Spatial clustering of remodeling osteons in the femoral neck cortex: A cause of weakness in hip fracture?

Intracapsular femoral neck fractures are associated with decreased cortical width and increased proportions of Haversian canals with diameters greater than the normal mean plus 3 SD (i.e., >385 mu m). Such canals might be for med if closely associated resorbing osteons merge; a cortical event analogo us with the loss of cancellous connectivity. To test this, we investigated the pattern of osteon distribution in the aging femoral neck to determine i f remodeling osteons were distributed in anatomical clusters. Femoral neck biopsies from female patients with intracapsular hip fractures (n = 13) wer e compared with age/gender-matched cadaveric controls (n = 13). Solochrome- stained sections were analyzed for Haversian canal location, canal diameter , and the presence of an osteoid surface. Clustering was investigated using statistical software with a cluster defined as two or more osteoid-bearing osteon centers within 0.75 mm of each other. Clusters occurred more freque ntly than would be expected by chance (p < 0.001). Fracture cases had more clusters per unit area (3.14 +/- 0.31 clusters/25 mm(2) of cortical bone) t han controls (1.89 +/- 0.22) (p = 0.002). In fracture cases, the antero-inf erior, antero-superior, and infero-anterior regions had more clusters per 2 5 mm(2) than comparable control regions (ant/inf: 4.12 +/- 0.79, 1.70 +/- 0 .60, p = 0.025; ant/sup: 5.31 +/- 1.1, 1.80 +/- 0.59, p = 0.013; inf/ant: 3 .15 +/- 0.49, 1.27 +/- 0.29, p = 0.004). The mean number of clusters per 25 mm(2) per region correlated with the Inean porosity per region (adjusted r (2) = 0.60; p = 0.014), and the total number of giant canals per region cor related with the total number of clusters per region (adjusted r(2) = 0.58; p = 0.011). In conclusion. remodeling osteons are clustered or grouped ana tomically, and fracture cases have more clusters than controls. Our data su ggest that merging of adjacent, clustered osteons during resorption could l ead to the rapid development of canals with escessive dialneters and focal weakness, Clustering is greatest in those regions that we have previously s hown to have the largest relative reductions in bone strength compared with controls and known to be maximally loaded during a sideways fall. This imp licates the remodeling process underlying clustering of remodeling osteons in the aetiology of hip fracture. (C) 2000 by Elsevier Science Inc. All rig hts reserved.