INTRODUCTION TO CARPAL MALUNIONS
The management of malunited fractures of the carpal bones requires a profound understanding of wrist kinematics and radiocarpal biomechanics. Unlike diaphyseal fractures of long bones where angular deformity may be tolerated within certain parameters, the carpus functions as a highly synchronized intercalated segment. However, surgical intervention for carpal malunion is rarely justified merely to restore radiographic alignment. In the vast majority of cases, a malunion is complicated by concomitant nonunion, chronic perilunate dislocation, or progressive carpal instability (such as Dorsal Intercalated Segment Instability [DISI] or Volar Intercalated Segment Instability [VISI]).
When a carpal bone—most frequently the scaphoid—heals in a malunited position (e.g., a "humpback" deformity), it alters the contact pressures across the radiocarpal and midcarpal joints. Over time, this leads to predictable patterns of degenerative arthrosis, mirroring the Scaphoid Nonunion Advanced Collapse (SNAC) pathway. In these advanced instances, joint-sparing corrective osteotomies are no longer viable. Instead, salvage procedures, including excision of one or more carpal bones (Proximal Row Carpectomy) or partial/total fusion of the wrist, become the indicated surgical pathways.
Clinical Pearl: Do not chase radiographic alignment in the presence of established midcarpal or radiocarpal arthrosis. If articular cartilage is compromised, corrective osteotomy will fail to relieve pain. Salvage procedures must be employed.
HAND MALUNIONS
Note: Malunited fractures of the metacarpals and phalanges present distinct biomechanical challenges, primarily affecting the flexor/extensor mechanism excursion and digital cascade. These are discussed extensively in dedicated hand trauma literature (see Chapter 64).
SURGICAL MANAGEMENT OF THE CARPUS: SALVAGE PROCEDURES
When carpal malunion is accompanied by irreversible articular degeneration, chronic dislocation, or irreparable nonunion, salvage procedures are indicated to provide a stable, painless wrist while preserving as much functional motion as possible.
Proximal Row Carpectomy (PRC)
Proximal row carpectomy involves the excision of the scaphoid, lunate, and triquetrum, converting the complex radiocarpal and midcarpal articulations into a simple hinge joint between the capitate head and the lunate fossa of the distal radius.
Indications:
* Symptomatic scaphoid malunion/nonunion with radioscaphoid arthrosis (SNAC stage I or II).
* Chronic perilunate dislocations with irreparable ligamentous damage.
* The capitate head and the lunate fossa of the radius must have preserved, healthy articular cartilage.
Surgical Technique:
1. Positioning and Approach: The patient is positioned supine with the arm on a hand table. A dorsal longitudinal incision is made centered over Lister’s tubercle.
2. Capsulotomy: The extensor retinaculum is divided over the third dorsal compartment, and the Extensor Pollicis Longus (EPL) is transposed radially. A ligament-sparing dorsal capsulotomy (e.g., Berger’s Mayo approach) is performed to expose the radiocarpal and midcarpal joints.
3. Neurectomy: A routine Posterior Interosseous Nerve (PIN) neurectomy is performed at the proximal margin of the incision to provide adjunctive pain relief.
4. Carpal Excision: The scaphoid, lunate, and triquetrum are systematically excised.
* Surgical Warning: Extreme care must be taken when excising the volar pole of the scaphoid and lunate to avoid injuring the stout volar extrinsic ligaments (specifically the Radioscaphocapitate [RSC] ligament). The RSC ligament is the primary restraint preventing ulnar translation of the carpus postoperatively.
5. Closure: The capitate is allowed to articulate with the lunate fossa. The dorsal capsule is meticulously repaired to prevent dorsal subluxation of the capitate.
Four-Corner Arthrodesis (Limited Intercarpal Fusion)
When the capitate head is arthritic (precluding a PRC), but the radiolunate joint is preserved, a four-corner fusion is the procedure of choice.
Indications:
* Advanced carpal malunion with capitate head degeneration (SNAC/SLAC stage III).
* Preserved articular cartilage at the radiolunate facet.
Surgical Technique:
1. Approach: A standard dorsal approach is utilized, identical to the PRC approach.
2. Scaphoid Excision: The malunited/nonunited scaphoid is completely excised. This eliminates the pathological radioscaphoid contact.
3. Joint Preparation: The articular surfaces between the capitate, hamate, lunate, and triquetrum are decorticated down to bleeding cancellous bone using a high-speed burr or osteotomes.
4. Reduction and Fixation: The lunate is reduced out of its extended (DISI) position to a neutral alignment with the radius. The four bones are compressed and rigidly fixed. Fixation options include a dorsal circular "spider" plate, headless compression screws, or memory-metal staples.
5. Bone Grafting: Cancellous bone graft (autograft from the distal radius or excised scaphoid) is packed into the interstices to promote robust arthrodesis.
Total Wrist Arthrodesis
For pan-carpal arthritis resulting from severe, neglected carpal malunions or massive crush injuries, total wrist arthrodesis provides reliable pain relief and a stable grip, albeit at the cost of all radiocarpal and midcarpal motion.
Indications:
* Pan-carpal arthrosis (SNAC/SLAC stage IV).
* Failed partial wrist fusion or failed PRC.
* Severe post-traumatic radiocarpal instability with bone loss.
Surgical Technique:
1. Preparation: The dorsal articular surfaces of the radius, scaphoid, lunate, capitate, and third metacarpal base are decorticated.
