The Impact of Hinge Position and Wedge Orientation in Zadek Osteotomy across Different Foot Morphologies: A Virtual Surgical Simulation Study.

BACKGROUND: The Zadek osteotomy (ZO) is a well-established surgical option for insertional Achilles tendinopathy. By modifying the position of the posterior calcaneal tuberosity, ZO may reduce posterosuperior calcaneal prominence, mechanical conflict at the Achilles insertion, and tensile stress on the tendon. Nevertheless, the biomechanical impact of wedge orientation and hinge position-and their relationship with underlying foot morphology-has not been clearly defined. METHODS: A weightbearing computed tomography (WBCT)-based virtual simulation was performed on 60 asymptomatic feet, categorized as cavus (n = 20), neutral (n = 20), or planus (n = 20) based on the calcaneal inclination angle. Nine ZO configurations were modeled by combining 3 hinge positions (posterior, A; mid-tuberosity, B; anterior, C) with 3 wedge inclinations. Pre- and post-simulation measurements were compared for calcaneal inclination angle (CIA), talocalcaneal angles, hindfoot moment arm (HMA), hindfoot alignment angle (HAA), Fowler-Philip (FP) angle, X/Y ratio, and plantar fascia (PF) length. RESULTS: Wedge inclination showed no significant influence on any variable (P ≈ .99). Hinge position, however, markedly affected sagittal alignment. Hinges B and C significantly reduced CIA (hinge B -0.5° [95% CI -0.66° to -0.4°]; hinge C -2.1° [95% CI -2.26° to -1.96°], both P < .001). Hinge B showed the largest reduction in FP angle (-7.6° [95% CI -8.63° to -6.59°], P = .16) and produced the greatest increase in X/Y ratio (+0.57 [95% CI +0.46 to +0.68], P = .007). In the pre- to post-simulation analysis, HMA increased slightly with hinge B (P = .03), and PF length increased only with hinge C (P < .001). Subgroup analysis revealed that cavus feet exhibited the greatest sagittal correction, particularly with hinge C. CONCLUSION: ZO significantly affected the Fowler-Philip angle, the primary radiographic outcome, with its overall foot alignment corrective power depending principally on hinge position rather than wedge inclination. These changes occurred predominantly in the sagittal plane while sparing coronal and axial alignment. CLINICAL RELEVANCE: WBCT-based virtual simulation may help surgeons tailor Zadek osteotomy hinge position to baseline foot morphology and anticipate morphology-specific alignment changes before surgery. LEVEL OF EVIDENCE: Level IV, pre-clinical simulation case series.