Constrained acetabular components

CIRCUMFERENTIAL PROXIMAL FEMORAL ALLOGRAFTS IN TOTAL HIP ARTHROPLASTY REVISION SURGERY

Objective: To evaluate the clinical and radiographic results from patients who underwent femoral reconstruction secondary to loosening of total hip arthroplasty, using circumferential proximal femoral allografts and cemented implants. Methods: A retrospective study was conducted on 32 patients (33 hips) who underwent femoral reconstruction secondary to loosening of total hip arthroplasty, using circumferential proximal femoral allografts and cemented implants. Among these patients, 28 (29 hips) fulfilled all the requirements for this study. The mean follow-up was five years and two months. The clinical evaluation was done in accordance with the Harris Hip Score. Radiographically, the patients were assessed regarding reabsorption and consolidation of the allograft, migration of the greater trochanter, stability of the femoral component and heterotypic calcification. Results: The average preoperative Harris Hip Score was 32 points. At the last postoperative follow-up, the average score was 82 points. Allograft resorption of some degree was seen in nine hips (31%). Regarding consolidation, 24 cases (82.8%) showed full consolidation, three (10.3%) showed partial consolidation and two (6.9%) showed pseudarthrosis. All femoral components were stable. According to the criteria established, 27 cases (93.1%) were considered to be successful reconstructions after a mean follow-up of five years and two months. Conclusion: From the results obtained, it was concluded that use of circumferential proximal femoral allografts in selected cases of femoral reconstruction secondary to loosening of arthroplasty presented a high survival rate from the reconstruction over an average follow-up of five years and two months.

Achilles allograft reconstruction for recurrent dislocation in total hip arthroplasty

Recurrent dislocation secondary to posterior soft tissue deficiency is a challenging complication of total hip arthroplasty. We describe the use of an Achilles allograft sling to improve hip stability. Eight patients treated with the sling were followed an average of 5 years. Seven patients had no recurrent instability and good postoperative range of motion. One graft failed in a patient with a neuropathic hip. Cadaveric biomechanical testing was also performed to investigate the stiffness and torque to failure of the sling in 6 specimens. Allograft slings can be used to improve hip stability. The technique is relatively easy to perform and does not limit postoperative range of motion. The graft decreases joint stiffness and has a greater torque to failure than the intact capsule.

The use of a constrained cementless acetabular component for instability in total hip replacement

Recurrent dislocation after total hip arthroplasty is a disabling complication that can be difficult to treat. We evaluated the early clinical and radiographic outcome associated with the use of a constrained acetabular component for instability in total hip arthroplasty. Fifteen patients underwent either primary or revision total hip arthroplasty with a cementless constrained acetabular component for different indications. The mean patient age at surgery was 57.4 years and the mean clinical and radiological follow-up period was 26.4 months. Clinical assessment was performed by the Harris hip score and at the latest follow up patients reported outcome using the Oxford hip score questionnaire. All radiographs were evaluated for evidence of loosening. Only one patient experienced redislocation with the constrained prosthesis. The average Harris hip score increased from a preoperative mean of 22 (range, 16 - 36) to a postoperative mean of 85 (range, 66-94). Preoperatively, the mean Oxford Hip Score was 48.6, which decreased to 20.5 at the final examination. All but one of the 15 hips had a well-fixed, stable cup. Femoral component stability with bone ingrowth was achieved in 10 cases. A constrained acetabular component is an effective option for the treatment of hip instability in primary and revision arthroplasty in those at high risk of dislocation. The potential for aseptic loosening requires evaluation by long term studies.

Treatment of recurrent THR dislocation using of a cementless dual-mobility cup: a 59 cases series with a mean 8 years' follow-up

INTRODUCTION

Instability is one of the most feared complications following total hip replacement (THR). In France, dual-mobility cups are widely used in acetabular revision for instability; few studies, however, have focused on this type of implant.

HYPOTHESIS

The gain in stability provided by the dual-mobility implant allows the risk of dislocation to decrease by the sole revision of the acetabular component in case of recurrent instability.

OBJECTIVES

This hypothesis was tested over medium-term follow-up of a series of cementless dual-mobility cups implanted during isolated acetabular revision for recurrent dislocation.

PATIENTS AND METHODS

A series of THR revision for instability was analyzed retrospectively. Inclusion criteria were: recurrent THR dislocation treated by cementless dual-mobility cup, between 1995 and 2001. Radiological analysis used Imagika™ software. Fifty-nine patients were included; nine died before radioclinical follow-up could be performed; none of the survivors were lost to follow-up. Mean follow-up was 8 years (range, 6-11 years).

RESULTS

There was one early dislocation without recurrence; the dislocation rate was 1.7%. At follow-up, mean PMA score was 16.5 (12-18) and mean Harris score 86.7 (49-99). Radiologically, there was no loosening or migration, but 19% of X-ray views showed less than 1mm wide peri-acetabular radiolucency. With dislocation as censoring criterion, 8-year survivorship was 98% (95% CI: 95-100%).

DISCUSSION

The dislocation rate (1.7%) and clinical results were better than in most series of revision by constrained cup for recurrent dislocation. The high rate of peri-acetabular radiolucency would seem to relate to the external coating of the cup: aluminum oxide in the Novae-1 implant and aluminum oxide/hydroxyapatite in the Novae-E.

CONCLUSION

The use of dual-mobility cups to treat THR instability gave satisfactory results. We recommend dual-mobility cups with hydroxyapatite surface treatment over a porous metallic substrate, rather than with an aluminum oxide or an aluminum oxide/hydroxyapatite bilayer coating.

LEVEL OF EVIDENCE

Level IV. Retrospective Study.

The use of a cemented dual mobility socket to treat recurrent dislocation

BACKGROUND

The treatment of recurrent dislocation after total hip arthroplasty remains challenging. Dual mobility sockets have been associated with a low rate of dislocation but it is not known whether they are useful for treating recurrent dislocation.

QUESTIONS/PURPOSES

We therefore asked whether a cemented dual mobility socket would (1) restore hip stability following recurrent dislocation; (2) provide a pain-free and mobile hip; and (3) show durable radiographic fixation.

METHODS

We retrospectively reviewed 51 patients treated with a cemented dual mobility socket for recurrent dislocation after total hip arthroplasty between August 2002 and June 2005. The mean age at the time of the index procedure of was 71.3 years. Of the 51 patients, 47 have had complete clinical and radiographic evaluation data at a mean followup of 51.4 months (range, 25-76.3 months).