2. Plate Placement: A specialized pre-contoured dorsal wrist fusion plate is applied. The plate is designed with a slight degree of extension (10 to 15 degrees) to optimize grip strength.
3. Fixation: Distal screws are placed into the third metacarpal diaphysis and capitate. Proximal screws are secured into the distal radius.
4. Grafting: Local bone graft from the excised dorsal carpal elements or distal radius is packed into the radiocarpal and midcarpal spaces.
Pitfall: Avoid placing screws into the carpometacarpal (CMC) joints of the index or middle fingers unless they are specifically targeted for fusion, as unintended CMC penetration can lead to chronic pain.
GLOBAL PRINCIPLES OF MALUNION: INTEGRATING LOWER EXTREMITY TRAUMA
While the carpus presents unique challenges, the fundamental principles of malunion management—restoring mechanical axes, normalizing joint contact pressures, and addressing limb length discrepancies—are universally applicable. The extensive literature on lower extremity malunions provides a robust framework for understanding post-traumatic deformity correction.
Calcaneal Malunion and Subtalar Arthrodesis
Malunited fractures of the calcaneus frequently result in a debilitating triad: loss of calcaneal height, varus deformity of the tuberosity, and lateral wall blow-out causing subfibular impingement. As demonstrated by Carr, Hansen, and Sanders, in situ subtalar fusion is often insufficient for late complications of os calcis fractures.
Subtalar Distraction Bone Block Arthrodesis:
To restore the talocalcaneal height and correct the talar declination angle, a distraction bone block arthrodesis is indicated.
1. A lateral approach is utilized, and the lateral wall exostosis is resected to decompress the peroneal tendons.
2. The subtalar joint is distracted using a lamina spreader, correcting the varus and restoring the calcaneal pitch.
3. A tricortical iliac crest bone graft is impacted into the distracted subtalar space.
4. Rigid fixation is achieved with large-fragment cannulated screws directed from the calcaneal tuberosity into the talar dome.
Ankle Malunion and Fibular Lengthening
Ankle fractures that heal in malunion, particularly those involving fibular shortening and external rotation, lead to lateral talar shift. Biomechanical studies (Ramsey and Hamilton) have shown that even 1 mm of lateral talar shift decreases tibiotalar contact area by 42%, exponentially increasing peak contact stresses and leading to rapid osteoarthrosis.
Fibular Lengthening Osteotomy:
Pioneered by Weber, corrective osteotomy of the fibula is critical for restoring the ankle mortise.
1. An oblique or step-cut osteotomy of the distal fibula is performed.
2. The fibula is distracted distally and internally rotated to reduce the talus anatomically beneath the tibial plafond.
3. A structural bone graft is interposed in the osteotomy gap.
4. The construct is stabilized with a robust lateral neutralization plate.
5. If the medial clear space remains widened, medial malleolar osteotomy or deltoid ligament reconstruction may be required.
Tibial and Femoral Deformity Correction
Diaphyseal malunions of the tibia and femur alter the mechanical axis of the lower extremity, leading to asymmetric loading of the knee and ankle joints. Correction requires meticulous preoperative planning, often utilizing trigonometric analysis to determine the Center of Rotation of Angulation (CORA).
Surgical Strategies:
* Intramedullary Nailing: For diaphyseal malunions without significant shortening, a corrective osteotomy followed by reamed intramedullary nailing provides excellent load-sharing biomechanics. Poller (blocking) screws are frequently utilized to direct the nail and maintain the corrected alignment.
* Ilizarov Techniques: For complex, multiplanar deformities (angulation, translation, rotation, and shortening), circular fine-wire external fixation (the Ilizarov method) allows for gradual, precise correction through distraction osteogenesis. This is particularly advantageous when soft tissue envelopes are compromised by previous trauma.
* Plating: Tension-band plating or locked plating is highly effective for metaphyseal malunions where intramedullary devices lack sufficient purchase.
POSTOPERATIVE REHABILITATION PROTOCOLS
Regardless of the anatomic location, the postoperative management of malunion reconstruction requires a delicate balance between protecting the osteotomy/arthrodesis and preventing adjacent joint stiffness.
For Carpal Salvage Procedures:
* Immobilization: The wrist is immobilized in a bulky dressing and volar splint for 2 weeks. Following suture removal, a short-arm cast or rigid orthosis is applied for an additional 4 to 6 weeks.
* Therapy: Digital range of motion (ROM) is initiated immediately to prevent tendon adhesions. For PRC and 4-corner fusions, active wrist ROM begins at 4 to 6 weeks postoperatively, progressing to strengthening at 8 to 10 weeks once radiographic consolidation is evident.
For Lower Extremity Reconstructions:
* Weight-Bearing: Strict non-weight-bearing is typically enforced for 6 to 8 weeks following subtalar bone block fusions or fibular lengthening osteotomies to prevent graft collapse or hardware failure.
* Progression: Weight-bearing is advanced gradually in a controlled ankle motion (CAM) boot once bridging callus is observed. Aggressive physical therapy focusing on proprioception, gait mechanics, and adjacent joint mobility is essential for optimal functional recovery.
Surgical Warning: Premature weight-bearing in lower extremity structural bone graft procedures (such as calcaneal distraction arthrodesis) is the leading cause of graft subsidence and recurrent deformity. Strict adherence to radiographic milestones is mandatory before advancing load.
