Cadaveric Analysis on the Spatial Properties of the Sural Nerve around the Lateral Malleolus

Abstract

Background The sural nerve (SN) provides cutaneous innervation to the posterolateral leg. There are six different morphologic formations of the SN but most frequently forms from the union of two proximal roots. It's typical course takes it from its formation in the mid-calf to course between the calcaneal tendon (CT) and the lateral malleolus (LM) eventually terminating in the dorsum of the foot. The SN is frequently used for donor nerve grafts peripheral neuropathic testing. Due to its clinical significance in clinical/surgical intervention in the lower extremity defining the course of this nerve is imperative. Purpose The principal objective of this research was to leverage a large sample cadaveric cohort to determine if the spatial course of the SN as it travels around the region of the LM differs based on its contributing morphology. Methods Previous dissection under IRB approval from Kansas City University and Creighton School of Dentistry allowed a sample of 208 lower extremities to be dissected. An incision was made 1-3 cm was made midway between the posterior boarder of the LM and CT. The SN and the small saphenous v. were identified and the nerve was dissected until the contributing morphology of the SN, CT, LM, and the SN inferior to the apex of the LM were observed. Pins were placed along with a forensic ruler to provide a unit standard for digital assessment. Digital images were captured from a standard distance to account for parallax changes. These were uploaded into ImageJ for data analysis to measure the LM to SN, CT to SN, and inferior apex of LM to SN. All statistics were calculated using Microsoft Excel. Results The frequency of SN types: Type 1) n = 86; Type 2) n = 18; Type 3) n = 72; Type 4) n = 1; Type 5) n = 1; Type 6) n = 0; Unassigned 1) n = 22; Unassigned 2) n = 8. Distance from the LM to the SN: Type 1) 1.65 ± 0.57 cm (CI: 1.63-1.66); Type 2) 1.48cm ± 0.45 (CI: 1.43-152); Type 3) 1.68 ± 0.58) (CI: 1.66-1.69); Type 4) 2.57cm; Type 5) 1.39cm; Unassigned 1) 1.48cm ± 0.77 (CI: 1.42-1.55)); Unassigned 2) 1.30cm ± 0.63 (CI:1.14-1.45) Distance from the distal tip of the LM to SN: Type 1) 1.99cm ± 0.77 (CI:1.96-2.00 ); Type 2) 2.09 ± 0.68(CI: 2.01-2.16); Type 3) 2.11cm ± 0.72(CI: 2.11-2.15); Type 4) 3.04cm; Type 5) 1.75cm; Unassigned 1) 1.76cm ± 0.90 (CI:1.67-1.83); Unassigned 2) 1.90cm ± 0.53(CI: 2.11-2.15) Distance from the distal tip of the LM to SN: Type 1) 2.39cm ± 0.85(CI: 2.36-2.4); Type 2) 1.48 ± 0.45(CI:1.42-1.52); Type 3) 1.68cm ± 0.58(CI: 1.66-1.69); Type 4) 2.57cm; Type 5) 2.51cm; Unassigned 1) 2.29cm ± 0.77(CI: 2.22-2.36); Unassigned 2) 1.30cm ± 0.63(CI: 1.14-1.45). Single Factor ANOVA show LM to SN with F = 1.32, F-crit = 2.42, and p = .2606; CT to SN show F = 0.42, F-crit = 2.41, and p= .7946; and lastly LM to SN F = 0.9822, F-crit = 2.42, and p=.4182. Conclusion The most frequently observed SN formations were Type 1 and Type 3. These nerves appear in 76% of our sample and report a range of 1.65 cm to 1.68 cm from the posterior board of the LM, a range of 2.39 cm to 2.54 cm from the CT to the SN, and 1.99cm to 2.09 cm from the inferior apex of the LM to the SN. Our large sample size is sufficient to determined that the distance of the SN (from any of these three surgical landmarks) is consistent regardless of contributing morphology of SN formation.