The effect of ankle position on the static tension in the Achilles tendon before and after operative repair: a biomechanical cadaver study

Abstract

Background: We hypothesized that there no need to position the foot in plantarflexion after operative repair of an Achilles tendon rupture.

Methods: In five fresh cadaver lower extremity specimens, the static tension in the Achilles tendon was measured as the ankle was sequentially dorsiflexed from 30, to 20, to 10, to 0 degrees of plantarflexion. The tendon was then transected and repaired using a modified Krakow locking loop suture technique. The tension in the tendon was again measured as the foot was sequentially dorsiflexed through the same range of motion: 30, to 20, to 10, to 0 degrees. The repair was then tensile tested to failure.

Results: The intact Achilles tendons generated on average 10 N, 10 N, 15.8 N and 31.9.0 N of tension at 30, 20, 10, and 0 degrees of plantarflexion, respectively. After a modified Krakow locking loop repair, the tension across the repair site was 10 N, 11.46 N, 18.4 N, and 30.3 N at 30, 20, 10, and 0 degrees of plantarflexion. Thus, moving the ankle from 30 degrees to neutral placed an additional force of 21.9 N on the intact tendon and 20.3 N on the repaired tendon. The mean tensile strength of the modified Krakow repair was 598.6 N (range 167 1129 N).

Conclusions: The tension in the repaired tendon at neutral position is only a small percentage (6.4%) of the strength of the tendon when operatively repaired by a modified Krakow locking loop suture technique.

Clinical relevance: Our results suggest that the ankle joint does not have to be positioned in plantarflexion after operative repair using the described technique.