A 26-year-old, right-hand-dominant man suffered an injury to the left (non-dominant) ring finger after falling from standing height. He suffered a fracture of the ring finger metacarpal base with minimal angulation and displacement on radiographs (▶Fig. 43.1a). He was treated with cast immobilization. Upon release of the cast, he noticed the ring finger overlapped over the long finger when making a composite fist (▶Fig. 43.1b). Buddy taping was unsuccessful. He admitted to significant limitations with grip.
This patient has an extra-articular, rotational malunion of the metacarpal. Malunions may be classified by the bone involved, the type of deformity (angular, shortening, rotatory, combination), location (intra-articular vs. extra-articular), adult versus pediatric, and with or without combined soft-tissue injury. In the metacarpal, a surgeon should give consideration for correction of a malunited fracture if the deformity is anticipated to limit function. Intra-articular malunions cause painful range of motion, stiffness, and accelerated degeneration of the articular cartilage. Metacarpal neck malunions most often present with apex dorsal angulation and are less functionally limiting. Although cadaveric models have shown that for every 2 mm of shortening a 7-degree extensor lag occurs, clinical trials have reported well-tolerated apex dorsal angulation in the small and ring fingers. However, angulation of the index or middle finger metacarpal neck exceeding 10 degrees may cause pain during grip from a prominent metacarpal head. Additionally, diaphyseal angulation greater than 20 degrees may reduce strength and cause intrinsic tightness. A rotational malunion at any level greater than 10 degrees often causes adjacent digits to overlap and interfere. Often a combination of rotational, shortening, or angular deformities is present; however, usually only one component is dominant and requires surgical correction to restore function.
Early identification and correction of rotational deformity may prevent malunited fractures. Radiographs may look relatively benign, as rotation of the fracture fragments may be difficult to define on plain films. All patients with metacarpal fractures should have a clinical examination out of cast to examine the rotational plane of the fingernails. In a painful hand, using the tenodesis effect (extending the wrist to observe passive flexion of the digits) can help the patient to make a composite fist. When flexing the fingers, the tips should point toward the scaphoid; overlapping of adjacent digits is usually more obvious at the midpoint of finger flexion. In addition, buddy taping a malunited fracture may appear to correct the deformity at first glance; however, this technique only rotates the digit through the metacarpophalangeal joint, which is promptly derotated when the straps are released.
Evaluation of the deformity should include the malunion classification, soft-tissue injury, joint contracture, skeletal fixation, and rehabilitation plan. Radiographs should include posteroanterior, lateral, and oblique views; a CT scan is useful especially for intra-articular fractures. Tracing the fragments on the radiographs and comparing them to the normal side can be helpful for planning fixation. Ideally, the correction should be made when a healthy soft-tissue envelope is present and the original fracture lines are still visible, which is often within 3 to 4 months from the injury. The type of osteotomy depends on the type of malunion, location, tendon balance, and joint mobility (▶Table 43.1). Simple intra-articular malunions may be treated with a corrective osteotomy; however, late deformities with degenerative disease or complex malunions are better treated with arthroplasty or arthrodesis. Angular deformities in the radial–ulnar plane are usually treated with an incomplete closing wedge osteotomy, which hinges on an intact far cortex; radial–ulnar malunions in the metacarpals are rare unless associated with bone loss. Angular deformities in the dorsal-to-volar direction are more common and often require an opening wedge osteotomy with wedge autograft and plate fixation to restore length for tendon balance; however, a closing wedge osteotomy may still be acceptable if significant shortening is not present. If shortening is the primary deformity, the surgeon’s options are either immediate lengthening with plate fixation and bone graft or progressive lengthening via distraction osteogenesis. Rotational malunions can be treated with a transverse derotation osteotomy or with a step-cut osteotomy as described by Manktelow and Mahoney. We prefer the step-cut osteotomy for a variety of advantages: bone contact is larger, control over the osteotomy is easier, deformity correction is more precise, and less internal fixation is required. Some surgeons may still prefer the transverse derotation osteotomy at the metacarpal base described by Weckesser; however, the healing surface and precision of correction are less and plate fixation may cause tendon adhesions.
Closing vs. opening wedge
Immediate vs. progressive lengthening
• Identify the type, location, and soft-tissue status of the malunion.
• Offer corrective surgery for functional limitation.
• Template the osteotomy using the contralateral metacarpal as a reference.
• Perform either a transverse or a step-cut derotational osteotomy.
Measure the amount of deformity at its largest margin, which is most often at the midpoint of finger flexion. The required deformity correction is used to calculate the amount of dorsal bone resection; a 20-degree (or 2-cm) correction is achieved with 2 mm of dorsal cortical wedge resection. The metacarpal is approached through a longitudinal dorsal incision. The extensor tendon is mobilized and protected. The step cut is planned to create a “Z osteotomy” with two hemitransverse cuts and a dorsal wedge using an oscillating saw. The direction of the hemitransverse cuts dictates the direction of rotation (▶Fig. 43.2a–c). It is easiest to visualize the distal hemitransverse cut on the same side as the deformity. Placing the cuts in the reverse orientation will rotate the fragment in the reverse direction. The hemitransverse cuts are made 2 to 3 cm apart (▶Fig. 43.2d). Then a dorsal wedge is resected from the dorsal cortex using two longitudinal cuts separated by the amount of correction calculated preoperatively. The volar cortex is left intact. Pointed reduction forceps can be used to close the dorsal gap; the volar cortex may crack, but the volar periosteum should still be intact (▶Fig. 43.2e). Clinical assessment of rotation confirms the correction; occasionally, more bone may need to be resected if more rotation is required. The osteotomy is secured using two 1.5- or 2.0-mm interfragmentary lag screws (▶Fig. 43.2f).
Finger motion may be allowed in the first postoperative day. A splint is provided for comfort. Release to full activities occurs when radiographic healing is evident usually around 3 to 4 months (▶Fig. 43.3).