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The Journal of Bone & Joint Surgery, Volume 78, Issue 9

Articles | September 01, 1996

Revision of the Acetabular Component without Cement after Total Hip Arthroplasty. A Follow-up Note Regarding Results at Seven to Eleven Years*

CRAIG D. SILVERTON, D.O.†; AARON G. ROSENBERG, M.D.†; MITCHELL B. SHEINKOP, M.D.†; LAURA R. KULL, M.S.†; JORGE O. GALANTE, M.D.†, CHICAGO, ILLINOIS

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Investigation performed at the Department of Orthopedic Surgery, Rush-Presbyterian-St. Luke's Medical Center, Chicago

The Journal of Bone & Joint Surgery. 1996; 78:1366-70

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Abstract

The results of revision of the acetabular component without cement, performed for aseptic loosening, were reported previously after a mean of forty-four months for 138 hips (132 patients). After an additional mean duration of follow-up of almost five years, twelve patients (twelve hips) had died before they could be followed long enough for the later study and nine patients (eleven hips) had been lost to follow-up; thus, a total of 111 patients (115 hips) were available for follow-up at a mean of 100 months (range, seventy-eight to 135 months). Between the earlier and later times of follow-up, six additional acetabuli had had a repeat revision: one, for recurrent dislocation; two, for infection; and three (which were stable), at the time of a revision of the femoral stem. No revision of the acetabular cup was performed because of aseptic loosening, and no cup was noted to have migrated.Radiographs were available for 105 patients (109 hips) at a mean of ninety-eight months (range, seventy-eight to 135 months). Five (5 per cent) of the 109 cups were surrounded by a complete radiolucent line and three (3 per cent), by a partial progressive radiolucent line. A radiolucent line adjacent to a screw was seen in association with two cups (2 per cent), and osteolysis was noted at the margin of four cups (4 per cent).Revision of the acetabular component with a porous-coated, nearly hemispherical fiber-metal component inserted without cement was associated with a high rate of excellent results at the seven to eleven-year follow-up examination.

Figures in this Article

Introduction

Introduction | Materials and Methods | Results | Discussion | References

One of the foremost problems associated with revision hip arthroplasty continues to be mechanical failure of the acetabular component with concomitant loss of acetabular bone stock^4,5,7,8,16.

In 1993, Padgett et al. reported our results, at a mean of forty-four months (range, thirty-six to eighty months), after 138 revisions in which a fiber-metal acetabular component had been inserted without cement. Seven acetabuli (5 per cent) had had a repeat revision: four, because of infection and three, because of instability. No hip had had a repeat revision because of aseptic loosening. Radiolucent lines were common; however, no component had migrated in the absence of infection. The purpose of the current study was to determine the results for the same group of patients after an additional mean duration of follow-up of almost five years. Longer-term follow-up is necessary to recognize time-dependent problems that may not be evident with shorter-term studies.

*One or more of the authors have received or will receive benefits for personal or professional use from a commercial party related directly or indirectly to the subject of this article. In addition, benefits have been or will be directed to a research fund or foundation, educational institution, or other non-profit organization with which one or more of the authors are associated. Funds were received in total or partial support of the research or clinical study presented in this article. The funding sources were Zimmer, Incorporated, and the Musculoskeletal Foundation.

†Department of Orthopedic Surgery, Rush-Presbyterian-St. Luke's Medical Center, 1653 West Congress Parkway, Suite 1471 Jelke, Chicago, Illinois 60612. Please address requests for reprints to Dr. Silverton.

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TABLE I COMPARISON OF THE RESULTS BETWEEN THE PREVIOUS AND CURRENT STUDIES

	Previous Study¹⁶	Current Study
Follow-up
Total no. followed	124 patients (129 hips)	111 patients (115 hips)
Mean durat. (mos.)	44 (range, 36—80)	100 (range, 78—135)
Died with inadequate follow-up	2 patients (2 hips)	12 patients (12 hips)
Lost to follow-up	6 patients (7 hips)	9 patients (11 hips)

Repeat revision of acetabular component	7 patients (7 hips; 5%)	13 patients (13 hips; 11%)
Infection	4 patients (4 hips; 3%)	6 patients (6 hips; 5%)
Dislocation	3 patients (3 hips; 2%)	4 patients (4 hips; 3%)
Cup stable; revised at time of revision of femoral component	0	3 patients (3 hips; (3%)
Aseptic loosening	0	0

