Success rate of modular component exchange for the treatment of an unstable total hip arthroplasty

Prior Instability is Strongly Associated With Dislocation After Isolated Head and Liner Exchange

BACKGROUND

Isolated head and liner exchange is an appealing alternative to a more extensive revision total hip arthroplasty in patients who have well-fixed components. Despite efforts to increase femoral offset and restore soft tissue tensioning, limited component revision may be associated with higher rates of postoperative instability.

METHODS

This retrospective analysis assessed 209 patients who had a head and liner exchange conducted at a large academic medical center between 2011 and 2019 and had >2 years of follow-up. Functional cup positioning within the Lewinnek safe zone was assessed on postoperative weight-bearing radiographs. Included patients were 56% women, had a mean age of 64 years (range, 24-89) and a mean body mass index of 28.8 kg/m² (range, 18.2-46.7). The most common indications for surgery included acetabular liner wear in 86 hips (41%), instability in 40 hips (19%), and infection in 36 hips (17%).

RESULTS

Twenty-eight hips (13%) had a dislocation within 2 years after surgery. The best-fit model predicting postoperative dislocation included a history of dislocation (adjusted-odds ratio [adj-OR] 5.67, 95% CI 2.39-14.09, P < .001), age (adj-OR 1.04 per 1-year increase, 95% CI 0.99-1.08, P = .10), and body mass index (adj-OR 0.90 per 1-kg/m² increase, 95% CI 0.80-0.99, P = .046).

CONCLUSION

In a large cohort of patients who had isolated head and liner exchange, patients who had prior instability had 7-fold elevated odds of postoperative dislocation. This risk remains significant after controlling for cup positioning outside the Lewinnek safe zone, liner type, head size, neck length, soft tissue compromise, neuromuscular disease, and dual mobility constructs.

LEVEL OF EVIDENCE

III, retrospective cohort study.

Femoral Head and Liner Exchange in Patients with Atraumatic Dislocation. Results of a Retrospective Study with 6 Years Follow-Up

Background and Objectives: Femoral head and liner exchange is an established treatment for polyethylene wear but has had a more limited role in the treatment of other conditions including dislocation, because of concerns about an increased postoperative dislocation rate. Some authors have considered dislocation associated with polyethylene wear to be a contraindication for this procedure. Materials and Methods: Our retrospective review evaluated the outcome of head and liner exchange in a small consecutively operated heterogeneous cohort of 20 patients who presented with dislocation unrelated to trauma, component malposition or component loosening. Of this group, 12 had prior primary total hip arthroplasty, and 8 had prior revision total hip arthroplasty, and included 4 patients with prior revision for dislocation. Mean follow-up was 6 ± 3.5 years (range 1–145 months). Results: Kaplan–Meier analysis revealed a revision-free implant survival from any cause of 80% (confidence interval 95%:64.3–99.6%) at 5 years after head and liner exchange (index surgery). At final follow-up, 83.3% of patients (n = 10) with prior primary total hip arthroplasty and 62.5% of patients (n = 5) with prior revision total hip arthroplasty, had not required subsequent revision for any cause. None (0%) of the primary total hip arthroplasty group and 3 (38%) of the revision arthroplasty group had required revision for further dislocation. Of the eight revision arthroplasty patients, four had a prior revision for dislocation and three of these four patients required further revision for dislocation after index surgery. The fourth patient had no dislocation after index surgery. One additional patient who had prior revision surgery for femoral component fracture suffered dislocation after index surgery, but was successfully treated with closed reduction. Conclusions: In our study population, femoral head and liner exchange was an effective treatment option for patients with prior primary total hip arthroplasty and also for a highly select group of revision total arthroplasty patients with no prior history of dislocation. Femoral head and liner exchange does not appear to be a viable treatment option for patients who have had revision total arthroplasty after prior dislocations.

Outcome of revision surgery in recurrent dislocation of primary total hip arthroplasty

BACKGROUND

The cause of recurrent dislocation following primary total hip arthroplasty (THA) is multifactorial. A re-dislocation rate of up-to 34% following revision is reported. The aim of this study was to determine the re-dislocation rates following revision for recurrent THR dislocation.

METHODOLOGY

Patients who underwent revision for recurrent dislocation between January 2008 and January 2015 were identified. We identified the date and type of primary implant, overall number and reasons for dislocation, revision implant details and complication data.

RESULTS

Over an 8-year period, 24 patients underwent revision. The median age was 77 (68-85) years, median time to first dislocation was 78 (23-160) months and median number of dislocations was 3 (2-4) with a mean follow-up of 18 months. Socket Mal-Orientation (10) and Abductor deficiency (5) were the main causes of recurrent dislocation. 21 patients (88%) underwent revision of both components, 1 patient underwent isolated cup revision and 2 patients had revision of acetabular component with insertion of a BioBall. There were no dislocations within 90 days of revision surgery. 4 patients had late dislocations (3 recurrent, 1 isolated). There was no significant increase risk of dislocation after revision surgery in the neck of femur group (p = 0.467).

CONCLUSIONS

We report favourable outcomes for revision of both components for recurrent dislocation with no dislocations within 90 days. The overall late dislocation rate was 16.7%, however, these patients have settled following closed reduction. Due to its multifactorial aetiology, both component revision can be considered in this patient population.

Risk Factors for Dislocation and Re-revision After First-Time Revision Total Hip Arthroplasty due to Recurrent Dislocation - A Study From the Danish Hip Arthroplasty Register

BACKGROUND

Persistent instability after hip revision is a serious problem. Our aim was to analyze surgical and patient-related risk factors for both a new dislocation and re-revision after first-time hip revision due to dislocation.

