Computed tomography in the assessment of periacetabular osteolysis

Decision/therapeutic algorithm for acetabular revisions

Background and aim:

Paprosky’s classification is currently the most used classification for periacetabular bone defects but its validity and reliability are widely discussed in literature. Aim of this study was to introduce a new CT-based Acetabular Revision Algorithm (CT-ARA) and to evaluate its validity. The CT-ARA is based on the integrity of five anatomical structures that support the acetabulum. Classification’s groups are defined by the deficiency of one or more of these structures, treatment is based on those groups.

Methods:

In 105 patients the validity of the CT-ARA was retrospectively evaluated using preoperative X-rays, CT-scan and surgery reports. The surgical indications suggested by Paprosky’s algorithm and by CT-ARA were compared with the final surgical technique. Patients were divided into two groups according to time of surgery.

Results:

We reported concordance of indications in 56,2% of cases with the Paprosky’s algorithm and in 63,8% of cases with the CT-ARA. Analysing only the most recent surgeries (group 2), we reported even higher difference of concordance (67,3% Paprosky’s algorithm and 83,7% CT-ARA). The concordance of the CT-ARA among Group 1 and Group 2 resulted significantly different.

Conclusions:

the CT-ARA may be a useful tool for the preoperative decision-making process and showed more correlation with performed surgery compared to the Paprosky’s algorithm.

Quantitative assessment of acetabular bone defects: A study of 50 computed tomography data sets

Objectives

Acetabular bone defect quantification and classification is still challenging. The objectives of this study were to suggest and define parameters for the quantification of acetabular bone defects, to analyze 50 bone defects and to present the results and correlations between the defined parameters.

Methods

The analysis was based on CT-data of pelvises with acetabular bone defects and their reconstruction via a statistical shape model. Based on this data, bone volume loss and new bone formation were analyzed in four sectors (cranial roof, anterior column, posterior column, and medial wall). In addition, ovality of the acetabulum, lateral center-edge angle, implant migration, and presence of wall defects were analyzed and correlations between the different parameters were assessed.

Results

Bone volume loss was found in all sectors and was multidirectional in most cases. Highest relative bone volume loss was found in the medial wall with median and [25, 75]—percentile values of 72.8 [50.6, 95.0] %. Ovality, given as the length to width ratio of the acetabulum, was 1.3 [1.1, 1.4] with a maximum of 2.0, which indicated an oval shape of the defect acetabulum. Lateral center-edge angle was 30.4° [21.5°, 40.4°], which indicated a wide range of roof coverage in the defect acetabulum. Total implant migration was 25.3 [14.8, 32.7] mm, whereby cranial was the most common direction. 49/50 cases showed a wall defect in at least one sector. It was observed that implant migration in cranial direction was associated with relative bone volume loss in cranial roof (R = 0.74) and ovality (R = 0.67).

Conclusion

Within this study, 50 pelvises with acetabular bone defects were successfully analyzed using six parameters. This could provide the basis for a novel classification concept which would represent a quantitative, objective, unambiguous, and reproducible classification approach for acetabular bone defects.

Sensitivity and specificity of post-operative interference gap assessment on plain radiographs after cementless primary THA

INTRODUCTION

Implant performance of cementless THA is often evaluated by radiolucency on plain radiographs, often classified as interference gaps on direct post-operative radiographs. However, the diagnostic performance is unknown. The aim was to evaluate the diagnostic performance of radiographic assessment of post-operative gaps after primary THA by comparing it with CT confirmed gaps, and secondary to define optimal cut-off criteria for assessing gaps on plain radiographs compared with CT.

MATERIAL AND METHODS

Patients (N = 40) with a primary cementless THA performed between July 2015 and March 2016 were enrolled in the study. Radiolucency was assessed on post-operative AP pelvic digital radiographs by two observers independently. Maximum width and percentage of coverage per zone were reported. Gap volume was measured by manual segmentation on CT images.

RESULTS

When defining a gap as a radiolucency extending through >50% of a zone, the interrater agreement Kappa was 0.241. Sensitivity was 65.8% for observer 1 (Kappa = 0.432), and 86.8% for observer 2 (Kappa = 0.383). When defining a gap as a radiolucency with a width >1 mm, the interrater agreement Kappa was 0.302. Sensitivity was 55.3% and 50% for observer 1 and observer 2, respectively. The ROC-curve resulted in an optimal threshold of 0.65 mm (AUROC = 0.888) and 0.31 mm (AUROC = 0.961) for the two observers.

CONCLUSION

The diagnostic performance of observers detecting interference gaps on radiographs showed low sensitivity. Further on, the inter-rater agreement is too low to do a general recommendation about thresholds for defining gaps. Evaluating progression of radiolucency on radiographs should be performed in the light of these findings.