RESULTS

The cemented dual mobility socket restored complete stability of the hip in 45 of the 47 patients (96%). The mean Merle d'Aubigné hip score was 16 ± 2 at the latest followup. Radiographic analysis revealed no or radiolucent lines less than 1 mm thick located in a single acetabular zone in 43 of 47 hips (91.5%). The cumulative survival rate of the acetabular component at 72 months using revision for dislocation and/or mechanical failure as the end point was 96% ± 4% (95% confidence interval, 90%-100%).

CONCLUSIONS

A cemented dual mobility socket was able to restore hip stability in 96% of recurrent dislocating hips. However, longer-term followup is needed to ensure that dislocation and loosening rates will not increase.

Constrained liner in neurologic or cognitively impaired patients undergoing primary THA

BACKGROUND

THA performed in patients with cognitive deficits or neuromuscular diseases has been associated with a high postoperative dislocation rate. The constrained liner reportedly provides stability in patients with recurrent dislocation. However, achieving stability could be offset by early loosening when used in patients with neurologic diseases.

QUESTIONS/PURPOSES

We therefore asked whether constrained liners had a higher risk of loosening when used in primary THA for patients with neurologic diseases.

METHODS

We retrospectively reviewed a 144 patients (164 hips) with neuromuscular disease who had a constrained polyethylene insert from 1999 to 2004 and compared them to another 120 patients (132 hips) with neuromuscular disease operated on immediately before this period (from 1994 to 1998) who had a conventional polyethylene insert.

RESULTS

Thirty-three (25%) of the 132 hips without a constrained liner were known to have had at least one dislocation and 21 had revision for recurrent dislocation. Ten other hips had revision for loosening of the cup. The survival rate was 82% at 5 years and 77% at 10 years with revision due to recurrent dislocation or loosening of the cup as the endpoint. With a constrained liner, at minimum 5-year followup (mean, 7 years; range, 5-10 years), the incidence of complications, particularly dislocation, was decreased (three dislocations among 164 hips; 2%), with one revision for recurrent dislocation and one revision for loosening.

CONCLUSIONS

This constrained acetabular component provides durable protection against dislocation without substantial increased loosening at midterm followup.

Constrained acetabular liners cemented into cages during total hip revision arthroplasty

The combination of acetabular bone loss and hip instability is challenging. Sixteen patients underwent revision total hip arthroplasty using constrained acetabular liners cemented into cages. The average follow-up was 28 months (range, 24-60 months). Clinical evaluation was obtained using the Harris hip score along with radiographic data. At latest follow-up, 13 patients were available for evaluation. Although the average postoperative Harris hip score was 62 points, which was better than the preoperative score of 27 points, the overall radiographic failure rate was 23%. The combination of poor acetabular bone stock and altered stresses from the increased constraint likely led to the poor outcome. We would only recommend use of a cemented, constrained acetabular liner in combination with a protrusio cage as a bail out or salvage procedure.

Closed reduction of a dislocated constrained total hip arthroplasty using a novel technique with a PEG board

This article describes a case of closed reduction of a dislocated total hip arthroplasty (THA) out of a constrained acetabular liner using a novel technique with a peg board secured to the operating table.A 79-year-old woman sustained multiple dislocations after a primary THA. She was converted to a constrained liner and sustained no further dislocations for 5 years. She presented after dislocating her hip while getting out of a chair. The patient was taken to the operating room, placed under general anesthesia, and laid supine on the operating table, to which a peg board had been previously securely attached. A padded perineal post was placed in the patient's groin into the peg board. Under fluoroscopy, in-line traction was applied to the right leg until the femoral head was perched on the acetabular liner. With internal rotation and pressure over the trochanter, the femoral head was reduced.This technique requires less set-up time than using a fracture table. It also securely stabilizes the patient without skilled assistants during longitudinal traction. Moreover, if closed reduction fails, the patient can be rapidly placed in the lateral decubitus position for open reduction or revision arthroplasty. Successful closed reduction of a dislocated constrained liner turns an emergent case into an elective case if revision arthroplasty is indicated. This technique can also be easily used for the more common reductions of dislocated nonconstrained THAs.

Are abductor muscle quality and previous revision surgery predictors of constrained liner failure in hip arthroplasty?

Dislocation is one of the most common complications of total hip arthroplasty. The use of constrained liners is an option for the management of chronic hip instability, typically used after other methods have failed. The purposes of this study were to evaluate the overall clinical outcomes and failure rates of a tripolar constrained liner design, to assess the radiographic outcomes of its use, and to examine whether various factors such as abductor mechanism quality and history of previous revision surgeries were associated with an increased risk of failure. Forty-three hips in 39 patients who had a mean follow-up of 51 months (range, 24-110 months) were reviewed. Ninety-one percent of the hips (39 of 43 hips) did not need any revisions over the study period. A new liner was implanted in all four failed hips with concurrent revision of the acetabular cup in three cases. No further dislocations occurred in this group. The mean hip score for surviving hips was 82 points (range, 38-100 points) at final follow-up. Radiographic evaluation revealed stable, well-fixed acetabular components in all surviving hips without progressive radiolucencies. No association was found between abductor muscle quality and the incidence of failure, but patients who experienced a constrained liner failure were more likely to have undergone at least one previous hip revision operation. Tripolar constrained acetabular liners can provide successful outcomes in patients with hip instability, although it is important not to rely on the use of a constrained liner alone in an attempt to compensate for other correctable factors such as component positioning.

Complications encountered with the use of constrained acetabular prostheses in total hip arthroplasty

At our department, 46 constrained acetabular components in 38 patients were placed successively for a period of 4 years. Indications included recurrent dislocation, septic and aseptic loosening with extensive bone loss, tumor surgery with extensive bone resection, and instability due to neurologic impairment. Because 2 cup failures and 10 dislocations were observed with the constrained devices at 4 to 7 years of follow-up, the authors started to use large-diameter metal-on-metal bearings for similar indications. A series of 36 such bearings in 38 patients revealed only one cup failure and one dislocation at 2 to 4 years of follow-up. Although the 2 series are different and therefore difficult to compare, the authors recommend judicious use of constrained devices because of the high failure rate (26%) and consideration of alternative options such as the use of large-diameter metal-on-metal bearings.

