Hiromichi Fujie

Effects of growth on the response of the rabbit patellar tendon to stress shielding: a biomechanical study

OBJECTIVEnTo know the effect of stress deprivation on the dimensions and mechanical properties of the patellar tendon during growth.nnnDESIGNnThe dimensions and tensile properties of stress-shielded patellar tendons were studied in growing rabbits and compared to those in mature animals.nnnBACKGROUNDnAlthough the effects of stress deprivation on the remodeling of ligaments and tendons have been studied in various animal models, the effect of growth on the remodeling has not been studied well.nnnMETHODnA stress shielding technique was applied to 1-, 2-, and 3-month-old Japanese white rabbits to completely remove stress in the patellar tendons for 4, 7, and 14 days. Changes in the dimensions and mechanical properties as well as fibroblast density of the tendon were determined.nnnRESULTSnThe tensile strength and tangent modulus of the patellar tendons were markedly decreased by stress shielding, while the cross-sectional area was significantly increased, with the largest changes in 1-month-old rabbits. Fibroblast density also increased; however, the degree of increase was highest in 3-month-old rabbits.nnnCONCLUSIONnThe changes in the dimensions and mechanical properties of the patellar tendons induced by stress shielding were greater in younger animals.nnnRELEVANCEnThe biomechanical response of tendons and ligaments to stress deprivation induced by, for example, limb immobilization is greater and occurs earlier in younger subjects, which is important for the surgical treatment and rehabilitation protocol of joint diseases in young subjects.

Mechanical Functions of Human ACL Bundles: Development and Application of a Robotic Knee Simulator

A novel and unique 6-degree of freedom (DOF) robotic simulator, consisting of a 1-DOF translational axis and serially linked 5-DOF axes, was designed and developed for the study of knee joint biomechanics. The position accuracy of the simulator was found to be high; error in displacement was less than 120 μm under the application of 500 N. The simulator was capable of applying combined loadings to the knee for simulating the quasi-static, physiological condition of the knee. The simulator was successfully applied to determine forces in the anteromedial (AM) and posterolateral (PL) bundles of the human anterior cruciate ligament (ACL) in response to externally applied loads to the knee. A reciprocal function of ACL bundles in response to anterior force was found; the PL bundle carried larger force than the AM bundle at flexion angles less than 30 degrees, while the converse was true at flexion angles larger than 30 degrees. We also found that the AM bundle always carried larger force than the PL bundle in response to varus and valgus moments at 0, 15, and 30 degrees of flexion. These data are important for better understanding the mechanical function of the ACL and improving the ACL reconstruction technique.