Malunion and Nonunion of Fingers and Hand
Tiffany Y. Wu
John R. Fowler
Malunions are usually multiplanar, though one component is predominant.
Nonunions are rare (0.2%-0.7% incidence) and mostly atrophic.
Nonunions can be due to bone loss, osteomyelitis, inadequate immobilization, or poor fixation.
Mechanism of injury
Metacarpal fractures typically have an apex dorsal angulation due to deforming forces of intrinsic muscles and extrinsic flexors.
Proximal phalanx fractures typically have an apex volar angulation due to the lumbricals flexing the proximal fragment and the central slip extending distal fragment.
Middle phalanx fractures typically have an apex dorsal angulation if the fracture is proximal to the flexor digitorum superficialis insertion and apex volar angulation if the fracture is distal to the flexor digitorum superficialis insertion.
If phalanx angulation >15°, then the bone is shortened relative to the extensor tendon. If phalanx angulation >25°, then both flexion and extension are compromised.
5° of malrotation results in 1.5 cm of digital overlap.
Shortening—comminuted fracture, crush injury, or open fracture
Metacarpal—2 mm of shortening results in 7° of extensor lag and 8% loss of power. 10 mm of shortening results in 45% to 55% loss of power.
Proximal phalanx— 1 m of shortening results in 12° extensor lag.
Injury, treatment, and duration
Location—phalanx versus metacarpal, extra-articular versus intra-articular
Complicating factors—infection, pain syndrome
Associated injuries—soft tissue defects, neurovascular injuries
Patient characteristics—skeletal maturity, hand dominance, occupation, pain, compliance with postoperative protocols
Scissoring—affected finger overlaps adjacent finger. Normally, fingertips should point to scaphoid tuberosity with fingers flexed.
Pseudoclawing—Proximal phalanx malunion >25° to 30° results in proximal interphalangeal (PIP) joint extensor lag, which can result in a fixed PIP joint flexion contracture, with resultant hyperextension at metacarpophalangeal joint.
Diminished grip and dexterity
Radiographs—anteroposterior, lateral, oblique
Radiographs of contralateral hand can be helpful as preoperative templates for complex malunions.
Consider computed tomography for complex malunions.