Surgical treatment of pelvic osteolysis

Polyethylene liner cementation into a well-fixed metal acetabular shell for the management of periacetabular osteolysis: a systematic review

PURPOSE

Although various papers have reported on the clinical performance of cup retention with cementation of a new liner and bone grafting in the management of well-fixed cups with polyethylene wear and periacetabular osteolysis after total hip arthroplasty (THA), no systematic review of this topic has been published to date.

METHODS

Medline, EMBASE and Cochrane Library were searched for articles published from January 1999 to January 2019 using "osteolysis" AND "well-fixed", "osteolysis" AND "retro-acetabular", "bone graft" AND ("retention" OR "retained" OR "stable") AND "cup", and "cemented liner" AND "well-fixed".

RESULTS

Nine articles were selected for review (186 cases, 76.1 months mean follow-up). The overall revision rate was 11.3% (21 hips) most commonly due to aseptic loosening (9/186 hips), dislocation (8/186 hips), and liner wear progression (2/186 cases). The reported square size of osteolytic lesions ranged from a mean of 465.84 mm² to a max of 4,770 mm². Almost all reported lesions treated with bone grafts resolved or did not progress 97% (72/74). All studies indicated improved pain and functional scores at follow-up.

CONCLUSION

Cementation of a new liner with periacetabular bone grafting provides an alternative option to isolated liner exchange and cup revision for the management of periacetabular osteolysis in well-fixed cups with a disrupted locking mechanism or unavailable exchange liner. Further higher quality studies are required in order to examine if the use of highly cross-linked polyethylene, highly porous-coated cups, hydroxyapatite-coated cups, and small-diameter cups influence the clinical outcome of liner cementation in well-fixed cups with periacetabular osteolysis.

Outcome and Risk Factors Associated with Failures of Isolated Bearing Exchange for Osteolysis in Well-Fixed Cementless Total Hip Arthroplasty

BACKGROUND

It is often challenging to decide whether to revise only the bearing or femoral acetabular component in the setting of progressive osteolysis without component loosening in revision total hip arthroplasty (THA). In this study, we aimed to (1) compare the survivorship of isolated bearing exchange and single/both component revision for patients with periprosthetic osteolysis without component loosening, and (2) identify potential risk factors associated with failures of isolated bearing exchange.

METHODS

A total of 228 consecutive cases of revision THA for progressive osteolysis without component loosening was evaluated in 2 groups: (1) 124 component revision and (2) 104 isolated bearing exchange. The primary outcome was survival, with failure defined as repeat revision or reoperation for any reason. Patient risk factors, such as demographics and medical comorbidities, were also analyzed.

RESULTS

There was no significant difference in survivorship between the component revision group and the bearing exchange group at 10 years (85% vs 82%; P = .89). There was no progression of osteolysis on radiographs at last follow-up for patients with isolated bearing change. Univariate regression modeling demonstrated that renal disease was associated with failure of isolated bearing exchange after revision THA.

CONCLUSION

This study demonstrated that isolated bearing exchange is associated with similar outcomes compared with component revision for aseptic osteolysis without loosening, demonstrating that isolated bearing exchange is a viable option for selected patients with osteolysis in the setting of well-fixed THA components. This provides clinically useful information for surgeons in the surgical treatment of THA patients with wear and osteolysis without component loosening.

Early failure for wear after ceramic-on-highly cross-linked polyethylene total hip arthroplasty: a case report

Background

Highly cross-linked polyethylene (HXLPE) enhances the anti-wear characteristics of the conventional polyethylene (PE). Early failure for wear after ceramic-on-highly cross-linked polyethylene (CoHXLPE) total hip arthroplasty (THA) is extremely rare.

Case presentation

We described the case of a 60-year-old man who underwent right CoHXLPE THA because of the developmental dysplasia hip (DDH) complained pain 32 months after this procedure. Plain radiographs showed that eccentric wear existed at the polyethylene insert. However, the patient refused surgery at that time and did not stop weight-bearing. The right hip pain continued for 7 months. Plain radiographs of the pelvis showed that the HXLPE liner was penetrated and partial inner wall of acetabular shell was worn. Acetabular cup revision was performed, and the ceramic head and HXLPE were exchanged.

Conclusions

Difficult reduction during primary THA, especially for DDH, can result in higher abductor tension, which may lead to early eccentric wear of the prosthesis. Whenever eccentric wear of HXLPE liner was found, weight-bearing must be stopped to avoid the accelerated wear and adverse reactions to metal debris (ARMD).

Isolated Acetabular Liner Exchange for Polyethylene Wear and Osteolysis with Well-Fixed Metal Shell

Background

The isolated liner and head exchange procedure has been an established treatment method for polyethylene wear and osteolysis when the acetabular component remains well fixed. In this study, the mid-term results of this procedure were evaluated retrospectively.

Methods

Among the consecutive patients operated on from September 1995, two patients (three hips) were excluded because of inadequate follow-up, and the results of remaining 34 patients (34 hips) were evaluated. There were 20 men and 14 women with a mean age of 49 years. A conventional polyethylene liner was used in 26 cases and a highly cross-linked polyethylene liner was used in eight cases. In three cases, the liner was cemented in a metal shell because a compatible liner could not be used.

Results

After a follow-up of 5 to 20.2 years, re-revision surgery was necessary in 10 cases (29.4%): in eight for wear and osteolysis at 55 to 101 months after liner exchange and in two for acetabular loosening at 1 and 1.5 years after liner exchange. Re-revision surgery included all component revision (four cases), cup revision (four cases), and liner exchange (two cases). In all re-revision cases, a conventional polyethylene liner was used initially. There was no failure in the cases in which a highly cross-linked polyethylene liner was used.

Conclusions

The results of this study suggest that isolated acetabular liner exchange is a reasonable option for wear and osteolysis when the metal shell is well fixed. More promising long-term results are expected with the use of highly cross-linked polyethylene liners.

Outcome of a hemispherical porous-coated acetabular component with a proximally hydroxyapatite-coated anatomical femoral component

Aims

We previously reported the long-term results of the cementless Duraloc-Profile total hip arthroplasty (THA) system in a 12- to 15-year follow-up study. In this paper, we provide an update on the clinical and radiological results of a previously reported cohort of patients at 23 to 26 years´ follow-up.

Patients and Methods

Of the 99 original patients (111 hips), 73 patients (82 hips) with a mean age of 56.8 years (21 to 70) were available for clinical and radiological study at a minimum follow-up of 23 years. There were 40 female patients (44 hips) and 33 male patients (38 hips).