Revision of femoral component	7 patients (7 hips; 5%)	30 patients (31 hips; 22%)

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TABLE I COMPARISON OF THE RESULTS BETWEEN THE PREVIOUS AND CURRENT STUDIES

	Previous Study¹⁶	Current Study
Follow-up
Total no. followed	124 patients (129 hips)	111 patients (115 hips)
Mean durat. (mos.)	44 (range, 36—80)	100 (range, 78—135)
Died with inadequate follow-up	2 patients (2 hips)	12 patients (12 hips)
Lost to follow-up	6 patients (7 hips)	9 patients (11 hips)

Repeat revision of acetabular component	7 patients (7 hips; 5%)	13 patients (13 hips; 11%)
Infection	4 patients (4 hips; 3%)	6 patients (6 hips; 5%)
Dislocation	3 patients (3 hips; 2%)	4 patients (4 hips; 3%)
Cup stable; revised at time of revision of femoral component	0	3 patients (3 hips; (3%)
Aseptic loosening	0	0

Revision of femoral component	7 patients (7 hips; 5%)	30 patients (31 hips; 22%)

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Anteroposterior radiograph made 105 months after revision with use of a seventy-millimeter-diameter acetabular component. The component is stable, with no changes compared with the appearance on radiographs made at sixty-four months. A radiolucent line of less than one millimeter in width is seen in zone C (arrow).

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Anteroposterior radiograph made eighty-six months after revision of the acetabular component with use of a bulk allograft. The component is stable, with no changes compared with the appearance on radiographs made at fifty-five months. The bulk allograft is incorporated and shows no resorption. A one-millimeter-wide radiolucent line is seen in zone C (arrow).

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Survivorship curve for the acetabular component, with removal of the component (repeat revision) or aseptic loosening as the end points. The dotted lines represent the 95 per cent confidence limits.

Materials and Methods

Introduction | Materials and Methods | Results | Discussion | References

Between October 1983 and December 1986, 138 consecutive revisions of the acetabular component were performed without cement in 132 patients, who were followed prospectively. There were seventy-five women (57 per cent) and fifty-seven men (43 per cent), and the mean age was fifty years (range, twenty to seventy-nine years). All components were of the Harris-Galante-I type (Zimmer, Warsaw, Indiana), were nearly hemispherical, and were coated with porous titanium fiber mesh. The shell and mesh were made of commercially pure titanium. The outer diameter of the cup ranged from forty-two to seventy-eight millimeters (median, sixty-two millimeters). In all hips, the initial fixation was secured with use of two to five 4.5-millimeter titanium-alloy cancellous-bone screws. The technique included so-called line-to-line reaming, with no attempt at so-called press-fitting of the component¹⁶.

Of the original 132 patients (138 hips), sixteen patients (seventeen hips) died during the study period. Of the patients who died, four (five hips) had had at least seventy-eight months of follow-up and were included in the study. Nine patients (eleven hips) were lost to follow-up. Six patients (six hips) could not return for radiographic evaluation but were interviewed by telephone. Thus, 111 patients (115 hips) were available for clinical evaluation at a mean of 100 months (range, seventy-eight to 135 months) and 105 patients (109 hips) were available for radiographic evaluation at a mean of ninety-eight months (range, seventy-eight to 135 months). In contrast, in our previous study, two patients (two hips) had died and six patients (seven hips) had been lost to follow-up, leaving a total of 124 patients (129 hips) for evaluation¹⁶.

The Harris hip-rating system was used for the clinical evaluation⁶. Serial anteroposterior radiographs of the pelvis were evaluated qualitatively by comparing the initial postoperative radiographs, those made at the earlier (three to five-year) evaluation, and those made at the latest follow-up evaluation. The radiographs were assessed for any evidence of migration, radiolucency adjacent to the component or the screws, separation of the porous pad from the metal shell, or breakage of the screws. The position of the component and evidence of migration were evaluated with a Sigma-Scan digitizing system (Jandel Scientific, San Rafael, California), and the serial radiographs were compared as described previously¹⁶. A difference of two millimeters or more in the serial measurements or a change of 3 degrees or more in the angle of the cup was considered to indicate migration.