Method for quantitative assessment of acetabular bone defects

The objective of the study was to suggest a novel quantitative assessment of acetabular bone defects based on a statistical shape model, validate the method, and present preliminary results. Two exemplary CT-data sets with acetabular bone defects were segmented to obtain a solid model of each defect pelvis. The pathological areas around the acetabulum were excluded and a statistical shape model was fitted to the remaining healthy bone structures. The excluded areas were extrapolated such that a solid model of the native pelvis per specimen resulted (i.e., each pelvis without defect). The validity of the reconstruction was tested by a leave-one-out study. Validation results showed median reconstruction errors of 3.0 mm for center of rotation, 1.7 mm for acetabulum diameter, 2.1° for inclination, 2.5° for anteversion, and 3.3 mm³ for bone volume around the acetabulum. By applying Boolean operations on the solid models of defect and native pelvis, bone loss and bone formation in four different sectors were assessed. For both analyzed specimens, bone loss and bone formation per sector were calculated and were consistent with the visual impression. In specimen_1 bone loss was predominant in the medial wall (10.8 ml; 79%), in specimen_2 in the posterior column (15.6 ml; 46%). This study showed the feasibility of a quantitative assessment of acetabular bone defects using a statistical shape model-based reconstruction method. Validation results showed acceptable reconstruction accuracy, also when less healthy bone remains. The method could potentially be used for implant development, pre-clinical testing, pre-operative planning, and intra-operative navigation. © 2018 The Authors. Journal of Orthopaedic Research® Published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society. J Orthop Res 9999:1-9, 2018.

Acetabular defect classification in times of 3D imaging and patient-specific treatment protocols

Parallel to the rising number of revision hip procedures, an increasing number of complex periprosthetic osseous defects can be expected. Stable long-term fixation of the revision implant remains the ultimate goal of the surgical protocol. Within this context, an elaborate preoperative planning process including anticipation of the periacetabular defect form and size and analysis of the remaining supporting osseous elements are essential. However, detection and evaluation of periacetabular bone defects using an unsystematic analysis of plain anteroposterior radiographs of the pelvis is in many cases difficult. Therefore, periacetabular bone defect classification schemes such as the Paprosky system have been introduced that use standardized radiographic criteria to better anticipate the intraoperative reality. Recent studies were able to demonstrate that larger defects are often underestimated when using the Paprosky classification and that the intra- and interobserver reliability of the system is low. This makes it hard to compare results in terms of defects being studied. Novel software tools that are based on the analysis of CT data may provide an opportunity to overcome the limitations of native radiographic defect analysis. In the following article we discuss potential benefits of these novel instruments against the background of the obvious limitations of the currently used native radiographic defect analysis.

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.

Cementless total hip replacements in sickle cell disease

BACKGROUND

Sickle cell disease (SCD) affects around 80,000 people in the USA and 12,000 in the UK. Up to 40% of patients will get osteonecrosis of the femoral head. Cemented acetabular components yield poor results with the rate of osteolysis ranging from 13.5 to 46%. We report on a consecutive cohort of patients with SCD who underwent uncemented THA with ceramic-on-ceramic (CoC) bearings.

METHODS

Since 2002 52 primary THAs were carried out in 40 patients. The average age was 36.1 years (17-54). 48 cases had exchange blood transfusion preoperatively and 3 had top-up transfusions.An S-ROM was used in 47 hips a Solutions stem in 4 hips and an AML in 1. It was necessary to drill the femur during 12 hips. There were 5 intra-operative peri-prosthetic fractures. 2 dislocations were observed. 2 superficial infections were detected.

RESULTS

All components have in-grown. There have been no cases of radiographic osteolysis, migration or loosening of the hip with average 5-year (2-10.1) follow-up.

CONCLUSIONS

The combination of a multidisciplinary team approach and uncemented implants, with ceramic-on-ceramic bearings used, has made THA in patients with SCD a safe and reliable procedure in our hospital.

Assessment of wear and periacetabular osteolysis using dual energy computed tomography on a pig cadaver to identify the lowest acceptable radiation dose

Objectives

Computed tomography (CT) plays an important role in evaluating wear and periacetabular osteolysis (PAO) in total hip replacements. One concern with CT is the high radiation exposure since standard pelvic CT provides approximately 3.5 millisieverts (mSv) of radiation exposure, whereas a planar radiographic examination with three projections totals approximately 0.5 mSv. The objective of this study was to evaluate the lowest acceptable radiation dose for dual-energy CT (DECT) images when measuring wear and periacetabular osteolysis in uncemented metal components.

Materials and Methods

A porcine pelvis with bilateral uncemented hip prostheses and with known linear wear and acetabular bone defects was examined in a third-generation multidetector DECT scanner. The examinations were performed with four different radiation levels both with and without iterative reconstruction techniques. From the high and low peak kilo voltage acquisitions, polychrmoatic images were created together with virtual monochromatic images of energies 100 kiloelectron volts (keV) and 150 keV.

Results

We could assess wear and PAO while substantially lowering the effective radiation dose to 0.7 mSv for a total pelvic view with an accuracy of around 0.5 mm for linear wear and 2 mm to 3 mm for PAO.

Conclusion

CT for detection of prosthetic wear and PAO could be used with clinically acceptable accuracy at a radiation exposure level equal to plain radiographic exposures.

Cite this article: B. Sandgren, M. Skorpil, P. Nowik, H. Olivecrona, J. Crafoord, L. Weidenhielm, A. Persson. Assessment of wear and periacetabular osteolysis using dual energy computed tomography on a pig cadaver to identify the lowest acceptable radiation dose. Bone Joint Res 2016;5:307–313. DOI: 10.1302/2046-3758.57.2000566.

Is the size of the acetabular bone lesion a predictive factor for failure in revisions of total hip arthroplasty using an impacted allograft?

