Most patients presenting with loss of hip motion secondary to FAI have a combination of cam and pincer morphology. In this study, we present a composite index for predicting joint ROM based on anatomic parameters derived from both the femur and acetabulaum using a single reformatted CT slice.

Computer models of the hip joint were reconstructed from CT scans of 31 patients with mixed-type FAI (Average alpha angle: 73.6±11.1°, average LCE: 38.9±7.2°). The internal rotation of the hip at impingement was measured at 90° flexion using custom software. With the joint in neutral, a single slice perpendicular to the acetabular rim was taken at the 2 o'clock position. A set of 11 femoral and acetabular parameters measured from this slice were correlated with hip ROM using stepwise logistic regression.

Three anatomic parameters provided significant discrimination of cases impinging at <15 and >15 degrees IR: femoral anteversion (28%, p=0.026), the arc of anterior femoral head sphericity (10%, p=0.040), and the LCE in the 2 o'clock plane (10%, p=0.048). This led to the following definition of the Impingement Index: 0.16*(fem version) +0.11*(ant arc)−0.17*(LCE) which correctly classified 82% of cases investigated. None of the traditional parameters (e.g. alpha angle) were significantly correlated with ROM.

Our study has identified alternative morphologic parameters that could act as strong predictors of FAI in preoperative assessments. Using this information, each patient's individual risk of impingement may be estimated, regardless of the relative contributions of deformities of the femur and the acetabulum.

My experience with Birmingham Hip Resurfacing began in July 2000 and continues to this day for selected cases including OA, AVN, CDH and also following old fracture deformity and Femoral/Pelvic osteotomy. Early on, the criteria for patient selection expanded with increasing experience and positive acceptance by patients but then moderated as adverse reports including those from our National Joint Replacement Registry suggested a need for caution with Surface Replacement.

Over 10 years, (July 2000 — July 2010), a personal series of 243 BHRs were followed (169 male — 74 female) with only one return to theatre in that time (4 days post op. to revise a poorly seated acetabular cup in a dysplastic socket). There were no femoral neck fractures in that 10 year period but 3 femoral cap/stem lucencies were known (2 female-1 male) with insignificant symptoms to require revision. The complete 10 year series of cases were then matched in the Australian National Joint Replacement Registry. No other revisions were identified by the Registry for all 243 cases.

Soon after completing this encouraging outcome study however 3 revision procedures have been necessary (2 for sudden late head/neck failure including one of the three with known cap/stem lucencies and one for suspected pseudotumour/ALVAL). One healing stress fracture of the femoral neck and another further cap/stem loosening have also presented recently but with little in the way of symptoms at this stage. Surprisingly, there is little indication which case is likely to present with problems even in the presence of many cases done earlier where one would be cautious now to use a BHR but which have ongoing good outcomes. (e.g., AVN or the elderly osteoporotic patient).

My journey therefore with Birmingham Hip Resurfacing over that first 10 years has been very positive and I believe it retains an important place for the younger patient with good bone quality. However it has become only recently apparent in my series of 243 cases that late onset unpredictable problems can arise which is likely to further narrow my selection criteria for this procedure. The likely outcome will be that it will have a more limited place in my joint replacement practice despite the very positive early experience.

Introduction

The feature of disc degeneration most closely associated with pain is a large fissure in the annulus fibrosus. Nerves and blood vessels are excluded from normal discs by high matrix stresses and by high proteoglycan (PG) content. However, they appear to grow into annulus fissures in surgically-removed degenerated discs. We hypothesize that anulus fissures provide a micro-environment that is mechanically and chemically conducive to the in-growth of nerves and blood vessels.

Purpose of the study

In a recent study, O'Leary et al. [2005] reported their observations on the patterns of Charité disc prosthesis motion under physiologic loads. The purpose of this study was to investigate whether the motion patterns observed in the in vitro model are replicated in clinical practice.