Histomorphometric and osteocytic characteristics of cortical bone in male subtrochanteric femoral shaft

Abstract

The histomorphometric properties of the subtrochanteric femoral region have rarely been investigated. The aim of this study was to investigate the age-associated variations and regional differences of histomorphometric and osteocytic properties in the cortical bone of the subtrochanteric femoral shaft, and the association between osteocytic and histological cortical bone parameters. Undecalcified histological sections of the subtrochanteric femoral shaft were obtained from cadavers (n = 20, aged 18-82 years, males). They were cut and stained using modified Masson-Goldner stain. Histomorphometric parameters of cortical bone were analysed with ×50 and ×100 magnification after identifying cortical bone boundaries using our previously validated method. Within cortical bone areas, only complete osteons with typical concentric lamellae and cement line were selected and measured. Osteocytic parameters of cortical bone were analyzed under phase contrast microscopy and epifluorescence within microscopic fields (0.55 mm² for each). The cortical widths of the medial and lateral quadrants were significantly higher than other quadrants (P < 0.01). Osteonal area per cortical bone area was lower and cortical porosities were higher in the posterior quadrant than in the other quadrants (P < 0.05). Osteocyte lacunar number per cortical bone area was found higher in the young subjects (≤ 50 years) than in the older ones (> 50 years) both before and after adjustments for body height and weight (P < 0.05). Moreover, significant but low correlations were found between the cortical bone and osteocytic parameters (0.20 ≤ R² ≤ 0.35, P < 0.05). It can be concluded that in healthy males, the cortical histomorphometric parameters differ between the anatomical regions of the subtrochanteric femoral shaft, and are correlated with the osteocytic parameters from the same site. These findings may be of use when discussing mechanisms that predispose patients to decreasing bone strength.

Keywords: bone histomorphometry; cortical bone; osteocyte; regional difference; subtrochanteric femoral shaft.

Figure 1

Cross‐sectional femoral shaft (thickness: 5–10 mm) extracted from the subtrochanteric region (between lesser trochanter and 5 cm distally) of proximal femur were indicated with dashed lines and a minor cut was circled in red on the medial bone edge. The entire cross‐sectional femoral shaft was scanned to acquire a complete histological image (×50), which was separated into two independent zones: the absolute cortex area and the endocortical bone area. The former showed four anatomical quadrants: medial, posterior, lateral and anterior shaft. In each of them, 10 regions of interests (ROI: 1.51 mm² for each) are indicated by solid yellow boxes.

Figure 2

Each microscopic field (0.55 mm² for each) was selected randomly, capturing two separate image types, phase contrast (A) and fluorescent (B) images, respectively. Quantification of total osteocyte lacunae and osteocytes per cortical bone area were semi‐automatically performed. 1: Haversian canals, 2: artificial cracks.

Figure 3

Mean values of cortical width in four anatomical quadrants of the subtrochanteric femoral shaft (n = 20). The error bars indicate the standard deviation of the mean (SD). The cortical widths in the medial and lateral quadrants were significantly higher than those detected in the anterior and posterior quadrants (P < 0.01).

Figure 4

The ×100 magnification cortical parameters of the subtrochanteric femoral shaft showed significant differences in pairwise comparisons between anatomical quadrants (P < 0.05). The error bars indicated the standard error of the mean (SEM).

Figure 5

Cortex of the subtrochanteric femoral shaft shows the variation of osteocyte lacunar number per cortical bone area in each age group (young: A, ≤ 50 years; old: B, > 50 years). Osteocyte lacunae (circled in red) was higher in the group of young subjects (A) than in the group of old subjects (B). 1: Haversian canals, 2: cortical pores. M: medial; P: posterior; L: lateral; A: anterior.