Super-osteons (remodeling clusters) in the cortex of the femoral shaft: Influence of age and gender

Previous studies of cortical remodeling in the fractured femoral neck indic ated that the merging of spatially clustered remodeling osteons could resul t in the formation of deleteriously large cavities associated with femoral neck fracture. This study aimed to identify whether remodeling osteons in t he femoral shaft were also clustered and to assess the influence of age and gender. Microradiographic images of femoral mid-shaft cross-sections from 66 subjects over 21 years of age were analyzed to determine the number, siz e and location of all Haversian canals. Those most recently remodeled were identified using an edge-detection algorithm highlighting the most marked d ifferential gradients in grey levels, Cluster analysis (JMP software) of th ese osteons identified the proportion of recently remodeled osteons that we re within 0.75 mm clusters. As in the femoral neck, remodeling osteons were significantly more clustered than could occur by chance (real, 59.4%; rand om, 39.4%; P < 0.0001). The density of these clusters (number/mm(2)) was no t significantly associated with subject age or gender but was greatest near the periosteum and decreased toward the marrow cavity (periosteal 0.043 +/ - 0.004; mid-cortex 0.028 +/- 0.003; endosteal 0.017 +/- 0.002). Cortical p orosity increased with age. The presence of giant canals (diameter >385 mum ) was inversely related to the presence of clusters (R-2 = 0.237, P < 0.000 1). This data suggest that remodeling osteons tend to be spatially colocali zed in the shaft as they are in the neck of the femur and their presence is independent of age or gender. We propose that these remodeling clusters be termed super-osteons. The negative relationship between super-osteons and giant canals raises the intriguing possibility that loss of the control of remodeling depth results in the merging of osteonal systems to form deleter iously large cortical cavities with a marked reduction in bone strength. An at Rec 264:378-386, 2001. (C) 2001 Wiley-Liss, Inc.