Common Peroneal Nerve Decompression

Indication. Surgical decompression is offered for a common peroneal nerve palsy at the fibular neck that is compressive in origin, has failed an adequate trial of non-operative care, or is caused by a space-occupying lesion. The patient typically presents with a foot drop (weak or absent ankle dorsiflexion and eversion) with sensory loss over the lateral leg and dorsum of the foot, a positive Tinel sign at the fibular neck, and an intact ankle jerk and gastrocnemius-soleus function (which exclude a sciatic or tibial lesion). Absolute indications are progressive motor weakness (foot drop) with a compressive lesion, failure of conservative management after 3-6 months of observation, a space-occupying lesion (ganglion cyst, schwannoma), and an open injury with the nerve in continuity requiring exploration. Relative indications are persistent symptoms with documented compression on imaging, an iatrogenic injury after total knee arthroplasty or proximal tibial surgery, and a positive Tinel sign at the fibular neck with EMG confirming compression. Timing drives the decision to operate, and depends on the mechanism:

Contraindications. Absolute: a complete nerve transection requiring grafting (a different procedure), active infection at the surgical site, and irreversible nerve damage with chronic denervation (greater than 18 months). Relative: a central cause of the foot drop (stroke, multiple sclerosis, spinal pathology), an L5 radiculopathy mimicking a CPN palsy, and an underlying polyneuropathy such as Charcot-Marie-Tooth disease, in which decompression is less effective. The differential of a foot drop must be excluded before operating - decompressing the peroneal nerve will not help an L5 radiculopathy:

Pre-operative assessment. Document motor function (tibialis anterior power, resisted ankle dorsiflexion), a Tinel sign at the fibular neck (positive in a regenerating or compressed nerve), and the sensory examination over the lateral leg, dorsum of the foot and first web space. Palpate for a mass - a ganglion is palpable about 60 percent of the time - and confirm gastrocnemius-soleus function is intact (excludes a sciatic or tibial lesion). EMG and nerve conduction studies are essential: a conduction block at the fibular neck implies a good prognosis, while fibrillation potentials in tibialis anterior indicate denervation. MRI excludes a mass lesion and assesses nerve signal change; ultrasound allows dynamic assessment and identifies ganglion cysts and nerve calibre change. Consent. Counsel that 60-80 percent improve when the aetiology is compressive and preoperative function is good, that a complete foot drop present for greater than 12 months carries a poor prognosis, and that there is a 2-5 percent risk of worsening, plus incomplete recovery and residual numbness. Setup. Lateral decubitus (affected side up) is preferred, or supine with a bump under the ipsilateral hip, with the knee flexed 15-20 degrees to relax peroneus longus. A standard soft-tissue tray with bipolar cautery (essential for haemostasis near the nerve), loupe magnification (2.5-3.5x), a headlight, fine dissecting scissors (Metzenbaum, tenotomy), Penfield dissectors, vessel loops for nerve retraction and a self-retainer (Weitlaner or Gelpi). General or regional anaesthesia; full leg prep; a thigh tourniquet is optional and, if used, should be deflated before closure to check haemostasis.

The goal is to expose the common peroneal nerve through a curvilinear incision centred on the fibular neck, find it safely in the proximal interval, trace it distally, and release every point of compression - above all the peroneus longus fascial arch - while protecting its branches and the lateral sural cutaneous nerve.

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Immediate post-operative care. No splinting is required unless a combined procedure has been performed. Elevate the leg for 24-48 hours to minimise swelling, allow weight-bearing as tolerated from the outset, and review the wound at 2 weeks. Ankle-foot orthosis. Continue an AFO for the foot drop until motor recovery is documented, using a custom-moulded AFO if prolonged use is anticipated. The priority is to prevent an equinus contracture while the nerve recovers. Rehabilitation and follow-up. Begin early ankle range-of-motion exercises, with physiotherapy strengthening as power returns and gait training with the AFO. Review clinically at 6 weeks, 3 months and 6 months, with a repeat EMG at 3-6 months to assess reinnervation. The first signs of recovery appear at 3-4 months and recovery may continue for 18-24 months. Expected recovery. Good-prognosis factors are a compressive aetiology, a short duration of symptoms, a partial lesion and a positive Tinel sign. Poor-prognosis factors are a traumatic transection, a duration greater than 12 months, an absent Tinel sign and no improvement on EMG. Overall, 60-80 percent of well-selected patients achieve meaningful improvement. Complications. Most are preventable with atraumatic handling, complete decompression of every site, and a loose closure.

