Avascular necrosis associated with fracture of the femoral neck after hip resurfacing: histological assessment of femoral bone from retrieval specimens.

The cause of fracture of the femoral neck after hip resurfacing is poorly understood. In order to evaluate the role of avascular necrosis we compared 19 femoral heads retrieved at revision for fracture of the femoral neck and 13 retrieved for other reasons. We developed a new technique of assessing avascular necrosis in the femoral head by determining the percentage of empty osteocyte lacunae present. Femoral heads retrieved as controls at total hip replacement for osteoarthritis and avascular necrosis had 9% (sd 4; n = 13) and 85% (sd 5; n = 10, p < 0.001) empty lacunae, respectively. In the fracture group the percentage of empty lacunae was 71% (sd 22); in the other group it was 21% (sd 13). The differences between the groups were highly significant (p < 0.001). We conclude that fracture after resurfacing of the hip is associated with a significantly greater percentage of empty osteocyte lacunae within the trabecular bone. This indicates established avascular necrosis and suggests that damage to the blood supply at the time of surgery is a potent risk factor for fracture of the femoral neck after hip resurfacing.

The five-year results of the Birmingham Hip Resurfacing arthroplasty: an independent series.

Few independent studies have reported the outcome of resurfacing arthroplasty of the hip. The aim of this study was to report the five-year clinical outcome and seven-year survival of an independent series. A total of 610 Birmingham Hip Resurfacing arthroplasties were performed in 532 patients with a mean age of 51.8 years (16.5 to 81.6). They were followed for between two and eight years; 107 patients (120 hips) had been followed up for more than five years. Two patients were lost to follow-up. At a minimum of five years' follow-up, 79 of 85 hips (93%) had an excellent or good outcome according to the Harris hip score. The mean Oxford hip score was 16.1 points (sd 7.7) and the mean University of California Los Angeles activity score was 6.6 points (sd 1.9). There were no patients with definite radiological evidence of loosening or of narrowing of the femoral neck exceeding 10% of its width. There were 23 revisions (3.8%), giving an overall survival of 95% (95% confidence interval 85.3 to 99.2) at seven years. Fractured neck of femur in 12 hips was the most common indication for revision, followed by aseptic loosening in four. In three hips (three patients) (0.5%), failure was possibly related to metal debris. Considering that these patients are young and active these results are good, and support the use of resurfacing. Further study is needed to address the early failures, particularly those related to fracture and metal debris.

The effect of hip resurfacing on oxygen concentration in the femoral head.

We inserted an electrode up the femoral neck into the femoral head of ten patients undergoing a metal-on-metal hip resurfacing arthroplasty through a posterior surgical approach and measured the oxygen concentration during the operation. In every patient the blood flow was compromised during surgery, but the extent varied. In three patients, the oxygen concentration was zero at the end of the procedure. The surgical approach caused a mean 60% drop (p < 0.005) in oxygen concentration while component insertion led to a further 20% drop (p < 0.04). The oxygen concentration did not improve significantly on wound closure. This study demonstrates that during hip resurfacing arthroplasty, patients experience some compromise to their femoral head blood supply and some have complete disruption.

Lateral ulnar collateral ligament of the elbow: optimization of evaluation with two-dimensional MR imaging.

PURPOSE: To compare, in a cadaveric model, magnetic resonance (MR) imaging techniques with differing contrast and spatial resolution properties in the evaluation of disruption of the lateral ulnar collateral ligament (LUCL) at the elbow. MATERIALS AND METHODS: LUCL tears were surgically created in eight of 28 cadaveric elbow specimens. All specimens underwent 1.5-T MR imaging with the following pulse sequences: T1-weighted spin echo (SE), intermediate-weighted fast SE, fat-suppressed T2-weighted fast SE, gradient-recalled echo (GRE) with high spatial resolution, intermediate-weighted fast SE with high spatial resolution, and fat-suppressed T1-weighted SE with intraarticular administration of gadopentetate dimeglumine (MR arthrography). All images were obtained in the oblique coronal plane. Two radiologists independently graded the LUCL with separate and side-by-side assessment. RESULTS: Areas under the receiver operating characteristic curve were as follows for readers A and B, respectively: T1-weighted SE imaging, 0.64 and 0.62; intermediate-weighted fast SE imaging, 0.87 and 0.67; T2-weighted fast SE imaging, 0.68 and 0.69; GRE imaging, 0.56 and 0.68; MR arthrography, 0.84 and 0.85; and intermediate-weighted imaging with high spatial resolution, 0.92 and 0.88. Interobserver reliability was poor with T1-weighted SE imaging (kappa = 0.13) and GRE imaging (kappa = 0.18), fair with T2-weighted fast SE imaging (kappa = 0.36), and moderate with MR arthrography (kappa = 0.46), intermediate-weighted fast SE imaging (kappa = 0.55), and intermediate-weighted imaging with high spatial resolution (kappa = 0.59). CONCLUSION: Intermediate-weighted imaging with high spatial resolution and MR arthrography showed the greatest overall ability to enable the diagnosis of LUCL tears.

Noncontrast MR imaging and MR arthrography of the ulnar collateral ligament of the elbow: prospective evaluation of two-dimensional pulse sequences for detection of complete tears.

OBJECTIVE: To compare MR imaging techniques with differing contrast and spatial resolution for evaluation of complete disruption of the ulnar collateral ligament (UCL) anterior bundle in a cadaveric elbow model. DESIGN: Complete UCL tears were surgically created at the typical location for clinical tears in eight of 28 fresh frozen cadaveric elbow specimens. All specimens underwent 1.5 T MR imaging in the oblique coronal plane, using an extremity coil. The sequences employed were: T1-weighted spin echo (T1 SE), proton density-weighted (PD) fast spin echo (FSE), fat-suppressed T2-weighted FSE (T2 FSE), gradient recalled echo (GRE) with a high matrix, PD FSE with a high matrix (HRPD), and fat suppressed T1-weighted SE with intra-articular gadolinium (MRAr). Two radiologists independently graded the UCL with separate and side-by-side assessments. RESULTS: Sensitivity/specificity pairs were as follows for reader A and reader B, respectively: T1 SE: 0.25/0.95, 0.50/0.95; PD FSE: 0.38/1.00, 0.25/1.00; T2 FSE: 0.50/0.95, 0.63/0.95; GRE: 0.63/0.85, 0.63/0.60; MRAr: 0.88/1.00, 1.00/0.80; HRPD: 0.50/1.00, 0.88/0.80. Kappa statistics for measuring interobserver reliability for each sequence were poor under T1 SE (-0.13) and GRE (0.19), moderate under HRPD (0.41) and T2 FSE (0.44) and good under MRAr (0.62) and PD FSE (0.78). For both readers, the rating for overall image quality was highest for HRPD, and the rating for UCL lesion conspicuity was the highest for MRAr. CONCLUSIONS: Of the MR imaging pulse sequences tested, MRAr showed the greatest ability to identify complete ligamentous injuries with good agreement between readers and had the highest subjective preference for lesion conspicuity. However, HRPD had the least interobserver variability and the highest subjective preference for overall image quality.