OBJECTIVE

The aim of this study was to determine the acetabular bone lesion size (in millimeters) from which impacted bone graft failure starts to occur more frequently, through simple anteroposterior hip radiographs, and whether measurement of the defect on simple radiographs maintains the same pattern in inter and intraobserver assessments.

METHODS

Thirty-eight anteroposterior pelvic-view radiographs from patients undergoing revision of an acetabular prosthesis were retrospectively analyzed and assessed. In the vertical plane, the bilacrimal line was measured in millimeters from the farthest point found on the bone edge of the acetabular osteolysis to the top edge of the cementation or of the acetabular implant in uncemented cases. The base was taken to be a line perpendicular to bilacrimal line, with the aim of eliminating any pelvic tilt effects. This measurement was named the vertical size of failure. Radiographs produced four years after the operation were analyzed to investigate any failure of the technique.

RESULTS

The graft failure rate in the study group was 26.3%. The failures occurred in cases with an initial bone defect larger than 11 mm. No cases with measurements smaller than this evolved with failure of the revision. The highest incidence of graft failure occurred in cases described as advanced according to the "Paprosky" classification.

CONCLUSION

Failure of acetabular revision arthroplasty using an impacted graft did not present any statistically significant correlation with the vertical extent of the lesion on simple anteroposterior radiographs, as a predictor of treatment failure.

Pelvic discontinuity: modern techniques and outcomes for treating pelvic disassociation

Pelvic discontinuity is an uncommon condition that usually presents in the revision total hip arthroplasty population. However, its incidence will most likely increase due to the increasing number of primary and revision total hip arthroplasties (THA) done in recent years. Pelvic discontinuity (acetabular disassociation) is perhaps one of the more challenging cases for the hip arthroplasty surgeon to manage. Historically, the management of pelvic discontinuity has been wrought with many challenges. What follows is a review of the current techniques and outcomes for acetabular reconstruction in patients with acetabular disassociation including: porous metal components, internal fixation with acetabular reconstruction, acetabular distraction with jumbo cups, cup and cage construct, and the use of custom triflange.The complexity of pelvic discontinuity and with the myriad of options available to the hip arthroplasty surgeon to address this particular issue, preoperative planning becomes all the more essential.

Denosumab for treating periprosthetic osteolysis; study protocol for a randomized, double-blind, placebo-controlled trial

Background

Wear-induced osteolysis is the main factor in reducing the longevity of total hip arthroplasty (THA). The transmembrane Receptor Activator of Nuclear Factor κ B (RANK) and its corresponding ligand RANKL is an important regulator of osteoclast activity and bone resorption and is associated with osteolysis around implant. Inhibiting RANKL with denosumab is effective in vivo in preventing osteoporosis-related fractures. In vitro, osteoclasts can be blocked in animal models of osteolysis. We hypothesize that denosumab is effective in reducing wear-induced osteolysis around uncemented acetabular implants in THA.

Methods/design

A randomized, double-blind, placebo-controlled trial will be conducted. We will include 110 patients, 40–85 years of age, with a known osteolytic lesion around an uncemented acetabular component ≥7 years after the primary operation. The patients will be randomized in a 1:1 ratio to subcutaneous injections of 60 mg denosumab or placebo for a total of 6 doses with start on day one and every 6 months with last treatment at 30 months. The primary endpoint will be the change in volume of the osteolytic lesion at 3 years measured with three-dimensional computed tomography (3D-CT). Secondary endpoints include functional outcome scores, change in bone mineral density of the lumbar spine, serological markers of bone turnover and adverse events.

Discussion

In vitro results of both bisphosphonates and RANKL inhibitors have been promising, showing reduced osteolysis with treatment. This is, to our knowledge, the first clinical trial testing the efficacy of denosumab in reducing wear-induced osteolysis. The study is an academic, phase II trial from an independent center and is designed to demonstrate efficacy in reducing volume of osteolytic lesions around a total hip arthroplasty.

Trial registration

ClinicalTrials.gov (NCT02299817) 2014-11-20

Limited significance of screening computed tomography after cementless total hip arthroplasty with highly cross-linked polyethylene at 7-10 years of follow-up

OBJECTIVES

The purpose of this retrospective study is to report the incidence of osteolysis and evaluate the significance of screening computed tomography (CT) compared to plain radiography in detecting osteolysis after total hip arthroplasty with metal-on-highly cross-linked polyethylene bearings.

METHODS

We retrospectively reviewed 264 primary cementless total hip arthroplasties of 211 patients, 24 males, 187 females, who received postoperative screening CT scan in addition to radiography at postoperative 7-10 years (average 8.2 years). First-generation highly cross-linked polyethylene was used in all cases.

RESULTS

On the plain radiographs, no acetabular osteolysis (0%) and two cases of femoral osteolysis (0.8%) were found in the follow-up period. No osteolysis was newly found by screening CT scan.

CONCLUSIONS

Very low incidence of osteolysis after total hip arthroplasty with highly cross-linked polyethylene at postoperative 7-10 years was confirmed, and routine screening CT scan for detecting osteolysis in this setting was not supported from this study.