Prevention of dislocation in total hip revision surgery using a dual mobility design

BACKGROUND

Postoperative dislocation is the commonest complication following revision total hip arthroplasty (THA). HYPOTHESIS AND TYPE OF STUDY: Dual mobility cups are supposed to reduce the risk of THA instability. The present retrospective study tested this hypothesis on revision THAs and also, assessed this design contribution to acetabular fixation longevity.

MATERIALS AND METHODS

The series was homogeneous and continuous, comprising a total of 163 revision THAs: 110 of them were bipolar revisions and 53 were restricted to the acetabular component exchange. Mean patient age was 68.7 years (range: 34-92 years). Novae (SERF, Décines) dual mobility cups were used in all cases: 110 cementless cups were used and 53 cups were cemented in a Kerboull reinforcement ring due to severe acetabular bone loss.

RESULTS

Mean patients' follow-up (FU) was 60.4 + or - 17.6 months. There were six early dislocations (which were reduced without additional surgery and remained recurrence-free) and two cases of acetabular loosening. The total postoperative dislocation rate at the end of follow-up was 3.7% and the 7-year cup survivorship rate was 96.1% (95% CI: 92.8-99.2%). In revision for aseptic loosening, the instability rate was 2.9%; in the higher instability risk groups (i.e., revision for infection and or recurrent instability) the dislocation rate was respectively 9% and 0%.

DISCUSSION

Dual mobility cups provided a dislocation rate of only 3.7% in revision THA, comparable to the one reported with standard implants for primary THA. This kind of cup design is especially suited to deal with high instability risk revision cases, where constrained components are generally recommended. It can also be indicated in cases of aseptic loosening, where it resulted in a 2.9% dislocation rate and only two impending failures of fixation. In terms of mechanical failure rate, these numbers compare well to the ones pertaining to tripolar and constrained implants. These later alternatives remain possible options but are not fully efficient in terms of long-term stability and fixation longevity. LEVEL OF STUDY: Level IV, retrospective or records-based.

Retrieval analysis of failed constrained acetabular liners

Despite the large loads placed upon constrained acetabular liners, little is known of their mechanical performance. We analyzed retrieved liners to determine wear and other damage modes and assess associations between types and severity of damage and clinical, radiographic, and implant variables. Outer rim impingement frequency and severity were higher than that for the inner rim. The 20 degrees elevation was most frequently affected by impingement. Inner rim impingement was more frequent with small heads. Outer bearing surface wear scores were higher than inner bearing scores. Liners removed for infection or stem failure had similar damage compared with other groups, demonstrating the complex relationship of impingement and wear with clinical performance. No association was found between liner damage and clinical and radiographic variables.

Modular femoral head and liner exchange for the unstable total hip arthroplasty

Outcomes of femoral head and nonconstrained liner exchange in treating hip instability were evaluated. Forty-eight modular component exchanges performed in 45 patients for recurrent hip dislocations were retrospectively reviewed. Mean follow-up was 4.7 years. Overall success rate was 73% (35/48 hips). Thirty-two (67%) of 48 hips experienced no further dislocations. Three patients had 1 dislocation each with no subsequent dislocations. Ten patients (13 hips) had additional surgery to stabilize their hips (27% failure rate). Demographic, clinical, and implant variables were not associated with outcome. Isolated modular component exchange can be successful in treating recurrent hip dislocations; however, a significant failure rate, not easily predicted, exists. This represents the largest series of modular head and nonconstrained liner exchange for hip dislocation (122/125).

Failure mechanisms and closed reduction of a constrained tripolar acetabular liner

Unlike traditional bipolar constrained liners, the Osteonics Omnifit constrained acetabular insert is a tripolar device, consisting of an inner bipolar bearing articulating within an outer, true liner. Every reported failure of the Omnifit tripolar implant has been by failure at the shell-bone interface (Type I failure), failure at the shell-liner interface (Type II failure), or failure of the locking mechanism resulting in dislocation of the bipolar-liner interface (Type III failure). In this report we present two cases of failure of the Omnifit tripolar at the bipolar-femoral head interface. To our knowledge, these are the first reported cases of failure at the bipolar-femoral head interface (Type IV failure). In addition, we described the first successful closed reduction of a Type IV failure.

Use of a dual mobility socket to manage total hip arthroplasty instability

Unconstrained tripolar hip implants provide an additional bearing using a mobile polyethylene component between the prosthetic head and the outer metal shell. Such a design increases the effective head diameter and therefore is an attractive option in challenging situations of unstable total hip arthroplasties. We report our experience with 54 patients treated using this dual mobility implant in such situations. We ascertained its ability to restore and maintain stability, and examined component loosening and component failure. At a minimum followup of 2.2 years (mean, 4 years; range, 2.2-6.8 years), one hip had redislocated 2 months postoperatively and was managed successfully without reoperation by closed reduction with no additional dislocation. Two patients required revision of the implant because of dislocation at the inner bearing. Technical errors were responsible for these failures. Three patients had reoperations for deep infections. The postoperative radiographs at latest followup showed very satisfactory osseointegration of the acetabular component because no radiolucent line or osteolysis was reported. Use of this unconstrained tripolar design was successful in restoring and maintaining hip stability. We observed encouraging results at short-term followup regarding potential for loosening or mechanical failures.

LEVEL OF EVIDENCE

Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Modes of failure of Osteonics constrained tripolar implants: a retrospective analysis of forty-three failed implants

BACKGROUND

The Osteonics constrained tripolar implant has been one of the most commonly used options to manage recurrent instability after total hip arthroplasty. Mechanical failures were expected and have been reported. The purpose of this retrospective review was to identify the observed modes of failure of this device.

METHODS

Forty-three failed Osteonics constrained tripolar implants were revised at our institution between September 1997 and April 2005. All revisions related to the constrained acetabular component only were considered as failures. All of the devices had been inserted for recurrent or intraoperative instability during revision procedures. Seven different methods of implantation were used. Operative reports and radiographs were reviewed to identify the modes of failure.

RESULTS

The average time to failure of the forty-three implants was 28.4 months. A total of five modes of failure were observed: failure at the bone-implant interface (type I), which occurred in eleven hips; failure at the mechanisms holding the constrained liner to the metal shell (type II), in six hips; failure of the retaining mechanism of the bipolar component (type III), in ten hips; dislocation of the prosthetic head at the inner bearing of the bipolar component (type IV), in three hips; and infection (type V), in twelve hips. The mode of failure remained unknown in one hip that had been revised at another institution.

