JBJS | Bipolar Hip Arthroplasty as a Salvage Treatment for Instability of the Hip*

The Journal of Bone & Joint Surgery, Volume 82, Issue 8

Articles | August 01, 2000

Bipolar Hip Arthroplasty as a Salvage Treatment for Instability of the Hip*

Javad Parvizi, M.D., F.R.C.S.; Bernard F. Morrey, M.D.

Investigation performed at the Department of Orthopedics, Mayo Clinic and Mayo Foundation, Rochester
*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.
Department of Orthopedics, Mayo Clinic, 200 First Street S.W., Rochester, Minnesota 55905.

The Journal of Bone & Joint Surgery. 2000; 82:1132-1132

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Abstract

Background: Recurrent instability of the hip in the absence of an identifiable cause is a challenging problem. It has been proposed that bipolar hip arthroplasty may have a role in the treatment of these complex cases. The purpose of our study was to evaluate the results of bipolar hip arthroplasty for the treatment of recurrent instability of the hip in a series of patients at our institution.

Methods: We reviewed the records of twenty-seven patients who had undergone bipolar hip arthroplasty as a salvage procedure for the treatment of recurrent instability of the hip after total hip replacement. All patients had undergone at least two, and a mean of three, stabilizing operative procedures on the hip prior to the bipolar arthroplasty. The mean duration of follow-up was five years (range, two to twelve years), with no patient lost to follow-up. There were six deaths, of unrelated causes.

Results: Bipolar arthroplasty prevented redislocation in twenty-two hips (81 percent). At the time of final follow-up, twenty-five patients (93 percent) had a stable hip. Five patients (19 percent) had had episodes of subluxation or dislocation following the bipolar arthroplasty. Two of these patients had only a single episode of dislocation that was treated successfully by immobilization. Two of the remaining three patients required a reoperation because of the instability. The hip was stabilized with the use of a constrained cup prosthesis in one of these patients, and the other patient eventually required resection arthroplasty. The third patient had continuing instability but improved function and pain relief, and a reoperation was not performed. There were a total of seven reoperations; these included revision because of disassembly of the cup in one hip, revision bipolar arthroplasty because of continuing instability in two, resection arthroplasty because of deep infection in two, revision arthroplasty because of recalcitrant groin pain in one, and revision arthroplasty because of deep infection and superior migration of the implant in one. The Harris hip score improved significantly, from a mean of 24 points (range, 5 to 45 points) preoperatively to a mean of 55 points (range, 35 to 80 points) postoperatively (p < 0.05).

Conclusions: We believe that, despite some potential problems, bipolar hip arthroplasty can have a role in the salvage management of recurrent instability of the hip in patients in whom other stabilization procedures have failed.

Figures in this Article

Introduction

Introduction | Materials and Methods | Results | Discussion | References

Dislocation is one of the major complications of total hip arthroplasty that may necessitate prolonged hospitalization, rehabilitation, and, if it is recurrent, operative intervention¹¹ with severe distress to the patient and the surgeon⁵. The overall prevalence of dislocation following primary total hip arthroplasty is approximately 3 percent^9,39. The prevalence increases dramatically after each revision operation and can be as high as 26 percent after multiple operations^16,23,24,32. The social, psychological, and financial costs associated with this relatively common complication of arthroplasty are great.

The outcomes of reoperations for the treatment of instability with no identifiable cause are unpredictable^{11,13,16,24,25}. The result is considerably better if the dislocation occurs early after the initial arthroplasty^10,26,39, if there is a single dislocation prior to the reoperation11, and if there is an identifiable cause of the dislocation¹¹. Alternatives for operative treatment include revision in order to correct the position of the arthroplasty components^11,14,19,25, advancement of the trochanter²³, removal of sources of impingement^13,14,24,31, augmentation of the acetabular lining^7,17,30,38, and the use of a confined cup mechanism^2,20. Other possible operative interventions that have been suggested, but not proven, to be of benefit are femoral rotational osteotomy⁸ and lengthening of the femoral neck¹⁵.

There is no single operative procedure that can uniformly address the problem of recurrent instability of the hip, and there remains a percentage of patients with chronic recurrent instability for whom there seems to be no good operative solution. These patients continue to have disabling problems with considerable anxiety and apprehension of dislocation⁵. The management of instability in these patients is complex. They almost always have extensive soft-tissue deficiency, and the majority undergo multiple operative procedures that fail to address the instability. These patients often face the possibility of resection arthroplasty.

Bipolar hip arthroplasty has been proposed to have a role in the treatment of these complex cases^21,33. There have been reports of small numbers of patients who were all successfully treated with bipolar arthroplasty^21,33. Some surgeons at our institution have performed bipolar hip arthroplasty as salvage treatment for recurrent instability of the hip in patients in whom other stabilization efforts have failed.

In the present study, we evaluated the long-term outcome of bipolar hip arthroplasty as a salvage treatment for recurrent instability of the hip.

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Fig. 1-A:: Figs. 1-A, 1-B, and 1-C: Case 16. Radiographs of a sixty-two-year-old woman with chronic dislocations (eighteen documented episodes) that were treated with multiple operative procedures for stabilization of the hip.
Fig. 1-A: Revision hip arthroplasty with femoral neck lengthening was performed three years after the primary hip arthroplasty. The patient had undergone six previous reconstructive operations on this hip.

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Fig. 1-B: Acetabular augmentation was performed at four years, but the hip continued to dislocate.

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Fig. 1-C: Bipolar hip arthroplasty was performed at seven years. The patient had undergone reconstruction of a pseudocapsule with removal of heterotopic ossification in the previous year. The hip was stable following the bipolar operation.

