Metacarpal Synostosis

Historical Overview

• The earliest known observation of metacarpal synostosis was published by Dr. Seerig in 1827.¹

Description

• In metacarpal synostosis, a rare congenital anomaly, the small finger is frequently hypoplastic and abducted. When the ring and small fingers are involved, the anomaly occurs bilaterally in 60–80% of cases. If the thumb and index fingers are involved, function is more likely to be impaired.¹
• The abduction deformity of the small fingers is a result of the proximal phalanx of the small finger being pushed into the ulnar side of the metacarpal head by the proximal phalanx of the ring finger.² This deformity also is characterized by laxity of the small finger’s metacarpophalangeal (MCP) joint radial collateral ligament.
• Some patients with metacarpal synostosis present with other congenital anomalies, such as mental and growth retardation, hypotonia and ptosis. It is best to consider surgery when the patient is 6 months to 2 years old.¹

Pathophysiology

• Metacarpal synostosis may arise from Apert’s syndrome, syndactyly, central polydactyly or cleft hand.¹ However, frequently it is the result of isolated congenital anomalies.

Instructions

1. Obtain a family history
2. Evaluate the patient for other congenital anomalies
3. Examine hand function bilaterally
4. Examine the ring and small fingers for abduction
5. Evaluate the involved metacarpals for partial or complete fusion²

Variations

• Often in metacarpal synostosis, one may observe a shortening of the middle phalanx of the small finger.²

• A positive result occurs when any of the metacarpals, most often of the ring and small fingers, are completely or partially fused. The proximal half of the ring finger metacarpal is usually attached to the ulnar side of the small metacarpal with both bones having a shared carpometacarpal (CMC) joint.

• A negative result occurs when there is no fusion of the metacarpals.

• Parents or guardians of patients with metacarpal synostosis may seek medical advice for functional or aesthetic purposes.¹

1. Buck-Gramcko D, Wood VE. The treatment of metacarpal synostosis. J Hand Surg Am 1993;18:565-81. PMID: 8394398
2. Miura T. Congenital synostosis between the fourth and fifth metacarpal bones. J Hand Surg Am 1988;13:83-8. PMID: 3351234