CONCLUSIONS

The Osteonics constrained tripolar total hip arthroplasty implant is a complex device involving many parts. We showed that failure of this device can occur at most of its interfaces. It would therefore appear logical to limit its application to salvage situations.

The use of a dual-articulation acetabular cup system to prevent dislocation after primary total hip arthroplasty: analysis of 384 cases at a mean follow-up of 15 years

The concept of a dual articulation acetabular cup was developed by Prof. Bousquet in 1974. This concept has been shown to provide high stability after revision and primary total hip arthroplasty. The aim of our study was to evaluate the incidence of prosthetic instability in a consecutive homogeneous series of 384 primary dual mobility cups. Incidence of instability and implant survival were evaluated. Mean follow-up was 15.3 years (range, 12-20). There was no early or late instability. On the acetabular side there were 13 aseptic loosenings, 14 intraprosthetic dislocations, and seven polyethylene wear cases that required replacement of the liner. The cumulative survival rate of the dual-articulation acetabular cup using surgical revision for aseptic loosening as the endpoint was 95.9% +/- 4.1% at 18 years postoperatively. Our series proves the good long term behaviour of dual-articulation acetabular components in primary arthroplasty. Their excellent survivorship rate and the absence of episodes of prosthetic instability increase our confidence in this concept.

Failure of constrained acetabular liner without metal ring disruption

Constrained acetabular liners can fail leading to recurrent dislocation. Failure can occur at any of the five possible interfaces: bone-acetabular shell, acetabular shell-constrained liner insert, constrained liner insert-bipolar head, bipolar head- femoral head and femoral head-trunion. We report a patient who presented with dissociation of the cemented Osteonics acetabular constrained liner (Stryker-Howmedica-Osteonics, Rutherford, New Jersey). The failure interface was at the factory pre-assembled constrained liner insert-bipolar head without any locking ring failure; instead there was deformation of the constrained liner insert's polyethylene rim, which facilitated dissociation. To our knowledge, there are no previous reports of such a failure mode pertaining to this type of constrained liner. Constrained acetabular liners are indicated during primary or revision total hip arthroplasty for patients who are at high risk for dislocations or who have had recurrent dislocations. Failure rates (typically recurrent dislocation) range from 4% to 29% at mid-term follow-up. The first report on the Osteonics acetabular constrained liner was published in 1994. Failures have been reported previously to occur at surgically controllable interfaces, such as the acetabular shell from the bony surface and the constrained liner insert from the acetabular metal shell, and have been attributable to excessive constraint or improper technique. All dissociations pertaining to factory-preassembled component interfaces have been attributed to breakage of the locking ring. This article presents the first case of disengagement of the tripolar constrained liner without disruption of the locking ring.

A unique failure mechanism of a constrained total hip arthroplasty: a brief review of the literature

Constrained acetabular systems are successful in achieving stability in patients with recurrent dislocations, abductor deficiency, or where a source of instability cannot be determined. We report on one patient with 2 dissociations of a tripolar constrained acetabular liner caused by impingement when the patient exceeded the allowed range of motion. The inner liner dissociated from the outer liner, whereas the reinforcing ring remained intact and in place. Despite an extensive literature search, we were unable to find any other published reports concerning this specific mode of failure for this constrained liner. Surgeons should be aware that constrained liners are not infallible and have limitations to range of motion. Maximizing the size of the femoral head may reduce the risk of this mode of failure.

Recurrent total hip arthroplasty dislocation in combination with massive osteolysis: an outline of management using a proximal femoral replacement

Recurrent dislocation of a total hip arthroplasty is a most distressing complication for both patient and surgeon. The situation is worsened when massive osteolysis occurs in combination with recurrent dislocation. Management options become more limited in this situation. We present such a case along with a discussion of the management options utilised.

Omnifit acetabular component: a solution to preventing and treating dislocation

PURPOSE

To assess short- to medium-term outcome of the Omnifit constrained acetabular component in preventing dislocation in at-risk patients after total hip arthroplasty (THA).

METHODS

81 patients (mean age, 77 years) underwent either primary or revision THA with an Omnifit constrained acetabular component and were followed up clinically and radiologically for a mean period of 24 months.

RESULTS

There was one dislocation and one revision for avulsion of the acetabulum. The remaining prostheses remained well fixed.

CONCLUSIONS

In the short- to medium-term, the Omnifit constrained acetabular component is effective in preventing primary and recurrent dislocation in at-risk patients. Long-term follow-up is needed to assess whether good fixation is maintained. The Omnifit acetabular cup is recommended for elderly patients with limited life expectancy and functional demands.

The constrained acetabular component for hip instability

One hundred four hips in 107 patients undergoing revision arthroplasty of the hip were identified at risk of dislocation and treated with the constrained cup. Radiostereometric analysis was performed to assess prosthesis migration. Mean follow-up was 3.0 years (range, 2.0-4.8). At last review, 19 patients had died and 6 were lost to follow-up. There were 5 revisions for cup loosening and a further 4 with radiographic evidence of loosening. There were 3 dislocations and 3 dissociations in 5 patients. Radiostereometric analysis demonstrated that cup migration at 24 months was up to 0.82 mm of translation and 1.58 degrees of rotation. Our results confirm that the constrained acetabular component is a highly effective option for the treatment for patients with instability of the hip. The aseptic loosening rate was higher than previously reported.

Constrained liners for recurrent dislocations in total hip arthroplasty

This study reports the results and complications from treating recurrent hip dislocations with a constrained liner (CL) after total hip arthroplasty (THA). Forty patients who had a CL inserted as a secondary prophylactic treatment were retrospectively reviewed after a median observation period of 27 months (range 7-77 months). During the observation period five patients had to be revised: one for deep infection and four on account of re-dislocations. Our results indicate that patients with recurrent THA dislocations can be treated with a CL and has a satisfactory low complication rate and a relatively low risk of re-dislocation.

