Operative Management of Carpal Malunions and Nonunions

INTRODUCTION TO CARPAL DERANGEMENTS

The management of malunited fractures of the carpal bones presents a formidable challenge to the orthopedic hand and upper extremity surgeon. As established in foundational operative orthopedics, surgery for carpal malunion is rarely justified merely to restore radiographic alignment. The intricate kinematic tolerances of the carpus dictate that by the time a malunion is clinically recognized, it is almost invariably accompanied by nonunion, chronic perilunate dislocation, or advanced degenerative arthrosis.

Because the carpal bones function as an intercalated segment without direct tendinous insertions, their stability relies entirely on complex ligamentous constraints and articular congruity. A malunion—most commonly of the scaphoid—alters the transmission of forces across the radiocarpal and midcarpal joints, inevitably leading to predictable patterns of cartilage wear, such as Scaphoid Nonunion Advanced Collapse (SNAC) or Scapholunate Advanced Collapse (SLAC). In these advanced stages, reconstructive osteotomies are often futile. Instead, the surgical algorithm shifts toward salvage procedures, specifically the excision of one or more carpal bones (e.g., Proximal Row Carpectomy) or partial/total fusion of the wrist.

BIOMECHANICS AND PATHOANATOMY

To understand the rationale behind carpal salvage procedures, one must first appreciate the biomechanical collapse that necessitates them. The scaphoid acts as the critical mechanical link between the proximal and distal carpal rows.

The Intercalated Segment and Carpal Collapse

The proximal row (scaphoid, lunate, triquetrum) functions as an intercalated segment. The scaphoid naturally tends to flex under axial load, while the triquetrum tends to extend. The lunate, bound to both, balances these opposing forces.
* Scaphoid Malunion/Nonunion: When the scaphoid fractures and heals in a "humpback" malunion (flexion and foreshortening) or progresses to nonunion, the mechanical linkage is lost.
* DISI Deformity: Uncoupled from the flexing force of the scaphoid, the lunate follows the extending force of the triquetrum, resulting in a Dorsal Intercalated Segment Instability (DISI) deformity.
* Articular Degeneration: The malaligned scaphoid articulates abnormally with the radial styloid, initiating a cascade of osteoarthritis that progresses from the radial styloid to the radioscaphoid joint, and eventually to the capitolunate joint (the SNAC sequence).

Clinical Pearl: The radiolunate joint is uniquely spared in both SLAC and SNAC wrists due to the concentric, spherical nature of the lunate fossa and the robust volar radiolunate ligaments. This anatomical preservation is the cornerstone that allows for motion-preserving salvage procedures like the Four-Corner Fusion.

CLINICAL EVALUATION AND INDICATIONS FOR SURGERY

Patient Assessment

Patients typically present with chronic, activity-related wrist pain, diminished grip strength, and restricted range of motion. A history of remote wrist trauma is common, though some patients may not recall a specific inciting event.

Imaging Protocols

1. Standard Radiographs: Posteroanterior (PA), lateral, scaphoid, and clenched-fist views are mandatory. Assess for the "humpback" scaphoid deformity, the scapholunate angle (normal is 30°–60°; >70° indicates DISI), and the presence of osteophytes.
2. Computed Tomography (CT): A fine-cut CT scan in the sagittal and coronal planes is the gold standard for evaluating carpal bone stock, the exact geometry of a malunion, and the extent of midcarpal arthrosis.
3. Magnetic Resonance Imaging (MRI): Useful for assessing the vascularity of the proximal scaphoid pole and the integrity of the interosseous ligaments, though less critical when advanced arthritis is already evident on plain films.

Indications for Salvage Surgery

Surgical intervention via excision or fusion is indicated when:
* The patient experiences intractable pain refractory to conservative measures (splinting, NSAIDs, corticosteroid injections).
* There is radiographic evidence of advanced midcarpal or radiocarpal arthritis (Stage II or III SLAC/SNAC).
* The malunion/nonunion is deemed irreparable due to severe bone loss, avascular necrosis, or chronic deformity precluding anatomical reconstruction.

SURGICAL DECISION-MAKING: EXCISION VS. FUSION

When joint preservation via corrective osteotomy is no longer viable, the surgeon must choose between motion-preserving salvage (Proximal Row Carpectomy or Partial Wrist Arthrodesis) and definitive salvage (Total Wrist Arthrodesis).

Proximal Row Carpectomy (PRC) vs. Four-Corner Fusion (4CF)

Both PRC and 4CF aim to preserve functional wrist motion while eliminating pain.
* PRC is indicated when the capitate head and the lunate fossa of the radius are free of significant arthritic changes. It is technically simpler, requires no bone healing (fusion), and allows for earlier mobilization.
* 4CF is indicated when the capitate head is arthritic but the radiolunate joint is preserved. It maintains carpal height and grip strength better than PRC but requires a period of immobilization for bony union and carries a risk of nonunion.

PROXIMAL ROW CARPECTOMY (PRC): STEP-BY-STEP TECHNIQUE

PRC involves the excision of the scaphoid, lunate, and triquetrum, allowing the capitate to articulate directly with the lunate fossa of the radius.