Results

All acetabular and femoral components were well fixed and showed signs of bone ingrowth. Nine acetabular components were revised due to wear-osteolysis-related problems and four due to late dislocation. The probability of not having component revision at 25 years was 83.2% (95% confidence interval (CI) 74.5 to 91.8; number at risk 41). Acetabular osteolysis was observed in ten hips. The mean femoral head penetration was 1.52 mm (sd 0.8) at 15 years and 1.92 mm (sd 1.2) at 25 years. Receiver operating characteristic (ROC) analysis revealed that mean femoral penetration with a value of 0.11 mm/year or more was associated with the appearance of osteolysis. The 25-year Kaplan–Meier survival with different endpoints was 89.9% for acetabular osteolysis (95% CI 83.3 to 96.5), 92.1% for proximal femoral osteolysis (95% CI 86.1 to 98.2), and 75.5% for femoral osteopenia (95% CI 66.5 to 84.5).

Conclusion

The Duraloc-Profile THA system showed excellent long-term bone fixation. Nevertheless, monitoring is recommended in order to detect wear and late dislocations in this population that was relatively young at the time of surgery. Cite this article: Bone Joint J 2019;101-B:378–385.

Osteolysis as it Pertains to Total Hip Arthroplasty

Osteolysis is a long-term complication of total hip arthroplasty (THA). As the projected number of THAs performed annually increases, osteolysis will likely continue to occur. However, because of advancements in prosthesis design, metallurgy, and enhanced bearing surfaces, fewer revision THAs will be linked to osteolysis and aseptic loosening. Despite these improvements, no preventative therapies are currently available for the management of osteolysis other than removing and replacing the source of bearing wear.

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.

Outcome of 4 Surgical Treatments for Wear and Osteolysis of Cementless Acetabular Components

BACKGROUND

Loosening and periprosthetic osteolysis are some of the most common long-term complications after hip arthroplasty. The decision-making process and surgical treatment options are controversial.

METHODS

We retrospectively reviewed 96 acetabular revisions (91 patients) performed between 2002 and 2012, with a minimum of 2 years of follow-up and a mean of 5.7 years of follow-up. Clinical outcome was assessed using the Harris Hip Score. The size and location of osteolytic lesions were evaluated using the preoperative radiographs; healing of the defects was categorized using a standardized protocol.

RESULTS

Thirty-three (34.4%) hips had isolated liner exchanges (ILEs), 10 (10.4%) hips had cemented liners into well-fixed shells (CLS), 45 (46.9%) hips had full acetabular revisions (FARs), and 8 (8.3%) hips had revision with a roof ring/antiprotrusio cage (RWC). All procedures showed significant improvement in Harris Hip Score after revision (P ≤ .001). Fifteen patients had moderate residual pain (pain score ≤20): 8 (24%) ILE, 3 (30%) CLS, and 4 (9%) FAR. Complete bone defect healing after grafting was lower with acetabular component retention procedures (ILE and CLS; 27%) compared with full acetabular component revision procedures (FAR and RWC; 57%). Fifteen patients underwent reoperation: 3 ILE, 1 CLS, 8 FAR, and 3 RWC.

CONCLUSION

Acetabular component retention demonstrates a low risk of reoperation; however, residual pain and limited potential for bone graft incorporation are a concern. FAR is technically challenging and may have an elevated risk of reoperation; however, higher degrees of bone graft incorporation and satisfactory clinical outcome can be expected.

Radiographic scoring system for the evaluation of stability of cementless acetabular components in the presence of osteolysis

AIMS

The stability of cementless acetabular components is an important factor for surgical planning in the treatment of patients with pelvic osteolysis after total hip arthroplasty (THA). However, the methods for determining the stability of the acetabular component from pre-operative radiographs remain controversial. Our aim was to develop a scoring system to help in the assessment of the stability of the acetabular component under these circumstances.

PATIENTS AND METHODS

The new scoring system is based on the mechanism of failure of these components and the location of the osteolytic lesion, according to the DeLee and Charnley classification. Each zone is evaluated and scored separately. The sum of the individual scores from the three zones is reported as a total score with a maximum of 10 points. The study involved 96 revision procedures which were undertaken for wear or osteolysis in 91 patients between July 2002 and December 2012. Pre-operative anteroposterior pelvic radiographs and Judet views were reviewed. The stability of the acetabular component was confirmed intra-operatively.

RESULTS

Intra-operatively, it was found that 64 components were well-fixed and 32 were loose. Mean total scores in the well-fixed and loose components were 2.9 (0 to 7) and 7.2 (1 to 10), respectively (p < 0.001). In hips with a low score (0 to 2), the component was only loose in one of 33 hips (3%). The incidence of loosening increased with increasing scores: in those with scores of 3 and 4, two of 19 components (10.5%) were loose; in hips with scores of 5 and 6, eight of 19 components (44.5%) were loose; in hips with scores of 7 or 8, 13 of 17 components (70.6%) were loose; and for hips with scores of 9 and 10, nine of nine components (100%) were loose. Receiver-operating-characteristic curve analysis demonstrated very good accuracy (area under the curve = 0.90, p < 0.001). The optimal cutoff point was a score of ≥ 5 with a sensitivity of 0.79, and a specificity of 0.87.

CONCLUSION

There was a strong correlation between the scoring system and the probability of loosening of a cementless acetabular component. This scoring system provides a clinically useful tool for pre-operative planning, and the evaluation of the outcome of revision surgery for patients with loosening of a cementless acetabular component in the presence of osteolysis. Cite this article: Bone Joint J 2017;99-B:601-6.

A case control study of cemented acetabular total hip arthroplasty components in patients less than 50 with 5-year minimum follow-up

BACKGROUND

This study investigates the outcomes of cemented sockets in young patients (<50 years) requiring a total hip replacement (THR) compared to older patients (>50 years) having the same procedure, under the same surgeon between June 2005 and May 2009.

METHODS

Prosthesis survivorship rates, patient outcomes and radiological findings were compared between a consecutive series of 56 young patients (mean 42, range 25-49) and 56 older patients (mean 69, range 53-81) that underwent a primary THR using a cemented Stryker® Exeter™ Contemporary™ flanged cup. The minimum follow-up was 5 years.

