Novel Approach of Femur Shortening With Insertion of Expandable Rod to Achieve End-to-End Repair of Sciatic Nerve Laceration

Abstract

BACKGROUND: 

Sciatic nerve injuries are challenging for diagnosis and treatment. Particularly in proximally located high-grade injuries, neurorrhaphy often has poor outcomes. Most advocate autologous grafting and some more recently have suggested the value of knee flexion braces to facilitate end-to-end repair.

OBJECTIVE: 

To describe a case of femur shortening to facilitate tension-free, end-to-end sciatic nerve neurorrhaphy.

METHODS: 

The patient was a 17-year-old man who was injured by the propeller of a motor boat and suffered a series of lacerations to both lower extremities including transection of his right sciatic nerve in the proximal thigh. After extensive mobilization of the nerve, a greater than 7-cm gap was still present. The patient was treated with femur shortening to facilitate end-to-end coaptation. He subsequently had an expandable rod placed which was lengthened 1 mm per day until his leg length was symmetric.

RESULTS: 

Within 7 months postoperatively, the patient had an advancing Tinel sign and paresthesias to the dorsum of his foot. Nine months postoperatively, he had early mobility in his plantarflexion.

CONCLUSION: 

We present a novel method of femur shortening with insertion of an expandable rod to facilitate direct end-to-end and tension-free sciatic nerve neurorrhaphy in a proximally located injury. Furthermore, larger scale and comparative studies are warranted to further explore this and other techniques.

Sciatic nerve injuries are challenging to both diagnose and manage. The mechanism of injury can be from pressure, iatrogenic injury, or from significant trauma such as combat-related or high-speed motor vehicle collisions.^1,2 Injuries that occur in conjunction with femur fractures are rare but have been reported as well.^3-6 Electrodiagnostics and imaging can be useful to fully elucidate the extent of nerve injury,⁷ and early mobilization is used to prevent contractures.⁸

When surgery is warranted, as in the case of high-grade nerve injuries, multiple algorithms exist. Earlier intervention is preferred to minimize pain and lead to better functional outcomes.⁹ For compressive etiologies, such as hematoma, and for sharp lacerations, urgent surgery is recommended.^1,7,10,11 For blunt injuries without transection, many recommend waiting to assess for return of function before surgical intervention.²

For sciatic nerve lacerations, the goal is to restore continuity of the nerve using end-to-end coaptation. Ideally, repairs should be performed under no tension, and, if possible, direct neurorrhaphy without grafting is optimal.^12-14 This is often difficult to achieve, and grafting with allograft or autograft may be warranted. In the setting of sciatic nerve transections occurring proximally in the thigh or buttocks, prognosis is poor.^3,15,16 Novel treatment algorithms in this setting may lead to better outcomes. In this article, we present a novel technique involving femur shortening, followed by insertion of an expandable rod to facilitate direct end-to-end tension-free sciatic nerve repair.

METHODS

Case Report

The patient was a 17-year-old man who was injured by the propeller of a motor boat and suffered a series of lacerations to both lower extremities. He was treated at his local hospital; however, the sciatic nerve was noted to be completely transected with a large gap, and there was no attempt to repair it. The patient was referred to our institution for further management and brought back to the operating room 7 days after the injury.

Operative Technique

The patient was positioned prone, and both lower extremities were prepped and draped including the buttocks and extending distally.

The original laceration on the back of the right thigh was reopened. Dissection was performed between the severed hamstring muscles that had been partially reapproximated. A completely divided sciatic nerve (Sunderland V) was identified in its usual anatomic position with a 5-cm gap between the ends. The ends were severely traumatized secondary to the original injury, requiring trimming of 2 to 3 cm both proximally and distally to reach healthy nerve. The skin incision was extended both proximally and distally, and the nerve was further dissected and mobilized, but it was clear that a primary end-to-end repair could not be achieved given the large gap.