The appearance, location, and size of any osteolytic lesions of the acetabulum were recorded. Any broken screw, radiolucent line adjacent to a screw, or fragmentation of the porous pad from the acetabular shell was noted.

The Kaplan-Meier survivorship analysis¹² was used to estimate the probability of failure of the implant as a function of the time since the operation. Failure was defined as removal of the component (repeat revision of the acetabulum) or aseptic loosening.

The Wilcoxon paired signed-rank test was used to compare the total number of zones with a radiolucent line as reported previously for these patients after a mean duration of forty-four months¹⁶ with the total number of zones with such a line in the current study after a mean duration of ninety-eight months. The McNemar test was used to compare the rate of cups with a radiolucent line in the individual zones (A₁, A₂, B₁, B₂, and C) in the previous study¹⁶ with the rate in the current one. The Wilcoxon signed-rank test was used to compare the rates of patients who had excellent, good, fair, and poor Harris hip scores at the latest follow-up evaluation in the two studies. The level of significance was p < 0.05.

Results

Introduction | Materials and Methods | Results | Discussion | References

The details concerning the perioperative complications and the earlier results for the original 132 patients (138 hips) have been reported previously¹⁶. The focus of the current report was the complications and results between the time of the original study and the current one.

Of the 115 hips that were available for follow-up, six had had a repeat revision of the acetabular component; when the seven hips that had had a repeat revision earlier¹⁶ are considered, the total rate of repeat revision was 11 per cent (thirteen hips). Of the six repeat revisions that were done after the time of the original study, one was performed for recurrent dislocation at seventy-five months, in a patient who had had a revision of the femoral component five months earlier. Late hematogenous infection necessitated a repeat revision in two hips (2 per cent); one revision was done at seventy-two months and the other, at 109 months. Three hips (3 per cent) had removal of a stable cup, at the surgeon's discretion, at the time of a later revision of the femoral stem at another institution. The three cups were found to be well fixed. No repeat revisions were performed for aseptic loosening of the acetabular component (Table I).

After the time of the original study¹⁶, an additional twenty-three patients (twenty-four hips) had a revision of the femoral component; when the seven patients (seven hips) who had such a procedure during the earlier follow-up period¹⁶ are included, the total rate of revision of the femoral component after the original revision of the acetabular component was 22 per cent (thirty patients; thirty-one hips). Of the twenty-three patients who had the revision of the femoral component during the later follow-up period, eighteen (nineteen hips) had it for aseptic loosening without a repeat revision of the acetabular component and five (five hips) had a revision of both components. The five revised acetabular components included the three stable cups that were revised at other institutions and the two that were revised because of infection.

For the 115 hips that were available for follow-up, the mean preoperative Harris hip score was 51 points (range, 6 to 91 points) and the mean postoperative score was 79 points (range, 26 to 100 points). Compared with the findings in the previous study¹⁶, there was an over-all decrease, from 71 per cent (of 126 hips) to 58 per cent, in the rate of hips that had a good or excellent result (80 to 100 points) and an increase, from 17 to 24 per cent, in the rate of hips that had a poor result (less than 70 points). However, these differences were not significant (p = 0.49).

One hundred and five patients (109 hips) were available for radiographic examination at a mean of ninety-eight months (range, seventy-eight to 135 months). As reported previously¹⁶, radiolucent lines with a width of less than two millimeters were common (Fig. 1). The total number of zones with a radiolucent line had decreased significantly compared with the number in the previous study (p = 0.004). Forty-nine (45 per cent) of the 109 hips in the current study had no radiolucent line, compared with twenty-four (19 per cent) of the 129 hips in the previous study. A radiolucent line was seen in only one zone in nineteen hips (17 per cent) in the current study, compared with forty-two hips (33 per cent) in the previous study. The numbers of radiolucent lines found in two, three, four, or five zones were similar between the two studies. Comparison, by individual zone, of the rates of cups with radiolucent lines that were less than two millimeters wide revealed a significant decrease, between the previous and current studies, in zone C only (zone A₁, p = 0.52; zone A₂, p = 0.86; zone B₁, p = 0.40; zone B₂, p = 0.84; and zone C, p < 0.0001). Radiolucent lines that were more than two millimeters wide and had not been seen in the previous study were noted in a total of three zones (two cups).

