Medial arch strain after lateral column lengthening: an in vitro study

Posterior tibial tendon dysfunction with concomitant progressive flatfoot deformity is associated with ligamentous failure along the medial arch. Lateral column lengthening is being used alone and in combination with other procedures with the expectation that it contributes to restoring and maintaining the arch. The primary objective of this study was to examine the effect of lateral column lengthening on medial arch strain. A secondary objective was to examine the effect of subtalar, talonavicular, double and triple fusions on medial arch strain. Whole cadaver feet were subjected to vertical loads while in a plantigrade position. Spring ligament length was monitored using liquid metal displacement gauges. Two outcomes were examined: the length of the ligament and the change in length of the ligament per unit of applied load. Ligament length was unchanged after lateral column lengthening. Ligament length was decreased after talonavicular, double and triple arthrodeses, consistent with the ligament being protected by these fusions. The change in length per unit of applied load after simulated lateral column lengthening was comparable to that for the intact foot, which is consistent with the ligament remaining functional during weightbearing and not being overloaded.

Medial arch strain after medial displacement calcaneal osteotomy: an in vitro study

Posterior tibial tendon dysfunction with concomitant progressive flatfoot deformity is associated with ligamentous failure along the medial arch. Medial displacement calcaneal osteotomy is being used alone and in combination with other procedures, with the expectation that it contributes to maintaining the arch. The objective of this study was to examine the effect of osteotomy on reducing medial arch strain. Whole cadaver feet were subjected to vertical loads while plantigrade. Spring ligament length was monitored using liquid metal displacement gauges. Two outcomes were examined: the length of the ligament under one-half body weight and the change in length of the ligament per unit of applied load. The medial displacement calcaneal osteotomy allowed elongation of the ligament with weightbearing, but at a shorter ligament length. This afforded the spring ligament protection from the levels of force experienced in the intact and lateral column-lengthened conditions.

Motion of the hindfoot after simulated arthrodesis

Arthrodesis of the subtalar joint, triple arthrodesis (involving the subtalar, talonavicular, and calcaneocuboid joints), double arthrodesis (involving the talonavicular and calcaneocuboid joints), arthrodesis of the talonavicular joint, and arthrodesis of the calcaneocuboid joint were simulated in a cadaver model, and the range of motion of each joint not involved in the simulated arthrodesis was measured with a three-dimensional magnetic space tracking system. The excursion of the posterior tibial tendon was also measured under all of these conditions. We found that any combination of simulated arthrodeses that included the talonavicular joint severely limited the motion of the remaining joints to about 2 degrees and limited the excursion of the posterior tibial tendon to 25 per cent of the preoperative value. Simulated arthrodesis of the calcaneocuboid joint had little effect on the range of motion of the subtalar joint, and it reduced the range of motion of the talonavicular joint to a mean of 67 per cent of the preoperative value; a mean of 73 per cent of the excursion of the posterior tibial tendon was retained. After simulated arthrodesis of the subtalar joint, a mean of 26 per cent of the motion of the talonavicular joint, 56 per cent of the motion of the calcaneocuboid joint, and 46 per cent of the excursion of the posterior tibial tendon was retained. The talonavicular joint is the key joint of the triple joint complex. The talonavicular joint had the greatest range of motion, and simulated arthrodesis of this joint essentially eliminated motion of the other joints of the complex.