Clinical evaluation and surgical options in acetabular reconstruction: A literature review

The purpose of this paper is to review the clinical indications for acetabular reconstruction in patients with underlying peri-prosthetic segmental and cavitary defects, evaluate steps in pre-operative planning, and present the American Academy of Orthopaedic Surgeons (AAOS) and Paprosky classification systems to categorize acetabular defects. We also present a review of the current surgical techniques to reconstruct the acetabular socket which includes a cementless acetabular component with morselized bone, structural allograft, jumbo and oblong cups, reinforcement rings, bone cages, custom triflange acetabular constructs, and trabecular metal components.

Performance of Porous Tantalum vs. Titanium Cup in Total Hip Arthroplasty: Randomized Trial with Minimum 10-Year Follow-Up

Porous tantalum monoblock cups have been proposed to improve survivorship of cementless primary THA. However, there are few direct comparative trials to established implants such as porous-coated titanium cups. 113 patients were randomized into two groups according to the cup: a porous tantalum monoblock cup (TM) or a porous-coated titanium monoblock cup (control). At a mean of 12 years after THA, no implants migrated in both groups. Two TM patients (4%) and 13 control patients (33%) presented with radiolucency around the cup (P<0.001). In the control group, 1 cup (2%) was revised for aseptic loosening. At 12 years post-implantation, porous tantalum monoblock cups demonstrated 100% survivorship, and significantly less radiolucency as compared to porous-coated titanium monoblock cups.

[CT and MRI of hip arthroplasty]

Metal-induced artifacts impair image quality of computed tomography (CT) and magnetic resonance imaging (MRI) in patients with hip prostheses. Due to new developments in metal artifact reduction both methods can now be used for evaluation of a painful hip prosthesis. Iterative reconstruction algorithms and dual-energy scans are among the newer CT techniques for artifact reduction, while slice-encoding for metal artifact correction (SEMAC) and multi-acquisition variable-resonance image combination (MAVRIC) have introduced substantial improvements for MRI. Loosening of the hip prosthesis, osteolysis from small wear particles and pseudotumors in metal-on-metal prostheses are specific pathologies in patients with total hip arthroplasty. Other causes of painful hip prostheses are infections, fractures, tendinopathies, tendon ruptures, muscle and nerve alterations and heterotopic ossifications.

The 27 to 29-year outcomes of the PCA total hip arthroplasty in patients younger than 50 years old

We previously reported our six and 19.4-year results of arthroplasty with the PCA total hip prosthesis. We now report on the performance of this prosthesis at 27-29years. Eighty-eight consecutive primary THAs using a PCA total hip system were performed in 70 patients (mean age, 45.6±11.1years). The mean follow-up was 28.4years (27-29). The mean Harris hip score was 89 points at final follow-up. Thigh pain was reported in 22 hips (25%). The mean annual polyethylene wear was 0.182±0.03mm. There were 75 acetabular (85%) and 40 femoral (45%) osteolysis. The rate of survival after 28.4years as the end point of revision was 66% for the acetabular component and 90% for the femoral component.

The revision acetabulum – allograft and bone substitutes

A common situation presenting to the orthopaedic surgeon today is a worn acetabular liner with substantial acetabular and pelvic osteolysis. The surgeon has many options for dealing with osteolytic defects. These include allograft, calcium based substitutes, demineralised bone matrix, or combinations of these options with or without addition of platelet rich plasma. To date there are no clinical studies to determine the efficacy of using bone-stimulating materials in osteolytic defects at the time of revision surgery and there are surprisingly few studies demonstrating the clinical efficacy of these treatment options. Even when radiographs appear to demonstrate incorporation of graft material CT studies have shown that incorporation is incomplete. The surgeon, in choosing a graft material for a surgical procedure must take into account the efficacy, safety, cost and convenience of that material.

Cite this article: Bone Joint J 2014;96-B (11 Suppl A):70–2.

High survivorship with a titanium-encased alumina ceramic bearing for total hip arthroplasty

BACKGROUND

Although ceramic-on-ceramic bearings for total hip arthroplasty (THA) show promising results in terms of bearing-surface wear, fracture of the bearing, insertional chips, and squeaking remain a concern.

QUESTIONS/PURPOSES

Our primary objective of this report was to determine overall survivorship of a titanium-encased ceramic-on-ceramic bearing couple. Our secondary objectives were to evaluate for ceramic fracture, insertional chips, osteolysis, and device squeaking.

METHODS

Six surgeons at six institutions implanted 194 patients (209 hips) with an average age of 52 years with cementless hips and alumina ceramic bearings. One hundred thirty-seven patients (146 hips) have 10-year followup (70%). We determined Kaplan-Meier survivorship of the bearing surface and implant system and collected radiographic and clinical data to evaluate for osteolysis and squeaking.

RESULTS

Survivorship using revision for any reason as the end point was 97% at 10 years and survivorship end point bearing surface failure or aseptic loosening of 99%. There was one ceramic insert fracture (0.5%), there were no insertional chips, there was no visible osteolysis on AP and lateral radiographs, and there was a 1% patient-self-reported incidence of squeaking at the last clinical followup. Six hips underwent revision (3.7%).

