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

Abstract

Femoral neck fractures are a major cause of morbidity and mortality in elderly humans. In addition to the age-related loss of cancellous bone, changes to the microstructure and morphology of the metaphyseal cortex may be a contributing factor in osteoporotic hip fractures. Recent investigations have identified a hypermineralised tissue on the neck of the femur and trochanteric region that increases in fractional area with advancing age in both males (Boyce & Bloebaum, 1993) and females (Vajda & Bloebaum, 1999). The aim of this study was to determine if the hypermineralised tissue previously observed on the proximal femur is calcified fibrocartilage. Regional variations in the fractional area of hypermineralised tissue, cortical bone, and porosity of the cortical bone along the neck of the femur and lesser trochanter were also quantified. Comparison of back scattered electron and light microscope images of the same area show that regions of hypermineralised tissue correlate with the regions of calcified fibrocartilage from tendon and capsular insertions. The hypermineralised tissue and calcified fibrocartilage had similar morphological features such as the interdigitations of the calcified 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 0n05) on the superior and inferior femoral neck in terms of the percentage area of hypermineralised calcified fibrocartilage, cortical bone, or cortical bone porosity. The lesser trochanter exhibited regional differences in the fractional area of hypermineralised calcified fibrocartilage (P l 0n007) and cortical bone (P l 0n007) but not porosity of the cortical bone (P 0n05). The effects of calcified fibrocartilage on femoral neck periosteal expansion, repair, and mechanics are unknown, but may play a role in osteoporotic fractures and intracapsular fracture healing.

Experimental confirmation of the sheep model for studying the role of calcified fibrocartilage in hip fractures and tendon attachments

“…This general structure has been shown to exist in numerous species, including human (Cooper and Misol, 1970;Benjamin et al, 1986;Evans et al, 1991;Shea et al, 2001b), rat Bland and Ashhurst, 1997;Benjamin et al, 2000), rabbit Clark and Stechschulte, 1998), dog (Clark and Stechschulte, 1998), and sheep (Clark and Stechschulte, 1998). However, this is the first investigation to compare the structure of the tendon insertions of the greater trochanter between different species.…”

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ABSTRACTResearch has shown that there is a dramatic increase in the fractional area of calcified fibrocartilage from tendon and capsular insertions on the human femoral neck Shea et al, 2001b). Additional information regarding the properties of the proximal femur's cortical shell, gained from the use of an animal model, may result in a better understanding of elderly hip fracture since the cortical shell is a significant contributor to the strength of the proximal femur.

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“…These changes include a decrease in cortical thickness, an increase in porosity, and an increase in the fractional area of a potentially brittle hypermineralized tissue (Boyce and Bloebaum, 1993;. A recent investigation by Shea et al (2001b) identified the hypermineralized tissue on the human femoral neck and trochanteric region as calcified fibrocartilage associated with tendon and capsular insertions. Despite the lack of concrete evidence associating calcified fibrocartilage with hip fractures, the tissue can comprise up to 60% of the cortical shell in some elderly individuals Shea et al, 2001b).…”

“…A recent investigation by Shea et al (2001b) identified the hypermineralized tissue on the human femoral neck and trochanteric region as calcified fibrocartilage associated with tendon and capsular insertions. Despite the lack of concrete evidence associating calcified fibrocartilage with hip fractures, the tissue can comprise up to 60% of the cortical shell in some elderly individuals Shea et al, 2001b). Additionally, finite element research and experimental evidence suggests that the cortical shell is a significant contributor to the strength of the proximal femur (Lotz et al, 1995;Cheung et al, 1997;Michelotti and Clark, 1999).…”

RETRACTED: The periosteum

“…Despite these studies there are some opposed observations claiming that the femoral neck periosteal covering exists. 8,34,98,112 Periosteal cellularity at the femoral neck is significantly lower than in the diaphyseal region even in young adults. Twenty percent of the femoral neck surface has cellular periosteum which suggests that anabolic osteogenic therapies may be effective in strengthening this clinically relevant site.…”