Femoral neck fractures complicating metal-on-metal resurfaced hips: a report of 2 cases

A displaced acetabular component causing femoral neck notching following hip resurfacing

We describe the case of a patient who developed a notch on the femoral neck following a hip resurfacing operation as a result of a displaced acetabular component. The acetabular cup displaced in the coronal plane and impinged on the femoral neck leading to a large notch in the inferior femoral neck.

Hip resurfacing femoral neck fracture influenced by valgus placement

Femoral neck fracture is the most common short-term concern after hip resurfacing arthroplasty. Currently, there is little basis to decide between neutral and valgus placement. We loaded 10 notched cadaveric femur pairs to failure; one side was implanted at 0 degrees relative to the femoral neck and the other at 10 degrees valgus. All 20 were dual-energy X-ray absorptiometry-scanned. Failure load correlated with bone mineral density. Valgus placement increased the fracture load by an average of 28% over neutral for specimens with normal bone mineral density but had no effect on fracture load in specimens with low bone mineral density. For specimens with normal bone mineral density (typical of patients undergoing resurfacing arthroplasty), neutral-valgus placement had a greater effect than bone mineral density, explaining 54% of the fracture load variance. Component placement greater than 10 degrees valgus is likely undesirable because this can lead to an increase in component size and a greater likelihood of notching. To reduce fracture risk, we recommend placing the femoral component in valgus and selecting patients with higher bone mineral density.

Changes in femur stress after hip resurfacing arthroplasty: response to physiological loads

BACKGROUND

Hip resurfacing arthroplasty is being increasingly considered as an alternative to total hip arthroplasty in young, active patients. Hip resurfacing arthroplasty is reported to preserve the normal joint mechanics. However, there is concern, in the short term, due to frequent occurrence of femoral neck fractures.

METHODS

We evaluated changes in femoral mechanics after hip resurfacing arthroplasty. We used an experimentally validated, distributed material finite element model of a cadaveric femur before and after hip resurfacing arthroplasty. Bone stiffness and strength values representing normal, elderly and osteoporotic bone were used. For a physiological load case, bone strains were compared with literature values for total hip arthroplasty and a risk of fracture scalar calculated.

FINDINGS

The changes in peak stresses after hip resurfacing arthroplasty were low in relation to the failure strength of bone and the fracture risk was low. The intact and implanted finite element models showed bone strains after hip resurfacing arthroplasty were closer to the intact condition than after total hip arthroplasty.

INTERPRETATION

The bone stresses predicted after resurfacing in both the normal and aged femoral neck were not sufficient to be a potential cause of fracture.

Hip resurfacing: a technology reborn

In recent years there has been a resurgence of interest in the concept of hip resurfacing. Much of this interest has stemmed from the work of McMinn in the West Midlands. Hip resurfacing is now emerging as a viable alternative to conventional hip replacement. In this article, we discuss the conceptual advantages offered by hip resurfacing and review the early clinical results and the ongoing clinical concerns regarding this technology.

Hip resurfacing: why does it fail? Early results and critical analysis of our first 60 cases

Resurfacing replacement represents the most conservative solution available for total arthroplasty of the hip. However, despite the excellent results reported by highly experienced surgeons, a small but not insignificant body of literature has been published on the more controversial aspects of this approach, mainly those related to the biological and mechanical vulnerability of the retained epiphysis. We report here our evaluation of most of the variables inherent to this procedure (surgical exposure, implant design, technical steps). Based on our results, we conclude that the short-term outcome is strongly related to the surgical approach and the relationship between implant design and cementing technique. Even if posterior approaches are currently widely accepted for resurfacing replacement, the ability to preserve the medial circumflex artery has been questioned, and an alternative exposure has been proposed with good results (antero-lateral, lateral and digastric trochanteric osteotomy). Moreover, a minimally invasive posterior approach could increase the risks of vascular damage. Alternatively, inner implant geometry could affect the distribution of cement over the epiphysis when other variables (direct or indirect cementing technique, viscosity) are not properly selected.

Stepwise introduction of a bone-conserving osseointegrated hip arthroplasty using RSA and a randomized study: II. Clinical proof of concept--40 patients followed for 2 years

BACKGROUND

We have developed a bone-conserving commercially pure titanium hip replacement system using osseointegration principles: a metaphyseal loading proximal femoral component affixing into the retained neck and metaphysis only, leaving the femoral canal untouched. The acetabular cup closely fits a dual-geometry cavity, avoiding stress protection at the dome.

PATIENTS AND METHODS

After extensive laboratory and clinical pilot trial investigations, the surface-engineered implants were submitted to a prospective randomized controlled clinical trial involving 40 patients (40 hips), in which they were compared to the cemented Spectron femoral component and cementless Trilogy cup as control implant. The following clinical measures were used to monitor progress at regular intervals for the first 2 postoperative years: radiostereometric analysis (RSA), Harris Hip Score, pain score, WOMAC, and SF-36.

RESULTS

After 2 years of follow-up, no statistically significant differences were seen between the groups concerning rotation or translation along the cardinal axes. The patients receiving the Gothenburg osseointegrated titanium (GOT) system had significantly higher Harris Hip Score at 6 months, suggesting more rapid recovery. WOMAC, SF-36 and pain analysis were similar for the first 2 postoperative years.

INTERPRETATION

Our RSA data suggest that osseointegration was achieved for all patients receiving the GOT hip system. This bone-conserving prosthesis may provide a good alternative, especially for young and active patients.