CONCLUSIONS

Ceramic bearings for THA with a titanium-encased insert have high survivorship at 10 years followup and a fracture risk of 0.5%. We found at last followup on routine radiographs no evidence of osteolysis, and no patient has been revised for squeaking or has reported dissatisfaction with the clinical result because of noise. IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Characterization of progression of pelvic osteolysis after cementless total hip arthroplasty: computed tomographic study

A retrospective analysis of 63 primary total hip arthroplasty cases was done using repeated computed tomography scans to evaluate the pelvic osteolytic lesions in early stage. The progression rate of osteolysis of hips with small osteolytic volume less than 766.97 mm(3) in initial CT was 85.82 mm(3)/year, and that of hips with osteolysis more than 766.97 mm(3) was 456.3 mm(3)/year (P < 0.001). Younger patients less than 52 years old with good Harris Hip Scores (more than 80) frequently showed much faster progression in volume of osteolytic lesions. The rate of osteolysis was accelerated when the amount of osteolysis reached a certain threshold volume in active young patients in a cascade manner even in early stage.

Computed tomography vs. digital radiography assessment for detection of osteolysis in asymptomatic patients with uncemented cups: a proposal for a new classification system based on computer tomography

Digital radiographic images in the anterior-posterior and lateral view have been gold standard for evaluation of peri-acetabular osteolysis for patients with an uncemented hip replacement. We compared digital radiographic images and computer tomography in detection of peri-acetabular osteolysis and devised a classification system based on computer tomography. Digital radiographs were compared with computer tomography on 206 hips, with a mean follow up 10 years after surgery. The patients had no clinical signs of osteolysis and none were planned for revision surgery. On digital radiographs, 192 cases had no osteolysis and only 14 cases had osteolysis. When using computer tomography there were 184 cases showing small or large osteolysis and only 22 patients had no osteolysis. A classification system for peri-acetabular osteolysis is proposed based on computer tomography that is easy to use on standard follow up evaluation.

Split cord malformation types I and II: a personal series of 131 patients

PURPOSE

A personal series of 131 patients with split cord malformation (SCM) operated on is presented.

METHODS

Age, gender, symptoms and signs, radiological and operative findings, complications, associated anomalies, outcome, and pathological specimens were analyzed.

RESULTS

There were 88 girls (73 %) and 43 boys (27 %). The female predominance was slightly more remarkable in type I SCMs than in type II SCMs. The presenting symptoms can be summarized as skin lesions, spina bifida aperta, scoliosis or kyphoscoliosis, sphincter disturbance, foot deformities and weakness, and/or atrophy in the lower extremities. The ages of patients with neurological deficits and orthopedic deformities were significantly older than those without deficits (P = 0.030). The duration of symptoms was longer in the patients with neurological deficits and orthopedic deformities than that in those without deficits (P = 0.00095). In six patients, composite SCMs were present. Only one patient with a type II SCM did not have an associated spinal cord lesion. A type I SCM was more frequently encountered in patients with spina bifida (P < 0.0005). Transient postoperative complications were seen in 29 patients (22 %). There was no permanent complication. Retethered cord syndrome developed in five patients with a type I SCM.

CONCLUSIONS

The risk of neurological and orthopedic deficits increases with the age of the patient. The risk of permanent deficit after surgery is very low. The whole spine must be examined for additional lesions. All patients should be surgically treated when diagnosed, especially before the development of orthopedic and neurological manifestations, and all associated lesions should also be treated at the same session.

The use of ceramic-on-ceramic bearings in isolated revision of the acetabular component

The practice of removing a well-fixed cementless femoral component is associated with high morbidity. Ceramic bearing couples are low wearing and their use minimises the risk of subsequent further revision due to the production of wear debris. A total of 165 revision hip replacements were performed, in which a polyethylene-lined acetabular component was revised to a new acetabular component with a ceramic liner, while retaining the well-fixed femoral component. A titanium sleeve was placed over the used femoral trunnion, to which a ceramic head was added. There were 100 alumina and 65 Delta bearing couples inserted. The mean Harris hip score improved significantly from 71.3 (9.0 to 100.0) pre-operatively to 91.0 (41.0 to 100.0) at a mean follow up of 4.8 years (2.1 to 12.5) (p < 0.001). No patients reported squeaking of the hip. There were two fractures of the ceramic head, both in alumina bearings. No liners were seen to fracture. No fractures were observed in components made of Delta ceramic. At 8.3 years post-operatively the survival with any cause of failure as the endpoint was 96.6% (95% confidence interval (CI) 85.7 to 99.3) for the acetabular component and 94.0% (95% CI 82.1 to 98.4) for the femoral component. The technique of revising the acetabular component in the presence of a well-fixed femoral component with a ceramic head placed on a titanium sleeve over the used trunnion is a useful adjunct in revision hip practice. The use of Delta ceramic is recommended.

Limitations of conventional radiographs in the assessment of acetabular defects following total hip arthroplasty

BACKGROUND

Conventional radiographs are routinely used to evaluate acetabular bone loss as part of the follow-up in patients who undergo total hip arthroplasty (THA). The objective of this study was to examine the accuracy and specificity of conventional radiographs reviewed by arthroplasty surgeons in detecting acetabular bone loss in patients with prior THA.

METHODS

Using a cadaveric pelvic model, a defined percentage of bone was incrementally removed from the posterior acetabular column, followed by implantation of uncemented cups into both acetabula. Ten orthopedic arthroplasty surgeons, blinded to the defect sizes, assessed the percentage of bone defect using standard anteroposterior, Judet and oblique conventional radiographs.

