The Effect of Calcaneal Displacement Osteotomies on Tarsal Tunnel Pressures

CATEGORY: Basic Sciences/Biologics INTRODUCTION/PURPOSE: Calcaneal displacement osteotomies are frequently utilized procedures to correct hindfoot varus and valgus deformities and are frequently used in conjunction with other procedures to restore normal alignment of the foot. Complications associated with this procedure include overcorrection, undercorrection, iatrogenic fracture, wound dehiscence, and infection. Additionally, neurologic deficit associated with lateralizing calcaneal osteotomy has been documented in the literature. Changes in ankle alignment have been shown to significantly alter tarsal tunnel pressure and volume, and a MRI study by Bruce et. al showed that lateral osteotomy fragment displacement results in significant reduction of tarsal tunnel volume. We hypothesized that a lateral displacement calcaneal osteotomy would result in an increase in tarsal tunnel pressure compared baseline tarsal tunnel pressures or those with a medial displacement calcaneal osteotomy. METHODS: We performed cadaveric dissections on five foot and ankle cadavers. The laciniate ligament covering the tarsal tunnel was visualized at 2 cm proximal to the medial malleolus and a nick incision was made to insert the ICP monitoring probe; the tunnel was left intact distally. A 45 degrees lateral incision was made in line with the osteotomy site and a calcaneal osteotomy was performed in line with the incision approximately 1 cm anterior to the attachment of the achilles tendon. A Codman ICP monitoring probe was then used to measure baseline tarsal tunnel pressure measurements prior to calcaneal displacement. The osteotomy was then displaced medially and laterally and fixed in place in place with a K-wire (Figure 1). Tarsal tunnel pressures were measured at 5 mm and 8 mm displacement in both directions. RESULTS: Average tarsal tunnel pressures at baseline were 2.8 mmHg (range, 1-5 mmHg). Average tarsal tunnel pressures with 5 mm and 8 mm of medial calcaneal displacement were 1.0 mmHg (range, 0-4 mmHg) and 0.8 mmHg (range, 0-3 mmHg), and with lateral calcaneal displacement were 7.4 mmHg (range, 3-13 mmHg) and 14.4 mmHg (range, 10-22 mmHg). There was no significant difference in tarsal tunnel pressures with either 5 mm (p=.067) or 8 mm (P=.067) of medial calcaneal displacement compared to baseline. There was, however, a significant increase in tarsal tunnel pressures with both 5 mm (p=.039) and 8 mm (p=.001) of lateral calcaneal displacement compared to tarsal tunnel pressures at baseline and with 5 mm (p=.002) and 8 mm (p=.001) of medial calcaneal displacement. CONCLUSION: Tibial nerve palsy following lateral displacement calcaneal osteotomy has recently been shown to have an incidence as high as 34%. Osteotomies decreasing volume in the tarsal tunnel could cause iatrogenic compression of the tibial nerve. Based on the results of our study, displacing the calcaneus laterally increases the tarsal tunnel pressures on average five times above baseline tarsal tunnel pressures. Medial displacement, however, does not appear to have any significant effect on pressures within the tunnel. The findings in this study provide further clinical evidence in support of prophylactic tarsal tunnel release prior to performing a lateralizing calcaneal osteotomy.