Complete transection of the sciatic nerve following closed femoral fracture

Abstract

Complete transection of the sciatic nerve following femoral fracture is extremely rare. In the setting of closed injury it has only been reported in two other cases. Here we present a teenage motorcyclist who sustained a closed left, mid-femoral fracture following a road traffic collision with complete transection of the sciatic nerve. Despite being a closed injury, the obvious limb deformity of the patient and extreme pain prompted immediate nerve block during the primary survey making formal neurological assessment difficult. This case highlights the possibility of complete major nerve transection in closed injuries, and the importance of careful clinical examination alongside repeat imaging.

Background

Complete transection of the sciatic nerve is a rare but devastating injury that compromises the entire function of the posterior compartment of the thigh and all motor function below the knee. The aim of this article is to present a case of complete sciatic nerve transection resulting from a closed femoral fracture—rarely reported in the literature.

The femur is the longest and strongest tubular bone in the body.¹ Given the kinetic energy required to break the bone, femoral shaft fractures in younger patients mainly stem from high-impact collisions.^{2 3} In high income countries, the estimated incidence of femoral shaft fractures ranges between 8.2 and 23.9 per 100 000.⁴

The sciatic nerve is the largest nerve in the body, originating from the convergence of the anterior rami of spinal nerves L4–S3.¹ Throughout its course, in the posterior aspect of the thigh, the nerve is encased in muscle. Thus the incidence of sciatic nerve injury following open femoral fracture is uncommon, reported in only ~0.4% of cases.⁵ Neurotmesis, or complete transaction, is exceedingly rare^{6 7} and in closed injuries has only been reported in two other cases.^{8 9} Raising awareness that complete transection, in the setting of a closed fracture, can occur is important to allow reviewing physicians to consider the diagnosis of major nerve injury and manage these patients appropriately in a timely fashion.

Case presentation

A young male, who was an avid motorcyclist, was travelling at approximately 40 mph when a large stone caught his bike’s front wheel. He reported jumping off the bike to avoid hitting a tree, landing foot first on the road. The primary survey conducted by the responding paramedics noted that the patient was alert and stable; however, he had an obviously displaced left femoral shaft fracture with a pale foot, bruising over the right side of the chest and lacerations over both hands. The patient was sedated, and the left leg was reduced in a Thomas splint and he was transferred to the nearest district general hospital.

Investigations

In the emergency department, the patient had plain limb X-rays, demonstrating a displaced midshaft femoral fracture (figure 1) and a pan scan CT revealing a small right sided pneumothorax. The patient’s foot was noted to be pink and perfused following splint reduction; however, he reported severe pain and numbness in the left leg. A femoral nerve block was placed, prior to orthopaedic review, for analgesia management; therefore, no formal neurological examination was conducted.

Figure 1.

Lateral view radiograph of the patient’s left femur on admission.

On the basis of clinical examination and radiological findings, the patient was booked for femoral fracture fixation. No surgical intervention was required for his pneumothorax.

The patient was transferred to theatre, where attempts to perform a closed reduction were unsuccessful. Despite being a closed injury, it was documented that the distal femur could be felt just deep to the skin puncturing through the posterior compartment muscles of the thigh. A lateral approach was carried out to facilitate open reduction with an intramedullary nail. The sciatic nerve was not visualised during this procedure as there were no immediate initial concerns regarding nerve injury.

Twenty-four hours postoperatively, the patient reported ongoing severe lower limb paraesthesia and weakness. Formal sensory examination noted normal sensation in L1–L4, altered sensation in L5, no sensation in S1 and normal sensation in the S2–3 distribution. Formal motor examination using the Medical Research Council scale of muscle power documented: L3=2/5, L4–S1=0/5.

Symptoms of significant paraesthesia and weakness continued 48 hours postoperatively. Further formal neurological examination by the orthopaedic team demonstrated persistent significant motor and sensory disturbance prompting an emergency MRI (figure 2). The initial MRI of the lower limb concluded: ‘Abnormal appearance to the sciatic nerve at the level of the mid thigh, corresponding to the level of the fracture, raising the possibility of neural transection within post-traumatic intermuscular haematoma’.

Figure 2.

T1-weighted MRI demonstrating sciatic nerve gap and haematoma in the left thigh.

Following discussion with the musculoskeletal radiology team, a second MRI with contrast was carried out, reporting: ‘…sciatic nerve transection at the posterior aspect of the left proximal thigh with approximately 6.8 cm nerve gap’. This confirmed the diagnosis of complete transection prompting referral to the plastic surgery service for delayed primary reconstruction.

Differential diagnosis

The discussion regarding management of nerve injury in the setting of closed fracture is one that has achieved little consensus in the literature.¹⁰ The main difficulty with these injuries is deciding on classification of the associated nerve injury, and ultimately if conservative management will provide acceptable outcomes. It is accepted that the majority of nerve injuries produced by closed fractures cause in-continuity lesions that need to be assessed on an individual basis using clinical, radiological and electrical diagnostic studies. In this case, recognition that the presenting symptoms were significant and persistent allowed appropriate radiological investigation, identifying this was a neurotemetic injury requiring surgical intervention and timely referral for definitive management. For in-conituity lesions, that do not demonstrate such significant findings on imaging, best management can be less clear.

