It has been suggested that a supramalleolar osteotomy can return the load distribution in the ankle joint to normal. However, due to the lack of biomechanical data, this supposition remains empirical. The purpose of this biomechanical study was to determine the effect of simulated supramalleolar varus and valgus alignment on the tibiotalar joint pressure, in order to investigate its relationship to the development of osteoarthritis. We also wished to establish the rationale behind corrective

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... eotomy of the distal tibia. We studied 17 cadaveric lower legs and quantified the changes in pressure and force transfer across the tibiotalar joint for various degrees of varus and valgus deformity in the supramalleolar area. We assumed that a supramalleolar osteotomy which created a varus deformity of the ankle would result in medial overload of the tibiotalar joint. Similarly, we thought that creating a supramalleolar valgus deformity would cause a shift in contact towards the lateral side of the tibiotalar joint. The opposite was observed. The restricting role of the fibula was revealed by carrying out an osteotomy directly above the syndesmosis. In end-stage ankle osteoarthritis with either a valgus or varus deformity, the role of the fibula should be appreciated and its effect addressed where appropriate. Valgus and varus malalignment of the ankle joint may be caused by trauma, neurological disorders, genetic predisposition and other unidentified factors, and result in asymmetrical joint loading. 1-5 This may cause wear of the articular cartilage in areas that are normally accustomed to less loading. Osteoarthritis may also develop in the presence of ligamentous laxity and muscular imbalance. 6 The nature of eccentric osteoarthritis of the ankle is not well understood, but, despite this, correction of angular deformities by supramalleolar and calcaneal osteotomies have become more popular. 2, 5, [7] [8] [9] There is limited data about the biomechanical changes that occur after corrective osteotomy. Consequently, it is not currently possible to plan the precise level and degree of correction of an osteotomy, nor is it possible to accurately predict its outcome. The ankle joint has been the subject of many biomechanical studies, in which cadaver specimens have been modified to simulate pathological processes that affect the tibiotalar joint. [10] [11] [12] [13] [14] Our study aimed to describe the effect of varus and valgus deformity of the distal tibia on the contact area and force transmission through the tibiotalar joint. We believe this to be of importance to our understanding of the predisposition of malalignment in the coronal plane to the development of osteoarthritis. Materials and Methods We used 17 fresh-frozen cadaveric lower legs; of which 11 were tested with an intact fibula (group A), and as a consequence of our findings in the remaining six we osteotomised the fibula directly above the level of the syndesmosis (group B). Before testing them, the limbs were thawed at room temperature for at least 24 hours. A normal range of movement in the ankle joint was established clinically, and malalignment was excluded radiologically. The specimens were prepared by disarticulation at the knee joint. The tibial epicondyles were removed with an oscillating saw and the medullary canal opened with a drill. A customised load transmitter with a stem in the tibial medullary canal was used to apply the axial load. The skin and subcutaneous tissues were removed down to the tarsus. The ankle ligaments and interosseous membrane were preserved. Each leg was mounted into a load frame (Instron model 8872; Instron Corp., Canton, Massachusetts) to simulate a single-leg barefoot stance (Fig. 1) . The foot was strapped to a friction plate with a band which only covered the forefoot. Cyclical loading of the limb was then performed 20 times with a load of 700 N. The preconditioning cycle was sufficient to absorb all plastic deformation of the lower leg.