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Table I: Indications for Use of Bipolar Revision for Treatment of Recurrent Instability

	Total No. of Patients	No. with Successful Bipolar Revision
Multiple failed previous stabilization procedures (multifactorial cause of instability)	18	17
12 operations	3	3
5-11 operations	3	2
3-4 operations	12	12
No single cause of instability (<2 operations)	9	8
Instability following primary hip arthroplasty	24	22
Instability following revision hip arthroplasty for aseptic loosening	3	2

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Table I: Indications for Use of Bipolar Revision for Treatment of Recurrent Instability

	Total No. of Patients	No. with Successful Bipolar Revision
Multiple failed previous stabilization procedures (multifactorial cause of instability)	18	17
12 operations	3	3
5-11 operations	3	2
3-4 operations	12	12
No single cause of instability (<2 operations)	9	8
Instability following primary hip arthroplasty	24	22
Instability following revision hip arthroplasty for aseptic loosening	3	2

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Table II: Data on the Patients Treated with Bipolar Arthroplasty Because of Recurrent Instability of the Hip

Case	Gender, Age at Bipolar Op. (yrs.)	Durat. of Follow-up (yrs.)	Primary Diagnosis	Direction of Dislocat.	Approach (Primary/Bipolar)	Date of Bipolar Op.	Type of Prosthesis	Type of Acetabular Bone-Grafting	Reops. and Complications	Outcome	Remarks
1	F, 73	3	Osteoarth.	Post.	Lat./lat.	12/5/85	Bateman UPF II	None	None	Stable	Died 1988 (closed head injury)
2	M, 69	5	Develop. dysplasia	Post.	Lat./anterolat.	10/5/93	Multipolar	Cancellous	Postop. migrat.	Stable	12 previous ops.
3	F, 80	12	Avasc. nec.	Post.	Lat./lat.	6/19/85	Bicentric	None	Reop. for cup disassembly; reop. for continuing instabil.; resect. arthroplasty for deep infect.	Unstable	Improved function, pain relief since revis.
4	M, 67	10	Osteoarth.	Super.	Anterolat./anterolat.	9/5/85	Bateman UPF II	None	Reop. for deep infect. and superior migrat.	Stable	12 previous ops., previous deep infect.
5	M, 70	3	Rheumat. arth.	Post.	Posterolat./posterolat.	6/16/94	Multipolar	None	Periprosth. fract.	Stable	Contralat. hip instabil.
6	F, 55	7	Osteoarth.	Ant.	Anterolat./anterolat.	7/11/90	Centrax	None	Sciatic neurapraxia; periprosth. fract.	Stable	6 previous stabilizat. proc.
7	F, 65	9	Osteoarth.	Post.	Anterolat./anterolat.	7/7/89	UHR	Cancellous	Superficial hematoma; groin pain	Stable	Radiographs suggested deep infect.; awaiting resection arthroplasty
8	M, 51	11	Develop. dysplasia	Post.	Posterolat./posterolat.	10/27/86	Bicentric	None	Disloc.	Unstable	Dislocat. after bipolar op., treated nonop.
9	M, 69	3	Osteoarth.	Post.	Anterolat./anterolat.	10/25/94	Multipolar	None	None	Stable	-
10	F, 63	3	Osteoarth.	Ant.	Anterolat.	3/8/94	Multipolar	Cancellous	None	Stable	1989: bipolar op., stable; 1990: revised to HGP-II prosth. for pain, became unstable; 1994: rerevised to bipolar prosth.
11	F, 68	9	Osteoarth.	Ant.	Lat./anterolat.	9/20/88	Centrax	None	Aseptic loosening with pain	Stable	Refused revis.
12	M, 35	8	Posttraumat. arth.	Post.	Anterolat./anterolat.	6/10/88	UHR	None	Reop. for pain at 5 yrs.; conversion to Girdlestone at 7 yrs.	Stable	Revised to total hip arthroplasty because of pain
13	M, 66	5	Osteoarth.	Post.	Lat./lat.	8/18/89	Centrax	None	Thigh pain	Stable	Died 1994 (closed head injury)
14	M, 69	2	Posttraumat. arth.	Post.	Anterolat./anterolat.	9/29/92	Centrax	None	Conversion to Girdlestone for deep infect.	Stable	Candida isolated; died 1994 (unrelated)
15	M, 72	5	Osteoarth.	Post.	Posterolat./posterolat.	11/30/92	Self Centering	None	Disloc.	Stable	9 previous stabilizat. proc.
16	F, 62	7	Avasc. nec.	Ant.	Anterolat./anterolat.	10/31/90	Centrax	Cancellous, cortical strut	None	Stable at all times	Severe acetab. deficiency
17	F, 75	5	Osteoarth.	Post.	Lat./anterolat.	11/15/90	Centrax	None	None	Stable	Died 1995
18	F, 30	3	Posttraumat. arth.	Post.	Anterolat./anterolat.	2/8/94	Centrax	Cancellous	None	Stable	-
19	F, 53	2	Osteoarth.	Super.	Anterolat./anterolat.	6/21/91	UHR	None	None	Stable	Died 1993 (breast carcinoma)
20	M, 57	4	Osteoarth.	Post.	Anterolat./anterolat.	12/8/93	Centrax	None	Reop. for instabil.; superficial infect.	Unstable initially	Multiple ops.; primary deep infect.; knee instabil.
21	F, 35	5	Osteoarth.	Super.	Anterolat./anterolat.	11/6/92	UHR	None	Groin pain	Stable	Contralat. hip instabil.; recent migrat.
22	M, 70	3	Osteoarth.	Post.	Anterolat./anterolat.	2/15/94	Multipolar	None	None	Stable	Strenuous activity
23	F, 60	3	Posttraumat. arth.	Post.	Posterolat./posterolat.	3/16/95	UHR	None	None	Stable	12 previous ops.
24	F, 69	2	Osteoarth.	Ant.	Ant./ant.	6/11/86	Centrax	None	None	Stable	Multiple previous stabilizat. proc.; died 1988
25	M, 57	3	Ankylos. spondylitis	Post.	Lat./lat.	11/29/94	Multipolar	None	None	Stable	7 previous ops.
26	M, 49	2	Osteoarth.	Ant.	Anterolat./anterolat.	4/18/95	Multipolar	None	None	Stable	Primary deep infect.; multiple revis.
27	M, 72	3	Osteoarth.	Post.	Lat./anterolat.	4/25/94	Multipolar	Cancellous	None	Stable	Multiple previous stabilizat. proc.

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Table II: Data on the Patients Treated with Bipolar Arthroplasty Because of Recurrent Instability of the Hip