METHODS

We included patients with a primary THA due to osteoarthritis and a first-time revision due to dislocation registered in the Danish Hip Arthroplasty Register (DHR) from 1996 to 2016. We identified dislocations in the Danish National Patient Register and re-revisions in the DHR. Risk factors were analyzed by a multivariable regression analysis adjusting for the competing risk of death. Results are presented as subdistribution hazard ratios (sHR).

RESULTS

We identified 1678 first-time revisions due to dislocation. Of these, 22.4% had a new dislocation. 19.8% were re-revised for any reason. With new dislocations treated by closed reduction as the endpoint, the sHR was 0.36 (95% CI, 0.27-0.48) for those who had a constrained liner (CL) during revision and 0.21 (0.08-0.58) for dual mobility cups (DMC), thereby lowering the risk of dislocation compared to regular liners. Changing only the head/liner increased the risk of dislocation (sHR = 2.65; 2.05-3.42) compared to full cup revisions. The protective effect of CLs and DMCs on dislocations vanished when re-revisions became the endpoint. The head/liner exchange was still found inferior compared to cup revision (sHR = 1.73; 1.34-2.23).

CONCLUSION

Patients revised with DMCs and CLs were associated with a lower risk of dislocation after a first-time revision but not re-revision, whereas only changing the head/liner was associated with a higher risk of dislocation and re-revision of any cause compared to cup revision.

Dual mobility acetabular construct with freedom constrained liner for treatment of recurrent dislocations after total hip arthroplasty: A case report and literature review

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Dual-mobility bearings improve stability in total hip arthroplasty (THA) but may fail to prevent postoperative dislocation.

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Dry revision with a compatible constrained liner system can provide an effective salvage option for instability after THA.

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The unique G7 constrained liner system offers good short-term stability and range of motion.

Introduction

Recurrent dislocation after total hip arthroplasty (THA) using the dual mobility cup system can present challenges, while dual-mobility THA bearings can improve stability in both primary and revision total hip arthroplasties.

Presentation of case

A 72-year-old woman with a history of schizophrenia underwent a left primary THA using the G7 dual mobility system. Two postoperative posterior dislocations occurred within 2 months post-surgery. The patient underwent revision surgery in which the metal liner and dual mobility head were exchanged using the Freedom constrained liner system without revision of the cup and stem. As of this writing, 28 months after the revision surgery, no further dislocations have occurred. The implants are stable, and the patient has good range of motion.

Discussion

Dual-mobility bearings are utilized to improve stability in both primary and revision total hip arthroplasties, but even if the dual mobility system is chosen, it sometimes fails to prevent postoperative dislocation. Although a relatively high failure rate has been reported in THA using the constrained liner system, this patient’s clinical course suggests that the G7 Freedom constrained liner system can be an efficacious option for some patients with unstable hip joints who undergo THA using the dual mobility system.

Conclusion

A modern constrained liner system such as the G7 Freedom liner may provide an improved salvage solution for joint instability in dual mobility THA.

Mid-term outcomes of titanium modular neck femoral stems in revision total hip arthroplasty

Background

Modular stems have been widely studied as they allow intraoperative adjustments (offset, anteversion, limb length) to better restore hip biomechanics. Many authors reported outcomes of revision total hip arthroplasty (THA) using modular stems with metaphyseal-diaphyseal junctions, however, little is known about modular neck femoral stems (MNFS) with metaphyseal-epiphyseal junctions. We therefore aimed to report outcomes and implant survival of a MNFS in a consecutive series of revision THA at a minimum follow-up of 5 years.

Methods

We reviewed a consecutive series of 28 revision THAs performed between February 2010 and March 2012 using an uncemented MNFS. The final study cohort included 25 patients living with their original components, at a mean follow-up of 68.4±7.4 months and aged 67.7±11.6 years at index operation.

Results

The Harris Hip Score (HHS) improved from 39.1±19.2 pre-operatively to 78.1±18.3 post-operatively, and the Postel Merle d'Aubigné score (PMA) improved from 9.8±3.0 pre-operatively to 14.8±2.8 post-operatively. The postoperative limb length discrepancy (LLD) was >10 mm in 18% of the hips. There were no significant differences of femoral offset and neck shaft angle (NSA) between operated and contralateral hips. Two hips (8.0%) showed new periprosthetic radiolucent lines. Periprosthetic fractures (PPF) occurred in 3 hips (12%). No subluxations, dislocations or implant breakages were reported. One revision (3.6%) was performed with retrieval of the revision stem for infection. The Kaplan-Meier (KM) survival at 5 years, using stem revision as endpoint, was 96.0%.

Conclusions

The Optimal^® MNFS provided a satisfactory survival and clinical outcomes at 5 years, with no noticeable adverse effects resulting from the additional modular junction.

Utilizing Dual Mobility Components for First-Time Revision Total Hip Arthroplasty for Instability

BACKGROUND

Dislocation following total hip arthroplasty (THA) remains a significant clinical problem. Few studies have focused on the use of dual mobility (DM) components in the setting of first-time revision for instability following THA. Here, we investigate patient outcomes following first-time revision THA with DM components for a diagnosis of instability.