RESULTS

No significant difference was observed between the groups' Oxford Hip Scores (p = 0.078) or satisfaction scores (p = 0.67). Worst case scenario analysis for revision, failure or lost to follow-up showed 94.6% survival in the <50 year olds and 92.9% survival in the >50 year olds at 5 years. This study demonstrates no significant difference in patient outcomes, survivorship or radiographic findings at a minimum of 5 years between patients <50 years old and those >50 years old undergoing THR with a cemented socket.

CONCLUSIONS

We believe the current trend towards uncemented cups may be driven by marketing rather than by evidence of improved outcomes. Cemented sockets provide very good outcomes for patients of all ages.

Complete Wear-Through of a Polyethylene Liner and Metal-Backed Acetabular Cup Resulting in a Unique Form of Catastrophic Total Hip Arthroplasty Failure: A Case Report

CASE

We describe a case of total hip arthroplasty failure where a cobalt-chrome femoral head completely wore through the polyethylene liner and the titanium acetabular cup. The patient subsequently underwent revision total hip arthroplasty with acetabular revision and femoral head exchange.

CONCLUSION

This case illustrates the natural history of catastrophic failure in a metal-on-polyethylene total hip arthroplasty design. If recognized earlier, this patient may have been a candidate for isolated liner and head exchange. Additionally, this case represents a unique complication in using mixed metals in total hip arthroplasty, where the harder cobalt-chrome femoral head wore completely through the much softer titanium component.

The surgical options and clinical evidence for treatment of wear or corrosion occurring with THA or TKA

BACKGROUND

Wear and corrosion occurring in patients with hip and knee arthroplasty are common causes of failure leading to revision surgery. A variety of surgical approaches to these problems have been described, with varying efficacy. Polyethylene wear, metal-on-metal (MoM) hip bearing wear, and problems associated with modular taper corrosion are the areas of greatest clinical impact; results of revisions for these problems are likely to dictate a large portion of revision resources for the foreseeable future, and so they call for specific study.

QUESTIONS/PURPOSES

We identified the most frequently reported procedures to treat hip polyethylene wear, knee polyethylene wear, MoM wear after THA, and modular taper corrosion and determined the timing and reasons these failed.

METHODS

We performed systematic reviews of the published literature on the four topics using MEDLINE(®) and Embase in October 2013; searches were supplemented by hand searches of bibliographies. Prespecified criteria resulted in the identification of 38 relevant articles, of which 33 were either case reports or Level IV evidence. Followup was generally at short term and ranged from 0.2 to 8 years.

RESULTS

The most frequently reported procedures for treating clinically important wear were a partial or complete revision. When treating polyethylene wear, the more frequently reported reasons for hip and knee rerevisions were loosening, continued wear, and instability. Soft tissue reactions were more common and occasionally extensive in patients with MoM or modular taper corrosion. Patients with soft tissue reactions had more complications and higher rerevision rates.

CONCLUSIONS

Studies with longer followup and higher levels of evidence are needed to direct the treatment of wear and corrosion. When soft tissue damage secondary to MoM wear or taper corrosion is present, the results of treatment can be poor. There is an urgent need to better understand these two mechanisms of failure.

Altered load transfer in the pelvis in the presence of periprosthetic osteolysis

Periprosthetic osteolysis in the retroacetabular region with cancellous bone loss is a recognized phenomenon in the long-term follow-up of total hip replacement. The effects on load transfer in the presence of defects are less well known. A validated, patient-specific, 3D finite element (FE) model of the pelvis was used to assess changes in load transfer associated with periprosthetic osteolysis adjacent to a cementless total hip arthroplasty (THA) component. The presence of a cancellous defect significantly increased (p &lt; 0.05) von Mises stress in the cortical bone of the pelvis during walking and a fall onto the side. At loads consistent with single leg stance, this was still less than the predicted yield stress for cortical bone. During higher loads associated with a fall onto the side, highest stress concentrations occurred in the superior and inferior pubic rami and in the anterior column of the acetabulum with larger cancellous defects.

Cemented liner exchange with bone grafting halts the progression of periacetabular osteolysis

The aims of this were to examine the effect of acetabular liner exchange and intra-operative bone grafting surgery on peri-prosthetic osteolysis. Seven patients with well-fixed Harris-Galante-1 acetabular components received cemented exchange liners for worn liners associated with pre-operatively CT-quantified osteolysis. During surgery, accessible osteolytic lesions were debrided and bone-grafted. Except for one patient with recurrent dislocation and acetabular component revision, the other patients had CT scans at a median of 4 months and at approximately 4 years after surgery. None of the pre-operative lesions increased in volume during the post-operative reporting period and no new lesions were detected. These results show that cemented liner exchange surgery can halt the progression of osteolysis and that bone grafting has the potential to restore bone.

Medium-term results of cementation of a highly cross-linked polyethylene liner into a well-fixed acetabular shell in revision hip arthroplasty

The present study was undertaken to document outcomes of cementation of a highly cross-linked polyethylene (PE) liner into a well-fixed acetabular metal shell in 36 hips. All operations were performed by a single surgeon using only one type of liner. Patients were followed for a mean of 6.1 years (range, 3-8 years). Mean Harris hip score improved from 58 points preoperatively to 91 points postoperatively. There were no cases of PE liner dislodgement or progressive osteolysis. 1 hip (2.8%) required revision surgery for acetabular cup loosening with greater trochanteric fracture. Complications included 1 peroneal nerve palsy and 1 dislocation. The results of this study and previous reports demonstrated that cementation of highly cross-linked PE liner into well-fixed metal shell could provide good midterm durability.

Osteolysis in the well-fixed socket

Osteolysis remains a common reason for revision after total hip arthroplasty (THA). For osteolysis associated with loose cups, revision is indicated. For osteolysis around a well-fixed cup, the decision is more controversial. The data available data support retention of the cupwith lesional treatment, working through screw holes and access channels for debridement and grafting. The choice of graft material to fill defects, if any, remains controversial. Several studies demonstrate good survivorship with cup retention strategies. Complete revision allows more complete debridement of the lesion and better graft fill, and allows implantation of a modern cup, typically with a full line of liners and bearing surfaces available. Additionally, revision allows fine tuning of the orientation of the cup, which may be advantageous for optimising hip stability. The author prefers to retain a well-fixed cup if it meets the following criteria: it is well-fixed to intra-operative testing, it is well-positioned, it is of sufficient size to allow insertion of a new liner with a reasonable head size, new liners are available, and the hip is stable to intra-operative trialing after liner insertion.