Anatomical course - the basis of the operation. The common peroneal nerve arises from nerve roots L4-S2. It separates from the tibial nerve in the distal thigh at the sciatic bifurcation, runs along the medial border of biceps femoris, and emerges between biceps and the lateral head of gastrocnemius. At the fibular neck it wraps around 1-2 cm distal to the fibular head and is subcutaneous for about 4 cm - its most superficial and vulnerable point. It gives off the lateral sural cutaneous nerve proximally, then enters peroneus longus through a fibrous tunnel where it divides into the deep peroneal nerve (which enters the anterior compartment through the anterior intermuscular septum and supplies the dorsiflexors) and the superficial peroneal nerve (which continues in the lateral compartment to supply the evertors and the dorsum of the foot). Why the peroneus longus fascia matters. The fibrous arch at the entry to peroneus longus is the most common compression site - the common peroneal nerve equivalent of the arcade of Frohse for the posterior interosseous nerve or Osborne's ligament for the ulnar nerve. This single anatomical fact is the most commonly tested point on the operation. Epidemiology and aetiology. Causes include external compression (lateral decubitus positioning or a leg holder, plaster casts, habitual leg crossing), rapid weight loss (loss of the protective fat pad), a ganglion cyst arising from the superior tibiofibular joint, and a fibular neck fracture. Iatrogenic palsy complicates about 0.3 to 1.8 percent of total knee arthroplasties, and is more likely with a preoperative valgus deformity, prior lumbar laminectomy and epidural analgesia. Nerve-injury classification and surgical decision-making. Seddon's classification underpins the decision to observe, decompress or graft:

Complete reference list 1. Kim DH, Murovic JA, Tiel RL, Kline DG. Management and outcomes in 318 operative common peroneal nerve lesions at the Louisiana State University Health Sciences Center. Neurosurgery. 2004;54(6):1421-1428. 2. Mont MA, Dellon AL, Chen F, Hungerford MW, Krackow KA, Hungerford DS. The operative treatment of peroneal nerve palsy. J Bone Joint Surg Am. 1996;78(6):863-869. 3. Fabre T, Piton C, Andre D, Lasseur E, Durandeau A. Peroneal nerve entrapment. J Bone Joint Surg Am. 1998;80(1):47-53. 4. Maalla R, Youssef M, Ben Lassoued N, Sebai MA, Essadam H. Peroneal nerve entrapment at the fibular head: outcomes of neurolysis. Orthop Traumatol Surg Res. 2013;99(6):719-722. 5. Spinner RJ, Atkinson JL, Tiel RL. Peroneal intraneural ganglia: the importance of the articular branch. A unifying theory. J Neurosurg. 2003;99(2):330-343. 6. Schmalzried TP, Amstutz HC, Dorey FJ. Nerve palsy associated with total hip replacement. J Bone Joint Surg Am. 1991;73(7):1074-1080. 7. Idusuyi OB, Morrey BF. Peroneal nerve palsy after total knee arthroplasty: assessment of predisposing and prognostic factors. J Bone Joint Surg Am. 1996;78(2):177-184. 8. Kang HJ, Choi YR, Kang ES. Outcomes of arthroscopic excision of proximal tibiofibular joint ganglion cysts. J Bone Joint Surg Am. 2012;94(18):1678-1683. 9. Humphreys DB, Novak CB, Mackinnon SE. Patient outcome after common peroneal nerve decompression. J Neurosurg. 2007;107(2):314-318. 10. George SC, Boyce DE. An evidence-based structured review to assess the results of common peroneal nerve repair. Plast Reconstr Surg. 2014;134(2):302e-311e.