METHODS

Institution-wide revision THAs using DM components performed between 2010 and 2013 were identified. Chart review identified 40 patients with average 3-year follow-up who had undergone first-time revision for instability, defined as instability after primary THA. Etiology of instability was classified by Wera type. Patient demographics, medical co-morbidities, re-dislocations, and re-revisions were recorded. Component position and leg-length discrepancy were measured on pre-operative and post-operative radiographs when available. Utilizing Student's t-test or Fisher's exact test, we analyzed differences between those who endured recurrent dislocation and those who did not.

RESULTS

Recurrent dislocation occurred in 2 patients (5%). Both patients underwent re-revision for recurrent instability and carried diagnoses of instability of unresolved etiology. Two patients underwent re-revision for reasons unrelated to the DM construct. All-cause re-revision rate at final follow-up was therefore 10% (4 patients). No medical, demographic, or radiographic factors were significantly associated with risk of recurrent instability (P > .05).

CONCLUSION

The use of DM components for first-time revision THA for a diagnosis of instability carried a re-dislocation rate of 5% and an all-cause re-revision rate of 10% at average 3-year follow-up. Instability of unresolved etiology was associated with re-dislocation following revision surgery.

Survivorship of Total Hip Joint Replacements Following Isolated Liner Exchange for Wear

BACKGROUND

Liner exchange for articular component wear in total hip joint replacements (THJRs) is a common procedure, often thought to be benign with reliable outcomes. Recent studies, however, suggest high failure rates of liner exchange revisions with significant complications. The primary aim of this study was, therefore, to analyze the survivorship of isolated liner exchange for articular component wear, and secondarily to assess the influence of patient demographics (gender, age, and American Society of Anaesthesiologists [ASA] ratings) on rerevisions following isolated liner exchange for wear.

METHODS

A retrospective review of the 15-year New Zealand Joint Registry (1999-2014) was performed, analyzing the outcomes of isolated liner exchange for articular component wear. The survivorship as defined as rerevision with component exchange was determined and 10-year Kaplan-Meier survivorship curves were constructed. These revision rates were compared to age, gender, and ASA rating groups using a log-rank test.

RESULTS

The 10-year survivorship of THJR following liner exchange revision for liner wear was 75.3%. If a rerevision was required, the median time to rerevision was 1.33 years with a rerevision rate of 3.33 per 100 component years (95% confidence interval 2.68-4.08/100 component years). The principle reasons for rerevision were dislocation (48.4%) and acetabular component loosening (20.9%). There was no statistically significant difference in rerevision rates based on gender, age categories, or ASA scores.

CONCLUSION

THJR isolated liner exchange for liner wear is not a benign procedure with a survivorship of 75.3% at 10 years. Surgeons contemplating liner exchange revisions should be cognisant of this risk and should adequately assess component position and stability preoperatively.

Total hip arthroplasty instability in Italy

Hip dislocation is a major and common complication of total hip arthroplasty (THA), which appears with an incidence between 0.3% and 10% in primary total hip arthroplasties and up to 28% in revision THA. The hip dislocations can be classified into three groups: early, intermediate and late. Approximately two-thirds of cases can be treated successfully with a non-operative approach. The rest require further surgical intervention. The prerequisite to developing an appropriate treatment strategy is a thorough evaluation to identify the causes of the dislocation. In addition, many factors that contribute to THA dislocation are related to the surgical technique, mainly including component orientation, femoral head diameter, restoration of femoral offset and leg length, cam impingement and condition of the soft tissues. The diagnosis of a dislocated hip is relatively easy because the clinical situation is very typical. Having identified a dislocated hip, the first step is to perform a closed reduction of the implant. After reduction you must perform a computed tomography scan to evaluate the surgical options for treatment of recurrent dislocation that include: revision arthroplasty, modular components exchange, dual-mobility cups, large femoral heads, constrained cups, elimination of impingement and soft tissue procedures. The objective is to avoid further dislocation, a devastating event which is increasing the number of operations on the hip. To obtain this goal is useful to follow an algorithm of treatment, but the best treatment remains prevention.

High Failure Rate of Modular Exchange With a Specific Design of a Constrained Liner in High-Risk Patients Undergoing Revision Total Hip Arthroplasty

BACKGROUND

Addressing recurrent instability in patients with poor bone stock and inadequate abductor tensioning remains a challenge in revision total hip arthroplasty. One treatment method is implantation of a constrained liner. The purpose of this study was to determine clinical outcomes, redislocation rate, and revisions of a focally constrained liner in a high-risk patient cohort.

METHODS

Fifty-eight hips between 2008 and 2011 underwent implantation of a focally constrained liner. Nineteen were placed concurrent with acetabular component revision and 39 were placed into a well-fixed acetabular shell. Mean age was 69 years and mean number of previous ipsilateral hip surgeries was 4.2. At mean follow-up of 3.5 years, we analyzed clinical outcomes, redislocation, and revisions.

RESULTS

Mean Harris Hip Scores was 74. Fourteen hips (24%) were revised and 3 hips (5%) required reoperation at final follow-up. Eleven hips (19%) redislocated at a mean time to dislocation of 12.2 months; 31% (11 of 36 patients) that underwent modular exchange specifically for instability redislocated. Risk factors for redislocation included number of previous surgeries (P = .013), implantation of a 28 mm femoral head (hazards ratio 12.8), revision indication of instability (P = .04), and modular exchange with constrained liner implantation without acetabular shell revision (P = .01).

CONCLUSION

Implantation of a focally constrained liner in revision total hip arthroplasty for recurrent instability has a high failure rate, especially with a modular exchange. Although concurrent acetabular revision had a lower redislocation rate, the decision to revise a well-fixed cup should be weighed with potential complications associated with cup revision.