Case	Gender, Age at Bipolar Op. (yrs.)	Durat. of Follow-up (yrs.)	Primary Diagnosis	Direction of Dislocat.	Approach (Primary/Bipolar)	Date of Bipolar Op.	Type of Prosthesis	Type of Acetabular Bone-Grafting	Reops. and Complications	Outcome	Remarks
1	F, 73	3	Osteoarth.	Post.	Lat./lat.	12/5/85	Bateman UPF II	None	None	Stable	Died 1988 (closed head injury)
2	M, 69	5	Develop. dysplasia	Post.	Lat./anterolat.	10/5/93	Multipolar	Cancellous	Postop. migrat.	Stable	12 previous ops.
3	F, 80	12	Avasc. nec.	Post.	Lat./lat.	6/19/85	Bicentric	None	Reop. for cup disassembly; reop. for continuing instabil.; resect. arthroplasty for deep infect.	Unstable	Improved function, pain relief since revis.
4	M, 67	10	Osteoarth.	Super.	Anterolat./anterolat.	9/5/85	Bateman UPF II	None	Reop. for deep infect. and superior migrat.	Stable	12 previous ops., previous deep infect.
5	M, 70	3	Rheumat. arth.	Post.	Posterolat./posterolat.	6/16/94	Multipolar	None	Periprosth. fract.	Stable	Contralat. hip instabil.
6	F, 55	7	Osteoarth.	Ant.	Anterolat./anterolat.	7/11/90	Centrax	None	Sciatic neurapraxia; periprosth. fract.	Stable	6 previous stabilizat. proc.
7	F, 65	9	Osteoarth.	Post.	Anterolat./anterolat.	7/7/89	UHR	Cancellous	Superficial hematoma; groin pain	Stable	Radiographs suggested deep infect.; awaiting resection arthroplasty
8	M, 51	11	Develop. dysplasia	Post.	Posterolat./posterolat.	10/27/86	Bicentric	None	Disloc.	Unstable	Dislocat. after bipolar op., treated nonop.
9	M, 69	3	Osteoarth.	Post.	Anterolat./anterolat.	10/25/94	Multipolar	None	None	Stable	-
10	F, 63	3	Osteoarth.	Ant.	Anterolat.	3/8/94	Multipolar	Cancellous	None	Stable	1989: bipolar op., stable; 1990: revised to HGP-II prosth. for pain, became unstable; 1994: rerevised to bipolar prosth.
11	F, 68	9	Osteoarth.	Ant.	Lat./anterolat.	9/20/88	Centrax	None	Aseptic loosening with pain	Stable	Refused revis.
12	M, 35	8	Posttraumat. arth.	Post.	Anterolat./anterolat.	6/10/88	UHR	None	Reop. for pain at 5 yrs.; conversion to Girdlestone at 7 yrs.	Stable	Revised to total hip arthroplasty because of pain
13	M, 66	5	Osteoarth.	Post.	Lat./lat.	8/18/89	Centrax	None	Thigh pain	Stable	Died 1994 (closed head injury)
14	M, 69	2	Posttraumat. arth.	Post.	Anterolat./anterolat.	9/29/92	Centrax	None	Conversion to Girdlestone for deep infect.	Stable	Candida isolated; died 1994 (unrelated)
15	M, 72	5	Osteoarth.	Post.	Posterolat./posterolat.	11/30/92	Self Centering	None	Disloc.	Stable	9 previous stabilizat. proc.
16	F, 62	7	Avasc. nec.	Ant.	Anterolat./anterolat.	10/31/90	Centrax	Cancellous, cortical strut	None	Stable at all times	Severe acetab. deficiency
17	F, 75	5	Osteoarth.	Post.	Lat./anterolat.	11/15/90	Centrax	None	None	Stable	Died 1995
18	F, 30	3	Posttraumat. arth.	Post.	Anterolat./anterolat.	2/8/94	Centrax	Cancellous	None	Stable	-
19	F, 53	2	Osteoarth.	Super.	Anterolat./anterolat.	6/21/91	UHR	None	None	Stable	Died 1993 (breast carcinoma)
20	M, 57	4	Osteoarth.	Post.	Anterolat./anterolat.	12/8/93	Centrax	None	Reop. for instabil.; superficial infect.	Unstable initially	Multiple ops.; primary deep infect.; knee instabil.
21	F, 35	5	Osteoarth.	Super.	Anterolat./anterolat.	11/6/92	UHR	None	Groin pain	Stable	Contralat. hip instabil.; recent migrat.
22	M, 70	3	Osteoarth.	Post.	Anterolat./anterolat.	2/15/94	Multipolar	None	None	Stable	Strenuous activity
23	F, 60	3	Posttraumat. arth.	Post.	Posterolat./posterolat.	3/16/95	UHR	None	None	Stable	12 previous ops.
24	F, 69	2	Osteoarth.	Ant.	Ant./ant.	6/11/86	Centrax	None	None	Stable	Multiple previous stabilizat. proc.; died 1988
25	M, 57	3	Ankylos. spondylitis	Post.	Lat./lat.	11/29/94	Multipolar	None	None	Stable	7 previous ops.
26	M, 49	2	Osteoarth.	Ant.	Anterolat./anterolat.	4/18/95	Multipolar	None	None	Stable	Primary deep infect.; multiple revis.
27	M, 72	3	Osteoarth.	Post.	Lat./anterolat.	4/25/94	Multipolar	Cancellous	None	Stable	Multiple previous stabilizat. proc.

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Table III: Final Outcome

*One reoperation was a resection arthroplasty in an infected unstable hip.

	No. of Hips
Total	Stable Postop.	Unstable Postop.
Bipolar revision arthroplasty	27 (100%)	22 (81%)	5 (19%)
Additional nonop. treatment (brace, cast)	2 (7%)	24 (89%)	3 (11%)
Reop. for instability*	2 (7%)	25 (93%)	2 (7%)

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Table III: Final Outcome

*One reoperation was a resection arthroplasty in an infected unstable hip.

	No. of Hips
Total	Stable Postop.	Unstable Postop.
Bipolar revision arthroplasty	27 (100%)	22 (81%)	5 (19%)
Additional nonop. treatment (brace, cast)	2 (7%)	24 (89%)	3 (11%)
Reop. for instability*	2 (7%)	25 (93%)	2 (7%)

Materials and Methods

Introduction | Materials and Methods | Results | Discussion | References

Between 1985 and 1996, 131 operative procedures were performed on 114 patients with recurrent instability of the hip at our institution. Twenty-eight of these patients were managed with bipolar arthroplasty. One died as a result of myocardial infarction on the day after the operation, leaving twenty-seven patients in the present study. The patients all had undergone multiple failed previous stabilization operations (eighteen hips) or had no clear cause of the hip instability (nine hips) (Table I). We retrospectively reviewed the preoperative and postoperative clinical and radiographic data on these patients after institutional approval and the consent of all patients had been obtained. No patient refused to participate in the study.

The diagnosis leading to the primary hip arthroplasty was osteoarthritis in seventeen hips, posttraumatic arthritis in four, developmental dysplasia of the hip in two, avascular necrosis in two, rheumatoid arthritis in one, and ankylosing spondylitis in one (Table II).

There were thirteen women and fourteen men, with a mean age of sixty-one years (range, thirty to eighty years) at the time of the bipolar arthroplasty. The mean duration of follow-up after the bipolar arthroplasty was five years (range, two to twelve years). There were six deaths in the series: three patients died at two years; one, at three years; and two, at five years. All deaths were unrelated to the bipolar operation.

