Ping Zhang, Kazunori Hamamura, Charles H. Turner and Hiroki Yokota
For devising clinical approaches to treating limb length discrepancies, strategies that will generate differential longitudinal growth need to be improved. This report addresses the following question: does knee loading increase bone length of the loaded hindlimb? Knee loading has been shown to induce anabolic responses on the periosteal and endosteal surfaces, but its effects on longitudinal bone growth have not yet been examined. In the present studies, loads were applied to the left hindlimb (5-min bouts at 0.5 N) of C57/BL/6 mice (21 mice, ~8 weeks old). Compared to the contralateral and age-matched control groups, knee loading increased the length of the femur by 2.3 and 3.5%, together with the tibia by 2.3 and 3.7% (all P < 0.001), respectively. In accordance with the length measurements, knee loading elevated BMD and BMC in both the femur and the tibia. Histological analysis of the proximal tibia revealed that the loaded growth plate elevated its height by 19.5% (P < 0.001) and the cross-sectional area by 30.7% (P < 0.05). Particularly in the hypertrophic zone, knee loading increased the number of chondrocytes (P < 0.01) as well as their cellular height (P < 0.001) along the length of the tibia. Taken together, this study demonstrates for the first time the potential effectiveness of knee loading in adjusting limb length discrepancy.