Biomechanical consequences of lateral column lengthening of the calcaneus: Part I. Long plantar ligament strain.

Lateral column lengthening of the calcaneus has been a powerful tool used to correct peritalar subluxation in symptomatic flat feet. The mechanical basis and limits for correction with this procedure are not well understood. A flatfoot model was created on 8 fresh-frozen cadaver feet by sectioning the deltoid ligament, talonavicular capsule, and spring ligament. Strain-gauge analysis of the long plantar ligament was performed (on 6 specimens) as the lateral column was sequentially lengthened from 4 to 12 mm in 2-mm increments. Results showed that only the lateral most one-third of the long plantar ligament measured positive strain during this procedure. The medial two-thirds of the long plantar ligament and plantar fascia decreased in tension and became fully lax during lengthening. Maximum tension in the long plantar ligament was measured after placing grafts 6 mm in thickness (P <.05). Larger grafts produced additional strain in the ligament, but were not significant. The authors conclude that grafts >6 mm have no additional corrective capacity without compromising the long plantar ligament. Either larger graft size or loss of the long plantar ligament could compromise the intrinsic stability of the lateral column of the foot. These findings may decrease the incidence of complications with this procedure, specifically lateral column pain, instability, and calcaneocuboid arthrosis.