Follow-up was continued for a minimum of two years or until the prosthesis failed or the patient died. No patient was lost to follow-up during the period of study. The follow-up included radiographic and clinical examination of the affected hip. Of the twenty-one patients who were alive at the end of the study period, thirteen were evaluated most recently (less than one year before the completion of the study) with a physical and radiographic examination as well as an interview in the physician's office and four returned a detailed questionnaire sent by mail. Four patients, who were unable to travel because of age and associated medical conditions, were interviewed by telephone for the latest follow-up examination. All patients who died had been evaluated by means of physical examination postoperatively and had been found to have a stable hip.

Instability was defined as a dislocation or subluxation. Subluxation was defined as a perception, by the patient, of abnormal hip movement accompanied by an audible thud or clunk of the hip often associated with pain. The direction of instability was determined by preoperative radiographic and clinical examination or intraoperative radiographic and clinical examination, or both. The direction of dislocation was posterior in eighteen patients (67 percent), anterior in six (22 percent), and superior in three (11 percent) (Table II).

The bipolar prostheses used in this series included nine Centrax (Howmedica, Rutherford, New Jersey), eight Multipolar (Zimmer, Warsaw, Indiana), five UHR (universal hip replacement) (Osteonics, Allendale, New Jersey), two Bicentric (Howmedica), and two Bateman UPF II (3M, Minneapolis, Minnesota) devices as well as one Self Centering device (DePuy, Warsaw, Indiana). No bilateral bipolar arthroplasties were performed in this series. All of the bipolar arthroplasties were performed at our institution by several different surgeons in the Adult Reconstruction Surgery Division. Acetabular reconstruction by means of cancellous bone-grafting or cortical bone-grafting, or both, was carried out at the time of the bipolar arthroplasty if deemed necessary. Six patients had acetabular deficiency that necessitated bone-grafting; five of them had cancellous grafting, and one required both cancellous and structural cortical grafting (Table II). Concurrent procedures in the form of capsulorrhaphy (twelve hips), trochanteric advancement (three hips), and excision of impinging bone (three hips) were also carried out.

All hips were initially immobilized with use of an abduction pillow for a mean of four days (range, two to twelve days) following the bipolar arthroplasty. Only eight (30 percent) of the patients had continuing postoperative protection following the index operation. Six wore an abduction brace and two wore a hip-spica cast for six to eight weeks. One patient was restricted to bed rest for two days prior to the application of a hip spica. Because of the small sample of patients who were managed with immobilization in our series, the importance of postoperative protection in preventing instability could not be determined.

Statistical Analysis

The data in this study were evaluated for significance, set at p < 0.05, with the use of analysis of variance.

Results

Introduction | Materials and Methods | Results | Discussion | References

Preoperative Data

All patients in this study (Table II) had undergone at least two, and a mean of three, reconstructive hip operations, including the initial implantation, prior to the bipolar arthroplasty. The operations included a previous bipolar hip arthroplasty (one patient), femoral neck lengthening (four), advancement of the greater trochanter (nine), removal of a source of impingement (ten), acetabular augmentation (twelve), component revision (eighteen), and multiple treatments (twenty-one). Eighteen patients (67 percent) had at least one revision procedure to stabilize the unstable hip. Three patients had twelve or more prior hip operations. Six patients underwent operative treatment, other than bipolar arthroplasty, that failed to control the recurrent instability. The stabilization attempts in these six patients included revision of the acetabular component (excluding the captured cup), revision of the femoral component, advancement of the greater trochanter, lengthening of the femoral neck, and removal of a source of impingement.

Twenty-four patients (89 percent) had the first episode of dislocation following the primary hip arthroplasty, and the remaining three patients (11 percent) had the first dislocation following revision hip arthroplasty that was performed for a reason other than instability. These three patients had no documented hip instability following the primary hip arthroplasty.

Postoperative Complications

Two patients (7 percent) had a periprosthetic fracture that was treated nonoperatively. Three patients (11 percent) had documented evidence of deep infection. All three had had an infection at the site of the primary prosthesis, which had been revised previously. Resection arthroplasty was eventually performed in two of these three patients. The third patient underwent staged component exchange following treatment with intravenous antibiotics and placement of a cement spacer; this successfully eradicated the infection. Sciatic neurapraxia with footdrop developed in one patient and resolved over seven months. There were two cases of superficial wound infection and three urinary tract infections. There was one myocardial infarction following the bipolar arthroplasty, in a patient who was not included in the series.

Reoperations

There were a total of seven reoperations in five patients (Table II). One patient underwent a reoperation because of disassembly of the bipolar cup. The same patient underwent revision bipolar arthroplasty four years later because of continuing subluxation and, subsequently, had resection arthroplasty because of deep infection. The other four reoperations, performed in one patient each, included resection of bipolar components because of deep infection at one year, revision of a bipolar prosthesis to a total hip arthroplasty because of deep infection and superior migration of the implant at four years, revision of a bipolar prosthesis to a constrained cup prosthesis because of continuing subluxation, and revision of a bipolar prosthesis to a total hip arthroplasty because of intractable groin pain (Table II).

Outcome

The bipolar hip arthroplasty restored complete stability of the hip in twenty-two patients (81 percent) (Fig. 1-A, Fig. 1-B, and Fig. 1-C). Two patients (7 percent) had recurrence of hip instability, consisting of a single transient episode, within the first week after the bipolar operation; this was treated successfully with hip immobilization in a spica cast in one of the patients and with an abduction brace in the other. The remaining three patients (11 percent) had continuing instability, with multiple dislocations of the hip, following the bipolar arthroplasty. Two of these hips required component revision, which was performed at one year in one and at four years in the other. Revision bipolar arthroplasty restored stability in one of these patients, but the other patient, who had deep infection, had functional difficulty due to continuing frequent dislocation of the hip; this necessitated resection arthroplasty at six years (Table III). The third patient had continuing instability, with a mean of one dislocation per month, but still had improvement in hip function and pain relief to an extent that a reoperation was not considered to be necessary.

The final functional outcome was assessed by calculating the Harris hip score²², which was available for twenty-four patients. The functional hip score improved modestly from a mean of 24 points (range, 5 to 45 points) preoperatively to a mean of 55 points (range, 35 to 80 points) after the bipolar arthroplasty (p < 0.05). Twelve patients had continuing hip pain, which was severe in three (11 percent), moderate in three (11 percent), and mild in six (22 percent). Twelve patients (44 percent) had no limp, eight (30 percent) had a mild limp, five (19 percent) had a moderate limp, and two (7 percent) were unable to walk because of severe mental impairment.

