Purpose of Study. Lengthening of the gastrocsoleus for equinus deformity is commonly performed in orthopaedic surgery. The aim of this study was to describe the precise details of each surgical procedure and assess each biomechanically in cadaver models. Description of Methods. The surgical anatomy of the gastrocsoleus was investigated and standardized approaches were developed for the procedures described by Baumann, Strayer, Vulpius, Baker, Hoke and White. The biomechanical characteristics of these six procedures were then compared, in three randomized trials, in formalin preserved, human cadaver legs. The lengthening procedures were performed and a measured dorsiflexion force was applied across the metatarsal heads using a torque dynamometer. Lengthening of the gastrocsoleus was measured directly, by measuring the gap between the ends of the fascia or tendon. Summary of Results. The gastrocsoleus muscle-tendon-unit was divided into three zones. In Zone 1, it was possible to lengthen the gastrocnemius alone or to lengthen the gastrocnemius and soleus by different amounts. These procedures (Baumann, Strayer) were very stable but limited in the amount of lengthening achieved. Zone 2 lengthenings (Vulpius, Baker) of the conjoined gastrocnemius aponeurosis and soleus fascia were not selective but were stable and resulted in significantly greater lengthening than Zone 1 (p < 0.001) 4. Conclusion. Surgery for equinus deformity correction by lengthening of the gastrocsoleus varies in terms of selectivity, stability and range of correction with differing anatomical and biomechanical characteristics. Clinical trials are needed to determine whether these differences are of clinical importance. It may be appropriate for surgeons to select a procedure from a zone, best suited to the clinical needs of a specific patient. NO DISCLOSURES