RESULTS

Observers were unable to accurately grade bone defects using conventional radiographs. For defects less than 50%, observers reported on average a defect of 11%. Although observer estimates of defects 50% or more increased, these treatment-altering bone deficiencies remained grossly underestimated, with a sensitivity and specificity of 36.6% and 97.6%, respectively.

CONCLUSION

Conventional radiographs reviewed by experienced arthroplasty surgeons do not reliably detect small bone lesions (< 50%). Although more successful in detecting larger bone lesions, surgeons tend to underestimate actual bone loss. Computed tomography scanning may be indicated if accurate estimation of acetabular bone loss is required in patients who have undergone previous THA.

Ten- to 15-year clinical and radiographic results for a compression molded monoblock elliptical acetabular component

The aim of this study was to report the long-term results from a previously published midterm follow-up of a titanium monoblock, elliptical acetabular component. A total of 258 primary total hip arthroplasties (212 patients) with a monoblock, acetabular component were followed up for a mean period of 11.1 years (10-15). Average yearly wear rate was 0.08 mm/y (0.0009-0.32). Acetabular radiolucencies were present in 6 hips (2.4%); all were nonprogressive and present in acetabular zone I. Acetabular osteolysis was present in 5 patients (5 hips, 1.9%); all cups were stable. Four acetabular components were revised, 3 because of recurrent instability. No acetabular components were revised for polyethylene wear or dissociation, acetabular osteolysis, loosening, or deep infection. This monoblock design demonstrates excellent long-term survival and low rate of osteolysis.

Comparative analysis of periarticular osteolysis in modern total hip bearings: a minimum 5-year study

The best bearing to use in the young active population remains unknown because there are currently no evidence-based data to rely on. This article compares the prevalence of periacetabular osteolysis using computerized tomography in patients with metal-on-metal, ceramic-on-ceramic, and metal-on-cross-linked bearings at a minimum 5-year follow-up.

Measuring femoral lesions despite CT metal artefacts: a cadaveric study

OBJECTIVE

Computed tomography is the modality of choice for measuring osteolysis but suffers from metal-induced artefacts obscuring periprosthetic tissues. Previous papers on metal artefact reduction (MAR) show qualitative improvements, but their algorithms have not found acceptance for clinical applications. We investigated to what extent metal artefacts interfere with the segmentation of lesions adjacent to a metal femoral implant and whether metal artefact reduction improves the manual segmentation of such lesions.

MATERIALS AND METHODS

We manually created 27 periprosthetic lesions in 10 human cadaver femora. We filled the lesions with a fibrotic interface tissue substitute. Each femur was fitted with a polished tapered cobalt-chrome prosthesis and imaged twice--once with the metal, and once with a substitute resin prosthesis inserted. Metal-affected CTs were processed using standard back-projection as well as projection interpolation (PI) MAR. Two experienced users segmented all lesions and compared segmentation accuracy.

RESULTS

We achieved accurate delineation of periprosthetic lesions in the metal-free images. The presence of a metal implant led us to underestimate lesion volume and introduced geometrical errors in segmentation boundaries. Although PI MAR reduced streak artefacts, it led to greater underestimation of lesion volume and greater geometrical errors than without its application.

CONCLUSION

CT metal artefacts impair image segmentation. PI MAR can improve subjective image appearance but causes loss of detail and lower image contrast adjacent to prostheses. Our experiments showed that PI MAR is counterproductive for manual segmentation of periprosthetic lesions and should be used with care.

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.

Radiology of the resurfaced hip

Hip resurfacing arthroplasty is an increasingly common procedure for osteoarthritis. Conventional radiographs are used routinely for follow-up assessment, however they only provide limited information on the radiological outcome. Various complications have been reported in the scientific literature although not all are fully understood. In an effort to investigate problematic or failing hip resurfacings, various radiological methods have been utilized. These methods can be used to help make a diagnosis and guide management. This paper aims to review and illustrate the radiographic findings in the form of radiography, computerized tomography (CT), magnetic resonance imaging (MRI), and ultrasound of both normal and abnormal findings in hip resurfacing arthroplasty. However, imaging around a metal prosthesis with CT and MRI is particularly challenging and therefore the potential techniques used to overcome this are discussed.

Osteolysis propensity among bilateral total hip arthroplasty patients

Because some patients with high wear rates demonstrate extensive osteolysis whereas other patients with similarly high wear rates show little or no evidence of osteolysis, we hypothesized that both polyethylene wear and a patient-specific propensity mediate the development of osteolysis. We evaluated wear and osteolysis using computed tomography and radiographs among 46 patients who had undergone bilateral total hip arthroplasties (THAs). A radiographic patient-specific propensity for osteolysis associated with each THA was quantified by dividing the amount of osteolysis by the volumetric wear. Using a multivariate regression analysis to simultaneously consider the influence of polyethylene wear and patient propensity, we found that both factors are associated with the amount of osteolysis around a THA and that they appear to be of similar importance.

A monoblock porous tantalum acetabular cup has no osteolysis on CT at 10 years

BACKGROUND

Aseptic osteolysis has been the single most important factor limiting the longevity of a THA. A great deal of attention has been focused on the development of implants and materials that minimize the development of osteolysis. The monoblock porous tantalum acetabular cup was designed to minimize osteolysis, but whether it does so is unclear.

