Osteoarthritis (OA) and osteoporosis (OP) of the hip rarely occur in the same patient. The purpose of this study was to determine whether this difference might be attributable to the different quantity and quality of subchondral cancellous bone in the two conditions.
Subchondral cancellous bone from the femoral head was obtained at the time of hip arthroplasty from 60 postmenopausal women, 30 with OA and 30 with OP. In each group, 10 specimens were subjected to compressive fatigue loading and 20 were left nonloaded. Specimens were examined by compressive mechanical testing, micro-computed tomography scanning, fluorescence microscopy, and nanoindentation techniques.
Both the ultimate stress and the elastic modulus of cancellous bone from OA patients were significantly higher than those of cancellous bone from OP patients (P < 0.05). Compared to cancellous bone from OP patients, the bone volume fraction and trabecular thickness were significantly increased, but bone matrix mineralization was significantly decreased, in cancellous bone from OA patients (P < 0.05 for each comparison). The microcrack density was significantly higher in OP cancellous bone than in OA cancellous bone (P < 0.001), irrespective of fatigue loading. In addition, fatigue loading resulted in a significant increase in microcrack density in both OA and OP cancellous bone (P < 0.001). There was no significant difference in nanoindentation elastic modulus and hardness between cancellous bone from OA and OP patients, as well as between bones with and without fatigue loading.
The difference in mechanical properties between OA and OP cancellous bone is attributed to different bone mass and bone structure. OP cancellous bone is susceptible to fatigue damage due to insufficient structure. However, increased bone volume and plate-like structure provide OA cancellous bone a superior capacity to resist fatigue damage.