A novel mechanism for induction of increased cortical porosity in cases ofintracapsular hip fracture

It has been suggested that, in hip fracture, the cortex on the inferoanteri or (IA) to superoposterior (SP) axis is thinned and shows increased porosit y. This is dependent on the presence of giant canals (i.e., diameter > 385 mu m), which are related to clusters of remodeling osteons. To investigate further the relationship between remodeling and bone loss, osteonal diamete r (On.Dm), wall thickness (W.Th), osteoid width (O.Wi), and extent (OS) wer e measured in femoral neck biopsies from 12 female intracapsular hip fractu re cases and 11 age- and gender-matched controls. Over 83% of giant canals were "composite" osteonal systems in which a single canal was surrounded by multiple packets of osteonal bone. Among smaller canals, over 80% of syste ms had a canal encircled by a single cement line containing one packet of b one ("simple"), Composites were nearly twice as prevalent in fractures (fra cture cases 9.8 +/- 0.7/25 mm(2), controls 5.3 +/- 0.4/25 mm(2), p < 0.0001 ), and were dependent (R-2 = 0.52) on femoral neck region (p = 0.0008) and the regional distribution of clusters of remodeling osteons (p = 0.0045). B oth the inferior (I) and anterior (A) regions had an elevated number of com posites (I: 263% of control values, p = 0.0054; A: 202% of control values, p = 0.0092). On.Dm was similar in fracture cases and controls (simple: frac ture cases 183 +/- 3 mu m, controls 191 +/- 1 mu m; composites: fracture ca ses 446 +/- 13 mu m, controls 460 +/- 13 mu m). W.Th in simples was similar in fracture cases and controls (fracture cases 51 +/- 0.8 mu m, controls 4 9 +/- 0.7 mu m), hut composites had significantly (p < 0.0001) thinner wall s, with the reduction in fracture cases (31%) being twice that of controls (12%, p < 0.0001). There were no differences in O.Wi. It was unusual for os teoid to fully surround the composite canal surface; OS was 38% lower in co mposite than simple canals (p < 0.0001), This study illdicates that, in the femoral neck cortex, the principal remodeling deficit in hip fracture Is s pecific to composite osteons. Hip fracture cases had zonal increases in com posite osteon density with reduced bone formation, The data suggest that ge neration of composite osteons is a plausible mechanism leading to increasin g porosity and trabecularization of the cortex, thus weakening the cortex i n regions maximally loaded on fall impart. (C) 2000 by Elsevier Science Inc . All rights reserved.