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Background:   The proximal opening wedge osteotomy (POWO) of the first metatarsal (TMT-1) is commonly performed in the operative treatment of hallux valgus. Limited work has been dedicated to study POWO’s effect on the TMT-1 joint, however. The purpose of this study is to evaluate the changes in TMT-1 joint contact stress following POWO of the first metatarsal.Methods:   Five fresh-frozen cadaveric below-knee specimens (mean age: 73 years) with hallux valgus deformities (mean hallux valgus angle [HVA]: 37.4 ± 8.5 degrees) were studied. The specimens were loaded to 400 N on an MTS servohydraulic load frame. Joint contact characteristics at TMT-1 joint were measured with a Tekscan pressure sensor (Model 6900, 1100 psi; Tekscan Inc, Boston, MA) with various opening wedge sizes of 3, 5, and 7 mm both without and with a distal soft tissue release (DSTR). The contact force, area, and peak contact stress were compared among groups using analysis of variance and post hoc multiple comparisons over the untreated (Dunnett test, P &lt; .05).Results:   The mean contact force was 47.7 ± 33.5 N for untreated specimens. This increased sequentially with opening wedge size and reached statistical significance for 7-mm opening wedge (129.7 ± 62.3 N, P = .01) and 7-mm wedge + DSTR (134.8 ± 60.5 N, P = .008). The mean peak contact stress was 2.8 ± 1.3 MPa for the untreated specimens and increased incrementally with wedge size to 5.7 ± 3.0 MPa for 7-mm wedge only ( P = .03) and 5.6 ± 2.5 MPa for 7-mm wedge + DSTR ( P = .05). The contact area increased with corrections, but none reached significance.Conclusion:   With increasing opening wedge size, loading of the TMT-1 joint increases. Joint stresses higher than 4.7 MPa have been shown to be chondrotoxic, potentially predisposing patients to arthritic joint changes following POWO.Level of Evidence:

foot and ankle orthopaedics

First Tarsometatarsal Joint Loading After Sequential Correction of Hallux Valgus Using a Proximal Opening Wedge Metatarsal Osteotomy and Distal Soft Tissue Procedure