Influence of talar neck and intra-articular calcaneal fractures on subtalar joint mechanics

Summary The effects of misalignment after talar neck and intra-articular fractures on the contact characteristics of the subtalar joint were determined. Sixteen fresh cadaver lower extremities were mounted in a loading apparatus and a vertical load [700 N] applied. Pressure-sensitive films were inserted into the posterior and anterior/middle articulations of the subtalar joint. After testing the normal conditions, the talar neck was osteotomized in seven cadaver specimens and stabilized in a displaced position with external and internal fixation (Hawkins classification type I). Intra-articular fractures of the calcaneus were simulated in nine specimens by osteotomy and stabilized in a displaced position by rigid fixation. The fracture type was simulated within the primary fracture line of the joint depression and tongue type fracture, according to Essex-Lopresti, with increasing plantar depression of the posterolateral fracture component with 2, 5 and 10 mm displacements. Measurements of the talar neck fractures showed a significant unloading in high-pressure areas of the anterior and middle facet of the subtalar joint by a dorsal, lateral and complex (varus angulation) displacement of the talar neck, but not after medial displacement. However, slight intra-articular calcaneal fracture displacements of 2mm within the subtalar joint already led to significant change in the posterior facet. These findings suggest that accepting minor displacements after talar neck fractures and intra-articular calcaneal fractures may lead to alterations in function of the subtalar joint when they are left unreduced.