Five cups (5 per cent) were surrounded by a complete radiolucent line. A partial progressive radiolucent line was seen in three hips (3 per cent), and one of the lines was subsequently found to be associated with an infection. In the other two hips, the radiolucent line involved only two zones and was less than one millimeter wide.

Two hips (2 per cent) had a radiolucent line associated with a screw. The porous coating was seen to be fragmented from the metal shell of two acetabular components (2 per cent). In the absence of infection, four hips (4 per cent) had progressive osteolysis at the margin of the acetabular component, at a mean of sixty-nine months (range, fifty-nine to seventy-six months) after the revision. None of these osteolytic areas was more than four millimeters in diameter, and all involved only zone A₁. No osteolysis of the retroacetabular area was noted on the radiographs made at the latest follow-up evaluation.

There was no radiographic evidence of additional resorption of non-structural bone grafts between the earlier and long-term follow-up examinations. The two bulk grafts also had no sign of resorption at the latest follow-up visit (Fig. 2).

Radiographs of the twenty-seven patients (twenty-nine hips) who were followed for less than seventy-eight months were also reviewed. Of these patients, one (one hip), who died, had had a complete radiolucent line of less than one millimeter in width at the bone-prosthesis interface at forty-three months. The width of this line had progressed to two millimeters at the last follow-up evaluation at sixty-six months; at that time, the patient was pain-free and had a Harris hip score of 84 points. The patient died three months later from causes unrelated to the hip arthroplasty. No other radiographic abnormalities were seen in the remaining hips.

The Kaplan-Meier survivorship curve for failure of the acetabular component (removal of the implant or aseptic loosening) revealed an 87 per cent chance of survival at 109 months (95 per cent confidence interval, 85 to 95 per cent) (Fig. 3).

Discussion

Introduction | Materials and Methods | Results | Discussion | References

Long-term follow-up data on revision total hip arthroplasty are limited. Short and intermediate-term studies have revealed varying degrees of success with revision with cement, with rates of repeat revision ranging from 5 to 43 per cent^{1-3,10,11,13,15,17-19,22}. Conversely, revision arthroplasty with use of an acetabular component without cement has yielded good short and intermediate-term results, with rates of repeat revision ranging from 1 to 6 per cent^{4,5,7,8,14,16,21}.

With an additional five-year follow-up, we found that no acetabulum had had a repeat revision for aseptic loosening of the component, five acetabuli (5 per cent) had a complete radiolucent line, and no acetabular component had migrated; these results are consistent with those in our initial study¹⁶.

The finding of late hematogenous infection in an additional two hips demonstrates that, although the prevalence of this complication is low, the possibility of late infection must always be considered.

In the current study, we noted an increase in the number of hips that were free of radiolucent lines of less than two millimeters in width (forty-nine [45 per cent] of 109 hips, compared with twenty-four [19 per cent] of 129 hips in the previous study¹⁶). This may be explained by the projection of the radiograph or the difficulty in interpreting small radiolucent lines in only one zone. While the distribution of the radiolucent lines in each zone remained similar, there was a decrease in the prevalence of radiolucent lines, between the previous and current studies, in zone C (63 compared with 31 per cent; p < 0.0001). This is probably due to inherent difficulties in the interpretation of the prosthesis-bone interface in the area of the teardrop.

As mentioned earlier, the prevalence of complete radiolucent lines (five hips; 5 per cent) did not change after the additional five-year follow-up, and the hips with a complete line continued to be stable.

A continuous radiolucent line adjacent to an acetabular component that has been inserted with cement has been associated with a 94 per cent probability of the component being loose⁹. However, the importance of such a line adjacent to an acetabular component that has been inserted without cement is still unclear. Recent retrieval studies have confirmed a relationship between the presence of radiolucent lines and the lack of bone ingrowth²⁰.

In contrast to the previous study¹⁶, in which there was no evidence of osteolysis adjacent to the acetabular component or of radiolucency adjacent to a screw at a mean of forty-four months, four hips in the current study had evidence of small marginal periacetabular osteolytic lesions recognized initially at a mean of fifty-nine months after the revision. In addition, two hips had a radiolucent line adjacent to a screw, and two had peripheral fragmentation of the porous pad. These time-dependent findings are of concern.