The first consideration to achieve end-to-end repair was to flex the knee and place the lower extremity in an external fixation device (with a plan for subsequent extension over time). When the knee was flexed to 90°, however, there still remained a 3-cm gap (pretrimming) between the nerve ends. Furthermore, given the proximal location of the injury, the large diameter of the injured sciatic nerve, the long gap between the nerve ends, and the distance to the target muscles, harvesting bilateral sural nerves as autograft would be insufficient to achieve meaningful motor recovery.

Ultimately, there was consensus that the highest chance of success would be through an end-to-end repair that could be attained by shortening the femur by 7 cm. The lead surgeon had an extensive discussion with the parents' and obtained consent to proceed.

At this point, the wound was temporarily closed and dressed, and the patient was rotated into a supine position. The orthopedic surgeon made a separate lateral longitudinal incision in the right thigh, and using fluoroscopy, the distal femur was exposed and the osteotomy location identified (Video). The osteotomies were performed proximally and distally, a 7-cm segment of femur was removed, and a femoral nail was inserted across the fracture gap (Figure A). The wound was then closed, and the patient was returned to a prone position for nerve repair.

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FIGURE.: Artistic rendering of the initial exposure showing A, the injured hamstring muscles and sciatic nerve as well as the initial femoral osteotomy and inserted growing rod B, the shortened leg C, followed by the tension-free end-to-end nerve coaptation D, and then the expanding rod/femur E, and early plantarflexion response. © 2021 Johns Hopkins University. All rights reserved. Ian Suk.

The right posterior thigh was then reopened and the sciatic nerve exposed. The scarred edges of the nerve were trimmed back until a fascicular pattern was seen, and tension-free direct coaptation was performed with interrupted 8-0 prolene sutures (Figure A-C). Coaptation site was then reinforced with fibrin glue. Given the long duration of the operation and extent of muscle swelling, a wound vac was placed at the end of surgery, and plastic surgery performed primary closure 4 days later.

RESULTS

The patient recovered well from surgery. Three months later, the patient was taken back for subtrochanteric osteotomy and insertion of a precise nail with growing rod placement. The patient was discharged the following day, and he magnetically lengthened the femur by 1 mm per day (Figure D). He was seen again 4 months later (7 months after initial operation), at which time he had an advancing Tinel sign at the fibular head causing paresthesias at the dorsum of his foot. As expected, he did not have motor function (distance from injury to target muscle was ∼75 cm), but the apparent progression of the Tinel sign suggested a recovery faster than the expected 1 mm/day of neural regeneration. At 9 months after the nerve repair, the patient sent a video showing plantarflexion of his right foot (Figure E, Video). At the most recent follow-up visit 15 months postoperatively, the patient presented to have his growing rod removed. At that time, his medical research council score for plantarflexion was 4/5, dorsiflexion and inversion were 0 to 1/5, and eversion was 2/5. On electromyography, there was abundant spontaneous activity in both the right tibialis anterior and peroneus longus muscles, with fast but irregularly firing voluntary motor units in both muscles.

The participants and any identifiable individuals consent to publication of their image. Institutional Review Board approval was not required for this study per institutional guidelines (Policy 102.3).

DISCUSSION

The case presented here is the first description of femur shortening to facilitate coaptation of transected sciatic nerve, precluding the need for grafting. Few studies have reported the use of shortening osteotomies in the upper extremity for primary repair¹⁷ and to facilitate nerve transfer without the need for an interpositional graft.^18-21 Lower extremity osteotomies for this purpose, however, have historically been avoided because of concern of functional limitations from leg length discrepancies.¹⁷

Studies have shown poor results with nerve graft repair of transected sciatic nerve, both at the buttock and thigh level, particularly in adult patients (although pediatric patients tend to do better).^3,15,16 In this case particularly, given the >7-cm gap and the proximal site of injury, we felt that using autograft from bilateral sural nerves would yield limited recovery. What we found in this case was that our patient tolerated the femur shortening, insertion of growing rod, and subsequent removal very well. We also were surprised to find postoperative neurological recovery and advancing Tinel sign faster than the 1 mm/day that we anticipated. Given the distance of approximately 30 inches from the coaptation to the target muscle, we expected it to take 2.5 years for recovery. We found that the patient already demonstrated some plantarflexion at 9 months.