Freedom Constrained Liner for the Treatment and Prevention of Dislocation in Total Hip Arthroplasty

BACKGROUND AND PURPOSE

Dislocation is one of the most common complications following total hip arthroplasty. The aim of our study was to assess failure rate of the Biomet Freedom constrained liner (Biomet, Warsaw, IN, USA) either in revision surgery for recurrent dislocation, or as a preventive method in high dislocation risk patients.

PATIENTS AND METHODS

We assessed retrospectively 105 consecutive surgical procedures in 103 patients where a Freedom constrained liner or cup was used in Turku University Hospital over a 7-year period from 2007 to 2014. The mechanical failure rate of the device was assessed based on medical records. The average age of the patients was 73.4 years. The number of male patients was 53 (51%). Mean follow-up time was 2.5 years. The association between failure of the device and potential risk factors-age, gender, indication, and approach-was analyzed with logistic regression. Results were expressed by odd ratios and 95% confidence intervals.

RESULTS

The mechanical failure rate of the Freedom device was 6 out of 105 (5.7%). None of the 11 preventive primary THAs against dislocation failed, 4 out of 52 (7.7%) preventive revision THAs against dislocation failed, and 2 out of 42 (4.8%) of the treated dislocation cases failed. Four out of six failures were dislocations due to impingement and failure of the locking mechanism. Two liners failed because of loosening. The risk factors assessed were not associated with failure of the device.

INTERPRETATION

We found out that the mechanical failure rate of a Freedom constrained device was low. These results encourage us to continue using the device.

Trochanteric impingement: is it a source of pain after THR?

While uncommon, trochanteric-pelvic impingement may lead to significant lateral hip pain. We defined “impingement distance” as the radiographic distance from the medial aspect of the greater trochanter and the corresponding lateral edge of the acetabular bone or component and compared this to the contralateral normal hip. We present two painful total hip replacement (THR) cases, each featuring a patient with severe lateral hip pain when walking and sitting. Both patients had diminished femoral offset and trochanteric-pelvic clearance, compared to the contralateral normal hip. The impingement distance was increased an average of 10 mm with the exchange to a longer femoral head. Both patients had immediate and complete pain relief with operative treatment to increase the impingement distance.

The use of a dual mobility cup in the management of recurrent dislocations of hip hemiarthroplasty

Background

Dislocation is one of the most frequent causes of failure of hemiarthroplasties of the hip, which is the most common treatment for femoral neck fractures in elderly patients. A revision with conversion to total hip arthroplasty is the gold standard in case of failure of closed reduction: however, the use of standard or modular components shows variable outcomes. The use of a dual mobility cup has been evaluated in patients with unstable implants, given the good outcomes obtained in primary and revision surgery. The aim of this study was to assess the results of revisions by dual mobility cups in unstable hemiarthroplasties.

Materials and methods

Thirty-one patients (mean age 75.4 years) were retrospectively evaluated between 2006 and 2010 after conversion to total hip arthroplasty with dual mobility cups for recurrent dislocations. The mean number of dislocations was 2.6 (range 2–5). The evaluation was performed by the American Society of Anesthesiologists physical function score (ASA) and the Harris hip score, and several radiologic criteria.

Results

The mean follow-up was 3.8 years. No recurrence of dislocation was recorded. The ASA score remained unchanged, and the mean Harris hip score improved from 62.2 before dislocation to 76.0 points postoperatively.

Conclusions

Dual mobility cups may be a useful option in the treatment of a hemiarthroplasty dislocation. No risk of a new revision due to instability after insertion of dual mobility cups resulted in our experience, and this option may be strongly considered in cases of revisions of unstable hemiarthroplasties.

Level of evidence IV.

[Analysis of the failures of a cemented constrained liner model in patients with a high dislocation risk]

OBJECTIVE

To evaluate the short-term results of an ultra high molecular weight polyethylene retentive cup in patients at high risk of dislocation, either primary or revision surgery.

MATERIAL AND METHOD

Retrospective review of 38 cases in order to determine the rate of survival and failure analysis of a constrained cemented cup, with a mean follow-up of 27 months. We studied demographic data, complications, especially re-dislocations of the prosthesis and, also the likely causes of system failure analyzed.

RESULTS

In 21.05% (8 cases) were primary surgery and 78.95% were revision surgery (30 cases). The overall survival rate by Kaplan-Meier method was 70.7 months. During follow-up 3 patients died due to causes unrelated to surgery and 2 infections occurred. 12 hips had at least two previous surgeries done. It wasn't any case of aseptic loosening. Four patients presented dislocation, all with a 22 mm head (P=.008). Our statistical analysis didn't found relationship between the abduction cup angle and implant failure (P=.22).

CONCLUSIONS

The ultra high molecular weight polyethylene retentive cup evaluated in this series has provided satisfactory short-term results in hip arthroplasty patients at high risk of dislocation.

Efficacy of revision surgery for the dislocating total hip arthroplasty: report from a large community registry

BACKGROUND

Historically, achieving stability for the unstable total hip arthroplasty (THA) with revision surgery has been achieved inconsistently. Most of what we know about this topic comes from reports of high-volume surgeons' results; the degree to which these results are achieved in the community is largely unknown, but insofar as most joint replacements are done by community surgeons, the issue is important.

QUESTIONS/PURPOSES

We used a community joint registry to determine: (1) the frequency of repeat revision after surgery to treat the unstable THA; (2) what surgical approaches to this problem are in common use in the community now; (3) are there differences in repeat revision frequency that vary by approach used; and (4) has the frequency of repeat revision decreased over time as surgical technique and implant options have evolved?

