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Hypothenar Hammer Syndrome
Hypothenar hammer syndrome (HHS) is a rare clinical condition that was first described in 1934 by von Rosen and was named in 1970 by Cone, Bergan, and Bell. HHS describes patients who experience signs and symptoms concerning for digital ischemia. Typically, patients have a history of blunt trauma to the palmar hypothenar eminence of the hand. Repetitive trauma to this area can disrupt the structural integrity of the ulnar artery and its arterial branches, resulting in aneurysmal dilation, thrombosis, occlusion, or distal embolization.
Traditionally the syndrome was thought to be an occupational hazard among manual laborers and craftsmen such as machinists, mechanics, miners, carpenters, construction workers, bakers, and butchers, who are more prone to use the hypothenar part of the hand as a hammer. In more recent times, however, HHS has also been described more broadly among recreationalists and athletes, such as baseball, basketball, football, hockey, golf, badminton, tennis, and squash players; mountain bikers; and weight lifters. The symptoms of HHS vary significantly, with a spectrum encompassing severe digital ischemia to subtle signs of discoloration or secondary Raynaud’s phenomenon.
Prevalence of Disease
Before 1982, only 52 cases of true vascular aneurysms of the hand from repetitive trauma were recorded in the scientific literature. Although modalities in diagnosing HHS have improved, it remains difficult to estimate the true incidence and prevalence of HHS owing to its relative rarity and variable degree of associated symptomatology. Nevertheless, a few studies have explored the prevalence of HHS in persons who are thought to be at higher risk for the disease process. Ferris and colleagues prospectively evaluated 1300 subjects who were exposed to vocational or occupational repetitive palmar trauma. Only 21 patients (1.6%) were found to develop symptoms that were consistent with HHS, including pain in the digits and recent onset of cold intolerance in the hands or digits. All but one of these patients also developed unilateral digital ischemia with or without ulceration. Others have reported that in a minority of subjects, ulnar artery injury can be extrapolated to a single episodic palmar trauma event.
Little and colleagues report a slightly higher incidence of HHS among 127 mechanical workshop employees. Of these workers, more than 60% were noted to be habitual hypothenar hammerers, and 8% were found to have symptoms of vascular insufficiency as well as objective evidence of arterial occlusion. Similarly, Kaji and coworkers found that among 330 workers who were exposed to repetitive occupational hand vibration in mining, forestry, and other industries, 24 subjects (7%) had angiographically detectable ulnar artery abnormalities. A survey of the demographics of patients affected by HHS reveals that the majority of subjects are male with a mean age of approximately 40 years. A review of 146 patients with HHS revealed that 89% were habitual cigarette smokers.
Depending on the mechanism and severity of palmar trauma, both the radial and ulnar arteries may also be affected, although the incidence of this is low and is only reported in the form of case reports. Although the majority of patients affected by HHS have unilateral symptoms that typically affect the dominant hand (53%–93%), some subjects also develop HHS in the nondominant hand (12%), and a few have bilateral hand involvement (5%). Several reports demonstrate that among HHS patients, the third, fourth, and fifth digits are the most commonly affected digits, and symptoms in the thumb have never been described.
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