Effects on the Tarsal Tunnel Following Malerba Z-type Osteotomy Compared to Standard Lateralizing Calcaneal Osteotomy.

BACKGROUND Tarsal tunnel syndrome is a known complication of lateralizing calcaneal osteotomy. A Malerba Z-type osteotomy may preserve more tarsal tunnel volume (TTV) and decrease risk of neurovascular injury. We investigated 2 effects on the tarsal tunnel of the Malerba osteotomy compared to a standard lateralizing osteotomy using a cadaveric model: (1) the effect on TTV as measured by magnetic resonance imaging (MRI) and (2) the proximity of the osteotomy saw cuts to the tibial nerve. METHODS Ten above-knee paired cadaveric specimens underwent MRI of the ankle to obtain a baseline measurement of TTV. One foot in each pair received a standard lateralizing calcaneal osteotomy, with the other foot receiving a Malerba osteotomy. MRIs were performed after each of 3 increasing amounts of lateral displacement, which were accompanied by increasing amounts of wedge resection in the Malerba osteotomy group. TTV was measured on MRI using previously described and validated parameters. Differences in TTV with osteotomy type, displacement, and their interaction were assessed with generalized estimating equations. After all MRIs were completed, each specimen was dissected and the nearest distance of tibial nerve branches to the osteotomy site was measured. RESULTS Baseline TTV averaged 13 229 ± 2354 mm(3) and did not differ between groups (P = .386). TTV decreased on average by 7% after the first translation, 14% after the second, and 27% after the third (P < .005 for each). The magnitude of the decrease in TTV did not differ between those specimens with standard osteotomies versus those with Malerba osteotomies (P = .578). At least one of the major branches of the tibial nerve crossed the osteotomy site in 5 of 5 specimens that received the Malerba osteotomy versus 2 of 5 that received a standard osteotomy. CONCLUSION Regardless of osteotomy type, lateralizing calcaneal osteotomy decreased TTV. In all specimens, the osteotomy was at the level of branches of the tibial nerve. CLINICAL RELEVANCE Our results demonstrate that lateralizing calcaneal osteotomies must be performed with care to avoid excessive lateral translation as well as direct nerve injury on the nonvisualized medial side of the calcaneus.