Leg Flexion for Sciatic Nerve Gap Repair: An Anatomic Study
Jasmine A. Thum, MD1, Justin Luk, BS2, Stanley Bazarek, MD, PhD3 and Justin M. Brown, MD2, 1Massachusetts General Hospita, Boston, MA, 2Massachusetts General Hospital, Boston, MA, 3Brigham & Women's Hospital, Boston, MA
Introduction:
Direct nerve repairs fare better than grafted nerves, especially for large caliber nerves. Numerous surgical techniques are used to achieve tension-free end-to-end repairs for large gaps in the sciatic nerve (SN) and common peroneal nerve (CPN), including distal nerve mobilization, transposition, side-branch neurectomy, or even shortening of the femur with distraction osteogenesis. However, leg flexion with serial distraction is the simplest, least morbid, and most easily implemented technique. This study aims to (1) quantify gap lengths that can be reliably overcome with knee flexion and subsequent side-branch neurectomy to enable direct repairs of the SN and CPN and (2) provide guidance on rates of post-operative leg distraction after nerve repair.
Materials & Method:
Eight fresh cadavers with pelvis intact were dissected to determine the relationship between degrees of knee flexion (ranged from 0 to 90-degree flexion) and the gap length overcome with nerve excursion. Additional excursion from SN side-branch neurectomy was also assessed.
Results:
We found an approximately linear relationship between knee flexion and nerve excursion. In the mid-thigh there was 7-9mm of SN excursion per 10 degrees of flexion, and 10-11mm of SN excursion per 10 degrees of flexion with neurectomy. There was 11-13mm of CPN excursion per 10 degrees of flexion in the distal half of the thigh.
Table 1.
Cadaver type, Mark / Distance (%) along femur | Excursion per 10 degrees knee flexion without neurectomy (mm) | Excursion per 10 degrees knee flexion with neurectomy of SHB only (mm) | Excursion per 10 degrees knee flexion with neurectomy of SHB and PHS (mm) |
Fresh, 25% | 7.2 | -- | 10.4 |
Fresh, 50% | 9.7 | 11.4 | -- |
Fixed, 25% | 0.8 | 1.3 | 12.5 |
Fixed, 50% | 5.0 | 10.4 | -- |
Table 2.
Cadaver type, Mark / Distance (%) along femur | Excursion per 10 degrees knee flexion (mm) |
Fresh, 75% | 12.2 |
Fresh, 100% | 10.9 |
Fixed, 75% | 8.1 |
Fixed, 100% | 3.4 |
Conclusions:
Knee flexion can significantly augment the ability to achieve an end-to-end repair of the SN and CPN. Simplified, each 10 degrees of knee flexion provides about 1 cm of additional length for both nerves, which is essentially constant throughout the arc of flexion. Neurectomy allows approximately 1-2cm in total additional length at full flexion in fresh cadavers. Approximately 10cm total excursion can be gained at 90-degree knee flexion with side-branch neurectomies. We recommend 45-90 days of progressive extension to respect the safe regeneration timing of 1-2mm/day from a repair performed with 90-degree knee flexion.
Image 1-Anatomic Drawing.png
Image 2-SN Graphs.png
Image 3-CPN graphs.png
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