Femoroacetabular impingement and classification of the cam deformity: the reference interval in normal hips.

BACKGROUND AND PURPOSE: Most patients with femoroacetabular impingement (FAI) have a cam deformity, which may be quantified by measuring the alpha angle and anterior offset ratio (AOR). Knowledge of what constitutes a "normal" alpha angle and AOR is limited. We defined the reference intervals of these measurements from normal hips in the general population. PATIENTS AND METHODS: 157 individuals from the general population were reviewed clinically and radiographically. 74 individuals with clinical evidence of hip disease or radiographic evidence of osteoarthritis (OA) were excluded, leaving a study group of 83 individuals (mean age 46 (22-69) years, 44 females) with normal hips. The alpha angles and AORs were measured from cross-table lateral radiographs taken in 15 degrees internal rotation. A validation study consisting of a cadaver study and a measurement reliability study was also performed. RESULTS: The mean alpha angle was 48 degrees in men and 47 degrees in women. The mean AOR was 0.19, the same in men and women. Thus, sexes were combined to derive 95% confidence intervals for the population mean alpha angle (46-49 degrees ) and AOR (0.18-0.20). The 95% reference interval for the alpha angle was 32-62 degrees degrees, and for the AOR it was 0.14-0.24. The validation study confirmed that these measurements were resistant to a reasonable degree of variation in positioning and that the repeatability and reproducibility of the measurements was good. INTERPRETATION: These reference intervals indicate that clinically and radiographically normal hips may have alpha angles and AORs that have previously been considered "abnormal". The thresholds provided by this study will aid classification of individuals involved in longitudinal studies of FAI and OA, and may be of use to the practicing clinician in evaluating the young adult with hip pain.

Early failure of the Dual coat Cormet 2000 metal on metal acetabular component.

We report a 10% failure rate for aseptic loosening and overall revision rate of 15% at 5 years mean follow up in 190 patients using the Cormet 2000 Dual coat acetabular component. Between 2001 and 2004, the original Dual coat component was used in our region by 4 experienced arthroplasty surgeons. 142 were used with resurfacing heads. The average age was 54 and 99 were male. Revision for aseptic loosening was required in 20 cups (10%) at a mean interval of 23 months including five within 2 months. Persistent groin pain was seen in a further three patients who have declined further surgery. Failure of the backing of this implant to integrate reliably with bone has led to an unacceptably high early loosening rate of the original design which was phased out in 2003.