Discussion

Introduction | Materials and Methods | Results | Discussion | References

Bipolar arthroplasty has been used most commonly for the treatment of femoral neck fracture, as popularized by Bateman³ and by Giliberty¹⁸. Although the device was not designed specifically to prevent instability, compound motion between the inner and outer bearing surfaces is thought to provide a greater range of hip motion, thereby giving this prosthesis an advantage, with regard to preventing dislocation, compared with conventional prostheses^{4,6,18,27,36,37}. A second theoretical advantage contributing to stability is that the larger femoral head of the bipolar device may provide additional protection against dislocation, as a greater volume must be displaced from the acetabulum for dislocation to occur^28,36.

In our series, bipolar arthroplasty for the treatment of complex recurrent instability was successful in preventing redislocation in twenty-two (81 percent) of twenty-seven patients and ultimately stabilized the hip in twenty-five (93 percent). The functional outcome of the bipolar arthroplasty was less impressive, with the Harris hip score²² improving modestly from a preoperative mean of 24 points to a postoperative mean of 55 points. Continuing hip pain, muscular weakness, and use of walking aids by some patients were some of the factors contributing to low functional scores. In addition, many patients in this study had substantial mental and physical disability that compromised their walking status. Two had severe Parkinson disease, two had Alzheimer disease, and at least three others had multi-joint disease. This study comprised a heterogeneous population of patients with complex problems that differed from the conventional population of patients undergoing arthroplasty, in whom much higher functional scores can be expected.

The high rate of success of bipolar arthroplasty in preventing redislocation compares favorably with most results reported in the literature. In a previously published study from our institution, fifty-eight (61 percent) of ninety-five hips with acute dislocation following conventional hip arthroplasty were treated successfully with operative intervention¹¹. The success rates of reoperation for instability were lower if the dislocation had occurred following revision hip surgery, with only two of eight hips stabilized in one study²⁵, and the results were also poor if no discrete cause for dislocation could be identified, with only nine of eighteen hips stabilized in another study¹¹. Fraser and Wroblewski, using conventional methods of revising malpositioned components or reattaching the greater trochanter when it was detached, observed a 76 percent success rate in their series of twenty-one patients with recurrent dislocation¹⁶. Kaplan et al. reported a success rate of 81 percent (seventeen of twenty-one patients) following trochanteric advancement for treatment of recurrent instability of the hip²³.

Our reported results of bipolar arthroplasty were not as favorable as those noted by Goetz et al., who reported only two redislocations (4 percent) and seven reoperations (13 percent) in a study of fifty-six procedures in which a constrained acetabular component had been implanted to treat a recurrently dislocating hip²⁰. Although the two patient populations are not comparable, on the basis of these results some may prefer to use a constrained acetabular component rather than a bipolar arthroplasty for treatment of recurrent dislocation. In fact, we use a constrained cup on some occasions. There are, however, some clear advantages to bipolar arthroplasty compared with a constrained acetabular component. There have been reports of a bipolar prosthesis being used, with excellent results, in patients with acetabular deficiency^29,35. One might therefore argue that bipolar arthroplasty should be considered as an early operative option for patients with acetabular deficiency who have symptomatic recurrent instability of the hip. In our series, six patients had documented radiographic evidence of segmental acetabular deficiency in all three zones described by DeLee and Charnley¹². It is possible that bipolar arthroplasty together with bone-grafting was the ideal operation with which to treat the instability in these patients. In addition, bipolar arthroplasty may be preferred over a constrained acetabular cup for patients with a reduced capacity for bone ingrowth, such as those with underlying avascular necrosis or previous irradiation of the pelvis. Bipolar arthroplasty also lacks the theoretical disadvantage, associated with constrained components, of possibly causing increased polyethylene wear and increased interfacial stresses leading to loosening.

The reoperation rate in our series was disappointingly high (26 percent). Bipolar arthroplasty was found to have other disadvantages as well. Twelve patients in our study had hip pain, and two had severe groin pain. The pain was intractable in one patient, which led to revision of the bipolar implant to a total hip prosthesis; this relieved the pain but destabilized the hip. Oral analgesia was adequate in relieving the groin pain in the other patient, who continued to have a fully functional hip. There was one case of mild acetabular protrusio, in a patient who also had severe acetabular deficiency. The main goal of the index operation was to prevent dislocation, and for this reason the surgeons were prepared to accept a higher complication rate with this procedure.

The operative complications in our series were comparable with those in other studies involving revision hip operations^1,20,25,34. The two periprosthetic fractures in our series may be explained by the severe femoral bone deficiency in these patients due to multiple previous arthroplasty procedures with cement. There were three cases of recurrent deep infection in the series. All of these patients had initially had a deep infection of the hip following the primary hip replacement at another institution. One of the patients was on immunosuppressive therapy because of a renal transplant.

In conclusion, the management of recurrent instability of the hip that occurs after a total hip replacement despite apparently adequate operative and nonoperative therapy is difficult. Any operation is likely to fail if there is no single identifiable cause of the instability that can be corrected by a reoperation. An unsuccessful operation increases the likelihood of additional instability. Patients who have been subjected to multiple stabilizing procedures that have failed to address the instability face the prospect of resection arthroplasty. Bipolar arthroplasty is an option for the treatment of a chronically symptomatic unstable hip in patients in whom other stabilization treatments have failed or are unlikely to be successful. Bipolar arthroplasty does have a high rate of failure and offers only modest improvement in function; thus, it should be considered only for select patients with a multifactorial cause of instability of the hip.

References

Introduction | Materials and Methods | Results | Discussion | References

Amstutz, H. C.; Lodwig, R. M.; Schurman, D. J.; and Hodgson, A. G.: Range of motion studies of total hip replacements. Clin. Orthop.,111: 124-130, 1975.111124 1975 [PubMed]

Anderson, M. J.; Murray, W. R.; and Skinner, H. B.: Constrained acetabular components. J. Arthroplasty,9: 17-23, 1994.917 1994 [PubMed]

Bateman, J. E.: Experience with a multi-bearing implant in reconstruction for hip deformities. Orthop. Trans.,1: 242, 1977.1242 1977

Bochner, R. M.; Pellicci, P. M.; and Lyden, J. P.: Bipolar hemiarthroplasty for fracture of the femoral neck. J. Bone and Joint Surg.,70-A: 1001-1010, Aug. 1988.70-A1001 1988

Chandler, R. W.; Dorr, L. D.; and Perry, J.: The functional cost of dislocation following total hip arthroplasty. Clin. Orthop.,168: 168-172, 1982.168168 1982 [PubMed]