The results of the current study indicate that, after a follow-up of seven to eleven years, there was no increase in the rate of aseptic loosening. We continue to use our original operative technique of inserting the acetabular component with so-called line-to-line reaming and screw fixation in most of our revisions of failed components, and we consider this approach to be a good option for revisions of such components. Although the prevalence of osteolysis adjacent to the acetabular component was low at a mean of ninety-eight months, the clinical implications of this and other changes at the interface will be appreciated only after additional follow-up.

References

Introduction | Materials and Methods | Results | Discussion | References

Amstutz, H. C.; Ma, S. M.; Jinnah, R. H.; and |and |Mai, L.: Revision of aseptic loose total hip arthroplasties. Clin. Orthop.,170: 21-33, 1982.17021 1982 [PubMed]

Callaghan, J. J.; Salvati, E. A.; Pellicci, P. M.; Wilson, P. D., Jr.; and |and |Ranawat, C. S.: Results of revision for mechanical failure after cemented total hip replacement, 1979 to 1982. A two to five-year follow-up. J. Bone and Joint Surg.,67-A: 1074-1085, Sept. 1985.67-A1074 1985

Ejsted, R., and |and |Olsen, N. J.: Revision of failed total hip arthroplasty. J. Bone and Joint Surg.,69-B(1): 57-60, 1987.69-B(1)57 1987

Emerson, R. H., Jr.; Head, W. C.; Berklacich, F. M.; and |and |Malinin, T. I.: Noncemented acetabular revision arthroplasty using allograft bone. Clin. Orthop.,249: 30-43, 1989.24930 1989 [PubMed]

Engh, C. A.; Glassman, A. H.; Griffin, W. L.; and |and |Mayer, J. G.: Results of cementless revision for failed cemented total hip arthroplasty. Clin. Orthop.,235: 91-110, 1988.23591 1988 [PubMed]

Harris, W. H.: Traumatic arthritis of the hip after dislocation and acetabular fractures: treatment by mold arthroplasty. An end-result study using a new method of result evaluation. J. Bone and Joint Surg.,51-A: 737-755, June 1969.51-A737 1969

Harris, W. H.; Krushell, R. J.; and |and |Galante, J. O.: Results of cementless revisions of total hip arthroplasties using the Harris-Galante prosthesis. Clin. Orthop.,235: 120-126, 1988.235120 1988 [PubMed]

Hedley, A. K.; Gruen, T. A.; and |and |Ruoff, D. P.: Revision of failed total hip arthroplasties with uncemented porous-coated anatomic components. Clin. Orthop.,235: 75-90, 1988.23575 1988 [PubMed]

Hodgkinson, J. P.; Shelley, P.; and |and |Wroblewski, B. M.: The correlation between the roentgenographic appearance and operative findings at the bone-cement junction of the socket in Charnley low friction arthroplasties. Clin. Orthop.,228: 105-109, 1988.228105 1988 [PubMed]

Hoogland, T.; Razzano, C. D.; Marks, K. E.; and |and |Wilde, A. H.: Revision of Mueller total hip arthroplasties. Clin. Orthop.,161: 180-185, 1981.161180 1981 [PubMed]

Hunter, G. A.; Welsh, R. P.; Cameron, H. U.; and |and |Bailey, W. H.: The results of revision of total hip arthroplasty. J. Bone and Joint Surg.,61-B(4): 419-421, 1979.61-B(4)419 1979

Kaplan, E. L., and |and |Meier, P.: Nonparametric estimation from incomplete observations. J. Am. Statist. Assn.,53: 457-481, 1958.53457 1958 [CrossRef]

Kavanagh, B. F.; Ilstrup, D. M.; and |and |Fitzgerald, R. H., Jr.: Revision total hip arthroplasty. J. Bone and Joint Surg.,67-A: 517-526, April 1985.67-A517 1985

Lachiewicz, P. F., and |and |Hussamy, O. D.: Revision of the acetabulum without cement with use of the Harris-Galante porous-coated implant. Two to eight-year results. J. Bone and Joint Surg.,76-A: 1834-1839, Dec. 1994.76-A1834 1994

Marti, R. K.; Schuller, H. M.; Besselaar, P. P.; and |and |Vanfrank Haasnoot, E. L.: Results of revision of hip arthroplasty with cement. A five to fourteen-year follow-up study. J. Bone and Joint Surg.,72-A: 346-354, March 1990.72-A346 1990

Padgett, D. E.; Kull, L.; Rosenberg, A.; Sumner, D. R.; and |and |Galante, J. O.: Revision of the acetabular component without cement after total hip arthroplasty. Three to six-year follow-up. J. Bone and Joint Surg.,75-A: 663-673, May 1993.75-A663 1993

Pellicci, P. M.; Wilson, P. D., Jr.; Sledge, C. B.; Salvati, E. A.; Ranawat, C. S.; and Poss, R.: Results of revision total hip replacement. In The Hip. Proceedings of the Ninth Open Scientific Meeting of The Hip Society, pp. 57-68. St. Louis, C. V. Mosby, 1981.

