Ainhum is a rare condition marked by the development of a constricting fibrous band around a digit, most commonly the base of the fifth toe. Over time this band tightens, leading to progressive swelling of the part distal to it, loss of bone support and eventually the spontaneous detachment (auto-amputation) of the digit.
Because the condition often advances unnoticed until significant tissue loss or deformity has occurred, prompt recognition and intervention are important to preserve function and avoid complications.
Anatomy and Pathophysiology
The process begins when a fibrous ring forms just proximal to the toe (typically the fifth toe). This band gradually encircles the digit and compresses the underlying soft tissues, lymphatic channels, blood vessels and nerves. The constriction impairs circulation and lymphatic drainage distal to the ring, causing swelling and hypertrophy of the distal digit. Simultaneously, bone resorption occurs as pressure persists, cortical thinning develops and the phalange begins to erode. As the band deepens and the bone weakens, the digit becomes increasingly unstable and may spontaneously separate without bleeding once the connection becomes a slender avascular cord.
Epidemiology
Ainhum is uncommon globally but is seen more frequently in tropical and subtropical regions, particularly in people of African descent. Cases have also been reported in South America and India. The condition tends to affect adults in the middle-age range, though younger and older individuals may be involved. Bilateral involvement (both feet) is reported in a substantial proportion of patients.
Clinical Presentation
Symptoms
Patients may initially notice a groove or fissure at the base of the fifth toe. As the condition progresses, they may develop pain, swelling, and a sensation of constriction. The distal part of the toe often becomes bulbous or enlarged due to impaired drainage. In advanced cases, the digit may loosen and eventually detach.
Physical Findings
On examination, the following may be seen:
- A circular groove or constricting band at the toe base.
- Swelling or bulbous change of the digit beyond the band.
- Thinning or tapering of the affected phalanx, often evident when palpated.
- In later stages, the toe may hang by a narrow stalk or may already have detached.
Because early signs may be subtle, careful inspection of both feet and comparison with the opposite side are important.
Diagnostic Evaluation
Diagnosis of ainhum is largely clinical, supported by imaging when needed. Key steps include:
- A detailed history of onset, progression and any local trauma or infection.
- Physical examination focusing on the toe-base ring, swelling distally and any signs of impending amputation.
- Plain radiographs of the affected toe can show narrowing at the base, tapering of the phalanx and in advanced stages, bone loss or detachment.
- Other imaging (such as ultrasound or CT) may assist in delineating soft tissue constriction or bone involvement, but are less commonly required.
It is important to distinguish true ainhum from pseudo-ainhum (similar constricting band syndromes occurring secondary to other causes such as congenital bands, trauma, infection or dermatologic diseases).
Treatment
Management aims to relieve constriction, preserve the digit where possible, prevent complications and maintain foot function.
Early (non-surgical) approaches
- If identified early (groove formation without bone involvement), surgical release of the fibrous band (for example via Z-plasty) may prevent progression.
- Localised treatment to relieve pressure, improve circulation and monitor progression.
- Foot care to reduce additional trauma, protective footwear, avoidance of barefoot walking in susceptible individuals.
Later (surgical) intervention
- Once bone involvement occurs or the digit is loose, more definitive surgery may be needed. This may involve partial or complete amputation of the affected toe to relieve pain and prevent infection.
- Reconstruction is rarely required, but attention to remaining foot mechanics and balance is important.
Early intervention offers the best chance to preserve the toe and function; once advanced bone resorption has occurred, prognosis for digit salvage is poor.
Follow-Up, Prognosis and Complications
Prognosis
When treated early, particularly in the stage before bone destruction, outcomes are favourable with preservation of the digit. However in many cases the diagnosis is delayed and progression to auto-amputation occurs over several years. Even when treated, residual problems such as altered foot mechanics or balance issues may persist.
Complications
Potential complications include:
- Secondary infection of the constricted region or detached digit.
- Pain, swelling or altered gait due to toe loss.
- Psychological effects of digit loss and altered appearance or function.
- Imbalance or gait disturbance if other toes or bilateral feet are involved.
Long-term monitoring of foot health, protective footwear and intervention at early signs are key to minimising these issues.
Prevention and Patient Education
Because the exact cause of ainhum remains unclear, prevention is not fully established. However practical measures include:
- Educating at-risk populations (particularly in tropical climates) about protective footwear and foot care.
- Early evaluation of any groove, ring or band at the toe base and prompt referral for specialist assessment.
- Avoiding repeated trauma, barefoot walking on rough surfaces, and prompt treatment of any foot infection or injury.
- Encouraging regular foot inspection and early presentation when changes appear.
Patients should understand that although the condition is rare, early recognition can make a substantial difference in outcome.
References
Barve, D. J., & Gupta, A. (2015). Ainhum: a spot diagnosis. Indian Journal of Surgery, 77(Suppl 3), 1411-1412.
Daccarett, M., Espinosa, G., Rahimi, F., Eckerman, C. M., Wayne-Bruton, S., Couture, M., & Rosenblum, J. (2002). Ainhum (dactylolysis spontanea): a radiological survey of 6000 patients. The Journal of foot and ankle surgery, 41(6), 372-378.
Rashid, R. M., Cowan, E., Abbasi, S. A., Brieva, J., & Alam, M. (2007). Destructive deformation of the digits with auto‐amputation: a review of pseudo‐ainhum. Journal of the European Academy of Dermatology and Venereology, 21(6), 732-737.
