Hypothenar Hammer Syndrome

Hypothenar hammer syndrome is ischaemia of the hand caused by repeated blunt trauma to the hypothenar eminence, producing ulnar artery injury with thrombosis, aneurysm or embolisation to the digits.

Exposure. Using the palm as a hammer, such as mechanics, machinists, carpenters, metalworkers and bricklayers; also vibrating tools, cycling, and sports such as karate and volleyball.

Epidemiology. Rare and underdiagnosed. It affects mainly men aged 30 to 50, and usually the dominant hand.

Anatomy and risk. The ulnar artery lies superficial as it crosses the hook of the hamate at the Guyon canal, with little soft tissue protection.

Course. Many patients improve with trauma avoidance and treatment. Untreated disease can lead to digital ulceration and gangrene.

Pathophysiology.

Repetitive impact damages the arterial intima and media, causing thrombosis, true aneurysm or false aneurysm. Thrombus can embolise to the ring, little and middle fingers.

Sympathetic overactivity and vasospasm add to the ischaemia.

• Cold intolerance with pallor or cyanosis of the ring, little and middle fingers, usually in one hand.
• Pain in the hypothenar eminence or ulnar border; palpable tender pulsatile mass.
• Numbness or paraesthesia (ulnar nerve compression).
• Fingertip ulcers, splinter haemorrhages and nail changes in advanced disease.

Red flags.

• Digital ulceration, gangrene or rest pain.
• Acute severe pain with a cold, pale or pulseless hand (acute arterial occlusion).
• Rapidly expanding pulsatile mass.

• Occupational and recreational history of palm trauma.
• Allen test for ulnar artery patency, digital pressures and handheld Doppler.
• Duplex ultrasound; CT or MR angiography to show occlusion or aneurysm; catheter angiography when intervention is planned (corkscrew appearance).
• Exclude other embolic sources: ECG, echocardiography and cardiac rhythm monitoring.
• Autoimmune screen (ANA, ENA, ANCA, complement), full blood count, and thrombophilia tests when indicated.

Differential diagnosis. Primary Raynaud phenomenon, vibration white finger, systemic sclerosis and other vasculitis, thoracic outlet syndrome, cardiac or aortic embolism, Buerger disease, atherosclerosis, ulnar nerve entrapment, ganglion or soft tissue mass.

• Stop palm trauma; use padded gloves; keep the hand warm; stop smoking and avoid vasoconstrictors including caffeine.
• Nifedipine modified release 30 mg orally once daily, increased after 2 weeks to 60 mg daily if needed. Usual maximum 60 mg daily. Give for the cold season or long term. Monitor blood pressure, ankle oedema and headache. Reduce dose in hepatic impairment; no renal adjustment; avoid in pregnancy unless benefit outweighs risk.
• Aspirin 75 mg orally once daily, long term. Maximum 75 to 100 mg daily. Monitor for bleeding and dyspepsia. Avoid in active peptic ulcer and bleeding disorders; caution in eGFR under 10.
• Acute thrombosis or embolism: urgent vascular assessment. Enoxaparin 1 mg/kg subcutaneously every 12 hours until the specialist plan is set. Maximum 1 mg/kg each dose. Monitor platelets, creatinine, and anti-Xa level in extremes of weight or renal impairment. When creatinine clearance is under 30 mL/min give 1 mg/kg once daily. Choice and duration of later anticoagulation are decided by the vascular team.
• Severe ischaemia or ulceration: iloprost 0.5 to 2 nanograms/kg/min intravenously over 6 hours daily for 3 to 5 days, titrated to tolerance. Maximum 2 nanograms/kg/min. Monitor blood pressure and heart rate; start low in renal impairment (creatinine clearance under 30 mL/min) and hepatic impairment; avoid in pregnancy and unstable cardiac disease.
• Aneurysm, occlusion with persistent ischaemia, or failed medical therapy: surgical resection with vein graft reconstruction or ligation, with or without sympathectomy.

Monitoring. Digit perfusion and ulcer healing at 2 to 4 weeks; repeat duplex after treatment changes; yearly review thereafter.

Referral and escalation. Vascular or hand surgery at diagnosis; emergency referral for acute ischaemia; occupational physician for work change; notification and compensation where required.

Special groups. Pregnancy: avoid iloprost, and manage anticoagulation with specialist advice.