Posterior tibial tendon dysfunction (PTTD) results in a debilitating flatfoot deformity which is increasingly recognized as a major problem in the treatment of foot and ankle disorders. In fact, this disorder is felt to be the number one foot and ankle problem requiring intensive scientific investigation. The deformity is caused, at least in part, by the loss of the tendon function with subsequent muscle imbalance. Bony procedures without major fusions are being used in an effort to treat deformity when possible. However, with a tendon transfer of one third the muscle mass and a similarly smaller tendon, the original problem of muscle imbalance remains. If the problem of muscle imbalance and increased strain could be resolved, patients could be treated early to eliminate those factors that promote deformity and decreased function. This would make for a successful long-term result. A cadaveric model has been developed for the posterior tibial tendon deficient foot. Physiologic tendon, bone and ground reaction loads can be applied and monitored, and the resulting strain in the arch of the foot can be measured. Using this model, the following fundamental questions in the treatment of PTTD will be addressed: 1) does loss of the posterior tibial tendon increase strain in the arch and thereby promote deformity?; 2) how well does the present flexor digitorum tendon transfer replace the posterior tibial tendon muscle unit and does it leave muscle imbalance and increased strain in the arch?; 3) does a bony procedure, like a medial calcaneal displacement osteotomy, adequately assist the flexor digitorum tendon transfer?; and, most importantly, 4) if the flexor digitorum longus tendon transfer is inadequate (as would be expected based on clinical results), are there procedures that can adequately normalize strain and joint position?
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