METHODS

We reviewed 6801 primary THAs performed in our community joint registry over the last 20 years. One hundred eighteen patients (1.7%) with a mean age of 67 years were revised within the registry for instability/dislocation. Failure was defined as a return to the operating room for rerevision surgery for instability. Minimum followup was 2 years (average, 9.4 years; range, 2-20 years) with six patients having incomplete followup. The frequency of rerevisions was calculated and compared using Pearson's chi-square test. Cumulative rerevision rates were calculated using the Kaplan-Meier method and types of revision procedures were compared using the log-rank test.

RESULTS

The initial revision procedure was successful in 108 patients (92%); 10 patients underwent repeat surgery for recurrent dislocation after their initial revision surgery. The most frequently performed procedure was revision of the head and liner only (35 of 118 [30%]); constrained devices were used in 19% (22 of 118) of the procedures. There was no difference in the cumulative rerevision rates for instability or dislocation by type of revision procedure performed. Six of 22 constrained liners were rerevised for varying indications. There was no difference in frequency of repeat revision for instability between those patients revised for THAs performed before 2003 and those managed more recently.

CONCLUSIONS

Revision surgery for unstable THA is successfully managed in the community with a variety of surgical interventions. Identifying the reason for dislocation and addressing the source remain paramount. Constrained liners should be used with caution; although typically used in the most problematic settings, rerevision for a variety of failure modes remains troublesome.

LEVEL OF EVIDENCE

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

Method of fixation does not influence the overall risk of rerevision in first-time cup revisions

BACKGROUND

During the last two decades, uncemented fixation has been increasingly preferred worldwide during cup revision surgery. In Sweden, the number of uncemented cup revisions has been increasing during the last decade. However, it is unclear whether the risk of rerevision differs between cemented and uncemented cups.

QUESTION/PURPOSES

We determined (1) the risk of rerevision after cemented and uncemented fixation; (2) the influence of concomitant stem revision on the risk of rerevision of the cup; (3) the difference in risk of rerevision of an uncemented cup revision compared with liner revision only; and (4) whether the surgical incision influenced the risk of rerevision.

METHODS

Between 1979 and 2010, 19,342 first-time cup revisions were reported to the Swedish Hip Arthroplasty Register. From these, 749 were excluded (hip resurfacing, cases with tumor diagnoses, and missing data) leaving 18,593 (73% cemented) for further analysis. We used a Cox regression model adjusted for age, sex, primary diagnosis, method of fixation, concomitant stem revision, and cemented/uncemented fixation to assess risk of rerevision.

RESULTS

The relative risk for rerevision for any reason did not differ between cemented and uncemented fixation (relative risk [RR], 0.94). If the stem was not revised at index revision, the risk of further cup revision increased twofold (RR, 1.91). Liner revisions were associated with a 70% increased risk for rerevision of the cup as a result of any reason and especially because of dislocation (RR, 2.94). The surgical incision did not influence the overall risk for rerevision (direct lateral/posterolateral: RR, 1.02) or the risk of rerevision resulting from dislocation (RR, 0.91).

CONCLUSIONS

We found no difference in the overall risk of rerevision between cemented and uncemented fixation. Liner exchange had a higher risk for rerevision when compared with cases being rerevised with a new uncemented cup.

Cementation of a dual-mobility acetabular component into a well-fixed metal shell during revision total hip arthroplasty: a biomechanical validation

Cementation of polyethylene (PE) liners into well-fixed metal shells has become a popular option during revision total hip arthroplasty (THA) particularly for older and frail patients. Although dramatic results were reported with dual-mobility acetabular components to manage hip instability during revision THA, no study evaluated the fixation strength of the cementation of dual-mobility components into well-fixed metal shells. Eight dual-mobility and eight all-PE components were cemented into a metal shell with a uniform 2- to 3-mm cement mantle. The cemented fixation strength was evaluated using lever-out and torsion testing. The interface at which failure occurred was determined. Lever-out testing showed that dual-mobility components failed at significantly higher maximum moment than the all-PE components. No direct comparison could be performed with torsion testing due to early failure of the all-PE component itself before failure of the cement fixation. However, the maximum moments measured were dramatically higher than the in vivo frictional moments classically reported in THA. In addition, failure was always observed at the metal shell/cement interface whenever it did occur. In conclusion, a dual-mobility acetabular component cemented into a well-fixed metal shell could constitute a biomechanically acceptable alternative to acetabular shell removal or PE liner cementation while simultaneously preventing instability of the THA revision. Clinical studies are warranted.

The medium term outcome of the Omnifit constrained acetabular cup

Recurrent dislocation requiring revision surgery occurs in approximately 4% of primary total hip arthroplasties (THAs). To reduce this risk, or to treat those patients who recurrently dislocate, a constrained acetabular component may be used, however there are concerns over the success of such components due to increased mechanical stresses. The purpose of this study was to analyse the survivorship and radiological results for the Omnifit constrained acetabular component, providing a longer patient reported outcome follow-up than previous studies. 117 patients (median age 82 years) underwent a THA with an Omnifit constrained acetabular component. Of these, 45 were primary replacements and 72 were revisions. Survivorship analysis was performed and patients were assessed both radiologically and functionally. At follow-up, 53 patients (45.3%) had died at a median time of 33 months from operation. The median overall follow-up was 7.0 (5.5-8.2) years. Survivors (median age 83 years) reported a median Oxford Hip Score (OHS) of 16.6 (0-48), 87.8% were satisfied with their surgery. 45 (91.8%) of the acetabular components were stable radiologically, 48 (96%) of the femoral components were stable (5 uncemented, 43 cemented) and two possibly unstable. Four of the 117 patients underwent further surgery. Only one required revision of the prosthesis and this was for a periprosthetic fracture. In the medium term the Omnifit constrained acetabular component prevents dislocation and does not cause excessive loosening of either the acetabular or femoral components in our patient population. Our results support the use of the Omnifit constrained acetabular component in elderly patients at risk of dislocation with low functional demand.