Finite element analysis of shear stresses at the implant-bone interface of an acetabular press-fit cup during impingement / Finite-Elemente-Berechnung der Schubspannungen im Implantat-Knochen-Interface einer acetabulären Press-Fit-Pfanne bei Impingement

After total hip replacement (THR) impingement of the implant components causes shear stresses at the acetabular implant-bone interface. In the current study the finite element method (FEM) was applied to analyse the shear stresses at a fully bonded implant-bone interface assuming total ingrowth of the cup. The FE model of a press-fit acetabular component and the proximal part of the femoral component incorporates non-linear material and large sliding contact. The model was loaded with a superior-medial joint load of 435 N simulating a two-legged stance. Starting at initial impingement, the femoral component was medially rotated by 20 degrees . The peak tilting shear stress of -2.6 MPa at the impingement site takes effect towards the pole of the cup. The torsional shear stress at the impingement site is zero. On each side of the impingement site, there are extrema of torsional shear stress reaching -1.8 and 1.8 MPa, respectively. The global peak shear stress during impingement may indicate a possible starting point for cup loosening. The pattern of the torsional shear stresses suggests that besides the symmetric lever-out, an additional asymmetrical tilting of the cup occurs that can be explained by the orientation of the applied joint load.

Operative and non-operative treatment options for dislocation of the hip following total hip arthroplasty

BACKGROUND

Dislocation following hip replacement is associated with significant morbidity and functional cost. The cause is usually multifactorial. A variety of treatment options are available which can broadly be classified into operative and non-operative.

OBJECTIVES

To determine the best methods of treatment of recurrent dislocation following total hip replacement.

SEARCH STRATEGY

The following databases were searched until August 2006: MEDLINE, EMBASE, CINAHL, the Cochrane Central Register of Controlled Trials (CENTRAL), Health Technology Assessment database (HTA), Database of Abstracts of Reviews of Effectiveness (DARE), International Standard Randomised Controlled Trial Number Register (ISRCTN), and MetaRegister of Controlled Trials (mRCT).

SELECTION CRITERIA

Randomised and quasi-randomised trials comparing operative and non-operative treatments for recurrent dislocation following total hip replacement.

DATA COLLECTION AND ANALYSIS

Two independent reviewers applied the inclusion criteria to identified studies.

MAIN RESULTS

Searches identified 269 studies. None fulfilled the inclusion criteria.

AUTHORS' CONCLUSIONS

The authors invite researchers to perform RCTs comparing different treatment options for recurrent dislocation of the hip. The heterogeneity of the population and variety of underlying causes would favour a multi-centre study to achieve an adequate sample size.

Constrained components for the unstable hip following total hip arthroplasty: a literature review

Patients with chronic instability or late dislocation following total hip arthroplasty often require operative management. Unfortunately, there is an increased risk of recurrent dislocation following revision in these patients. Over the past decade the use of constrained devices for patients with chronic instability has gained increased interest; however, there is a paucity of studies available in the literature regarding the use of these devices. The purpose of this study was to analyze the available literature over the past 15 years, focusing on larger, long-term studies, to obtain recommendations from the respective articles for indications and contraindications for the use of constrained devices. Our review of eight reports included 1,199 hips in 1,148 patients with a total mean follow-up of 51 months (range, 24 to 124 months). The mean rate of dislocation following revision with a constrained liner was 10% and the mean re-operation rate for reasons other than dislocation was 4%. We concluded that constrained liners are an option for patients who have failed management of instability with other implants, those with instability of unclear etiology, those with cognitive problems who are unable to follow dislocation precautions, those with deficient abductors, and elderly or low-demand individuals with well-positioned implants requiring revision.

Constrained components for the unstable hip following total hip arthroplasty: a literature review

Patients with chronic instability or late dislocation following total hip arthroplasty often require operative management. Unfortunately, there is an increased risk of recurrent dislocation following revision in these patients. Over the past decade the use of constrained devices for patients with chronic instability has gained increased interest; however, there is a paucity of studies available in the literature regarding the use of these devices. The purpose of this study was to analyze the available literature over the past 15 years, focusing on larger, long-term studies, to obtain recommendations from the respective articles for indications and contraindications for the use of constrained devices. Our review of eight reports included 1,199 hips in 1,148 patients with a total mean follow-up of 51 months (range, 24 to 124 months). The mean rate of dislocation following revision with a constrained liner was 10% and the mean re-operation rate for reasons other than dislocation was 4%. We concluded that constrained liners are an option for patients who have failed management of instability with other implants, those with instability of unclear etiology, those with cognitive problems who are unable to follow dislocation precautions, those with deficient abductors, and elderly or low-demand individuals with well-positioned implants requiring revision.

A constrained acetabular component for recurrent dislocation

We treated 34 patients with recurrent dislocation of the hip with a constrained acetabular component. Roentgen stereophotogrammetric analysis was performed to assess migration of the prosthesis.

The mean clinical follow-up was 3.0 years (2.2 to 4.8) and the radiological follow-up was 2.7 years (2.0 to 4.8). At the latest review six patients had died and none was lost to follow-up. There were four acetabular revisions, three for aseptic loosening and one for deep infection. Another acetabular component was radiologically loose with progressive radiolucent lines in all Gruen zones and was awaiting revision. The overall rate of aseptic loosening was 11.8% (4 of 34). Roentgen stereophotogrammetric analysis in the non-revised components confirmed migration of up to 1.06 mm of translation and 2.32° of rotation at 24 months. There was one case of dislocation and dissociation of the component in the same patient. Of the 34 patients, 33 (97.1%) had no further episodes of dislocation.

The constrained acetabular component reported in our study was effective in all but one patient with instability of the hip, but the rate of aseptic loosening was higher than has been reported previously and requires further investigation.

Design factors influencing performance of constrained acetabular liners: finite element characterization

Constrained acetabular liners are utilized to deal with the infrequent but devastating problem of recurrent dislocation. While an encouraging treatment of last resort, the clinical performance of contemporary constrained liners has been somewhat mixed. There are multiple factors contributing to this variability, one of which is the limited understanding of the intrinsic mechanical characteristics of these specialty devices. To address this issue, a three-dimensional, materially nonlinear, multi-surface contact finite element model of a representative constrained liner was created. The model was physically validated, and then used for parametric testing to explore the effects of individual design features. The model was exercised for both intra-operative assembly and lever-out dislocation. It was found that the coefficient of friction between the femoral head and the liner substantially affected both the force required to seat the femoral head into the liner during assembly, and the peak moment resisting dislocation (226% increase in assembly force for friction coefficients of 0.2 versus 0.0; 49% reduction in dislocation moment for friction coefficients of 0.013 versus 0.135). As expected, the cup opening radius also had a dominant effect on both maneuvers: decreasing the opening radius from 13.9 to 13.6 mm increased assembly force by 506 N and increased the dislocation moment by over 3.5 N-m, whereas the influence of other design parameters was much more modest.

