Microvascularization of the hypermineralized calcified fibrocartilage and cortical bone in the sheep proximal femur

Abstract

It is well known that the incidence of hip fractures is increasing as the population ages, and that vascularity is one of the most important characteristics for any tissue (the proximal femur being no exception). Additionally, calcified fibrocartilage from tendon and ligament insertions comprises a significant portion of the fractional area of the proximal femur's cortical shell. The goal of the present investigation was to quantify and compare the microvascularity of the cortical bone and calcified fibrocartilage of the proximal femur in a sheep model. There were no regional differences in the vascular density of the cortical bone. However, the calcified fibrocartilage from tendon and capsular insertions were determined to be avascular, and regions of the proximal femur with insertions lacked a vascularized periosteum. If a vessel was present in the calcified fibrocartilage, it was located within an isolated region of bone tissue or osteoid. Since blood vessels appear to be a significant contributor to the health and remodeling of mineralized tissue, it is hypothesized that the large areas of avascular calcified fibrocartilage present on the elderly femoral neck may predispose these regions to damage accumulation. Therefore future research should examine the role of the vascularity to the proximal femur in the mechanisms of numerous pathological conditions, such as avascular necrosis, osteopenia, and hip fractures.

Remodeling capacity of calcified fibrocartilage of the hip

“…This does not mean that the calcified fibrocartilage may not have some other currently unknown biological mechanism for remodeling and repairing microcracks that may accumulate. However, the data from this study, and the absence of blood supply (Shea et al, 2002b), suggest that the healing capacity of calcified fibrocartilage would be minimal. A limited remodeling capacity for calcified fibrocartilage has also been indicated in recent tendon healing studies (Leung et al, 2002;Weiler et al, 2002).…”

“…The cortical bone of the femoral neck and trochanteric regions has been shown to thin and become more porous with age (Boyce and Bloebaum, 1993;Vajda and Bloebaum, 1999), likely as a result of endosteal re-sorption and cortical bone remodeling. As the cortical bone thins, a larger proportion of the cortex shell along regions of the femoral neck and greater trochanter then consists of hypermineralized calcified fibrocartilage, which is known to be very friable (Shea et al, 2002b) and to have limited capacity to remodel and heal. As the volume fraction of this tissue increases with the decrease in viable cortical bone, the potential for calcified fibrocartilage to share more of the stresses and forces of the hip increases.…”

“…The regional distribution of calcified fibrocartilage and periosteum on the human femoral neck should also be examined to understand the healing capacity of the proximal femur. While there has been some controversy in the past as to the presence of a periosteum on the femoral neck (Sherman and Phemister, 1947;Frost, 1964Frost, , 1995Bagi et al, 1997), Shea et al (2002b) identified a well-vascularized periosteum on regions of the human femoral neck where there was not calcified fibrocartilage. The regional distribution and relative amounts of each tissue on the proximal femur are unknown, but almost certainly have an effect on the mechanics and healing capacity of the region and subsequently hip fracture.…”

“…Additionally, an increase in the fractional area of calcified fibrocartilage has been associated with an increase in the brittleness and decrease in ultimate strength of the cortical bone in the femoral neck (Shea, 2002). Furthermore, calcified firbrocartilage has been shown to be an avascular tissue (Shea et al, 2002b); thus, as the fractional area of calcified fibrocartilage increases with age, larger proportions of the femoral neck in the elderly are composed of this brittle avascular tissue rather than vascularized cortical bone.…”

Estrutura e ultraestrutura da junção miotendínea do músculo pterigóideo medial de ratos wistar com envelhecimento.

“…A fibrocartilagem calcificada das inserções tendíneas e capsulares dos colos femurais de ovelhas envelhecidas foi determinada avascular por Shea et al (2002), e nas regiões do fêmur proximal que possuíam inserções, o periósteo era avascular.…”