Effects of Femorotibial and Tibiotarsal Joint Ranges of Motion on the Gastrocnemius Muscle-Tendon Working Length in the Canine Cadaveric Limb.

Objective This study aimed to describe changes in the length of the gastrocnemius muscle-tendon unit between the medial fabella and the calcaneus (MF-C) at different femorotibial joint (FTJ) and tibiotarsal joint (TTJ) angle combinations in the canine limb. Study Design This is an ex vivo kinematic study. Animals Canine cadaveric pelvic limbs (n = 11). Procedures One cadaveric pelvic limb was dissected to identify the anatomical origin and insertion of the gastrocnemius muscle-tendon unit for the radiographic landmark determination. The radiographic landmarks of the FTJ and TTJ were identified by lateral view radiographs. A series of lateral radiographs were evaluated to measure the linear MF-C at all combinations of the FTJ and TTJ angles. A mathematical model was defined for MF-C. Results The MF-C is associated with the FTJ and TTJ by a linear trigonometric relationship. Higher rate of increase in the MF-C was observed when the FTJ was > 135 degrees and the TTJ was  125 degrees in all groups. Conclusions Thirty degrees of free range of motion of the TTJ between 140 and 170 degrees did not elongate MF-C in this cadaveric limb study. Clinical Relevance Some degrees of free range of motion may be possible in the TTJ during tendon healing based on our cadaveric study without causing excessive change in the MF-C, although this concept should not be applied until isometric contractions of muscles are clearly understood. The relationship between the MF-C and tension at tenorrhaphy should be evaluated.