Chen, S. C.; Badrinath, K.; Pell, L. H.; and Mitchell, K.: The movements of the components of the Hastings bipolar prosthesis. J. Bone and Joint Surg.,71-B(2): 186-188, 1989.71-B(2)186 1989

Cobb, T. K.; Morrey, B. F.; and Ilstrup, D. M.: The elevated-rim acetabular liner in total hip arthroplasty: relationship to postoperative dislocation. J. Bone and Joint Surg.,78-A: 80-86, Jan 1996.78-A80 1996

Cohn, B. T., and Krackow, K. A.: Femoral component retroversion treated by supracondylar rotational osteotomy. Orthopedics,10: 1057-1059, 1987.101057 1987 [PubMed]

Coventry, M. B.; Beckenbaugh, R. D.; Nolan, D. R.; and Ilstrup, D. M.: 2,012 total hip arthroplasties: a study of postoperative course and early complications. J. Bone and Joint Surg.,56-A: 273-284, March 1974.56-A273 1974

Coventry, M. B.: Late dislocations in patients with Charnley total hip arthroplasty. J. Bone and Joint Surg.,67-A: 832-841, July 1985.67-A832 1985

Daly, P. J., and Morrey, B. F.: Operative correction of an unstable total hip arthroplasty. J. Bone and Joint Surg.,74-A: 1334-1343, Oct 1992.74-A1334 1992

DeLee, J. G., and Charnley, J.: Radiological demarcation of cemented sockets in total hip replacement. Clin. Orthop.,121: 20-32, 1976.12120 1976 [PubMed]

Dorr, L. D.; Wolf, A. W.; Chandler, R.; and Conaty, J. P.: Classification and treatment of dislocations of total hip arthroplasty. Clin. Orthop.,173: 151-158, 1983.173151 1983 [PubMed]

Eftekhar, N. S.: Dislocation and instability complicating low friction arthroplasty of the hip joint. Clin. Orthop.,,121: 120-125, 1976.121120 1976

Fackler, C. D., and Poss, R.: Dislocation in total hip arthroplasties. Clin. Orthop.,151: 169-178, 1980.151169 1980 [PubMed]

Fraser, G. A., and Wroblewski, B. M.: Revision of Charnley low-friction arthroplasty for recurrent or irreducible dislocation. J. Bone and Joint Surg.,63-B(4): 552-555, 1981.63-B(4)552 1981

Gie, G. A.; Scott, T. D.; and Ling, R. S. M.: Cup augmentation for recurrent hip replacement dislocation. In Proceedings of the British Orthopaedic Association. J. Bone and Joint Surg.,71-B(2): 338, 1989.71-B(2)338 1989

Giliberty, R. P.: A new concept of a bipolar endoprosthesis [abstract]. Orthop. Rev.,3: 40, 1974.340 1974

Goergen, T. G., and Resnick, D.: Evaluation of acetabular anteversion following total hip arthroplasty: necessity of proper centring. British J. Radiol.,48: 259-260, 1975.48259 1975

Goetz, D. D.; Capello, W. N.; Callaghan, J. J.; Brown, T. D.; and Johnston, R. C.: Salvage of a recurrently dislocating total hip prosthesis with use of a constrained acetabular component. J. Bone and Joint Surg.,80-A: 502-509, April 1998.80-A502 1998

Grigoris, P.; Grecula, M. J.; and Amstutz, H. C.: Tripolar hip replacement for recurrent prosthetic dislocation. Clin. Orthop.,304: 148-155, 1994.304148 1994 [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

Kaplan, S. J.; Thomas, W. H.; and Poss, R.: Trochanteric advancement for recurrent dislocation after total hip arthroplasty. J. Arthroplasty,2: 119-124, 1987.2119 1987 [PubMed]

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

Kavanagh, B. F., and Fitzgerald, R. H.: Multiple revisions for failed total hip arthroplasty not associated with infection. J. Bone and Joint Surg.,69-A: 1144-1149, Oct 1987.69-A1144 1987

Khan, M. A. A.; Brakenbury, P. H.; and Reynolds, I. S. R.: Dislocation following total hip replacement. J. Bone and Joint Surg.,63-B(2): 214-218, 1981.63-B(2)214 1981

Krein, S. W., and Chao, E. Y. S.: Biomechanics of bipolar hip endoprosthesis. J. Orthop. Res.,2: 356-368, 1984.2356 1984 [PubMed]

Langan, P.: The Giliberty bipolar prosthesis. A clinical and radiographical review. Clin. Orthop.,141: 169-175, 1979.141169 1979 [PubMed]

McFarland, E. G.; Lewallen, D. G.; and Cabanela, M. E.: Use of bipolar endoprosthesis and bone grafting for acetabular reconstruction. Clin. Orthop.,268: 128-139, 1991.268128 1991 [PubMed]

Mogensen, B.; Arnason, H.; and Jonsson, G. T.: Socket wall addition for dislocating total hip. Report of two cases. Acta Orthop. Scandinavica,57: 373-374, 1986.57373 1986

Murray, D. W.: Impingement and loosening of the long posterior wall acetabular implant. J. Bone and Joint Surg.,74-B(3): 377-379, 1992.74-B(3)377 1992

Nolan, D. R.; Fitzgerald, R. H.; Beckenbaugh, R. D.; and Coventry, M. B.: Complications of total hip arthroplasty treated by reoperation. J. Bone and Joint Surg.,57-A: 977-981, Oct 1975.57-A977 1975

Ries, M. D., and Wiedel, J. D.: Bipolar hip arthroplasty for recurrent dislocation after total hip arthroplasty. A report of three cases. . Clin. Orthop.,278: 121-127, 1992.278121 1992 [PubMed]

Ritter, M. A.: Dislocation and subluxation of total hip replacement. Clin. Orthop.,121: 92-94, 1976.12192 1976 [PubMed]

Roberson, J. R., and Cohen, D.: Bipolar components for severe periacetabular bone loss around the failed total hip arthroplasty. Clin. Orthop.,251: 113-118, 1990.251113 1990 [PubMed]

Simon, S. R.: New concepts in femoral head replacement: the place of the Bateman prosthesis in hip surgery. Bull. Hosp. Joint Dis.,,38: 59-61, 1977.3859 1977

Verberne, G. H. M.: A femoral head prosthesis with a built-in joint. A radiological study of the movements of the two components. J. Bone and Joint Surg.,65-B(5): 544-547, 1983.65-B(5)544 1983

Watson, P.; Nixon, J. R.; and Mollan, R. A. B.: A prosthesis augmentation device for the prevention of recurrent hip dislocation. A preliminary report. Clin. Orthop.,267: 79-84, 1991.26779 1991 [PubMed]

Woo, R. Y. G., and Morrey, B. F.: Dislocations after total hip arthroplasty. J. Bone and Joint Surg.,64-A: 1295-1306, Dec 1982.64-A1295 1982

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Fig. 1-B: Acetabular augmentation was performed at four years, but the hip continued to dislocate.

