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Hypothenar hammer syndrome (HHS) is caused by repetitive use of the hand as a hammer so that there is thrombosis of the superficial palmar arch of the ulnar artery. There is trauma over the hook of hamate, where the superficial branch of the palmar artery lies. This leads to vascular insufficiency of the ulnar side of the hand.
- Hypothenar hammer syndrome (HHS) is probably rare, but may be underdiagnosed.
- Typically, it occurs in men around age 40 years, in occupations and sports where the heel of the hand is used as a hammer or is subject to repeated force; for example:
- Occupations such as metal workers, machinists, mechanics, miners, sawmill workers, carpenters, bricklayers, butchers, bakers and those using vibrating tools.
- Various sports, including golf, mountain biking, baseball, softball, hockey and martial arts.
Likely factors involved in causation are:
- Single or repeated blows to the heel of the hand
- Pre-existing abnormalities of the arteries or variations in arterial anatomy (eg incomplete superficial palmar arch)
- Underlying prothrombotic factors
- Other anatomical variations, eg an anomalous hypothenar muscle.
The ulnar artery is vulnerable in the distal portion of Guyon's canal, where it is not protected by the palmaris brevis muscle. Guyon's canal is a depression between the pisiform and hook of hamate that is converted into a fibro-osseous tunnel by the pisohamate ligament. At this site, the superficial branch of the ulnar artery can be compressed against the bony hook of the hamate.
Repetitive blunt trauma may lead to arterial damage, thrombus formation, aneurysm of the artery or microemboli, leading to digital ischaemia.
Sensory branches of the ulnar nerve run nearby and their involvement may contribute to symptoms.
- Digital symptoms (in the index, middle, ring or little fingers) - pain, paraesthesia, cold sensitivity, blanching or claudication.
- Hypothenar pain.
Possible signs are:
- A hypothenar callus or tenderness.
- Pulsatile hypothenar mass (if aneurysm present).
- Discolouration of fingers - white or purplish, usually lacking the 'blush' (red) phase of Raynaud's phenomenon.
- Cool fingertips.
- Positive Allen's test (see below).
- In severe cases, other signs of digital ischaemia, eg finger pulp wasting, ulcers, eschar or gangrene.
The Allen's test assesses the patency of the superficial palmar arch. The test is performed as follows:
- The patient sits with the hands supinated on the knees.
- The examiner compresses the radial and ulnar arteries (using his thumbs).
- The patient opens and closes their fist rapidly several times, to exsanguinate the hand (taking care not to overextend the fingers).
- The ulnar artery is released; normal colour should return to the palm of the hand within 5 seconds. If the ulnar artery is occluded, colour will return to the palm only on release of the radial artery. This is termed a 'positive Allen's test'.
A positive Allen's test indicates occlusion or incomplete development of the superficial palmar arch or distal ulnar artery. However, there are false positives and false negatives using the Allen's test.
- The 'gold standard' is arteriography, although this is invasive.
- Noninvasive tests are:
- Doppler colour imaging
- Cold stress testing
- Digital pulse volumes
- Hand-arm vibration syndrome
- Raynaud's phenomenon from other causes. Features which differ between hypothenar hammer syndrome (HHS) and classical Raynaud's are:
- Male preponderance and occupational history
- Allen's test
- Lack of the normal hyperaemic flush phase of Raynaud's phenomenon
- Digital ulcers in area the supplied by the affected vessel
- Reduced ulnar/radial pulse
- Avoidance of cold.
- Possible drug treatment includes calcium channel blockers, vasodilators and platelet inhibitors, pentoxifylline and anticoagulation. 
- Treat underlying atherosclerotic and prothrombotic factors, eg smoking cessation and lipid management.
- Urokinase has been used to clear obstruction, as has prostaglandin E1 with heparin.
There are various aims of surgery - to remove a source of embolism or a painful mass, to relieve ulnar nerve compression or to create a local periarterial sympathectomy.
Various surgical procedures may be used:
- Vascular procedures, eg ligation, vein graft or arterial graft.
- Intra-arterial vasodilators or thrombolysis
- Endoscopic thoracic sympathectomy - although this has been said to give poor results.
- Ischaemic complications, eg digital ulcers or gangrene.
- Interference with occupation or sport.
Many patients improve with nonsurgical treatments (above). Results of reconstructive surgery have been shown to be variable, with fairly common recurrence.
- Improve work practices so as to avoid using the palm of the hand as a hammer.
- Occupational screening (where relevant) has been advocated, since some degree of ulnar arterial damage may occur preclinically.
Further reading and references
; Ulnar artery thrombosis: hypothenar hammer syndrome. J Am Coll Surg. 2008 Jan206(1):188-9. Epub 2007 Oct 1.
; Use of Doppler in the diagnosis of hypothenar hammer syndrome. Occup Med (Lond). 2009 May59(3):185-90. Epub 2009 Mar 17.
; Hypothenar hammer syndrome: Long-term follow-up of selective thrombolysis by Eur J Radiol. 2009 Nov 30.
; Hypothenar hammer syndrome: a discrete syndrome to be distinguished from hand-arm vibration syndrome. Occup Med (Lond). 2003 Aug53(5):320-4.
; Hypothenar hammer syndrome: case reports and brief review. Clin Med Res. 2008 May6(1):3-8.
; Hypothenar hammer syndrome: proposed etiology. J Vasc Surg. 2000 Jan31(1 Pt 1):104-13.
; Hypothenar hammer syndrome successfully managed with intravenous prostaglandin E1 and heparin and with correction of the thrombogenic risk profile. A case report. Angiology. 1996 Nov47(11):1111-6.
; Ulnar artery thrombosis associated with anomalous hypothenar muscle. J Surg Orthop Adv. 2008 Summer17(2):85-8.
; Long-term follow-up of hypothenar hammer syndrome: a series of 47 patients. Medicine (Baltimore). 2007 Nov86(6):334-43.
; The use of intra-arterial urokinase in the management of hand ischemia secondary to palmar and digital arterial occlusion. Ann Plast Surg. 1996 Oct37(4):356-62
; Surgical management of hypothenar and thenar hammer syndromes: a retrospective study of 31 instances in 28 patients. J Hand Surg (Br). 2005 Aug30(4):419-23.
; Long-term results of surgical treatment for hypothenar hammer syndrome. Plast Reconstr Surg. 2009 Jul124(1):210-6.
; Hypothenar hammer syndrome in two collegiate athletes: immediate versus delayed Clin J Sport Med. 2007 Nov17(6):500-3.
; Hypothenar hammer syndrome: apropos of six cases and review of the literature. Vascular. 2008 Sep-Oct16(5):279-82.
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