Percutaneous acetabuloplasty: a cadaveric study

Periacetabular osteolysis is a common etiology of prosthesis failure in patients who undergo total hip arthroplasty. These lesions are treated by open and, more recently, percutaneous techniques. The purpose of this study was to determine the relevant surface anatomy and bony landmarks in establishing percutaneous access to periacetabular regions and identifying critical at-risk structures in establishing access. Percutaneous access to the periacetabular region was established superiorly, anteroinferiorly, and posteroinferiorly by using 5 L5-to-mid thigh fixed cadaver pelvises with latex-injected vessels using threaded guidewires. Dissection was completed to identify structures at risk, with the distance from the wires recorded to the nearest millimeter. C-arm position for the optimal visualization and placement of guidewires was recorded. Average distance from the pin and the at-risk structures ranged from 11.2 to 38.7 mm. All 3 approaches allowed for safe percutaneous access to the periacetabular regions without injuring significant anatomical structures. This study established safe starting points and orientation for guidewires and radiograph projections associated with percutaneous access to the periacetabular regions. The findings in this study will be useful for developing minimally invasive approaches to these regions for the treatment of osteolytic lesions of diverse etiology. However, a biomechanical evaluation of the impact of these bony channels on the strength of pelvis under physiological and unanticipated loading must be performed before this technique can be safely translated to clinical practice.

Retention of a well-fixed acetabular component in the setting of acetabular osteolysis

PURPOSE

The treatment strategy for pelvic osteolysis with a well-fixed acetabular component after total hip arthroplasty(THA) involves replacing the acetabular cup liner and femoral head, débriding osteolytic lesions, and grafting.

METHODS

We investigated whether retention of a well-fixed acetabular component using the two-approach technique—the ilioinguinal approach combined with the posterolateral approach—was compatible with socket survival. Were viewed clinical and radiographic findings for 24 patients(24 hips) who had undergone acetabular revision arthroplasty of a well-fixed socket for progressive osteolysis. The surgical techniques used included osteolytic lesion débridement and bone grafting through the ilioinguinal approach,and replacement of the acetabular liner and femoral head through the posterolateral approach.

RESULTS

The mean duration of follow-up after revision was 2.3 (range 2.1–3.9) years. At follow-up evaluation, all acetabular components were well fixed and showed no evidence of loosening, osseous integration was apparent and there was no radiographic evidence that any lesions had progressed. No new osteolytic lesions were identified, and there were no clinical or radiographic complications.

CONCLUSIONS

Curettage and bone grafting under direct vision, cup liner and femoral-head replacement because of progressive retroacetabular osteolysis and retention of well fixed components using the two-approach technique results in good osseous integration of lysis. Larger studies with longer follow-up periods are required to establish the longterm success of this technique.

Complete acetabular cup revision versus isolated liner exchange for polyethylene wear and osteolysis without loosening in cementless total hip arthroplasty

INTRODUCTION

Revision surgery in patients showing polyethylene wear and acetabular osteolysis without visible acetabular cup loosening involves the difficult decision of whether to revise only the liner or both the cup and the liner. The purpose of this study is to compare the outcomes of complete acetabular revision and isolated liner exchange in patients showing wear and osteolysis without loosening.

MATERIALS AND METHODS

We evaluated 80 cases of revision surgery for polyethylene wear and osteolysis without cup loosening performed between October 1997 and December 2008. The cup revision group consisted of 45 patients who underwent a complete acetabular cup replacement, and the cup retention group consisted of 35 patients who underwent either an isolated liner exchange or a liner cementing procedure. Comparisons between the two groups were performed.

RESULTS

There were differences in femoral stem revision, estimated blood loss, and hospital stay. Other variables including complications, osteolysis progression, re-revision rate, clinical score, and satisfaction showed no differences between the two groups. There was one case of early loosening and subsequent re-revision surgery in the cup revision group, as well as one case of wear progression and liner dislodgement leading to complete re-revision of the acetabular component and femoral stem in the cup retention group.

CONCLUSION

We found no differences in acetabular osteolysis progression, fixation failure, or complication between the cup revision and retention groups. Therefore, isolated liner exchange without cup extraction in cases of osteolysis that includes a well-fixed and well-positioned shell could be considered as a viable treatment option.

Management of acetabular bone loss in revision total hip arthroplasty

Most acetabular revisions can be managed with a hemispherical component with screw fixation. Areas of segmental bone loss that preclude acetabular component stability may be managed with structural allograft or second-generation porous metal augments. Acetabular cages have a limited application but can be a useful tool in the management of massive bone loss and pelvic discontinuity.

Large acetabular defects can be managed with cementless revision components

BACKGROUND

Optimal techniques for acetabular revision in the setting of major pelvic osteolysis have not been established. Bilobed components, structural grafts, and reinforcement cages have demonstrated 10-24% midterm failure rates. While cementless hemispherical components have been utilized to treat large acetabular defects, most reports have not focused specifically on patients with extensive deficiencies.

QUESTIONS/PURPOSES

We report midterm clinical scores, component revisions, and complications following focal bone grafting and cementless acetabular revision in cases with major periacetabular osteolysis.

METHODS

We identified 30 patients (32 hips) who underwent cementless acetabular revision to treat massive acetabular bone loss at an average followup of 53 months. We excluded three patients lost to followup and two patients who died prior to minimum 24 month followup. Harris Hip Scores were assessed before and after surgery. Postoperative radiographs were evaluated for graft incorporation and component migration. Component revision and component migration are reported as failures.

RESULTS

Mean Harris Hip Score improved from 52.5 (range, 17.7-90.7) to 87.3 (range, 25.3-100) points. Three hips (9%) were revised for aseptic loosening. Three components (10.7%) demonstrated radiographic migration, but were not revised. Complete graft incorporation was seen in 17 cases (68%). There were five major complications (14%).

CONCLUSIONS

Cementless acetabular fixation and bone grafting result in clinical scores and survivorship comparable to other options at midterm followup, with potential for biological fixation.

LEVEL OF EVIDENCE

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

The fate of grafting acetabular defects during revision total hip arthroplasty

BACKGROUND

Acetabular defects are frequently grafted during revision THA. Previous studies using plain radiographs report high rates of graft incorporation. However, given plain radiographs underestimate osteolysis, it is unclear whether plain radiographs adequately reflect graft fill or incorporation.

