Locating the danger zone to avoid injury to the sural nerve during Achilles calcaneal tendon repair. A systematic review of cadaveric studies with clinical implications.

INTRODUCTION: Although iatrogenic injuries to the sural nerve (SN) are commonly encountered in calcaneal (Achilles) tendon (CaT) repair surgeries, the relationship between both structures have anatomical variations. A quantitative evidence synthesis has not been yet conducted. Our systematic review aims to better define the safe zone where the SN crosses the lateral border of CaT. METHODS: Electronic databases were searched to locate relevant anatomical studies recording details regarding the distance at which SN crosses the CaT. The Checklist for Anatomical Reviews and Meta-Analyses (CARMA) was followed. The primary outcome was the mean distance from CaT insertion to SN crossing site, to locate a safe zone. The secondary outcome was the mean horizontal distance from the SN to the CaT lateral border. RESULTS: Seven studies met the inclusion criteria with a total of 204 cadaveric limbs. The danger zone was located 2 cm distal and proximal to the mean distance of the crossing point. The mean distance from CaT insertion to the SN crossing site was 9.91 ± 0.67 cm. The mean horizontal distance between SN and the CaT lateral border decreased from a mean of 19.8 ± 2.06 mm at the calcaneal tuberosity level to 3.6 ± 0.4 mm at 10 cm proximal to the tuberosity. DISCUSSION: This review demonstrated that 10 cm is the average distance from the CaT insertion onto the calcaneal tuberosity to the point of crossing of the SN. A safe zone would be 2 cm away proximally and distally from the crossing point. We recommend placing the proximal lateral sutures away from this region. This finding should help surgeons avoid SN injuries during open or percutaneous approaches for calcaneal tendon rupture.