Constrained liners in revision: total hip arthroplasty an overuse syndrome: in opposition

Use of constrained liners in revision total hip arthroplasty is frequently a necessary evil. Concomitant with the increasing complexity of the operative intervention is the deterioration of periarticular soft-tissue envelope integrity, causing increased risk of dislocation. Risk factors can be categorized as impingement independent or impingement related. Impingement-independent risk factors include those related to compromised soft-tissue tension, patient-specific issues, and surgical approach. Impingement-related risk factors include head-to-neck size and geometry, acetabular liner geometry, and surgical technique. Indications for constraint include recurrent hip instability after arthroplasty, intraoperative multidirectional hip instability, neuromuscular diseases that impair hip dynamics, neurologic diseases that impair the patient's ability to restrict activities, and proximal muscle weakness with or without deficiency of the protective muscular. Newer designs featuring large heads, improved range of motion, and reduced impingement hold the promise of improved results.

Constrained liners in revision total hip arthroplasty: an overuse syndrome: in the affirmative

Instability after primary and revision total hip arthroplasty continues to be problematic for the surgeon. The use of constrained liners, which use a locking mechanism to capture the femoral head, has increased to help manage this problem. Constrained liners, however, present problems with acetabular component loosening, dissociation of the liner/shell interface, failure by breakage, and excessive polyethylene wear. Rather than resort to constrained liners, our approach has been to restore joint stability with large-diameter femoral heads. The advantages are increased range of motion due to more favorable head/neck ratio, increased resistance to dislocation due to increased jump distance, and the avoidance of skirted femoral heads. With the addition of cross-linked polyethylene, the volumetric wear associated with large heads is much decreased and makes this a viable option today.

Recurrent instability after total hip arthroplasty: beware of subtle component malpositioning

Most patients exhibiting instability after total hip arthroplasty can be treated nonoperatively. However, instability may become recurrent and require surgical intervention. Abductor insufficiency and component malpositioning constitute two of the most important causes of recurrent instability, although the exact cause may not be identifiable in some patients. There is relative scarcity of reports in the literature regarding the outcome of surgical intervention for recurrent instability; however, it is known that surgical intervention is likely to have a better outcome in patients for whom the cause of recurrent instability can be identified. We hypothesized that component malpositioning, which may be subtle in some cases, is the cause of recurrent instability for many patients. The outcomes of revision arthroplasty in 93 patients who were treated at our institution for recurrent instability were reviewed. Component malpositioning was found to be the major cause of recurrent instability in this successfully treated cohort.

A constrained device with increased range of motion prevents early dislocation

Constrained components can treat or prevent instability after total hip arthroplasty. Some previous designs have shown a high rate of early dislocation. These early dislocations appear to be secondary to component impingement and levering out of the femoral head. We report the early rate of dislocation in 81 consecutive patients undergoing constrained total hip arthroplasty using a novel constrained device that allows substantially more range of motion and a higher lever out strength. One hip redislocated at 6 months followup, for a success rate of 98.8%. The success rate was 93% for patients for whom a constrained device was placed during revision for recurrent instability. This device allows a higher range of motion before prosthetic impingement and maintains a higher levering out strength when impingement occurs. These changes should provide long lasting hip stability in these difficult cases.

[Dual articulation retentive acetabular liners and wear: surface analysis of 40 retrieved polyethylene implants]

PURPOSE OF THE STUDY

The original concept of dual articulation retentive liners has been implemented in routine clinical practice for total hip arthroplasty since 1976. The retentive liner improves stability and the dual mobility favors preservation of joint motion. In this study, we analyzed wear of the two concave and convex surfaces in 40 retrieved polyethylene implants in order to search for factors favoring wear.

MATERIAL AND METHODS

Forty polyethylene inserts were examined. These implants had been removed after mean implantation of eight years. Mean patient age at implantation was 48 years. The inserts were removed because of prosthesis infection or mechanical failure. Macroscopic examination was followed by a surface analysis with direct measurement of alterations of the curvature radii. Internal concavity was measured in the three dimensions using a 4-mm stylus (BNH 706). External convexity was measured by lateral projection. The estimated error was +/- 5 microm for both measurement methods. Manufacturers' tolerances for these implants were approximately 50 microm. Linear and volumetric wear was determined by comparing the measured dimensions with the theoretical dimensions of new inserts.

RESULTS

Macroscopically, all of the pieces studied had lost their initial striation on the convex surface; 40% of the pieces displayed visible wear of the retentive collar. Mean annual wear was 9 microm (SD 9microm) for the convex surface and 73 microm (SD 69 microm) for the concave surface. Mean total wear, taken as the sum of the wears on the convex and concave surfaces was 82 microm (SD 72 microm). Volumetric wear was 28.9 mm3/yr for the convex surface (SD 27.6) and 25.5 for the concave surface (SD 23.2) giving a mean annual total volumetric wear of 54.3 mm3/yr (SD 39.6).

DISCUSSION

Total wear observed for these 40 dual articulation liners which had functioned in vivo was to the same order as reported for the metal-polyethylene bearing with 22.2 mm femoral heads. Considering the wear on both the convex and concave surface, the dual articulation was not associated with increased wear compared with the conventional metal-polyethylene bearings, but with the advantages of retention and greater stability.

CONCLUSION

Use of a dual articulation acetabular liner is an attractive solution when a metal-polyethylene bearing is considered. The benefit in terms of joint stability does not increase wear.

Constrained acetabular components in complex revision total hip arthroplasty

We retrospectively reviewed 39 consecutive hips in 38 patients to examine the outcome of acetabular fixation and stability in patients with the tripolar constrained acetabular component who had complex revision surgery at 2 to 5 years of followup. Preoperative indications included recurrent dislocation, loose acetabular component with instability, migrated bipolar, resection arthroplasty conversions, and primary arthroplasty. Postoperative radiographs were reviewed for radiolucencies, loosening, migration, or breakage. The patients' average age was 65 years (range, 44-83 years). Thirty-five of the 39 acetabular components (91%) are well fixed and bony ingrown. There were no dislocations. One patient was involved in an motor vehicle accident 1 year postoperatively and sustained a fracture of the ilium and a 2 mm radiolucency about the component which is now stable. Three patients had acetabular revisions. Two patients were revised to a tripolar cemented into a cage and are doing well. The tripolar constrained acetabular component offers reliable fixation and joint stability in patients at high risk for dislocation in this short term followup.

