Biomechanical Changes to the Hindfoot After Zadek Osteotomy

Background: Insertional Achilles tendinopathy (IAT) is a common source of heel pain in active adults and athletes. The Zadek osteotomy (ZO) is a calcaneal dorsal closing wedge osteotomy that has demonstrated clinical success as a treatment for IAT, purported to favorably improve tendon mechanics, decrease impingement, and decrease pressure within the retrocalcaneal bursa. The present study aims to evaluate the biomechanical effects of ZO on Achilles strain, position of the Haglund prominence relative to the Achilles insertion, and retrocalcaneal pressure. Methods: The ZO was performed on 10 fresh-frozen foot and ankle mid tibia-fibula cadaveric specimens. An osteotomy was performed using a 1-cm dorsal closing wedge procedure secured with a 7.0 mm cannulated screw. Point pressure sensor catheters and differential variable reluctance transducers were used to measure the retrocalcaneal pressure and Achilles strain, respectively, pre- and postosteotomy. Paired t-tests were utilized to detect statistical differences (P < .05). Results: After the ZO, the Haglund prominence was translated 9.9 mm anteriorly with respect to the insertion of the Achilles (P < .05) and the Achilles tendon insertion was translated 3.4 mm proximally (P < .05). The ratio of calcaneal length to greater tuberosity length, the X/Y ratio, increased from 2.56 to 3.52 with the osteotomy (P < .05). At maximum dorsiflexion, retrocalcaneal pressure decreased from 117 to 66 mm Hg (44%, P = .018). The Achilles strain changed from 0.00362 to 0.00436 in the anterior fibers (P = .484) and changed from 0.00467 to 0.00283 in the posterior fibers (P = .088). Conclusion: Biomechanical testing in a cadaveric model demonstrates that the ZO decreased retrocalcaneal pressure, shifted the Achilles tendon insertion proximally, increased the X/Y ratio of the calcaneus, and did not significantly change the strain of the Achilles tendon. Clinical Relevance Despite the clinical success demonstrated in recent literature, there are no biomechanical studies describing the effect of the ZO on the biomechanics of the hindfoot, and the mechanism of symptom relief of the ZO for IAT is not well understood. The present study measures two potential ZO effects relative to Haglund prominence by measuring retrocalcaneal pressure and displacement of the Achilles tendon with respect to the Haglund prominence, and measures one ZO effect relative to calcification of the tendon by measuring the Achilles tendon strain.