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Table I: Indications for Use of Bipolar Revision for Treatment of Recurrent Instability

	Total No. of Patients	No. with Successful Bipolar Revision
Multiple failed previous stabilization procedures (multifactorial cause of instability)	18	17
12 operations	3	3
5-11 operations	3	2
3-4 operations	12	12
No single cause of instability (<2 operations)	9	8
Instability following primary hip arthroplasty	24	22
Instability following revision hip arthroplasty for aseptic loosening	3	2

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Table I: Indications for Use of Bipolar Revision for Treatment of Recurrent Instability

	Total No. of Patients	No. with Successful Bipolar Revision
Multiple failed previous stabilization procedures (multifactorial cause of instability)	18	17
12 operations	3	3
5-11 operations	3	2
3-4 operations	12	12
No single cause of instability (<2 operations)	9	8
Instability following primary hip arthroplasty	24	22
Instability following revision hip arthroplasty for aseptic loosening	3	2

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Table II: Data on the Patients Treated with Bipolar Arthroplasty Because of Recurrent Instability of the Hip

Case	Gender, Age at Bipolar Op. (yrs.)	Durat. of Follow-up (yrs.)	Primary Diagnosis	Direction of Dislocat.	Approach (Primary/Bipolar)	Date of Bipolar Op.	Type of Prosthesis	Type of Acetabular Bone-Grafting	Reops. and Complications	Outcome	Remarks
1	F, 73	3	Osteoarth.	Post.	Lat./lat.	12/5/85	Bateman UPF II	None	None	Stable	Died 1988 (closed head injury)
2	M, 69	5	Develop. dysplasia	Post.	Lat./anterolat.	10/5/93	Multipolar	Cancellous	Postop. migrat.	Stable	12 previous ops.
3	F, 80	12	Avasc. nec.	Post.	Lat./lat.	6/19/85	Bicentric	None	Reop. for cup disassembly; reop. for continuing instabil.; resect. arthroplasty for deep infect.	Unstable	Improved function, pain relief since revis.
4	M, 67	10	Osteoarth.	Super.	Anterolat./anterolat.	9/5/85	Bateman UPF II	None	Reop. for deep infect. and superior migrat.	Stable	12 previous ops., previous deep infect.
5	M, 70	3	Rheumat. arth.	Post.	Posterolat./posterolat.	6/16/94	Multipolar	None	Periprosth. fract.	Stable	Contralat. hip instabil.
6	F, 55	7	Osteoarth.	Ant.	Anterolat./anterolat.	7/11/90	Centrax	None	Sciatic neurapraxia; periprosth. fract.	Stable	6 previous stabilizat. proc.
7	F, 65	9	Osteoarth.	Post.	Anterolat./anterolat.	7/7/89	UHR	Cancellous	Superficial hematoma; groin pain	Stable	Radiographs suggested deep infect.; awaiting resection arthroplasty
8	M, 51	11	Develop. dysplasia	Post.	Posterolat./posterolat.	10/27/86	Bicentric	None	Disloc.	Unstable	Dislocat. after bipolar op., treated nonop.
9	M, 69	3	Osteoarth.	Post.	Anterolat./anterolat.	10/25/94	Multipolar	None	None	Stable	-
10	F, 63	3	Osteoarth.	Ant.	Anterolat.	3/8/94	Multipolar	Cancellous	None	Stable	1989: bipolar op., stable; 1990: revised to HGP-II prosth. for pain, became unstable; 1994: rerevised to bipolar prosth.
11	F, 68	9	Osteoarth.	Ant.	Lat./anterolat.	9/20/88	Centrax	None	Aseptic loosening with pain	Stable	Refused revis.
12	M, 35	8	Posttraumat. arth.	Post.	Anterolat./anterolat.	6/10/88	UHR	None	Reop. for pain at 5 yrs.; conversion to Girdlestone at 7 yrs.	Stable	Revised to total hip arthroplasty because of pain
13	M, 66	5	Osteoarth.	Post.	Lat./lat.	8/18/89	Centrax	None	Thigh pain	Stable	Died 1994 (closed head injury)
14	M, 69	2	Posttraumat. arth.	Post.	Anterolat./anterolat.	9/29/92	Centrax	None	Conversion to Girdlestone for deep infect.	Stable	Candida isolated; died 1994 (unrelated)
15	M, 72	5	Osteoarth.	Post.	Posterolat./posterolat.	11/30/92	Self Centering	None	Disloc.	Stable	9 previous stabilizat. proc.
16	F, 62	7	Avasc. nec.	Ant.	Anterolat./anterolat.	10/31/90	Centrax	Cancellous, cortical strut	None	Stable at all times	Severe acetab. deficiency
17	F, 75	5	Osteoarth.	Post.	Lat./anterolat.	11/15/90	Centrax	None	None	Stable	Died 1995
18	F, 30	3	Posttraumat. arth.	Post.	Anterolat./anterolat.	2/8/94	Centrax	Cancellous	None	Stable	-
19	F, 53	2	Osteoarth.	Super.	Anterolat./anterolat.	6/21/91	UHR	None	None	Stable	Died 1993 (breast carcinoma)
20	M, 57	4	Osteoarth.	Post.	Anterolat./anterolat.	12/8/93	Centrax	None	Reop. for instabil.; superficial infect.	Unstable initially	Multiple ops.; primary deep infect.; knee instabil.
21	F, 35	5	Osteoarth.	Super.	Anterolat./anterolat.	11/6/92	UHR	None	Groin pain	Stable	Contralat. hip instabil.; recent migrat.
22	M, 70	3	Osteoarth.	Post.	Anterolat./anterolat.	2/15/94	Multipolar	None	None	Stable	Strenuous activity
23	F, 60	3	Posttraumat. arth.	Post.	Posterolat./posterolat.	3/16/95	UHR	None	None	Stable	12 previous ops.
24	F, 69	2	Osteoarth.	Ant.	Ant./ant.	6/11/86	Centrax	None	None	Stable	Multiple previous stabilizat. proc.; died 1988
25	M, 57	3	Ankylos. spondylitis	Post.	Lat./lat.	11/29/94	Multipolar	None	None	Stable	7 previous ops.
26	M, 49	2	Osteoarth.	Ant.	Anterolat./anterolat.	4/18/95	Multipolar	None	None	Stable	Primary deep infect.; multiple revis.
27	M, 72	3	Osteoarth.	Post.	Lat./anterolat.	4/25/94	Multipolar	Cancellous	None	Stable	Multiple previous stabilizat. proc.

