Evidence of a hypermineralised calcified fibrocartilage on the human femoral neck and lesser trochanter

Femoral neck fractures are a major cause of morbidity and mortality in elde rly humans. In addition to the age-related loss of cancellous bone, changes to the microstructure and morphology of the metaphyseal cortex may be a co ntributing factor in osteoporotic hip fractures. Recent investigations have identified a hypermineralised tissue on the neck of the femur and trochant eric region that increases in fractional area with advancing age in both ma les (Boyce & Bloebaum, 1993) and females (Vajda & Bloebaum, 1999). The aim of this study was to determine if the hypermineralised tissue previously ob served on the proximal femur is calcified fibrocartilage. Regional variatio ns in the fractional area of hypermineralised tissue, cortical bone, and po rosity of the cortical bone along the neck of the femur and lesser trochant er were also quantified. Comparison of back scattered electron and light mi croscope images of the same area show that regions of hypermineralised tiss ue correlate with the regions of calcified fibrocartilage from tendon and c apsular insertions. The hypermineralised tissue and calcified fibrocartilag e had similar morphological features such as the interdigitations of the ca lcified fibrocartilage into the bone, lacunar spaces, and distinctly shaped pores adjacent to the 2 tissues. Regions of the neck that did not contain insertions were covered with periosteum. There were no regional differences (P > 0.05) on the superior and inferior femoral neck in terms of the perce ntage area of hypermineralised calcified fibrocartilage, cortical bone, or cortical bone porosity. The lesser trochanter exhibited regional difference s in the fractional area of hypermineralised calcified fibrocartilage (P = 0.007) and cortical bone (P = 0.007) but not porosity of the cortical bone (P > 0.05). The effects of calcified fibrocartilage on femoral neck periost eal expansion, repair, and mechanics are unknown, but may play a role in os teoporotic fractures and intracapsular fracture healing.