INTRODUCTION:. Acetabular retroversion has been implicated as a risk factor for the development of early hip osteoarthritis. In clinical practice standard osseous signs such as the cross-over sign (COS) and the posterior wall sign (PWS) are widely used to establish the diagnosis of acetabular retroversion on plain radiographs. Despite standardized radiological evaluation protocols, an increased pelvic tilt can lead to a misdiagnosis of acetabular retroversion in AP radiographs and 2D MR or CT scans. Previous studies have shown that the elimination of observer bias using a standardized methodology based on 3D-CT models and the anterior pelvic plane (APP) for the assessment of COS and PWS results in greater diagnostic accuracy. Using this method a prevalence of 28% for COS and 24% for PWS has been found in a cohort of patients with symptoms indicative of FAI, however the prevalence of both signs in asymptomatic adults remains unknown. This study therefore sought to establish the prevalence of the COS and PWS in relation to the APP in an asymptomatic population using a reliable and accurate 3 D-CT based assessment. METHODS:. A large pool of consecutive CT scans of the pelvis undertaken in our department for conditions unrelated to disorders of the hip was available for analysis. Scans in subjects with a Harris hip score of less than 90 points were excluded leaving a sample of 100 asymptomatic subjects (200 hips) for this study. A previously established 3D analysis method designed to eliminate errors resulting from variations in the position and orientation of the pelvis during CT imaging was applied to determine in order to assess the prevalence of the COS and PWS in relation to the APP. Here, the acetabuli were defined as retroverted if either the COS, PWS or both were positive. RESULTS:. From the total of 200 hips a positive COS was identified in 24% (48/200) and a positive PWS was detected in 6.5% (13/200) relative to the APP using the CT data. A. In male adults a COS was observed in 25.4% (29/114) and a PWS in 10.5% (12/114). In female adults a COS were observed in 22.1% (19/86) and a PWS in 1.2% (1/86). DISCUSSION:. The high incidence of acetabular retroversion observed using an accurate 3D-CT based methodology shows that this anatomic configuration might not differ in frequency between asymptomatic individuals and patients with symptomatic FAI. Patients presenting with hip pain and evidence of FAI should therefore be subjected to strict diagnostic scrutiny, as the presence of a COS and/or PWS shows a poor correlation with the presence of symptomatic disease. In our collective of asymptomatic adults the COS showed a higher incidence than the PWS. Additionally a deficiency of the posterior acetabular wall was rare in asymptomatic adults compared to FAI patients. Therefore, the question whether an abnormal acetabular version does indeed lead to the development of osteoarthritis in all patients warrants further study. Although an association between osteoarthritis and femuro-acetabular impingement is believed to exist, long-term epidemiological studies are needed to establish the natural history of these anatomical configurations

Purpose. Diagnosis of acetabular retroversion is essential in femoroacetabular impingement (FAI), but its assessment from radiographs is complicated by pelvic tilt and the two-dimensional nature of plain films. We performed a study to validate the diagnostic accuracy of the crossover sign (COS) and the posterior wall sign (PWS) in identifying acetabular retroversion. Method. COS and PWS were evaluated from radiographs and computed tomography (CT) scans as the standard of reference in 50 hips of subjects with symptoms of FAI. A CT-based method using 3-D models was developed to measure the COS, PWS, true acetabular version and pelvic tilt relative to the anterior pelvic plane. The new CT-based method aimed to eliminate errors resulting from variations in the position and orientation of the pelvis during imaging. Results. A low level of agreement for COS and PWS was found between radiographs and CT scans. A positive COS strongly correlated with pelvic tilt. Conclusion. These results suggest that COS and PWS determined from anteroposterior (AP) radiographs are considerably limited by pelvic tilt and inherent limitations of radiographs. Their use as the sole basis for deciding whether or not surgical intervention is indicated seems questionable. NO DISCLOSURES

It has been suggested that metal ion levels are indicative of in vivo bearing performance of metal-on-metal hip replacements. A cobalt or Chromium level of 7μg/L or higher is proposed to be indicative of a bearing malfunction and the need for clinical intervention. Component design, size, acetabular orientation, patient gender and activity level have been suggested as factors leading to accelerated wear and elevated metal ions. The contact patch to rim (CPR) distance is a calculation that describes the distance from the point where a theoretical joint reaction force intersects the cup to the acetabular rim for a patient in standing position, dependent on the coverage, size, and orientation of the acetabular component. It has been suggested that CPR distance determines the hip joint susceptibility to edge loading, and the risk for increased wear and high ion levels (Langton et al JBJS Br 91: 2009). This study examined the effects of patient activity, gender, and CPR distance on serum metal ion concentrations in a series of patients treated with one type of metal on metal hip resurfacing arthroplasty (MMHRA) performed by one surgeon. 182 patients (73 females and 109 males)with a unilateral Conserve Plus (WMT, TN USA) MMHRA and had who had provided blood for metal ion analysis data from December 2000 to June 2011 were retrospectively studied. Only measurements made more than 12 months after surgery were included in order to exclude hips that had yet to reach steady-state wear. For patients with multiple draws, the most recent qualifying draw was used. Activity level was assessed by the UCLA activity score. The mean age was 51.5 years (20.0 to 77.5 years). The mean follow-up time for the last blood draw was 70 months (range, 12 to 165). Serum cobalt (CoS) and chromium (CrS) levels were analyzed using inductively coupled plasma mass spectrometry in a specialized trace element lab. Using acetabular abduction and anteversion measured by EBRA, component size, and reported coverage angle of the acetabular component, the CPR distance was calculated as previously described. Multiple logistic regression was performed to identify significant relationships between high metal ion levels (7 μg/L or greater) and gender, activity and CPR distance. The median CoS level for the entire cohort was 1.13 μg/L (range, 0.15 to 175.30), and the median CrS level was 1.49 μg/L (range, 0.06 to 88.70). The average CPR distance was 13.8 mm (range, 3.2 to 22.1). There was a significant association between low CPR values and CoS and CrS. There was a 37-fold increase in the risk of CoS >7μg/L (p=0.005) and 11-fold increase in the risk of CrS > 7μg/L (p=0.003) when CPR distance was 10 mm or less. No associations were shown for gender and UCLA activity scores. CPR distance was found to be a reliable predictor of ion levels > 7μg/L and appears to be a useful indicator to evaluate the multi-factorial process of edge-loading and wear. Patients with a low CPR distance should be monitored for increased metal ion levels

Aims

Bone demonstrates good healing capacity, with a variety of strategies being utilized to enhance this healing. One potential strategy that has been suggested is the use of stem cells to accelerate healing.