Instability after total hip arthroplasty

Instability following total hip arthroplasty (THA) is an unfortunately frequent and serious problem that requires thorough evaluation and preoperative planning before surgical intervention. Prevention through optimal index surgery is of great importance, as the management of an unstable THA is challenging even for an experienced joints surgeon. However, even after well-planned surgery, a significant incidence of recurrent instability still exists. Non-operative management is often successful if the components are well-fixed and correctly positioned in the absence of neurocognitive disorders. If conservative management fails, surgical options include revision of malpositioned components; exchange of modular components such as the femoral head and acetabular liner; bipolar arthroplasty; tripolar arthroplasty; use of a larger femoral head; use of a constrained liner; soft tissue reinforcement and advancement of the greater trochanter.

Constrained cups appear incapable of meeting the demands of revision THA

BACKGROUND

Failure rates of constrained cups for treating recurrent dislocation in revision THA range from 40% to 100%. Although constrained liners are intended to stabilize the hip by mechanically preventing dislocation, the resulting loss of range of motion may lead to impingement and, ultimately, implant failure.

QUESTIONS/PURPOSES

We therefore documented the mechanisms of failure of constrained acetabular cups in revision THA and determined the type and severity of damage (wear, fracture, and impingement) that occurs in situ.

METHODS

We retrieved 57 constrained components of four different designs at revision THA and examined for the presence of rim impingement, oxidation, cracks within the liner, backside wear, pitting, scratching, abrasion, burnishing, and the presence of embedded particles. Articular wear was calculated from the volume of the concave articular bearing surface, which was measured using the fluid displacement method.

RESULTS

Failure of the locking ring was responsible for 51% of failures, whereas 28% of revisions were the result of acetabular cup loosening, 6% backside wear, and 22% infection. Impingement damage of the rim of the polyethylene liner was seen in all retrievals with moderate or severe damage in 54%. The average volumetric wear rate of the articular surface was 95 mm(3)/year.

CONCLUSIONS

Failure of the locking liner ring and loosening of the acetabular cup are the primary causes of mechanical failure with constrained liners; polyethylene is an inadequate material for restricting motion of the hip to prevent instability. The durability of these devices is unlikely to improve unless the mechanical demands are modified through increased range of motion leading to less frequent rim impingement.

Classification and management of the unstable total hip arthroplasty

Seventy-five total hip arthroplasty revisions for instability were classified into 6 primary etiologies: I, acetabular component malposition; II, femoral component malposition; III, abductor deficiency; IV, impingement; V, late wear; or VI, unresolved etiology. The most common etiologies were cup malposition (type I; 33%) and abductor deficiency (type III; 36%). At a mean of 35.3 months, 11 redislocations occurred (14.6%). Acetabular revisions were protective against redislocation (P < .015). The number of previous operations (P = .0379) and previously failed constrained liners (P < .02) were risk factors for failure. Tripolar constrained liners demonstrated improved survivorship vs locking ring types (P < .02); cemented constrained liners failed more often than modular constrained liners (P < .0018). The highest risk of failure was in patients with abductor insufficiency with revisions for other etiologies having a success rate of 90%.

Revision for recurrent instability: what are the predictors of failure?

Dislocation is a common complication following total hip arthroplasty (THA). In this study, we evaluated treatment strategies in patients undergoing revision THA for instability. A total of 156 hips in 154 patients underwent revision THA for instability between 2000 and 2007 at our institution. Demographic data and surgical treatment used were analyzed to determine risk factors for failure. Revision treatments included acetabular components in 100 hips, liner exchange in 56 hips, and femoral and acetabular components in 13 hips. Thirty-three (21.2%) had further dislocation. Isolated liner revision (P = .004), previous revision arthroplasty (P < .05), and the use of a 28-mm femoral head were associated with higher failure rates. A total of 20.3% (12/59) of constrained liners failed. Isolated liner exchange, history of revision, and use of a 28-mm head were associated with failure in revision THA for instability.

Stem modularity alone is not effective in reducing dislocation rate in hip revision surgery

Background

Dislocation is a serious complication following total hip arthroplasty (THA). Femoral revision using monoblock components has been associated with high incidence of subsidence and dislocation. Advantages of modular stems in THA have long been debated. The aim of this retrospective study is to assess the capability of an uncemented modular stem in decreasing the incidence of early dislocation subsequent to revision THA.

Materials and methods

We evaluated the dislocation rate during the first 2 years following revision surgery in two groups of patients who were treated by implantation of a cementless tapered femoral prosthesis; a standard-modularity stem (Wagner SL) and an increased-modularity stem (Profemur R) were used, respectively, in 66 hips (group I, 64 patients) and 102 hips (group II, 97 patients). Group I consisted of 47 females and 17 males with average age of 66 years (range 29–84 years). Group II included 60 females and 37 males with average age of 70 years (range 48–89 years).

