Biomechanical properties of the triceps surae muscle after limb lengthening

The hindlimb of New Zealand white rabbit was osteotomized and then slowly lengthened at a rate of 1 mm/day until a 2.0-cm gain in length was reached. The triceps surae muscle-tendon unit was then tested either with or without 2 months fixation for bony consolidation. After limb lengthening, the strain at peak load was decreased and the axial rigidity was increased significantly; but other biomechanical parameters such as peak load, maximal deformation at peak load, stiffness, and energy absorption before peak load did not show any significant difference. We conclude that healthy triceps surae muscle has a great potential to be lengthened despite the changes in intrinsic structural properties of the muscle. The change in the biomechanical properties occurred during the time of distraction and was not affected by the time of bony consolidation. RELEVANCE: As noted in this study, many biomechanical parameters of the triceps surae muscle were not affected after prolonged distraction. This fact suggested that the healthy muscle-tendon unit is not a main causative factor of joint contracture after limb lengthening. However, there were intrinsic changes in the structural properties of the triceps surae muscle. Equinus contracture after limb lengthening may be caused by the aggravated intrinsic structural changes of the injured or denervated scarred muscular tissue.