Pellicci, P. M.; Wilson, P. D., Jr.; Sledge, C. B.; Salvati, E. A.; Ranawat, C. S.; and |and |Poss, R.: Revision total hip arthroplasty. Clin. Orthop.,170: 34-41, 1982.17034 1982 [PubMed]

Pellicci, P. M.; Callaghan, J. J.; Wilson, P. D., Jr.; Sledge, C. B.; Salvati, E. A.; Ranawat, C. S.; and Poss, R.: Results of revision total hip replacement. In The Hip. Proceedings of the Twelfth Open Scientific Meeting of The Hip Society, pp. 247-253. St. Louis, C. V. Mosby, 1984.

Sumner, D. R.; Jasty, M.; Turner, T. M.; Urban, R. M.; Galante, J. O.; Bragdon, C.; and |and |Harris, W. H.: Bone ingrowth in porous-coated cementless acetabular components retrieved from human patients. Trans. Orthop. Res. Soc.,12: 509, 1987.12509 1987

Tanzer, M.; Drucker, D.; Jasty, M.; McDonald, M.; and |and |Harris, W. H.: Revision of the acetabular component with an uncemented Harris-Galante porous-coated prosthesis. J. Bone and Joint Surg.,74-A: 987-994, Aug. 1992.74-A987 1992

Weber, B. G.: Total hip replacement revision surgery: surgical technique and experience. In The Hip. Proceedings of the Ninth Open Scientific Meeting of The Hip Society, pp. 3-14. St. Louis, C. V. Mosby, 1981.

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Survivorship curve for the acetabular component, with removal of the component (repeat revision) or aseptic loosening as the end points. The dotted lines represent the 95 per cent confidence limits.

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TABLE I COMPARISON OF THE RESULTS BETWEEN THE PREVIOUS AND CURRENT STUDIES

	Previous Study¹⁶	Current Study
Follow-up
Total no. followed	124 patients (129 hips)	111 patients (115 hips)
Mean durat. (mos.)	44 (range, 36—80)	100 (range, 78—135)
Died with inadequate follow-up	2 patients (2 hips)	12 patients (12 hips)
Lost to follow-up	6 patients (7 hips)	9 patients (11 hips)

Repeat revision of acetabular component	7 patients (7 hips; 5%)	13 patients (13 hips; 11%)
Infection	4 patients (4 hips; 3%)	6 patients (6 hips; 5%)
Dislocation	3 patients (3 hips; 2%)	4 patients (4 hips; 3%)
Cup stable; revised at time of revision of femoral component	0	3 patients (3 hips; (3%)
Aseptic loosening	0	0

Revision of femoral component	7 patients (7 hips; 5%)	30 patients (31 hips; 22%)

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TABLE I COMPARISON OF THE RESULTS BETWEEN THE PREVIOUS AND CURRENT STUDIES

	Previous Study¹⁶	Current Study
Follow-up
Total no. followed	124 patients (129 hips)	111 patients (115 hips)
Mean durat. (mos.)	44 (range, 36—80)	100 (range, 78—135)
Died with inadequate follow-up	2 patients (2 hips)	12 patients (12 hips)
Lost to follow-up	6 patients (7 hips)	9 patients (11 hips)

Repeat revision of acetabular component	7 patients (7 hips; 5%)	13 patients (13 hips; 11%)
Infection	4 patients (4 hips; 3%)	6 patients (6 hips; 5%)
Dislocation	3 patients (3 hips; 2%)	4 patients (4 hips; 3%)
Cup stable; revised at time of revision of femoral component	0	3 patients (3 hips; (3%)
Aseptic loosening	0	0

Revision of femoral component	7 patients (7 hips; 5%)	30 patients (31 hips; 22%)