QUESTIONS/PURPOSES

We determined if (1) graft fill; or (2) incorporation (measured as graft-bone contact) differed with complete revision and grafting compared to liner exchange and grafting; (3) defect fill and incorporation could be assessed on plain radiographs; and (4) the cost of bone grafting differed with these two procedures.

METHODS

We identified 40 patients who underwent revision THA for aseptic loosening or polyethylene wear and osteolysis, either with retention of a well-fixed cup or complete acetabular revision in which bone graft was used. Lesion size, percent fill, and graft healing was quantified from CT scans. A limited cost analysis was performed using the current hospital costs for implants, bone grafts, and bone graft substitutes. The minimum followup was 1 year (mean, 4.8 years; range, 1-11 years).

RESULTS

The average defect fill was 30% (range, 0%-81%). The average percent of healing to host bone was 24% (range, 0-66%). Complete revisions had a higher percent defect fill compared to head/liner changes (47% versus 17%) as well as a higher degree of graft healing to host bone compared to head/liner changes (36% versus 14%). High resolution CT demonstrated lower percentages of defect fill and graft healing than previous reports based on plain radiographs. Bone grafting costs exceeded implant costs in the head/liner exchange group; however, the overall cost was higher in the complete revision group.

CONCLUSIONS

Higher degrees of defect fill and healing were seen with complete revisions compared to head/liner exchanges. Compared to CT scans, plain radiograph assessment tended to overestimate defect fill and healing.

Relationship between the pelvic osteolytic volume on computed tomography and clinical outcome in patients with cementless acetabular components

The purpose of this study was to evaluate the relationship between the pelvic osteolytic volume on computed tomography (CT) and clinical outcome in patients with cementless acetabular components. We reviewed 87 patients (104 hips) who met the following inclusion criteria: (1) there was evidence of pelvic osteolysis on CT at a minium of five years postoperatively, (2) all cups and stems were radiographically stable at the time of CT, (3) the follow-up period after CT was a minimum of two years clinically. The mean pelvic osteolytic volume was 2.3 ± 6.9 cm(3). The mean Harris hip score (HHS) at CT was 92.3 ± 7.9 points. Inversely moderate correlation (r = -0.569, P < 0.05) was found between the HHS at CT and pelvic osteolytic volume. In ten cases of hips with acetabular revisions, the mean pelvic osteolytic volume was 16.3 ± 26.9 cm(3). The mean HHS at CT and HHS at reoperation was 87.6 ± 9.2 points and 73.4 ± 8.8 points, respectively, with significant difference (P < 0.05). The area under curve (ROC) analysis showed that the optimal cutoff value of the osteolytic volume was 4.8 cm(3) with 100% each for sensitivity and specificity. We conclude that the amount of pelvic osteolytic volume on CT may be used to guide treatment decision-making in patients with well-fixed cementless acetabular components who show evidence of pelvic osteolysis.

Granuloma debridement and the use of an injectable calcium phosphate bone cement in the treatment of osteolysis in an uncemented total knee replacement

Polyethylene particulate debris-induced periprosthetic osteolysis is a known complication of knee arthroplasty surgery, and may result in the need for revision surgery. The management of these bony defects can be surgically challenging, and full revisions of well-fixed total knee components can lead to substantial bone loss. We present the case of a 71 year old man who developed knee pain and osteolysis around an uncemented total knee replacement. Due to significant medical comorbidies he was treated by percutaneous cyst granuloma debridement and grafting using an injectable calcium phosphate bone substitute. There were no wound complications, and the patient was allowed to fully weight-bear post-operatively. Histopathology and microbiology of the cyst material confirmed polyethylene granulomata without any evidence of infection. At 6 weeks post-operatively the patient's previous knee pain had resolved, he was able to comfortably fully weight-bear. Preoperative scores (Knee Society Score (KSS) 41, WOMAC score 46.2, and Oxford Knee Score 39) had all improved at the 12-month post-operative review KSS 76, WOMAC 81.7 and Oxford Knee score 21). This is a safe and effective technique with minimal morbidity and may be an appropriate treatment modality when more extensive revision surgery is not possible. The case is discussed with reference to the literature.

Early catastrophic failure of a porous-coated acetabular cup due to bead shedding. A case report

We present a patient in whom an uncemented porous-coated acetabular cup underwent early catastrophic failure due to debonding and was successfully managed with a revision total hip arthroplasty. Early bead shedding of an acetabular cup leading to a sudden component failure requiring revision surgery is a rare event.

Cementation of cross-linked polyethylene liner into well-fixed acetabular shells: mean 6-year follow-up study

The purpose of this study was to evaluate retrospectively the outcomes of cementation of cross-linked polyethylene (PE) liner in a well-fixed metal shell in 23 hips with an average follow-up period of 6 years. The mean Harris hip score was 69.6 +/- 12 (range, 46-83) points preoperatively. The average postoperative follow-up was 72.3 months (range, 56-100 months). At the final follow-up, the mean Harris hip score was 95.5 +/- 3 (84-100) points. There was no change in the bone-shell interface. No new osteolytic lesions were identified. The lesions impacted with bone graft had united completely. The remaining osteolytic lesions had decreased in size. There was no recurrent osteolysis, hip dislocation, component migration, and failure at the cement-metal interface. The results of the current study revealed that cementation of cross-linked PE liner into a well-fixed shell provided good midterm durability.

A three-dimensional method for evaluating changes in acetabular osteolytic lesions in response to treatment

The treatment of asymptomatic osteolysis among well-fixed cementless cups remains controversial. To compare the effectiveness of different treatment strategies, an objective technique for evaluating bone remodeling would be useful. By matching and comparing serial CT images with the aid of a computer-assisted imaging program, we developed a method to evaluate three-dimensional mineralization changes within osteolytic defects. Preoperative, immediate postoperative, and followup CT images were normalized based on a phantom with known densities and matched using image registration so that the same region could be analyzed on each image. New bone mineralization within the preoperative osteolytic lesion volume was quantified based on a patient-specific trabecular bone density threshold. As a pilot study, we applied this technique in 10 patients treated by polyethylene liner exchange with débridement and grafting of periacetabular osteolytic lesions using a calcium sulfate bone graft substitute. Relative to the preoperative osteolytic lesion volume, an average of 43% (range, 8%-72%) of each defect was filled with graft at revision. After resorption of the graft, an average of 24% (range, 9%-44%) of the original defect volume demonstrated evidence of new mineralization at 1-year followup. The amount of new mineralization was directly proportional (r(2) = 0.70) to the defect filling achieved at revision. CT-based image analysis offers an objective method for quantifying three-dimensional bone remodeling and can be used to evaluate the effectiveness of osteolysis treatment strategies.