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Table II: Data on the Patients Treated with Bipolar Arthroplasty Because of Recurrent Instability of the Hip

Case	Gender, Age at Bipolar Op. (yrs.)	Durat. of Follow-up (yrs.)	Primary Diagnosis	Direction of Dislocat.	Approach (Primary/Bipolar)	Date of Bipolar Op.	Type of Prosthesis	Type of Acetabular Bone-Grafting	Reops. and Complications	Outcome	Remarks
1	F, 73	3	Osteoarth.	Post.	Lat./lat.	12/5/85	Bateman UPF II	None	None	Stable	Died 1988 (closed head injury)
2	M, 69	5	Develop. dysplasia	Post.	Lat./anterolat.	10/5/93	Multipolar	Cancellous	Postop. migrat.	Stable	12 previous ops.
3	F, 80	12	Avasc. nec.	Post.	Lat./lat.	6/19/85	Bicentric	None	Reop. for cup disassembly; reop. for continuing instabil.; resect. arthroplasty for deep infect.	Unstable	Improved function, pain relief since revis.
4	M, 67	10	Osteoarth.	Super.	Anterolat./anterolat.	9/5/85	Bateman UPF II	None	Reop. for deep infect. and superior migrat.	Stable	12 previous ops., previous deep infect.
5	M, 70	3	Rheumat. arth.	Post.	Posterolat./posterolat.	6/16/94	Multipolar	None	Periprosth. fract.	Stable	Contralat. hip instabil.
6	F, 55	7	Osteoarth.	Ant.	Anterolat./anterolat.	7/11/90	Centrax	None	Sciatic neurapraxia; periprosth. fract.	Stable	6 previous stabilizat. proc.
7	F, 65	9	Osteoarth.	Post.	Anterolat./anterolat.	7/7/89	UHR	Cancellous	Superficial hematoma; groin pain	Stable	Radiographs suggested deep infect.; awaiting resection arthroplasty
8	M, 51	11	Develop. dysplasia	Post.	Posterolat./posterolat.	10/27/86	Bicentric	None	Disloc.	Unstable	Dislocat. after bipolar op., treated nonop.
9	M, 69	3	Osteoarth.	Post.	Anterolat./anterolat.	10/25/94	Multipolar	None	None	Stable	-
10	F, 63	3	Osteoarth.	Ant.	Anterolat.	3/8/94	Multipolar	Cancellous	None	Stable	1989: bipolar op., stable; 1990: revised to HGP-II prosth. for pain, became unstable; 1994: rerevised to bipolar prosth.
11	F, 68	9	Osteoarth.	Ant.	Lat./anterolat.	9/20/88	Centrax	None	Aseptic loosening with pain	Stable	Refused revis.
12	M, 35	8	Posttraumat. arth.	Post.	Anterolat./anterolat.	6/10/88	UHR	None	Reop. for pain at 5 yrs.; conversion to Girdlestone at 7 yrs.	Stable	Revised to total hip arthroplasty because of pain
13	M, 66	5	Osteoarth.	Post.	Lat./lat.	8/18/89	Centrax	None	Thigh pain	Stable	Died 1994 (closed head injury)
14	M, 69	2	Posttraumat. arth.	Post.	Anterolat./anterolat.	9/29/92	Centrax	None	Conversion to Girdlestone for deep infect.	Stable	Candida isolated; died 1994 (unrelated)
15	M, 72	5	Osteoarth.	Post.	Posterolat./posterolat.	11/30/92	Self Centering	None	Disloc.	Stable	9 previous stabilizat. proc.
16	F, 62	7	Avasc. nec.	Ant.	Anterolat./anterolat.	10/31/90	Centrax	Cancellous, cortical strut	None	Stable at all times	Severe acetab. deficiency
17	F, 75	5	Osteoarth.	Post.	Lat./anterolat.	11/15/90	Centrax	None	None	Stable	Died 1995
18	F, 30	3	Posttraumat. arth.	Post.	Anterolat./anterolat.	2/8/94	Centrax	Cancellous	None	Stable	-
19	F, 53	2	Osteoarth.	Super.	Anterolat./anterolat.	6/21/91	UHR	None	None	Stable	Died 1993 (breast carcinoma)
20	M, 57	4	Osteoarth.	Post.	Anterolat./anterolat.	12/8/93	Centrax	None	Reop. for instabil.; superficial infect.	Unstable initially	Multiple ops.; primary deep infect.; knee instabil.
21	F, 35	5	Osteoarth.	Super.	Anterolat./anterolat.	11/6/92	UHR	None	Groin pain	Stable	Contralat. hip instabil.; recent migrat.
22	M, 70	3	Osteoarth.	Post.	Anterolat./anterolat.	2/15/94	Multipolar	None	None	Stable	Strenuous activity
23	F, 60	3	Posttraumat. arth.	Post.	Posterolat./posterolat.	3/16/95	UHR	None	None	Stable	12 previous ops.
24	F, 69	2	Osteoarth.	Ant.	Ant./ant.	6/11/86	Centrax	None	None	Stable	Multiple previous stabilizat. proc.; died 1988
25	M, 57	3	Ankylos. spondylitis	Post.	Lat./lat.	11/29/94	Multipolar	None	None	Stable	7 previous ops.
26	M, 49	2	Osteoarth.	Ant.	Anterolat./anterolat.	4/18/95	Multipolar	None	None	Stable	Primary deep infect.; multiple revis.
27	M, 72	3	Osteoarth.	Post.	Lat./anterolat.	4/25/94	Multipolar	Cancellous	None	Stable	Multiple previous stabilizat. proc.

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Table III: Final Outcome

*One reoperation was a resection arthroplasty in an infected unstable hip.

	No. of Hips
Total	Stable Postop.	Unstable Postop.
Bipolar revision arthroplasty	27 (100%)	22 (81%)	5 (19%)
Additional nonop. treatment (brace, cast)	2 (7%)	24 (89%)	3 (11%)
Reop. for instability*	2 (7%)	25 (93%)	2 (7%)

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Table III: Final Outcome

*One reoperation was a resection arthroplasty in an infected unstable hip.

	No. of Hips
Total	Stable Postop.	Unstable Postop.
Bipolar revision arthroplasty	27 (100%)	22 (81%)	5 (19%)
Additional nonop. treatment (brace, cast)	2 (7%)	24 (89%)	3 (11%)
Reop. for instability*	2 (7%)	25 (93%)	2 (7%)