Dynamic Ultrasound Assessment of the Effects of Knee and Ankle Position on Achilles Tendon Apposition Following Acute Rupture

Background: Previous reports have suggested that knee flexion improves tendon edge apposition following acute rupture of the Achilles tendon. The aim of the present study was to determine, with use of ultrasonography, the effects of knee and ankle position on the Achilles tendon gap distance in patients with an acute rupture. Methods: Twenty-six patients with a unilateral acute complete Achilles tendon rupture that had been confirmed with ultrasonography were recruited within a week after the injury. The mean age at the time of presentation was forty-one years. Ultrasound measurements included the location of the rupture and the gap distance between the superficial tendon edges with the ankle in neutral and the knee extended. The gap distance was sequentially measured with the foot in maximum equinus at the ankle and with 0 degrees, 30 degrees, 60 degrees, and 90 degrees of knee flexion. Results: The mean distance of the rupture from the calcaneal enthesis was 52 mm (range, 40 to 76 mm). The mean gap distance with the ankle in neutral and the knee extended was 12 mm (95% confidence interval, 10 to 13 mm). This distance decreased to 5 mm (95% confidence interval, 4 to 7 mm) when the foot was placed in maximum ankle equinus with 0 degrees of knee flexion and to 4 mm (95% confidence interval, 3 to 5 mm) with 30 degrees of knee flexion, 3 mm (95% confidence interval, 2 to 4 mm) with 60 degrees of knee flexion, and 2 mm (95% confidence interval, 1 to 2 mm) with 90 degrees of knee flexion. Expressing the reduction in gap distance with each successive position as a percentage of the gap distance with the knee extended and the ankle in neutral revealed a mean reduction of 55.7%, 64.4%, 75.4%, and 84.8% with maximum ankle equinus and 0 degrees, 30 degrees, 60 degrees, and 90 degrees of knee flexion, respectively. The difference in gap distance between each of these positions was significant (p < 0.05). Conclusions: Maximum ankle equinus alone significantly reduces the gap distance after acute Achilles tendon rupture. Increasing knee flexion further reduces the gap distance by small increments that, although significant, may not be clinically important.