LEVEL OF EVIDENCE

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

Correlation of computed tomography with histology in the assessment of periprosthetic defect healing

Computed tomography (CT) may more accurately assess the healing of grafted osteolytic lesions around acetabular components compared with plain radiographs, although clinical validation is lacking. To determine whether clinical or micro-CT imaging could assess accurately the grafted lesion compared with histology, we therefore quantified bone healing and ingrowth to determine an effective rhBMP-2 dose and ratio to allograft bone when grafted adjacent to a cementless porous-coated component. We grafted surgically created acetabular defects in canines (n = 20) before uncemented total hip arthroplasty. At 6 weeks, embedded acetabula were imaged and the CT slice images matched to histology section images. The percentage of bone in the defect and growth into the porous surface was assessed quantitatively. Low-dose rhBMP-2 with allograft (1:5 ratio) resulted in a higher percentage of defect healing (43.8%) than rhBMP-2 alone (29.2%) and a higher percentage of bone ingrowth (15.7%) than allograft bone alone (1.1%) as measured by histology. Micro-CT measurements were similar to histologic measurements of defect healing, whereas clinical CT overestimated periprosthetic bone by 38%. Neither clinical CT nor micro-CT techniques are adequate for assessing ingrowth or the bone-implant interface with metal artifacts.

Retroacetabular osteolytic lesions behind well-fixed prosthetic cups: pilot study of bearings-retaining surgery

Background

Osteolytic lesions are common radiological findings behind acetabular prosthetic cups. If the cup is well-fixed, the management is quite controversial. Although implant exchange is the most reliable procedure, in most cases it could be considered overtreatment, with the potential for further morbidity and bone loss. Liner exchange associated with lesion debridement and grafting represents an alternative option that is less invasive. Here we present our experiences from a small pilot study of minimally invasive osteolysis treatment without bearings exchange in patients with no evidence of liner wear.

Materials and methods

Inclusion criteria: retroacetabular osteolytic lesions in ceramic-on-polyethylene or metal-on-polyethylene cementless total hip arthroplasties, affecting more than 50% of the bone–prosthesis interface on anteroposterior radiography. Exclusion criteria: head penetration into the liner, suspected loosening or infection. Six patients were selected, two asymptomatic and four symptomatic. Only the symptomatic patients accepted the proposed treatment (performed between June 2004 and March 2006). All of them received fluoroscopy-assisted lesion debridement through an iliac cortical window, morcellized bone allograft mixed with autologous platelet-rich plasma, joint exploration for culture and lavage through a small capsular window. Patients were followed up clinically and radiologically at six months, 12 months, and then yearly.

Results

Three patients out of four showed clinical and radiological improvement. One showed radiological improvement only, and recently underwent cup exchange for subsequent loosening. The visual analog scale (VAS) values for pain decreased on average, but not significantly. No major complications occurred. No recurrence was noted at 2.25–4 years’ follow-up.

Conclusions

Although the small series does not allow any absolute conclusions to be drawn, the reported results seem to justify further, wider studies. It is still unclear if osteolytic lesions associated with no wear of the poly liner would progress to implant failure if left untreated. Until the problem is better understood, this procedure might represent an interesting way to prevent potential loosening and severe bone loss in intact sockets.

Isolated acetabular liner exchange

During the past two decades, most total hip arthroplasties were performed with metal or ceramic heads on conventional polyethylene, an articulation associated with wear and limited life expectancy. Wear is associated with acetabular osteolysis. Isolated liner exchange has become a common surgical intervention when the acetabular component remains well-fixed. The purpose of isolated liner exchange is to prevent loosening of the components secondary to osteolysis and catastrophic mechanical failure caused by bearing wear-through. Treatment options for polyethylene wear include observation (in the asymptomatic hip), liner exchange, and more extensive revision procedures. Patients frequently present with asymptomatic but substantial polyethylene wear with or without associated osteolysis, the treatment of which is controversial. Other areas of debate include complete acetabular component removal to allow bone grafting and placement of an improved bearing surface, reuse of modular mechanisms, cementation into well-fixed shells, and whether to use periacetabular bone grafting.

What is the outcome of treatment for osteolysis?

Periprosthetic osteolysis secondary to wear-induced particle generation is a common long-term complication of hip and knee replacement and frequently results in the need for revision surgery. Management of significant bone defects remains a surgical challenge. Surgical intervention must address the wear particle generator (usually, but not always, the bearing surface), the osteolytic defects, and implant-related issues, primarily fixation and alignment. Indications for surgical intervention in the absence of loosening and pain are not well established. In general, patient age and activity level, the location and size of the osteolytic defect, and the clinical record of the implant system will dictate treatment choices.

Titanium particles that have undergone phagocytosis by macrophages lose the ability to activate other macrophages

Titanium particles derived from the wear of the orthopaedic implant surfaces can activate macrophages to secrete cytokines and stimulate osteoclastic bone resorption, causing osteolysis around orthopaedic implants. However, what happens to the titanium particles after being phagocytosed by macrophages is not known. We prepared titanium particles (as received, clean, and LPS-coated), and exposed them to macrophages in culture. Free particles were washed away after 24 h and the intracellular particles were kept in culture for additional 48 h until being harvested by lysing the cells. Particles that had been cell treated or noncell treated were examined by scanning electronic microscopy to analyze the shape, size, and concentration of the particles. The cell treated and noncell treated particles were exposed to macrophages in culture with a particle to cell ratio of 300:1. After 18 h, the levels of TNF-alpha in culture medium and the viability of the cells were examined. Clean particles did not stimulate TNF-alpha secretion by macrophages, while LPS-coated particles dramatically increased that response. Phagocytosis by macrophages did not change the shape and size of the particles, but depleted the ability of the particles to stimulate TNF-alpha secretion by macrophages. This indicates that macrophages are capable of rendering titanium particles inactive without degrading the particles, possibly by altering the surface chemistry of the particles.

