Ulnar Nerve Decompression at Guyon's Canal

Indication. Surgical decompression of Guyon's canal is offered for ulnar nerve compression at the wrist (ulnar tunnel syndrome) that is progressive, disabling, or driven by a space-occupying lesion — after a documented failure of conservative care (activity modification, splinting, and addressing any vascular or occupational cause). Typical triggers are progressive intrinsic weakness with atrophy, a mass compressing the nerve, persistent symptoms for 3 to 6 months despite non-operative management, electrodiagnostic studies localising compression to the wrist, or acute trauma with an expanding haematoma in the canal.

The decision turns on the zone and the cause. Document which zone is compressed pre-operatively (it predicts recovery) and decide whether the operation is a simple release or a release plus lesion management (ganglion excision, hook excision, or ulnar artery work). The single pre-operative test that changes the operation is the Allen test — it determines whether the ulnar artery can be safely ligated if it is diseased. Consent specifically for hypothenar numbness or a painful neuroma of the palmar cutaneous branch (the most common nerve injury, 5 to 10 percent), the rare but devastating deep motor branch injury (less than 1 percent), incomplete or delayed recovery (motor recovery is slow and may be incomplete if atrophy is severe), recurrence (5 to 10 percent), and — if arterial work is planned — a small risk of digital ischaemia. Setup. Supine with the arm on a radiolucent hand table, shoulder abducted about 90 degrees, elbow extended and forearm fully supinated. Regional anaesthesia (axillary or Bier block) is preferred, general anaesthesia if regional is contraindicated. An upper-arm pneumatic tourniquet at 250 mmHg (about 100 mmHg above systolic) with Esmarch exsanguination gives a bloodless field. Loupe magnification (×2.5 to ×3.5) is mandatory — identifying and protecting the small nerve branches and the artery is the whole game.

The goal: open the canal through a curvilinear ulnar-palmar incision, identify and protect the palmar cutaneous branch and the ulnar artery, divide the roof completely (proximal to distal), decompress both branches of the ulnar nerve — especially the deep motor branch around the hook of hamate — remove any compressing lesion, and close the skin only. The exposure is laid out in full below.

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Rehabilitation | Phase | Timing | Immobilisation | Therapy | |-------|--------|----------------|---------| | 1 | 0 to 3 days | Bulky dressing, wrist neutral, fingers free, no splint | Elevation and ice; immediate finger ROM | | 2 | 3 to 14 days | Lighter dressing from day 2 to 3 | Finger ROM hourly while awake, gentle wrist ROM; sutures out at 10 to 14 days | | 3 | 2 to 6 weeks | None | Scar massage, progressive wrist and grip strengthening; return to light work at 2 to 3 weeks; avoid repetitive palm impact | | 4 | 6 weeks to 6 months | None | Heavy work at 6 to 8 weeks, sport at 8 to 12 weeks, full grip strength around 3 months; cyclists avoid handlebars for 6 to 8 weeks | Sensory symptoms recover first (weeks to months); motor recovery is slower (3 to 6 months) and depends on the severity of pre-operative atrophy — if wasting was severe, some deficit may be permanent despite an adequate decompression. Around 80 to 90 percent report good to excellent results, with sensory recovery in 85 to 95 percent and useful motor recovery in 70 to 85 percent; about 90 percent return to their previous occupation.

Epidemiology. Ulnar nerve compression at the wrist is far less common than carpal tunnel syndrome or cubital tunnel syndrome. It is strongly associated with occupational and recreational palmar trauma — mechanics, carpenters, baseball catchers, martial artists and cyclists (handlebar palsy) — and with repetitive gripping against the hypothenar eminence. Hypothenar hammer syndrome and hook of hamate fractures share the same mechanism: the ulnar artery and nerve compressed against the hook of hamate. Canal anatomy. Guyon's canal is a roughly 4 cm fibro-osseous tunnel running from just proximal to the pisiform to the fibrous arch of the hypothenar muscles.

