What Is Hypothenar Hammer Syndrome?
Hypothenar hammer syndrome is a disorder of the muscles of the hand in which the vascular supply to the fingers is considerably reduced. The word “hypothenar” refers to the group of hand muscles that control the little finger movements. Some of these muscles constitute the fleshy side of the palm beneath the little finger also known as hypothenar eminence.
It usually develops when the workers especially use the hypothenar eminence of the palm of the hand repeatedly as a hammer to twist, push, pull and twirl or twist rigid objects. Certain blood vessels of the palm of the hand, especially the ulnar artery get damaged due to these repetitive exercises. The ulnar artery passes through the hypothenar region of the palm and is responsible for supplying blood to the fingers. In case, the ulnar artery is damaged, it results in the cessation of blood supply to the fingers. Sometimes a single episode is significant enough to initiate the pathogenesis of hypothenar hammer syndrome.
This syndrome usually develops in middle-aged men. The people who work as auto mechanics, metal workers, miners, machine operators, butchers, bakers, carpenters, and bricklayers are at a higher risk of developing this disorder. Workers using vibrating tools at work are also at high risk. Certain sports like karate, judo, baseball, biking, golf, lawn tennis, hockey, throwball, volleyball, badminton, break-dancing, and lifting weights can also exacerbate the condition.
What Is the Cause of Hypothenar Hammer Syndrome?
Hypothenar hammer syndrome mainly occurs due to trauma caused to the distal ulnar artery at the Guyon’s canal leading to post-traumatic ischemia. This occurs as a result of trauma repeatedly at the hypothenar eminence area. Trauma to the ulnar artery can cause arterial dissection, narrowing, occlusion, or pseudo aneurysm formation. This may further be complicated by thromboembolism present distally.
The syndrome is usually seen in patients using hammers and screwdrivers like carpenters and also in individuals who are involved in sports like handball, lawn tennis, and basketball.
The predisposing factors include:
- Repetitive blows to hypothenar prominence located beneath the little finger of the palm of the hand.
- Pre-existing abnormality in the ulnar artery.
- Variations in the anatomy of the palmar arch such as the incomplete formation of the superficial palmar arch or in the anatomy of the hypothenar muscles of the palm.
- Prothrombotic factors may be deficient.
What Is the Epidemiology of Hypothenar Hammer Syndrome?
- This is a rare syndrome with an estimated incidence of less than one per 100,000 individuals worldwide.
- Males are more commonly affected than females.
- People falling in the age group of 40 years to 50 years are most frequently affected by the syndrome.
- The most commonly affected sites are the ring finger and the little finger. Less commonly, the middle and index fingers are involved. The thumb is however spared from getting affected.
What Are the Symptoms of Hypothenar Hammer Syndrome?
The typical clinical features of the syndrome include:
- Feeling of cold sensation in the palms.
- Pain and paresthesia in the palm below the little or ring fingers.
- Raynaud syndrome (a disorder affecting small blood vessels of the fingers and toes).
- Hypothenar eminence will be tender.
- Ischemia or gangrene of the little finger or ring finger.
- Prominent callus formation over the hypothenar eminence of the palm.
- Sometimes ulcerations are present at the fingertips.
- Bleeding points over the digits supplied by the ulnar artery.
- Bluish discoloration of the skin or cyanosis is also observed in some cases.
- Positive Tinel sign (tingling sensation that occurs due to compression of ulnar nerve at the site of injury).
- Positive Allen’s test (this test is used to assess the blood supply flowing collaterally to the hands).
How Is the Diagnosis of Hypothenar Hammer Syndrome Done?
Diagnosis is usually established with the help of vascular studies including Doppler ultrasound and computed tomography angiography.
1. Angiography- It is a mandatory test. In a computed tomography angiogram, the following details can be observed.
- Irregular corkscrew (beaded appearance) of the distal ulnar artery of the palm of the hands.
- False aneurysm formation.
- Stenosis (narrowing) or occlusion of the ulnar artery segment overlying the hypothenar eminence.
- The distal digital arteries of the ulnar artery distribution are either occluded or under-filled.
2. Doppler Ultrasound- This test is used to assess the blood flow through the ulnar artery by making use of high-frequency sound waves.
- It is a first-line test.
- It measures the brachial index digitally.
- If the measurement is less than 0.7, then reconstruction is necessary.
What Is the Treatment of Hypothenar Hammer Syndrome?
The management of these patients is mainly done either two ways. These primarily include:
- Nonoperative Management- These include lifestyle changes, symptomatic treatment of the affected individual, and consulting the doctor about vascular changes. This nonoperative treatment should be carried out in cases that have thrombosis without aneurysm formation for more than two weeks. The affected individual is asymptomatic and there is no gangrene formation in the fingers leading to the threat of loss of fingers involved. The lifestyle modifications include quitting the smoking habit and avoiding repeated trauma to the affected area. The prognosis of this nonoperative therapy is good with more than 80 % success in most cases.
- Surgical (Operative) Management- This includes endovascular fibrinolysis (fibrinolysis is a process that prevents the blood clots from getting deposited and creating problems). This surgical management is recommended in cases that are less than two weeks old where there is thrombosis with pseudo aneurysm formation. Here, the affected segment is surgically excised and reconstruction is carried out with or without inserting a vein graft. It is also usually carried out in cases that have a brachial index of less than 0.7. When the ischemia (reduced blood supply) is in more than two digits, surgery can be considered. Also, if the nonoperative management fails with the repetitive symptoms, the doctor should consider surgery. Arterial ligation is another treatment option in cases where the digital brachial index is more than 0.7.
Conclusion
Hypothenar hammer syndrome is a rare vascular condition caused due to repetitive trauma to the palm of the hands or wrist. The ulnar artery is usually damaged thereby progressively causing ischemia or gangrene in the affected area. The affected individual should not take the clinical features lightly and should avoid doing the activity that is leading to this condition immediately. One should immediately visit the healthcare clinician immediately to find the correct treatment for this problem.