The quality of osteolysis grafting with cementless acetabular component retention

Periprosthetic osteolysis is a common cause for revision of total hip arthroplasty. When modular cementless acetabular components are stable, curettage and grafting of the osteo-lytic lesion while retaining the component are a good surgical option. Although the midterm outcome of this procedure is known, the quality of the surgical technique is not. We used preoperative and postoperative computed tomography to determine the percentage of periacetabular lesions that was grafted and the percentage of the lesion volume filled with an injectable bone graft substitute. We discovered, even with preoperative computed tomography reconstructions and surgical planning, four of 22 lesions were neglected at the time of surgery. In the 18 lesions that were treated, we were able to fill an average of 49% (range, 0-83%) of the lesion volume. These inconsistent results illustrate a need to further refine surgical techniques and instrumentation to treat one of the most common complications in total hip arthroplasty. Longer followup with repeat computed tomography scans or other imaging techniques would determine if the percentage of lesion fill has an effect on clinical outcome.

Revision total hip arthroplasty for pelvic osteolysis with well-fixed cementless cup

Treatment of pelvic osteolysis after total hip arthroplasty (THA) remains controversial. Clinical and radiographic outcomes of revision THA were evaluated in 62 hips with pelvic osteolysis and well-fixed cementless cups. The patients' mean age was 50.9 years, and the mean interval from primary to revision THA was 9.7 years. For revision, cementless cups were used in 51 hips, and cemented cups in 11 with acetabular reinforcement rings in 9. The mean duration of follow-up after revision THA was 5.9 years (range, 3.0-9.7 years). At final follow-up, the average Harris Hip Score was 92.4, and there was no radiographic complication except for 1 with change of inclination. Revision THA for pelvic osteolysis with well-fixed cementless cups showed favorable outcomes, and it can be preferentially used in young patients.

No effect of bone morphogenetic protein-7 (OP-1) on the incorporation of impacted bone grafts in a realistic acetabular model

Bone morphogenetic proteins (BMPs) accelerate bone repair in experimental and clinical conditions. Impacted Morsellized Cancellous Bone grafts (MCB) are successfully used to reconstruct bone defects after failed hip implants. The main question in this study was if BMP-7 (OP-1) mixed with MCB could accelerate the incorporation of MCB and prevents the formation of a soft tissue interface after remodeling of the MCB. A large loaded defect in the acetabulum of goats was reconstructed with a wire mesh and with MCB or MCB mixed with OP-1. After 6 weeks, no differences were found in the revascularization process, in the number of osteoclasts resorbing the MCB, and in the thickness and appearance of the fibrous interface between MCB with or without OP-1. After 6 weeks, enchondral bone had formed in the bone graft layer and on the periosteal anterior and superior rim in the OP-1 group only. More periosteal bone and more bone in the holes of the mesh had been formed in most OP-1 goats. Most MCB was replaced by new lamellar bone after 15 weeks in both groups. We speculate that during or directly after impaction most of the OP-1 is released from the carrier inducing an early effect outside the reconstructive layer at the periosteal side of the acetabulum. Probably most OP-1 has left the reconstruction by the time new vessels and progenitors reached the bone graft. These results do not support the use of OP-1 in impaction bone grafting in patients.

Computed tomographic follow-up evaluation of operative intervention for periacetabular lysis

Computed tomography (CT) accurately evaluates periacetabular lytic lesions. The purpose of this study is to determine the fate of osteolytic lesions after treatment with liner exchange and bone grafting. Fifteen patients who had undergone liner exchange with grafting for progressive lytic lesions, as demonstrated by preoperative CT scans, were identified. Postoperative CT scans were performed at a minimum of 2 years post revision. The largest cross sectional lytic area was compared with the postoperative scan to determine the fate of the lesion. The mean size of the measured lytic lesions preoperatively was 6.38 cm(2). Postoperatively, lesions decreased to 2.94 cm(2) (P = .000). Modular liner exchange with grafting is effective in treating osteolytic lesions in the pelvis, as demonstrated by CT.

Isolated liner exchange using the anterolateral approach is associated with a low risk of dislocation

Authors of reports on the outcome of isolated liner exchange for osteolysis and wear have reported high dislocation rates. Twenty-six patients (27 hips) with a minimum of 2 years of followup had isolated liner exchange for wear and osteolysis done using the abductor splitting anterolateral approach. The mean followup was 41 months. The average age at time of surgery was 51 years. Preoperative Harris hip scores averaged 70, and increased to 82 at the most recent followup. We observed improvements in pain and functional scores. The average operating time was 82 minutes, and the average blood loss was 255 mL. Only three (12%) patients required transfusion. No components were rerevised for aseptic loosening, and one patient (one hip) had a dislocation (3.7%). Isolated liner exchange for osteolysis and wear done using the anterolateral approach has a lower risk of dislocation than previously reported and provides substantial improvements in pain, function, and Harris hip score.

LEVEL OF EVIDENCE

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

The acetabular insert-metal backing interface: an additional source of polyethylene wear debris

In cementless acetabular arthroplasty, the interface between the metal backing and the ultra-high-molecular-weight polyethylene acetabular insert surface is a potential source of polyethylene debris. This study of 55 early-generation acetabular inserts found that severe wear of the convex insert surface correlates with osteolysis. Wear of the concave insert surface did not correlate strongly with osteolysis probably owing to prevalent micromotion and wear at the convex surface interface. Although concern over linear wear predominates with contemporary designs, if initial liner engagement is compromised or locking mechanism failure occurs with time, the convex insert surface again may become a significant source of debris contributing to osteolysis.

Cementation of a metal-inlay polyethylene liner into a stable metal shell in revision total hip arthroplasty

The purpose of this study was to evaluate the results of liner cementation into a stable acetabular shell using a metal-inlay polyethylene liner in 39 revision total hip arthroplasties. After an average of 2.8 years, 1 cemented liner dislodged from its metal shell at a postoperative 4 years. In the other 38 hips, mean Harris hip scores improved from 65 preoperatively to 86.9 at the final follow-up. Eighteen patients were rated as having excellent results, 17 as good, and 3 as fair. There were no changes in cup position and no cases of osteolytic lesion progression around the femoral and acetabular components in the last follow-up radiographs. Metal-inlay polyethylene liner cementation into a stable acetabular shell was found to provide an alternative option with short-term excellent results, and it also offers more liner options, the preservation of bone stock, and lower surgical morbidity.

Retroacetabular osteolysis: when to operate?