Nerve anatomy within the canal. Proximally the mixed ulnar nerve carries both motor and sensory fibres. It bifurcates — usually at the level of the hook of hamate (variable by 5 to 10 mm) — into a superficial sensory branch (pure sensory, supplying the small finger and ulnar half of the ring finger, running distally under the hypothenar muscles) and a deep motor branch (pure motor, curving radially around the hook of hamate with the ulnar motor artery, passing between abductor digiti minimi and flexor digiti minimi brevis, crossing the palm deep to the flexor tendons, and supplying all intrinsic muscles except the thenar muscles and the lateral two lumbricals). The dorsal cutaneous branch and the palmar cutaneous branch both arise proximal to the canal, so dorsal hand sensation and hypothenar sensation are spared in a pure canal lesion.

Clinical presentation. Motor findings (deep motor branch) are intrinsic weakness, hypothenar and interosseous atrophy, a positive Froment sign (thumb IP flexion on key pinch from weak adductor pollicis with compensatory FPL), a positive Wartenberg sign (small finger abduction from weak palmar interosseous with unopposed EDM), and clawing of the ring and small fingers in severe cases. Sensory findings (superficial branch) are numbness of the palmar small finger and ulnar ring finger only — the dorsal ulnar hand is spared (dorsal cutaneous branch arises proximal to the wrist). Vascular findings (hypothenar hammer) are cold sensitivity, digital pallor or cyanosis, Raynaud-like change, and a pulsatile mass if an aneurysm. A Tinel sign at the canal and a pressure-provocative test support the diagnosis. Investigations. EMG/NCS is the key test: prolonged distal motor latency, abnormal sensory conduction (unless the lesion is an isolated Zone 2, where sensory studies are normal — a key discriminator), and needle EMG showing denervation in the ulnar intrinsics (FDI, ADM, interossei) with a normal FDP and FCU, which localises the lesion to the wrist rather than the elbow. Imaging: a carpal tunnel view X-ray for a hook of hamate fracture, CT as the gold standard for hook pathology, MRI for soft-tissue masses and denervation change, ultrasound for dynamic assessment and arterial disease, and CT or digital-subtraction angiography for hypothenar hammer syndrome. The Allen test is mandatory before any ulnar artery intervention. Outcomes. Good to excellent results are reported in 80 to 90 percent, with sensory recovery in 85 to 95 percent (faster, over weeks to months) and useful motor recovery in 70 to 85 percent (slower, over 3 to 6 months); about 90 percent return to their previous occupation. Good prognostic factors are a short symptom duration (under 6 months — the strongest predictor), minimal pre-operative atrophy, an identifiable and removable mass, complete decompression, pure sensory symptoms (Zone 3) and younger age. Poor prognostic factors are chronic severe compression (over 12 months), severe intrinsic atrophy, a double crush (cubital tunnel plus Guyon's canal), incomplete initial decompression, significant comorbidity (diabetes, vascular disease), and workers' compensation claims. Guidelines, registries and global practice. No single national framework governs this operation — ulnar tunnel decompression is described consistently across hand-surgery teaching worldwide (ASSH, BSSH/FESSH, IFSSH), and the core principles (complete canal release, address the space-occupying cause, skin-only closure) are universal across the advanced orthopaedic practice (Tr and Orth), advanced orthopaedic practice, EBHS/FESSH, advanced orthopaedic practice and DNB/MS curricula. No implant registry applies, because this is a soft-tissue decompression without an implant, so evidence comes from case series and reviews rather than NJR, AJRR, AOANJRR or SHAR data. For hook of hamate fractures, international consensus favours excision over ORIF for symptomatic fractures and non-unions because of the tenuous blood supply, the deforming pull of attached muscles, the high non-union rate after fixation, and the proximity of the deep motor branch. For hypothenar hammer syndrome, practice varies globally by perfusion status: with a normal Allen test most surgeons resect and ligate the diseased segment, while with an abnormal Allen test vein-graft reconstruction is preferred. Smoking cessation, cold avoidance, and ergonomic and occupational modification are universally recommended to prevent recurrence.