Bone Mineral “Quality”: Differing Characteristics of Calcified Microsphere Populations at the Osteoporotic and Osteoarthritic Femoral Articulation Front

Abstract

The mineral front consists of large populations of organically enshrouded calcified microspheres (filamentous clusters) about 1 micron in diameter and associated smaller numbers of variably dense nanospheres, 30 - 40 nm in diameter. The discrete objects persist and modulate in maturity, and may constitute a variable “qualitative” factor in the skeletal inorganic phase, exemplified by the biomechanically contrasting pathologies of osteoporosis (OP; fracture, low stress condition) and osteoarthritis (OA; non fracture, high stress condition). The aim was to compare the articulation front material for morphological and trace element diversity using fresh female femoral head discards (from Dewsbury District Hospital NHS Mid-Yorkshire Trust). These were prepared for histology of the cartilage/bone interface region by immersion in hydrazine hydrate to expose the anorganic mineral topography for microscopy and FEGSEM microanalysis. 1) Mineral microsphere morphology (compared to animals as arbitrary controls) suggested that calcified microspheres from OP (n = 19) tended to be small (0.5 - 0.7 microns), smooth and compacted; those from OA (n = 19) were large (0.5 - 4.0 microns), uneven and irregularly dispersed. Respective calcified nanospheres from OP were similarly smaller (30 - 50 nm) than those from OA (>100 nm). In subchondral bone a proportion of the filamentous microspheres had fused into a fine-textured phase in OP and a coarse-textured phase in OA. 2) Trace element analysis (compared to positive porcine Si and Mg and other peaks) suggested a diminution with mineral maturity, and also with age effecting OP and OA similarly, with minor differences detected between them. It was concluded that calcified objects constituting the inorganic phase vary regionally with age and in fracture and nonfracture, being diminished in size (not number) in weak OP and enlarged (compared to porcine control) in stronger OA, with Si or Mg “doping” diminishing with time, perhaps influencing their individual bioactivity and matrix dynamics.