Results

Dislocation occurred in six hips (9.1%) of group I and in seven hips (6.8%) of group II (P = 0.401). Dislocations were observed early in both groups, except one hip in group II that dislocated 434 days postoperatively and required surgical reduction. All other dislocations were treated by closed reduction. No recurrence was observed.

Conclusions

The use of an increased-modularity revision stem alone did not prove to be effective in reducing the risk of postoperative dislocation.

Revision for recurrent dislocation of total hip replacement

BACKGROUND AND PURPOSE

Dislocation is one of the commonest complications of total hip arthroplasty with an incidence of between 0.5 and 9.2%. Despite this, little is known of the outcome of treatment strategies for dislocation. The aim of this study was to establish the optimal strategy for the operative management of recurrent dislocation following THA taking account of the surgical approach employed in the replacement that became unstable and the direction of the instability that followed.

METHODS

We reviewed 70 patients who underwent revision surgery for recurrent dislocation after total hip arthroplasty (THA), 38 through the transgluteal (Hardinge) and 32 through the posterior approach.52 of these followed primary and 18 followed revision THA for reasons other than instability.We recorded the surgical approach, the direction of dislocation and the operative strategy employed for each case.

RESULTS

We achieved stability in 75% of patients who dislocated after primary and 50% after revision THA. 77% of dislocations performed initially through the transgluteal approach were anterior and 88% through the posterior approach were posterior. Following the transgluteal approach, we stabilised anterior dislocation in 54% of cases. Following the posterior approach we stabilised posterior dislocation in 79%. The most successful operative strategy overall was cup augmentation which conferred stability in 90% of cases.

INTERPRETATION

Instability after primary total hip replacement is easier to treat (75% chance of success) than after revision total hip replacement (50% chance of success). Although previous studies have shown that the posterior approach has a slightly higher risk of dislocation, this study has shown that achieving stability after a posterior dislocation is more likely than after an anterior dislocation. The outcome of revision for instability depends on the surgical approach used initially, and the direction of dislocation.

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).

Outcome of treatment for dislocation after primary total hip replacement

We have studied the natural history of a first episode of dislocation after primary total hip replacement (THR) to clarify the incidence of recurrent dislocation, the need for subsequent revision and the quality of life of these patients.

Over a six-year period, 99 patients (101 hips) presented with a first dislocation of a primary THR. A total of 61 hips (60.4%) had dislocated more than once. After a minimum follow-up of one year, seven patients had died. Of the remaining 94 hips (92 patients), 47 underwent a revision for instability and one awaits operation (51% in total). Of these, seven re-dislocated and four needed further surgery. The quality of life of the patients was studied using the Oxford Hip Score and the EuroQol-5 Dimension (EQ-5D) questionnaire. A control group of patients who had not dislocated was also studied. At a mean follow-up of 4.5 years (1 to 20), the mean Oxford Hip Score was 26.7 (15 to 47) after one episode of dislocation, 27.2 (12 to 45) after recurrent dislocation, 34.5 (12 to 54) after successful revision surgery, 42 (29 to 55) after failed revision surgery and 17.4 (12 to 32) in the control group. The EuroQol-5 dimension questionnaire revealed more health problems in patients undergoing revision surgery.

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.

Isolated polyethylene exchange versus acetabular revision for polyethylene wear

Polyethylene wear and osteolysis are not uncommon in THA mid- and long-term. In asymptomatic patients the dilemma faced by the orthopaedic surgeon is whether to revise the cup and risk damage to the supporting columns and even pelvic discontinuity or to perform isolated polyethylene exchange and risk a high rate of postoperative recurrent instability and dislocation that will necessitate further surgery. We retrospectively reviewed 62 patients (67 hips) who underwent revision arthroplasty for polywear and osteolysis. Thirty-six hips had isolated polyethylene exchange, while 31 had full acetabular revision. The minimum followup was 2 years (mean, 2.8 years; range, 2-5 years). Three of 36 hips with a retained cup grafted through the cup holes failed within 5 years due to acetabular loosening. One of 31 hips with full revision underwent re-revision for aseptic cup loosening at 5 months postoperatively. Although we do not recommend prophylactic revision of all cups for polywear and osteolysis, the patient may be warned of the possibility of an approximate 10% failure rate when retaining the acetabular component. We do, however, advocate cup extraction in the following situations: damage to the locking mechanism, erosion of the femoral head through the liner and into the cup damaging the metal, and a malpositioned component that may jeopardize the stability of the revision.

LEVEL OF EVIDENCE

Level II, prognostic study. See the Guidelines for Authors for a complete description of levels of evidence.

Risk factors for revision for early dislocation in total hip arthroplasty

Risk factors were investigated for revision for dislocation in primary total hip arthroplasties (THAs) between September 1, 1999, and December 31, 2004, as reported by the Australian Orthopaedic Association National Joint Replacement Registry. For 65992 primary THAs, the only initial diagnoses with significantly increased relative risk (RR) of revision for dislocation compared to osteoarthritis were fractured neck of femur (RR, 2.03; P < .001), rheumatoid arthritis (RR, 2.01; P < .01), and avascular necrosis (RR, 1.57; P < .05). A total of 58109 primary THAs for osteoarthritis were investigated for effect of age group, sex, and fixation method. There were 428 (0.7%) revisions for dislocation, 369 (0.8%) with a cementless acetabulum, and 59 (0.6%) with cemented acetabulum (RR, 1.59; P < .01). There is a significantly increasing risk of revision for dislocation as head size decreases (P < .001). Cementless acetabula, particularly with smaller heads, have a higher rate of revision for dislocation.