LEVEL OF EVIDENCE

Therapeutic study, Level IV (case series). See the Guidelines for Authors for s complete description of levels of evidence.

High failure rate of a constrained acetabular liner in revision total hip arthroplasty

Fifty-five consecutive revision total hip arthroplasties (THAs) in 51 patients in which a constrained acetabular liner was used (Duraloc Constrained Liner, DePuy, Warsaw, Ind) were reviewed. In these revisions, 41 constrained liners were placed for recurrent instability and 14 for inadequate stability at the time of revision THA. The mean age of the cohort was 62 years, and 38 of the hips were in female patients (69%). At a minimum of 2 years, 9 of the 55 hips (16%) dislocated. Of these 9 dislocations, 8 occurred in patients who had undergone revision to a constrained liner for recurrent instability without femoral or acetabular component revision. Revision THA for recurrent instability by placing a constrained liner without optimizing other aspects of the reconstruction leads to a high rate of recurrent failure.

The long-term outcome of 755 consecutive constrained acetabular components in total hip arthroplasty examining the successes and failures

Constrained acetabular components can treat or prevent instability after total hip arthroplasty (THA). We examine long-term results of 755 consecutive constrained THA in 720 patients (1986-1993; 62 primary, 59 conversion, 565 revision, 60 reimplantation, and 9 total femur). Eighty-three patients (88 THAs) were lost before 10-year follow-up, leaving 639 patients (667 THAs) available for study. Dislocation occurred in 117 hips (17.5%), in 37 (28.9%) of 128 constrained for recurrent dislocation, and 46 (28.2%) of 163 with dislocation history. Other reoperations were for aseptic loosening (51, 7.6% acetabular; 28, 4.2% stem; 16, 2.4% combined), infection (40, 6.0%), periprosthetic fracture (19, 2.8%), stem breakage (2, 0.3%), cup malposition (1, 0.1%), dissociated insert (1, 0.1%), dissociated femoral head (1, 0.1%), and impingement of 1 broken (0.1%) and 4 (0.6%) dissociated constraining rings. Although constrained acetabular components prevented recurrent dislocation in 71.1%, they should be used cautiously, with a 42.1% long-term failure rate observed in this series. Dislocation was common despite constraint with previous history as a significant risk.

Constrained acetabular liners: mechanisms of failure

Although constrained acetabular liners have been successfully used for the treatment of recurrent hip instability, their usage has led to a growing number of associated complications. Twenty-seven patients (29 hips) who experienced failure of the constrained acetabular construct were retrospectively reviewed to define mechanisms of failure. Of these patients, 8 had a recurrent failure of another constrained liner. The 4 modes of failure were failure of fixation to the pelvis, liner dissociation, biomaterial failure, and femoral head dislocation. As constrained liners are highly subject to mechanical overload, the risk of failure can be minimized by reducing prosthetic impingement and avoiding technical errors.

Use of constrained acetabular liners in total hip arthroplasty

The use of constrained acetabular liners is indicated when soft-tissue tensioning techniques such as femoral neck lengthening, component repositioning, and use of lateralized acetabular liner are ineffective. It is most commonly used as a salvage procedure in revision situations. However, a locking acetabular insert may be used for primary THAs in patients with joint or soft-tissue laxity, neuromuscular disease, or intraoperative instability. In addition to the described commercially available liners, several manufacturers will provide customized components on request.

Results of reoperation for hip dislocation: the big picture

Hip instability remains a costly complication of primary (3%) and revision (10%) procedures. In those with well-oriented components, instability may be anticipated in about 70% from advancement of the trochanter. Articular reorientation readily is affected by the use of modular cups with elevated rims. This has proven to be an effective strategy both to lessen the likelihood of an initial dislocation after both primary and revision procedures. It has also proven to be an effective strategy to treat the unstable implant, especially if cup orientation has been defined as the primary problem. Larger head sizes in the range of low-friction arthroplasty, such as 32 mm, are not any more stable than 22-mm diameter implants. Anatomic-sized heads as used in bipolar devices are effective in treating established instability in up to 90% of instances. The most popular current option is that of the constrained head/cup articulation. Good short-term results have revealed success in more than 90%. However, the effectiveness is design dependent, and the long-term effectiveness understandably is questioned as reports of mechanical failure begin to emerge.

Prevention and treatment of dislocation after total hip replacement using large diameter balls

The purpose of this study was to review safety and efficacy of total hip arthroplasty using large-diameter femoral heads in treatment and prevention of dislocation. One hundred forty hips in 135 patients were replaced using femoral heads at least 36 mm in diameter. The average age of the patients was 61.6 years. The patients were grouped into three categories depending on their diagnoses: recurrent dislocations from previous total hip replacements (Group 1; 29 hips); revision surgeries not including revisions for dislocations (Group 2; 54 hips); and primary surgeries (Group 3; 57 hips). The average followup was 5.5 years (range, 1-17 years). A total of 16 hips were revised: six for instability, four for fracture or disassociation of a conventional polyethylene liner, three for aseptic loosening of the socket, and three for sepsis. One hip from Group 1 dislocated at 12.5 years postoperatively, was treated with closed reduction, and since has been nonrecurring. UCLA hip scores all improved significantly. The prevalence of dislocation varied among the three groups, with 13.7% for Group 1, 1.8% for Group 2, and 3.5% for Group 3. The failure in the six cases that required revision for instability was attributable to poor socket orientation. All the hips became stable after revision without the use of a constrained acetabular liner. Large-diameter femoral heads provide additional stability not only for patients with recurrent dislocations, but also for patients having revision. The new, more wear-resistant bearings now enable the surgeon to extend the use of big femoral heads to primary total hip arthroplasty. Metal-on-metal seems to be the material of choice for a bone-conserving reconstruction with large femoral heads.

Use of a constrained tripolar acetabular liner to treat intraoperative instability and postoperative dislocation after total hip arthroplasty: a review of our experience

Constrained acetabular components have been used to treat certain cases of intraoperative instability and postoperative dislocation after total hip arthroplasty. We report our experience with a tripolar constrained component used in these situations since 1988. The outcomes of the cases where this component was used were analyzed for component failure, component loosening, and osteolysis. At average 10-year followup, for cases treated for intraoperative instability (2 cases) or postoperative dislocation (4 cases), the component failure rate was 6% (6 of 101 hips in 5 patients). For cases where the constrained liner was cemented into a fixed cementless acetabular shell, the failure rate was 7% (2 of 31 hips in 2 patients) at 3.9-year average followup. Use of a constrained liner was not associated with an increased osteolysis or aseptic loosening rate. This tripolar constrained acetabular liner provided total hip arthroplasty construct stability in most cases in which it was used for intraoperative instability or postoperative dislocation.

