater frictional torque (8), and hence higher stresses on the b o n e - c e m e n t interface. Other causes inherent to the prosthesis m a y include larger prosthetic necks and alternations of the anatomical center of rotation of the replaced hip, thus leading to higher forces en- countered by the b o n e - c e m e n t interface. The larger head prostheses required more superior and lateral placement of the acetabular componen t (11). Fi- nally, the 32 m m femoral componen t was not ce- mented while the 22 m m was. Theoretically, the ce- mented 32 m m acetabular components could have been under higher stresses secondary to the nnce- mented femoral component .

Although the acetabular demarcat ion rates and loosening rates are skewed towards the 32 m m group, mean Charnley pain scores be tween the two groups were equal. The 32 m m group had signifl-

Table 4. Women Under Age 60

32 mm 22 mm P Value

Women 15 17 Weight 142 lbs. 134 lbs. NS Follow-up period 30 mos. 23 mos. P = .0033 Age 50 yrs. 56 yrs. P = .0141 3-Zone demarcation 67% 18% P < .00l Radiographic motion 13% 0%

NS, not significant.

cantly higher mean function and mean range of mo- tion scores. The range of mot ion is probably a result of the larger diameter of the femoral head. The higher functional score probably reflects the smaller per- centage of Charnley C patients in the 32 m m group in comparison to the 22 m m group. The equal pain scores in both groups suggest that radiographic ac- etabular loosening is welI tolerated and not a source of pain, at least at this early fol low-up period.

In conclusion, acetabular componen t loosening rates, as determined by three-zone demarcat ion and componen t migration, were significantly higher in a larger femoral head diameter prosthesis despite metal backing and modern cement techniques. We recommend that the surgeon avoid the combinat ion of large femoral head prosthesis and cement. This study also suggests the necessity to find alternative methods of fixation in young active patients.

References

1. Chamley J: Low friction arthroplasty of the hip; the- ory and practice. Springer Verlag, Berlin, 1979

2. Charnley J, Cupic Z: The nine and ten year results of the low friction arthroplasty of the hip. Clin Orthop 95:9, 1973

3. Cornell CN, Ranawat CS: The impact of modem ce- ment techniques on acetabulum fixation in cemented total hip replacement. J Arthroplasty 1:197, 1986

4. D'Aubigne RM, Postel M: Individual results of hip ar- throplasty with acrylic prosthesis. J Bone Joint Surg 36A:451, 1954

5. DeLee J, Chamley J: Radiological demarcation of ce- mented sockets in total hip replacement. Clin Orthop 121:20, 1976

6. Harris WH, White RE Jr: Socket fixation using a metal backed acetabular component for total hip replace- ment. J Bone Joint Surg 64A:745, 1982

7. Johnston RC, Crowninshield RD: Roentgenologic re- sults of total hip arthroplasty. Clin Orthop 181:92, 1983

8. Ma SM, Kabo JM, Amstutz HC: Frictional torque in surface and conventional hip replacement. J Bone Joint Surg 65A:366, 1983

9. Morrey BF, Ilstmp D: Size of the femoral head and acetabular revision in total hip arthroplasty. J Bone Joint Surg 71A:50, 1989

10. Ritter MA, Campbell ED: Long-term comparison of the Chamley, Muller, and Trapezoidal-28 total hip prostheses. J Arthroplasty 2:299, 1987

11. Stauffer RN: Ten year follow-up study of total hip re- placement. J Bone Joint Surg 64A:983, 1982