CASE 63

By: Dr. Ahmad M. Aljefri M.B.B.S

HISTORY: Withheld.

What are your findings?

What is the differential diagnosis?

What are the causes?

FINDINGS:

AP and lateral radiographs of the hand demonstrate flexion deformity in the third DIP joint. No associated fractures are noted. On the sagittal T1 and PD fat-suppressed images, the distal portion of the extensor digitorum tendon is not seen at its expected attachment site at the dorsal base of the terminal phalanx. The tendon is noted at the level of the mid proximal phalanx. There’s a flexion deformity at the DIP joint with no associated fractures.

DIAGNOSIS:

Mallet finger with extensor digitorum tendon tear.

PEARLS AND DISCUSSION:

The extensor tendons are stabilized at the level of the metacarpophalangeal joint by the sagittal bands. At the level of the proximal phalanx, the extensor tendon divides into three components, two lateral bands and the central slip. The intrinsic muscles join the lateral bands to form the two conjoined tendons. The latter will merge to form the terminal tendon that inserts on the base of the terminal phalanx. The central band inserts on the base of the middle phalanx.

Forced flexion at the level of the distal interphalangeal joint during active extension of the fingers will result into avulsion of the terminal tendon from its attachment. This can occur with or without a fracture to the bone resulting into the characteristic flexion deformity at the DIP (mallet finger). Central slip on the other hand occur at the base of the middle phalanx and will result into boutonniere deformity where there’s hyperextension at the DIP and flexion at the PIP joints.

In children, Seymour fracture can mimic the clinical presentation of mallet finger with the same deformity. It occurs when there’s a fracture involving the proximal metaphysis or Salter 1-2 fractures of the physeal plate resulting into deformity at the fracture site and not at the joint. The extensor tendons insert on the epiphysis of the terminal phalanx and it will be excluded from the unopposed flexion force carried by the flexor tendons. Avulsion fractures related to extensor tendon injuries occur at the epiphyseal portion of the terminal phalanx.

Treatment of terminal tendon injury usually involves splinting the finger with an extended DIP joint.

FURTHER READING:

1. Clavero, Juan A., et al. "MR Imaging of Ligament and Tendon Injuries of the Fingers 1." Radiographics 22.2 (2002): 237-256.

2. Clavero, Juan A., et al. "Extensor Mechanism of the Fingers: MR Imaging–Anatomic Correlation 1." Radiographics 23.3 (2003): 593-611.