[Role of sagittal spinal curvature in early dislocation after revision total hip arthroplasty: prospective analysis of 49 revision procedures]

PURPOSE OF THE STUDY

Hip dislocation after revision total hip arthroplasty (RTHA) is a frequent post-operative complication. Certain risk factors are well identified (nonunion of the greater trochanter, history of recurrent dislocation or infection, multiple procedures), the role of spine morphological remains to be fully examined. The purpose of this prospective analysis was to assess the role of spine morphology in post-operative dislocations.

MATERIAL AND METHODS

Forty-nine patients who underwent RTHA between September 2002 and March 2002 were evaluated prospectively. A complete pre- and postoperative spinal work-up was available for all patients to evaluate the lumbopelvic static using the Legaye and Duval Beaupère morphology criteria and the pelvic-femoral angle to assess hip joint extension. Pre-, per- and post-operative data including the usual risk factors for dislocation related to the clinical situation and the technique used were recorded on a digital datasheet. Five patients developed postoperative dislocation despite the absence of defective implant position. There was no relation with access (p=0.832) or pelvic-femoral angle (p=0.515).

RESULTS

The mean value of the sacral slope was significantly different (p=0.006) in patients who developed dislocation in comparison with the other patients. This difference remained significant (p=0.017) for the cohort of 33 patients who had no associated risk factor for postoperative dislocation (history of recurrent dislocation or infection, multiple procedures, tight nonunion of the greater trochanter).

DISCUSSION

Our results suggest that the morphology of the lumbar spine can be involved in the risk of postoperative dislocation. The morphology of the lumbar spine affects the pelvic static and thus the landmarks usually used for implantation, but it can also limit the amplitude of pelvic movement when changing from the sitting to the standing position, which would be compensated for by greater hip movement, particularly extension. The method we used did not fully take into account the consequences of changes in spinal balance due to thoracic deformations nor to analgesic (or not) hip flexion and subsequent deformation of the lumbar spine.

A constrained liner cemented into a secure cementless acetabular shell

BACKGROUND

Constrained acetabular components have been used to treat hips with recurrent instability following total hip arthroplasty and hips that demonstrate instability during revision surgery. In such hips, when a secure cementless acetabular shell is present, the surgeon can cement a constrained liner into the existing shell. The purpose of this study was to evaluate the clinical and radiographic outcome of this technique with use of a tripolar constrained liner that was cemented into a well-fixed cementless acetabular shell.

METHODS

Between 1988 and 2000, constrained liners were cemented into thirty-one well-fixed cementless acetabular shells at three centers. The average age of the patients at the time of the index surgery was 72.1 years, and the indications for the procedure were recurrent hip instability in sixteen hips and intraoperative instability in fifteen hips. The patients were evaluated with respect to the clinical outcome and radiographic evidence of shell loosening and osteolysis.

RESULTS

At an average duration of follow-up of 3.9 years, twenty-nine liners (94%) were securely fixed in the cementless shells and two constrained liners had failed. One liner failed because it separated from the cement, and one failed because of fracture of the capturing mechanism. Both hips were successfully revised with another cemented tripolar constrained liner. No acetabular component demonstrated radiographic evidence of progressive loosening or osteolysis.

CONCLUSIONS

A constrained tripolar liner cemented into a secure, well-positioned cementless acetabular shell provides stability and durability at short-term follow-up. Careful attention to the preparation of the liner, the sizing of the component, and the cementing technique are likely to reduce the failure of this construct, which can be used for difficult cases of total hip instability.

Dislocation after total hip arthroplasty

Dislocation is one of the most common complications after total hip arthroplasty (THA). Risk factors include neuromuscular and cognitive disorders, patient non-compliance, and previous hip surgery. Surgical considerations that must be addressed include approach, soft-tissue tension, component positioning, impingement, head size, acetabular liner profile, and surgeon experience. Recent improvements in posterior soft-tissue repair after primary THA have shown a reduced incidence of dislocation. When dislocation occurs, a thorough history, physical examination, and radiographic assessment help in choosing the proper intervention. Closed reduction usually is possible, and nonsurgical management frequently succeeds in preventing recurrence. When these measures fail, first-line revision options should target the underlying etiology. This most often involves tensioning or augmentation of soft tissues, as in capsulorrhaphy or trochanteric advancement; correction of malpositioned components; or improving the head-to-neck ratio. If instability persists, or if a primary THA repeatedly dislocates without a clear cause, a constrained cup or bipolar femoral prosthesis may be as effective as a salvage procedure.

Bipolar reconstruction for recurrent instability of the hip

Between 1986 and 1998, 81 total hip revisions were performed for recurrent instability. Twenty-three revisions were fixed cups to bipolars. Average follow-up was 50 months. Radiographic evaluation showed no significant osteolysis and average migration of 1.7 mm. The average postoperative Harris hip score was 74. All patients who underwent revision to a bipolar prosthesis had no further instability. Acetabular revision to a bipolar prosthesis provides stability in recurrent prosthetic hip instability.

Modular revision for recurrent dislocation of primary or revision total hip arthroplasty

Two surgeons who used the same implants and surgical approach performed 23 revisions for recurrent dislocation of modular total hip arthroplasty (THA) with retention of components. For 17 primary hips, there was a mean of 3.8 (range, 2-10) dislocations before revision. Fifteen hips had exchange of the acetabular liner, 13 had a change in neck length, and 5 had a change in size of the femoral head. At a mean follow-up of 4 years (range, 2-7 years), 14 patients (82%) had no further dislocation, 1 had 1 additional dislocation, and 2 required additional surgery. For the 6 revision procedures, the mean number of dislocations was 3.8 (range, 2-10) before re-revision. Liner exchange was performed in 4 hips, neck length changed in 3 hips, and head size increased in 2 hips. At a mean follow-up of 3 years (range, 2-5 years), only 3 patients (50%) had no further dislocation, and 2 required additional surgery. Modular revision can be a successful method of treatment of recurrent dislocation after primary THA, but is much less successful after revision THA.