The innominate tubercle of the femur is a consistent surgical landmark and shows no variation between sex and side: An osteological study.

INTRODUCTION: During direct anterior approach hip arthroplasty, the innominate tubercle (IT) of the femur is used as a reference point for femoral neck osteotomy. A recent study found that IT dimensions are unaffected by femoral length, neck-shaft angle, and neck length. This study investigated the position of the tubercle relative to femoral side, sex and femoral neck dimensions. MATERIALS AND METHODS: One hundred and ninety femora (95 pairs, complete with biographical data) from St. Bride's Church, London, were photographed with the apex of the tubercle marked. Using imaging software, axes were superimposed onto the image, allowing the X and Y co-ordinates of the tubercle apex to be derived. Statistical analysis was carried out. RESULTS: The position of the tubercle did not vary significantly and did not correlate with femoral side (p > .05). P values for variation of the X and Y coordinates were 0.351 and 0.996 in left and right femora, respectively. The tubercle position did not vary significantly with sex (p > .05). p Values for variation of the X and Y coordinates were 0.254 and 0.634 in males and females, respectively. There was little variation between tubercle position and femoral neck dimensions: correlation coefficient -0.20 (x coordinate) and -0.12 (y coordinate). CONCLUSIONS: The data showed that the position of the IT did not vary significantly with either sex or side and that, therefore, the tubercle can be considered a reliable surgical landmark during arthroplasty surgery.

Use of high resolution dual-energy x-ray absorptiometry-region free analysis (DXA-RFA) to detect local periprosthetic bone remodeling events.

Dual-energy x-ray absorptiometry (DXA) is the gold standard method for measuring periprosthetic bone remodeling, but relies on a region of interest (ROI) analysis approach. While this addresses issues of anatomic variability, it is insensitive to bone remodeling events at the sub-ROI level. We have validated a high-spatial resolution tool, termed DXA-region free analysis (DXA-RFA) that uses advanced image processing approaches to allow quantitation of bone mineral density (BMD) at the individual pixel (data-point) level. Here we compared the resolution of bone remodeling measurements made around a stemless femoral prosthesis in 18 subjects over 24 months using ROI-based analysis versus that made using DXA-RFA. Using the ROI approach the regional pattern of BMD change varied by region, with greatest loss in ROI5 (20%, p < 0.001), and largest gain in ROI4 (6%, p < 0.05). Analysis using DXA-RFA showed a focal zone of increased BMD localized to the prosthesis-bone interface (30-40%, p < 0.001) that was not resolved using conventional DXA analysis. The 20% bone loss observed in ROI5 with conventional DXA was resolved to a focal area adjacent to the cut surface of the infero-medial femoral neck (up to 40%, p < 0.0001). DXA-RFA enables high resolution analysis of DXA datasets without the limitations incurred using ROI-based approaches.

Biomechanics of short hip endoprostheses--the risk of bone failure increases with decreasing implant size.

BACKGROUND: Short uncemented metaphyseally anchored femoral endoprostheses are becoming popular and are proposed to be less invasive than longer conventional implants. However, it is proposed here that shortening femoral endoprostheses can increase the risk of periprosthestic fracture. METHODS: A simple analytical model of a femoral hip implant was developed to estimate the risk of bone overload for varying implant size, implantation geometry, implantation force and bone quality. The load capacity of a particular short implant design in poor quality cadaveric bone specimens was also measured experimentally, to validate the model. FINDINGS: The model demonstrated a high risk of bone overload for a short endoprosthesis in poor quality bone. The experimental results and a clinical example of failure, to which the model was applied, supported this finding. Bone stresses increased with decreasing implant length and diameter, varus implantation, incomplete seating and high implantation forces, approaching the strength of good quality bone in extreme cases. INTERPRETATION: Correct implantation and patient selection is essential for short femoral endoprostheses.