LOCAL BONE DEFORMATION AT 2 PREDOMINANT SITES FOR STRESS-FRACTURES OFTHE TIBIA - AN IN-VIVO STUDY

Local bone deformation was registered at two predominant injury sites for tibial stress fractures in a healthy female volunteer. Two instrum ented strain gauge staples were inserted under local anesthesia to the anterior middiaphysis (AM) and to the posteromedial part of the dista l tibia (PD). Calibration and reliability of the instrumented staple s ystem have previously been demonstrated in vitro. Concomitant ground r eaction forces were registered with a Kistler force plate. Studying pe ak values, it was shown that during a voluntary 30-cm forward jump, PD deformation was greater during forefoot landing (2700-4200 microstrai n) than during a heel strike landing (1200-1900 microstrain) and also compared with the concomitant AM deformation under both above testing conditions (1300-1900 microstrain). The stance phase during walking re sulted in PC deformation of 950 microstrain, whereas the concomitant A M deformation was 334 microstrain, The greatest AM deformation (mean, 2128 microstrain) was registered during ground contact after a volunta ry vertical drop from a height of 45 cm, concomitant with a PD deforma tion of 436 microstrain. These data are the first to show different lo cal deformations at various sites of the tibia in vivo. The PD deforma tion was larger than previously noted from other parts of the tibia, w hereas the middiaphysis data are consistent with other reports. The re sults may support the clinical assumption of different etiologies for stress fractures at these predominant sites.