Polyethylene liner exchange for retroacetabular osteolysis should be done before the shell becomes loose. The purpose of this study was to determine the radiographic quantity of osteolysis that will predict impending loosening of the cementless shell. Between 1992 and 2002, 46 cementless shells were revised at our institution for aseptic osteolysis. Radiographs and a computer-assisted technique were used to quantify osteolysis. Implant stability was confirmed intraoperatively. Of 26 stable and 20 loose shells, the average area of osteolysis on anteroposterior radiographs showed no significant difference, whereas lateral radiographs showed a difference. The percentage of shell circumference with associated osteolysis seen on anteroposterior and lateral radiographs showed a significant difference. Diagnostic criterion of 50% shell circumference associated with osteolysis on lateral films has a sensitivity of 0.84 and a specificity of 0.54, and on anteroposterior views, a sensitivity of 1.0 and a specificity 0.27 for predicting shell loosening. Percent of shell circumference with surrounding osteolysis seems to be more predictive of loosening than the area of osteolysis. When 50% of the shell circumference has osteolysis evident on anteroposterior or lateral radiographs, but preferably anteroposterior radiographs, liner exchange should be considered so that the exchange procedure is still possible, rather than allowing the osteolysis to increase and compromise shell fixation.

Early morbidity of modular exchange for polyethylene wear and osteolysis

This study assessed the early morbidity associated with modular component exchange surgery for the treatment of accelerated polyethylene wear and osteolysis in 55 patients. Review of the surgical records revealed no significant intraoperative complications, little intraoperative blood loss (mean 333 mL), no allogenic blood transfusions, and no recorded postoperative deep vein thromboses. Eighteen percent of patients, however, experienced postoperative dislocation. Five patients dislocated multiple times, 3 of which required rerevision surgery. Two patients required rerevision for femoral implant fractures related to osteolysis and 1 additional patient required rerevision due to catastrophic failure of the acetabular component 5 years postoperatively. With an average follow-up of 30 months, 6 of the 55 patients treated with modular exchange required rerevision. The results of this study suggest that instability is the most prevalent early complication associated with modular component exchange. As such, we believe that more stable constructs should be emphasized, possibly at the expense of polyethylene thickness.

Isolated liner exchange in revision total hip arthroplasty: clinical results using the direct lateral surgical approach

Twenty-four hips (23 patients) underwent isolated polyethylene liner exchange (modular and nonmodular liners) via the direct lateral surgical approach for a preoperative diagnosis of polyethylene wear and acetabular osteolysis. Accessible osteolytic lesions were bone grafted with cancellous allograft. Patients were followed up clinically and radiographically, with a mean follow-up time of 36 months (range, 12-100 months). A computer-assisted method measured lesional area from the radiographs of the 18 hips that presented with osteolysis. Seventeen of 18 lesions either regressed or resolved since the procedure. Two patients required repeat revisions, and no dislocations were noted. Clinically, both Harris Hip and Western Ontario and McMaster Universities Osteoarthritis Index scores improved postoperatively. In selected patients, isolated liner exchange with or without bone grafting is effective for treating polyethylene wear and associated osteolysis. Dislocation rates with revision may be reduced using a surgical approach that preserves an adequate capsular layer for closure in liner exchange surgery.

Isolated acetabular polyethylene exchange through the anterolateral approach

Isolated exchange of an acetabular liner, in the presence of a well-fixed acetabular component, has become an established method for the management of polyethylene wear. Various experienced adult-reconstruction surgeons have noted a high incidence of instability following isolated liner exchange. We report the results of isolated liner exchange in 35 patients with polyethylene wear and osteolysis (16 patients) or polyethylene wear and instability (19 patients) with a minimum follow-up of 2 years. Isolated liner exchange was performed through an anterolateral approach in all cases. Postoperative dislocation occurred in 2 of the 35 patients (6%), both with polyethylene wear and osteolysis. Isolated liner exchange was successful in addressing instability in all 19 patients who presented with polyethylene wear and dislocation. Isolated acetabular liner exchange performed through an anterolateral approach carries an acceptable dislocation rate.

Computed tomography to assess pelvic lysis after total hip replacement

To assess the accuracy of a computer-assisted computed tomography image analysis program in determining the location and volume of periacetabular osteolysis, we designed an osteolysis model by implanting bilateral total hip replacements in human pelvic cadavers and creating osteolytic lesions of varying sizes. The volumes of 48 defects were measured physically, and axial computed tomography scans were obtained. The computed tomography images were processed with streak artifact reduction and segmentation algorithms. The location and volume of lesions were determined from these images. Eighty-one percent (39 lesions) were identified correctly from the computed tomography scans. Detection was location-dependent. More lesions were detected in the ilium (100%) and at the rim (89%) than in the ischium (78%) or the pubis (50%). Computed tomography overestimated lesion volume by a mean of 0.5 +/- 2.3 cm. The volumetric error was unrelated to lesion location but was dependent on lesion size. As lesion size increased above 10 cm, the mean percentage error decreased to 1.8%. Computed tomography image analysis can be used more accurately than plain radiographs to investigate the effectiveness of treatment and the natural history of pelvic osteolysis.

The pumping of fluid in cementless cups with holes

Ten patients who were scheduled for revision for pelvic osteolysis were studied. All had bone-ingrown metal-backed cups with holes and polyethylene liners. Pressures were measured in the osteolytic lesion and in the hip joint while applying cyclic forces across the artificial joint. In 4 cases with lesions that were fully contained by bone, loading of the hip produced a pressure wave in the osteolytic lesion. Cyclic forces, such as those that occur in normal gait, can act on the polyethylene liner, the metal shell, and the supporting bone to pump fluid in the retroacetabular osteolytic lesion. This pumping action may contribute to the pathogenesis of osteolysis by the mechanisms of fluid pressure, fluid flow, or the transportation of wear particles.

Acetabular liner fixation by cement

Many situations in revision THA require the exchange of a PE liner in the setting of a well-fixed cementless acetabular shell. Unfortunately, a replacement liner is not always available, the locking mechanism of the metal shell may be damaged or incompatible with the desired liner, or the shell is malpositioned. Revision of a well-fixed cementless acetabular shell has been associated with considerable morbidity. This raises several questions: can a new PE liner be fixed in the existing shell using bone cement, and if so, which techniques can improve the end result, and in which patients should they be used? Biomechanical testing of cemented PE liners has shown initial fixation strengths that exceed conventional locking mechanisms. It is not known during what period this initial fixation will fail, but clinical reports with followup of as many as 6 years have shown survival in approximately 90% of cases. These studies have shown the importance of proper patient selection, accurate sizing of the PE liner, careful preparation of the substrate of the liner and the shell, and good cement technique. The potential advantages of this technique are less surgical morbidity, more rapid surgery and patient recovery, the ability to incorporate antibiotics in the cement, and more liner options.