Biomechanical Changes to the Ankle After Zadek Osteotomy
Authors: Bellas Nicholas , Nayak Raghunandan , Pasha Mehreen , Wolf Megan R. , Obopilwe Elifho , McDonald Thomas , Geaney Lauren E. 
Published: December 2024

Category: Hindfoot; Sports Introduction/Purpose: Insertional Achilles tendinopathy is a common source of heel pain in active adults and athletes. This may occur in conjunction with Haglund’s deformity, a calcaneal prominence that can be associated with inflammation of the retrocalcaneal bursa. Corrective surgery may be indicated after failed nonoperative treatment. One option includes the Zadek osteotomy, a calcaneal dorsal closing wedge osteotomy, which may relieve retrocalcaneal pressure, resulting in improved clinical outcomes. However, a gap in the knowledge base exists regarding the postoperative effects of the procedure on the biomechanics of the calcaneus and Achilles tendon. This study aims to evaluate the biomechanical changes of the Zadek osteotomy on retrocalcaneal pressure, position of the Haglund’s prominence relative to the Achilles insertion, and Achilles strain. Methods: Ten fresh-frozen foot and ankle cadaveric specimens underwent dissection for exposure of the Achilles tendon and retrocalcaneal space. The Zadek osteotomy was performed by making a 1-cm dorsal closing wedge osteotomy fixed by a single threaded 7.0-mm cannulated screw. Radiographic markers were placed on the Haglund’s prominence and the Achilles tendon insertion. Pre- and post-procedure simulated weightbearing, perfect lateral radiographs were taken to measure displacement in the superior-inferior and anterior-posterior axes. The Achilles tendon was loaded with 170 N to simulate weightbearing. The ankle was then maximally dorsiflexed for 3 cycles at 0.25 Hz. Catheter pressure sensors and voltage transducer linear displacement sensors were placed on the specimens to measure retrocalcaneal pressure and Achilles strain respectively at maximum dorsiflexion. The testing protocol was completed before and after the osteotomy, and paired student’s t-tests were done to detect statistical differences (p < 0.05). Statistical outliers were removed from analysis. Results: After the Zadek osteotomy, the Haglund’s prominence was displaced by 9.9 mm anteriorly (N = 10, p < 0.0001) and the Achilles insertion was displaced by 3.4 mm superiorly (N = 10, p < 0.001) with respect to each other. The calcaneal X/Y ratio increased from 2.56 to 3.52 (N = 10, p < 0.0001). At maximum dorsiflexion, retrocalcaneal pressure dropped from 117 mmHg to 66 mmHg (N = 7, -44%, p = 0.018) after the procedure. Our study did not find significant changes in the anterior or posterior Achilles strain secondary to the osteotomy. The strain increased in the anterior fibers by 20% (N = 9, p = 0.484) and decreased in the posterior fibers by 39% (N = 9, p = 0.088). Conclusion: Biomechanical testing in a cadaveric model demonstrates that the Zadek osteotomy significantly decreased retrocalcaneal pressure, shifted the Haglund's prominence anteriorly, shifted the Achilles tendon insertion superiorly, increased the X/Y ratio of the calcaneus, and did not significantly change the strain on the Achilles tendon. These results may explain the improvements in pain and function seen in clinical studies. However, nonpathological foot and ankle specimens were used in this study, which should affect interpretation. Overall, the current results support the Zadek osteotomy can be a viable treatment option for relieving pressure within the retrocalcaneal bursa for insertional Achilles tendinopathy. Zadek Osteotomy and Mechanical Testing Setup i-iii) Illustration of the Zadek Osteotomy technique performed. A & B) Illustration depicting cadaveric foot and ankle specimen in testing rig before and after dorsiflexion respectively