QUESTIONS/PURPOSES

We evaluated the incidence of osteolytic lesions after THA using a monoblock porous tantalum acetabular component.

METHODS

We retrospectively reviewed 51 patients who had a THA using a monoblock porous tantalum acetabular cup. At a minimum of 9.6 years postoperatively (average, 10.3 years; SD, 0.2 years; range, 9.6-10.8 years), a helical CT scan of the pelvis using a metal suppression protocol was obtained. This scan was evaluated for the presence of osteolysis.

RESULTS

We found no evidence of osteolysis on CT scan at an average of 10.3 years.

CONCLUSIONS

Osteolysis appears not to be a major problem at 10 years with this monoblock porous tantalum acetabular component, but longer term followup will be required to determine whether these findings persist.

LEVEL OF EVIDENCE

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

The incidence of acetabular osteolysis in young patients with conventional versus highly crosslinked polyethylene

BACKGROUND

Osteolysis is a major mode of hip implant failure. Previous literature has focused on the amount of polyethylene wear comparing highly crosslinked polyethylene (HXPLE) with conventional liners but has not clarified the relative incidence of osteolysis with these two liners.

QUESTIONS/PURPOSES

We determined (1) the incidence of osteolysis in HXLPE versus conventional polyethylene (CPE), (2) the ability to detect and evaluate the size of lytic lesions using radiographs compared with CT scans, (3) head penetration in hips without and with lysis, and (4) determined whether acetabular position, head size, and UCLA activity score contributed to lysis.

METHODS

We compared head penetration and osteolysis on plain radiographs and presence and volume of osteolysis on CT scans in 48 patients with HXLPE (mean, 46.5 years) and 50 patients with CPE (mean, 43.2 years). The minimum followup was 5 years (average, 7.2 years; range, 5.1-10.9 years),

RESULTS

Osteolysis was apparent on CT in a larger number of patients with CPE liners than HXLPE liners: 12 of 50 (24%) versus one of 48 (2%), respectively. We found no correlation between head penetration and volume of osteolytic lesions. Head penetration was greater in patients with osteolysis. Smaller head sizes were associated with greater wear and those with osteolysis had smaller head sizes; however, there was no difference in acetabular component position or UCLA activity in those with lysis compared with those without.

CONCLUSIONS

HXLPE diminished the incidence of osteolysis, but the lack of correlation between penetration and volume of osteolysis suggests other factors other than wear contribute to the development of osteolysis.

LEVEL OF EVIDENCE

Level III, therapeutic study. See 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.

Distribution of periacetabular osteolytic lesions varies according to component design

Using computed tomography, the volume, location, and number of osteolytic lesions were determined adjacent to 38 Harris-Galante 1 (HG-1) acetabular components fixed with screws and 19 porous-coated anatomic (PCA) acetabular components press-fitted without screws. The median implantation times were 16 and 15 years, respectively. The mean total lesion volumes were similar: 11.1 cm(3) (range, 0.7-49 cm(3)) and 9.8 cm(3) (range, 0.4-52 cm(3)), respectively, for hips with HG-1 and PCA components (P = .32). There was a significant difference in the proportion of rim-related, screw or screw hole-related, and combined lesions between the 2 component designs (P < .0001). HG-1 components had more screw and screw hole-related lesions, and PCA components had more rim-related lesions. Although there are concerns regarding screw and screw hole-associated osteolysis, these findings suggest that peripheral fixation may be well maintained in the long term with the use of multiple-hole acetabular components with screw fixation.

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.

Pelvic osteolysis relationship to radiographs and polyethylene wear

The relationship of radiographic pelvic osteolysis to computed tomographic (CT) volume and polyethylene wear remains controversial. We evaluated the sensitivity and specificity of radiographs in detecting osteolysis considering CT scan as the true value, in 118 hips with cementless cups. Correlation between osteolysis volume in CT, area of osteolysis in radiograph, and linear wear of polyethylene was assessed. The sensitivity and specificity of anteroposterior radiographs for detection of osteolysis was 57.6% and 92.9%, respectively. Addition of oblique radiographs increased the sensitivity to 64.4% without changing the specificity. The sensitivity increased to 92.8% for lesion more than 1000 mm(3). There was good correlation between 2-dimensional (2D) osteolytic area in radiograph and 3-dimensional (3D) volume (r = 0.74) in CT scan and linear wear of polyethylene showed good correlation with 3D CT volume (r = 0.62) and 2D area in radiograph (r = 0.60). Thus radiographs are useful to screen clinically significant osteolysis.

Computed tomography assessment of pelvic osteolysis and cup-lesion interface involvement with a press-fit porous-coated acetabular cup

We used computed tomography to investigate the 3-dimensional pattern of expansile osteolysis that occurs with a modular cementless acetabular component incorporating a central hole. We measured pelvic osteolysis volume and evaluated how much of the porous-coated surface area was involved with osteolytic defects. Among the 34 total hip arthroplasties we studied, osteolysis almost always originated from the dome hole and typically expanded inferiorly or superiorly without involving the anterior or posterior surfaces of the cup. Larger-volume lesions generally involved greater amounts of the cup surface area, but the cup-lesion interface involvement plateaued at 40% for radiographically stable cups without clinical complications. We hypothesize that the plateauing surface area involvement may explain the absence of cup loosening among these cases despite the presence of large osteolytic lesions.