One potential explanation is that the minimal tension induced by expanding the rod by 1 mm/day may have a beneficial impact on nerve regeneration and therefore yielded better outcomes than expected. Early studies revealed the adverse impact of tension on nerve regeneration secondary to scar formation,^22,23 which popularized the use of nerve grafting and the importance of tension-free coaptation. In more recent decades, however, animal studies have been used to quantify the extent of tension that leads to the adverse outcome, and some studies have found that perhaps minimal tension may induce superior nerve regeneration.^24-26 It is possible that lengthening the femur at 1 mm/day provided an advantageous tension. Important to recognize, however, is that orthopedic studies have shown the potential for nerve injury with limb lengthening, particularly for those with congenital pathologies (as opposed to shortening performed for other etiologies such as trauma).^27,28 Another potential explanation for the relatively faster neural regeneration may be related to the magnet that was used to expand the growing rod. Previous animal and clinical studies have shown that low-frequency electrical stimulation and magnetic stimulation may promote nerve regeneration.^29-32 It is plausible that the magnet used for the femur lengthening contributed to the faster recovery. Finally, it is also feasible that the fractured bone releases growth factors in an attempt to fuse and that these factors may induce growth of the nerves as well.³³

Another interesting finding is that, although still relatively early in the postoperative period, there has been a difference in the recovery of the tibial nerve (4/5 strength at the last follow-up) relative to the morel limited peroneal nerve recovery. Peroneal nerve function has shown to be particularly poor in situations where nerve grafts are used for repair rather than primary nerve coaptation, likely because of its decreased blood supply in comparison with the tibial nerve.^1,14 For this reason, some advocate the use of vascularized nerve grafts or tendon transfers either primarily in conjunction with sciatic nerve repair or secondarily to address peroneal nerve deficits.^16,23,34-36 Most agree, however, is that a tension-free sciatic nerve coaptation should be attempted even when large gaps are present, using whatever modality possible to diminish the gap size. It is possible that in this case there may have been a partial rupture of the coaptation site leading to the discrepancy in the recovery of the peroneal vs the tibial nerves, although we feel this is less likely given the early and robust tibial nerve recovery. Some advocate for the use of ultrasound to follow the integrity of the nerve suture (which we have had limited success in doing), and ultimately if the peroneal nerve does not recover, we may consider more definitive imaging using MRI to fully evaluate.

To facilitate a tension-free primary sciatic nerve repair, many studies advocate the use of knee flexion at 60° to 90° for 6 weeks.^34,37,38 This prolonged immobilization does create temporary stiffness and knee contracture, although this seems to resolve in most cases with no long-term sequelae.³⁷ Sciatic nerve gaps of up to 8 cm can potentially still undergo primary nerve repair with the knee in full flexion, although injuries in the upper and midthigh do not mobilize as easily and may be more difficult to repair even with knee flexion and other such maneuvers.³⁶ It is important to note that in this case, even with complete flexion, the gap did not sufficiently close to allow for an end-to-end coaptation. For this reason, we elected to proceed with the femur shortening. We hope that nerve surgeons add this technique to their armamentarium for circumstances such as presented here; ultimately, the decision of grafting vs joint flexion vs limb shortening needs to be individualized to the patient and to the specific injury presentation.

CONCLUSION

Repair of proximally located high-grade sciatic nerve injuries are challenging. Several methods exist including direct neurorrhaphy when possible, autologous grafting with the sural nerve, and fixating the knee in a flexed position with external braces. Outcomes tend to be poor for multiple reasons. In this article, we present a novel method of femur shortening with insertion of an expandable rod to facilitate direct end-to-end and tension-free neurorrhaphy that led to a successful outcome. Furthermore, larger scale and comparative studies are warranted to further explore this and other techniques.