Treatment

On the basis of the MRI findings, the patient underwent formal surgical exploration of the sciatic nerve. The patient was placed prone and a mid-posterior approach to the sciatic nerve, between the biceps femoris and semitendinosus muscles, was carried out. A significant volume of organised haematoma was evacuated. The transected nerve was identified just proximal to the terminal division into the tibial and common peroneal. An associated nerve gap of 5 cm (figure 3) was identified and reconstructed with ipsilateral grouped fascicular sural nerve grafts. The patient was placed in a foot drop splint and transferred back to the ward uneventfully.

Figure 3.

Intraoperative image of sciatic nerve transection and measurement with surgical tape.

Outcome and follow-up

The patient made an uneventful postoperative recovery, with intensive multidisciplinary team input; physiotherapy incorporated ankle-foot orthosis to support gait and function. At 3 months, a Tinel’s sign was present just above the knee and the patient had altered sensation to the mid-calf. At 14 months postoperatively the patient is ambulating, with a progressing tinnels in the posterior calf and return of motor function in the posterior compartment, demonstrating plantarflexion (figure 4) and slight eversion on standing. On clinical examination, the patient had altered sensation to the medial malleolus but no return of motor function to the anterior compartment at this stage.

Figure 4.

Patient standing in plantar flexion, 14 months postoperatively.

Discussion

To our knowledge, complete sciatic nerve transection secondary to a closed femoral fracture is extremely rare.^{8 9} Review of EMBASE and MEDLINE databases retrieved four articles which report sciatic, tibial or peroneal nerve transection secondary to isolated closed femoral fracture.8 9 11 12 In two cases, transection of the common peroneal with sparing of the tibial division occurred.^{11 12} This case is therefore the third published example of complete proximal sciatic nerve transection in a closed fracture.

The patients described usually present as complex trauma cases requiring advanced trauma life support management. Incidences of complete proximal transection, including the patient described in this case, all occurred in the setting of high energy trauma.^{8 9} This can lead to distraction from not immediately life-threatening injuries.

Once the patient is stable and the secondary survey is underway, frequently the patient is analgesed or sedated, as was the case with this patient; this can mask serious ongoing pathology. Although a detailed physical examination is important, it cannot reliably distinguish between neurapraxia, axonotmesis or neurotmesis nerve injury in the acute phase. This prompts a need for further investigation and close clinical follow-up, as was carried out in this case.

In the contemporary setting MRI can be a useful tool in assessing nerve injury, with MRI changes seen as soon as 4 days postinjury. MRI classification of high grade peripheral nerve injuries remains challenging; sensitivity and specificity have been reported at 75% and 83%, respectively.¹³ Indicators of severity include bulbous enlargement, perineural fibrosis and muscle denervation changes, with nerve discontinuity being the most specific predictor.¹³

Similar to the MRI reported by Zelle et al⁸ the initial imaging was also inconclusive in this case; however, repeat MRI expressed sciatic nerve pathology, with evidence of an associated gap, that fundamentally prompted surgical intervention. Therefore, evaluation of the benefit of additional MRI, following consistent clinical evidence of sciatic nerve disruption, should be considered in future cases.

This is particularly important when considering that delayed diagnosis, and ultimately delayed intervention, can affect the return of motor and sensory function. A study of peripheral nerve regeneration in rat models demonstrated that repair beyond 3 months is likely to limit functional outcomes.¹⁴ This is highlighted in the case by Zelle et al⁸ where there is a 7-month delay between insult and surgery, with subsequent follow-up at 10 months demonstrating no return of motor function. Given this potential effect, in the event where nerve injury is not conclusively visualised on MRI, but findings on clinical examination and other testing modalities are persistent and congruent with significant sciatic nerve injury, surgical exploration should still be considered.

Distally, the common peroneal nerve is recognised to be more susceptible to injury in comparison to the tibial nerve.¹⁵ A study analysing the management of 380 patients with sciatic nerve injuries observed higher rates of success, and improved outcomes, in patients who underwent graft repair for lacerated tibial nerves in comparison to those who underwent repair of a lacerated peroneal nerve.⁷ Whether this is due to the intrinsic healing potential of the individual nerve or initial mechanism of injury is unclear. Despite differences in nerve repair technique, this case and that of Spiegel et al⁹ would support the finding that tibial nerve injuries perhaps show improved regeneration potential, given the motor recovery demonstrated in the tibial nerve distribution that is as yet lacking in the peroneal distribution.

Although the occurrence of sciatic nerve laceration secondary to a closed femoral fracture is rare, clinicians should always rule out the possibility of significant peripheral nerve injury; particularly if the patient is in a high energy accident. Given the devastating impact of sciatic nerve laceration, early recognition of the pathology in open or closed fractures may improve clinical outcomes.

Learning points.

• In closed high energy-femoral fractures significant sciatic nerve injury should be considered.

• MRI scanning in this case was a useful adjunct to identify sciatic nerve transection.

• Musculoskeletal radiology should be consulted if the initial imaging is inconclusive.

• Patients with a significant peripheral nerve injury should be monitored closely postoperatively by a team familarial with nerve injury management. Those demonstrating no neurological improvement should have prompt discussion with an appropriate nerve surgery centre to improve outcomes.

Ethics statements

Patient consent for publication

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