[Polyethylene liner replacement: behavior and morbidity in 68 cases]

PURPOSE OF THE STUDY

Isolated acetabular polyethylene exchange is advocated as an advantage of metal-backed cups, since the acetabular bone stock can be spared and operative time is shorter. The purpose of this study was to determine whether this is true.

MATERIAL AND METHODS

A consecutive serie of 68 THA revisions involving replacement of the polyethylene liner was analyzed retrospectively (liner replacement alone for 37 hips and liner replacement plus femoral component revision for 31). The posterolateral approach was used for the revision in all cases. This series was compared with a control series of revisions involving the acetabular component with revision of the femoral component in patients matched for age, sex, and BMI.

RESULTS

Operative time and hospital stay were significantly shorter when the revision involved the polyethylene liner alone. In 19 hips, a limited zone of osteolysis was observed around the liner before replacement. At last follow-up, new zones of osteolysis were noted in two hips and aggravation in five, one of which required revision because of acetabular loosening. Episodes of dislocation were observed in nine hips (2 anterior and 7 posterior) of which three underwent revision because of recurrence. These dislocations occurred after liner replacement (n=4) or combined liner and femoral component replacement (n=5). Dislocations were more frequent after multiple hip operations and when the cup inclination was less than 40 degrees . Ten revisions were required for: an unclipped liner (n=2), recurrent dislocation (n=3), acetabular loosening (n=1), infection which was cured after a one-stage procedure (n=1). At seven years, survival was comparable between liner replacement alone (82+/-10%), combined liner replacement and femoral component revision (84+/-11%), and femoral component and acetabular component revision (82+/-11%).

DISCUSSION

Changing the cup liner can limit morbidity compared with a more complex revision, but liner replacement alone is insufficient in the event of acetabular osteolysis. It would be preferable to combine osteolysis debridement with a graft or a complete revision. The survival rate after liner replacement is comparable with that observed after more complex revision but the risks of dislocation or unclipped insert are significant. For this reason, liner replacement alone should only be proposed if the cup is correctly aligned and if the new liner can be solidly clipped into the metal back. In addition, this simplified procedure should not be attempted after multiple hip operations.

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.

Polyethylene insert exchange for wear after total shoulder arthroplasty

Virtually no information is available in the literature to guide clinical decision-making in regard to modular polyethylene exchange with metal-backed glenoid components in total shoulder arthroplasty for the indication of polyethylene wear. This level IV study reports our experience with exchange of the modular polyethylene glenoid component during revision total shoulder arthroplasty. We retrospectively identified 12 shoulders in 11 patients who underwent exchange of the modular polyethylene glenoid component during revision arthroplasty. The primary reason for revision arthroplasty with polyethylene exchange was wear-through or displacement of the polyethylene portion of the glenoid component, but rotator cuff tearing and instability often coexisted. The average follow-up from time of revision to latest evaluation or repeat revision arthroplasty was 68 months. Preoperative pain was a mean of 4.5 (range, 4-5), and postoperative pain was a mean of 2.6 (range, 1-5). Preoperative average active forward elevation was 93 degrees, and external rotation was 51 degrees. Postoperative active forward elevation was 89 degrees, and external rotation was 64 degrees. Average patient satisfaction was rated as the same. According to the modified Neer rating system, 4 shoulders (33%) had a satisfactory result, and 8 (62%) had an unsatisfactory result. Polyethylene exchange of glenoid component after total shoulder arthroplasty can be an effective treatment option in patients who do not have coexistent rotator cuff tear or instability. For most, instability, rotator cuff tear, and glenoid wear occur together, and this is a challenging problem to treat successfully.

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.

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.

Revision of an acetabular liner has a high risk of dislocation

Polyethylene liners of modular acetabular components wear sometimes need to be replaced, despite the metal shell being well fixed. Replacing the liner is a relatively simple procedure, but very little is known of the outcome of revision. We prospectively followed up 1126 Harris-Galante I metal-backed, uncemented components for between nine and 19 years. We found 38 (3.4%) liners of 1126 acetabular components wore and required revision. These revisions were then followed up for a mean of 4.8 years. The rate of dislocation was 28.9%. Nine of the dislocations occurred once and two were recurrent.

The overall secondary revision rate was three of 38 total hip replacements (7.9%) at a mean follow-up of 4.8 years. This gives a 92.1% survivorship (35 of 38) at under five years. In isolated revision of a liner, we had a complication rate of 23% (three of 13). In revision of a liner combined with revision of the femoral stem, there was a complication rate of 48% (12 of 25). We discuss possible reasons for the high dislocation rates.

Leaving the well-fixed acetabular shell in situ leads to an increased risk of instability. However, this needs to be balanced against the otherwise low complication rate for revision of the liner. Patients should be consented accordingly.

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.

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.

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.

The dislocating hip: what to do, what to do

Dislocation complicates between 1% and 3% of primary total hip arthroplasties (THAs) and 7% to 10% of revision procedures. Sixty percent of dislocations occur within the first 5 weeks. Closed reduction is successful in 67% of cases. If the hip keeps dislocating, revision surgery for instability is successful in only about 61% of patients. Many successful techniques have been described to deal with recurrent instability, including trochanteric advancement, modular component exchange, jumbo femoral heads, a bipolar or tripolar arthroplasty, or a constrained acetabular component. This article discusses the results of various surgical interventions and presents a treatment algorithm.