Computer-assisted technique to delineate osteolytic lesions around the femoral component in total hip arthroplasty

There are currently no ideal quantitative measures assessing osteolysis after total joint arthroplasty. This study reports a new approach for quantification of osteolytic lesions on radiographs of total hip arthroplasty with the hypothesis that computer-assisted lesion quantification improves analysis precision over currently used qualitative visual assessment and thus improves progression monitoring. Duplicate exposure sets of anterior-posterior and frog-leg view radiographs of 15 volunteer total hip arthroplasty patients with radiographically evident periprosthetic lucencies were used. Two independent readers delineated the lesions using on-screen digital marker tools. Based on duplicate readings of the first exposure set only, intraoperator precision had a coefficient of variation (CV) from 1.5% to 3.4%, whereas interoperator precision CV ranged from 3.2% to 4.6%. The reproducibility of the x-ray technique as assessed by single readings of both sets of x-rays was CV 3.2% to 4.8%. The new technique compares favorably to precision of qualitative visual assessment and permits more accurate detection and quantitation of osteolytic lesions.

The unstable total hip replacement

BACKGROUND

Dislocation is one of the most common complications of total hip arthroplasty with a reported dislocation rate of 3.2%. Despite increased experience with hip replacement, the overall rate has not yet changed. The aim of this paper is to review the most recent literature published on this topic and indexed in Medline, in order to clarify the main risk factors, and to standardize a treatment protocol of such an important complication of prosthetic surgery.

MATERIALS AND METHODS

Medline database was searched using key words: "hip dislocation", "hip instability" from 1980-2007. Studies were eligible for review and included if they met the following criteria: (1) publication in English, (2) clinical trials (3) review papers.

RESULTS

The risk of first-time dislocation as a function of time after the surgery is not well understood. Most, but not all, series have demonstrated that the risk of dislocation is highest during the first few months after hip arthroplasty; however, first-time late dislocation can also occur many years after the procedure. Several risk factors were described, including the surgical approach, the diameter of the head, impingement, component malposition, insufficient abductor musculature. In addition, there are also many treatment options, such as long-term bracing after closed reduction, component reorientation, capsulorraphy, trochanteric advancement, increasing offset, exchange of the modular head and the polyethylene liner, insertion of constrained liner.

CONCLUSION

Preventing hip dislocation is obviously the best strategy. Surgeons must take into account patient and surgical risk factors. For patients at high risk for dislocation the surgeon should accurately restore leg length and femoral offset; the use of larger femoral heads, posterior transosseous repair of the capsulotendinous envelope if posterior approach is chosen or the use of a lateral approach should be considered. Proper patient education and postoperative care are very important.

Patient sensitivity to polyethylene particles with cemented total hip arthroplasty

To determine whether sensitivity to polyethylene particles varies among patients, we studied 25 patients who had undergone total hip arthroplasty. We used pelvic radiographs to measure annual polyethylene wear and the area of osteolysis. The ratio of the area of osteolysis to the volumetric polyethylene wear was defined as sensitivity index. Adherent cells from peripheral blood were cocultured with polyethylene particles, and the amount of bone-resorptive cytokines was measured. The amount of interleukin-6, but not of interleukin-1beta or tumor necrosis factor-alpha, released from adherent cells in the in vitro experiment correlated with the in vivo sensitivity indices. This technique appears capable of predicting the development of polyethylene-induced osteolysis, allowing surgeons to avoid using polyethylene as the bearing surface in patients at risk for osteolysis.

Incidence and volume of pelvic osteolysis at early follow-up with highly cross-linked and noncross-linked polyethylene

Highly cross-linked polyethylene has shown decreased wear rates as compared to conventional polyethylene. However, the impact of this decrease on the occurrence of osteolysis remains uncertain. Forty hips implanted with noncross-linked Enduron and 36 implanted with 5-Mrad cross-linked Marathon polyethylene had a computed tomography at a minimum of 5 years after arthroplasty. Polyethylene wear, osteolysis incidence, location, and volume were compared. The incidence of osteolysis was statistically greater for patients with noncross-linked Enduron (11/40, 28%) compared to patients with the moderately cross-linked Marathon (3/36, 8%; P = .04). The average lesion volume for hips with Enduron liners (7.5 +/- 6.7 cm(3)) was significantly greater than the average lesion volume for hips implanted with Marathon liners (1.2 +/- 0.1 cm(3), P = .01). Marathon cross-linked polyethylene has shown to have a decreased incidence and volume of pelvic osteolysis. Longer follow-up is necessary to determine if Marathon cross-linked polyethylene will continue to demonstrate the encouraging improved wear and osteolysis characteristics.

CT and MRI of hip arthroplasty

Plain films are the initial imaging method of choice for evaluation of hip arthroplasty. Recent advances in technology and imaging techniques have largely overcome the problems of beam hardening in computed tomography (CT) and magnetic susceptibility artefact in magnetic resonance imaging (MRI). CT and MRI have now become useful imaging techniques in the assessment of hip arthroplasty.

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.