summary Hypothenar Hammer Syndrome is post-traumatic digital ischemia from thrombosis of the ulnar artery at Guyon's canal. Diagnosis is made with vascular studies including Doppler ultrasound and CT angiography. Treatment can be observation, fibrinolysis, vessel ligation or reconstruction depending on the chronicity of symptoms, the digital brachial index, and the presence of an aneurysm. Epidemiology Incidence rare < 1 per 100,000 Demographics male: female ratio is 9:1 age bracket is 40s-50s Anatomic location unilateral, dominant ring finger +/- small finger less commonly, index and middle fingers thumb is spared Risk factors occupations using vibrating tools such as carpenters, machinists, mechanics sports such as baseball catchers, mountain biking, golf, volleyball, karate Etiology Pathophysiology mechanism single or repetitive blunt impact on hypothenar eminence leads to ulnar artery thrombosis or aneurysm hook of hamate functions as an anvil, causing thrombosis distal embolisation leads to ulceration, gangrene Anatomy Ulnar artery ulnar artery branches into 2 branches as it exits Guyon's canal deep branch superficial palmar arch in Guyon's canal relation to hook of hamate over distal 2cm, the artery is directly anterior to the hook of the hamate, covered by palmaris brevis, subcutaneous tissue and skin Presentation History occupational or sporting risks (see above) Symptoms pain over hypothenar eminence and ring finger may involve small, middle and index fingers cold sensitivity paresthesia Physical exam inspection blanching, mottling, cyanosis, pallor, gangrene tenderness over hypothenar eminence prominent callus (calloused skin over hypothenar eminence) pulsatile mass if aneurysm is present fingertip ulcerations over ulnar digits splinter hemorrhages over ulnar digits provocative tests Allen's test positive if occlusion is present negative if an aneurysm is present Imaging Doppler ultrasound indications first line test measure digital brachial index <0.7 necessitates reconstruction Angiogram, CT angiogram or MR angiogram indications mandatory for diagnosis findings tortuous "corkscrew" ulnar artery occlusion or aneurysm at the hook of the hamate Differential Raynaud's disease involves the thumb (hypothenar hammer syndrome does not) Treatment Nonoperative lifestyle modifications, symptomatic treatment, and vascular consult indications thrombosis without aneurysm > 2 weeks asymptomatic no threat of digital loss lifestyle modifications smoking cessation avoid recurrent trauma outcomes 80% success Operative endovascular fibrinolysis indications thrombosis without aneurysm < 2 weeks excision of involved segment and reconstruction with or without a vein graft indications digital brachial index <0.7 thrombosis with aneurysm ischemia in multiple digits failed conservative treatment with recurrent symptoms arterial ligation (Leriche procedure) indications digital brachial index >0.7