Positional effects of the knee and ankle on the ends of acute Achilles tendon ruptures.

Conservative management of acute Achilles tendon ruptures in a plantarflexed short leg cast or functional brace is a viable alternative to surgery. The ideal plantarflexion angle to allow the free ends of the tendon to oppose one another has not been clearly defined. The purpose of this cadaveric study was to define a plantarflexion angle where the free Achilles tendon ends reliably oppose one another. Ten cadaveric legs amputated at the distal femur were obtained. A laceration of the Achilles tendon was made 4 cm above the calcaneal insertion. A joint-spanning external fixator was placed across the knee. With differing degrees of knee flexion (0, 45, and 90 degrees), the diastasis between the free ends of the Achilles tendon was measured as the ankle was moved from 20 degrees of dorsiflexion to 30 degrees of plantarflexion (-20, -10, neutral, 10, 20, and 30 degrees). Regardless of knee flexion angle, the ankle plantarflexion angle where the free ends of the Achilles tendon opposed one another was 28.0 (95% confidence interval: 25.0-33.6) degrees. The ideal ankle angle in which to immobilize patients appears tightly clustered around 28 degrees of plantarflexion.