Positioning and Preparation

• Position: Supine with the operative arm extended on a radiolucent hand table.
• Tourniquet: A well-padded pneumatic tourniquet is applied to the proximal arm and inflated to 250 mm Hg after exsanguination.
• Anesthesia: Regional block (supraclavicular or axillary) or general anesthesia.

Surgical Approach

1. Incision: A dorsal longitudinal incision is made, centered over Lister's tubercle, extending from the distal radius to the base of the third metacarpal.
2. Extensor Retinaculum: The third extensor compartment is opened, and the extensor pollicis longus (EPL) is transposed radially. The second and fourth compartments are elevated subperiosteally to expose the dorsal wrist capsule.
3. Neurectomy: The posterior interosseous nerve (PIN) is identified at the floor of the fourth compartment. A 1-cm segment is excised to provide partial denervation of the wrist capsule, significantly improving postoperative pain relief.
4. Capsulotomy: A ligament-sparing capsulotomy (e.g., Mayo or Berger approach) is performed to expose the radiocarpal and midcarpal joints.

Carpal Excision

1. Scaphoid Excision: The scaphoid is often fragmented. It is excised piecemeal using a rongeur or osteotome. Care must be taken to protect the volar radioscaphocapitate (RSC) ligament, which prevents ulnar translation of the carpus.
2. Lunate and Triquetrum Excision: A threaded Steinmann pin or reduction forceps can be used to grasp the lunate and triquetrum. Sharp dissection releases their volar ligamentous attachments.
3. Articular Assessment: The capitate head and lunate fossa are inspected. If the capitate head shows severe eburnation, a PRC is contraindicated, and the surgeon must convert to a total wrist fusion or perform a capitate resurfacing (e.g., RCPI implant).

Surgical Warning: Aggressive volar dissection during carpal excision can damage the RSC ligament. Disruption of this ligament will lead to catastrophic ulnar translation of the capitate and failure of the PRC.

Closure

The dorsal capsule is meticulously repaired using non-absorbable sutures to prevent dorsal subluxation of the capitate. The extensor retinaculum is repaired, leaving the EPL transposed subcutaneously. The skin is closed, and a bulky volar splint is applied.

PARTIAL WRIST ARTHRODESIS: FOUR-CORNER FUSION

The Four-Corner Fusion involves the excision of the scaphoid and the arthrodesis of the capitate, lunate, hamate, and triquetrum.

Surgical Technique

1. Approach: The dorsal approach and capsulotomy are identical to the PRC technique.
2. Scaphoid Excision: The scaphoid is completely excised. The excised bone is morselized to serve as autologous bone graft.
3. Joint Preparation: The articular surfaces between the lunate, capitate, hamate, and triquetrum are meticulously decorticated down to bleeding cancellous bone using a high-speed burr or osteotomes.
4. Reduction: The DISI deformity of the lunate must be corrected. A K-wire is used as a joystick to flex the lunate into a neutral position relative to the radius. The capitate is then reduced onto the lunate.
5. Fixation: Rigid internal fixation is achieved using a specialized dorsal circular plate (spider plate), headless compression screws, or memory-metal staples.
6. Bone Grafting: The morselized scaphoid autograft (supplemented with distal radius cancellous graft if necessary) is packed tightly into the interstices of the four bones.

TOTAL WRIST ARTHRODESIS

When pan-carpal arthritis is present, or as a salvage for a failed PRC or partial fusion, total wrist arthrodesis is the gold standard for achieving a painless, stable wrist.

Indications

• Post-traumatic pan-carpal arthrosis.
• Severe carpal malunion/nonunion with profound bone loss.
• Rheumatoid arthritis with severe deformity.
• Paralytic deformities (e.g., brachial plexus injury).

Surgical Technique

1. Incision and Exposure: A straight dorsal incision is utilized. The dorsal capsule is excised entirely.
2. Joint Decortication: The articular cartilage is removed from the radiocarpal joint, the midcarpal joint, and the carpometacarpal joint of the third digit. The distal radioulnar joint (DRUJ) is strictly avoided unless a concurrent Darrach or Sauvé-Kapandji procedure is planned.
3. Plate Application: A pre-contoured dorsal wrist fusion plate (typically featuring 10° to 15° of dorsiflexion) is applied.
4. Fixation Sequence:
   • The plate is fixed distally to the third metacarpal using cortical screws.
   • The plate is fixed proximally to the distal radius.
   • A central compression screw is often placed through the plate into the capitate to compress the radiocarpal and midcarpal arthrodesis sites.
5. Bone Grafting: Copious cancellous autograft, typically harvested from the distal radius or iliac crest, is packed into the decorticated joint spaces prior to final compression.

Pitfall: Fusing the wrist in excessive dorsiflexion or ulnar deviation can severely impair grip biomechanics and cause extensor tendon irritation. The optimal position is 10° to 15° of extension and neutral radioulnar deviation.

POSTOPERATIVE PROTOCOLS AND REHABILITATION

The postoperative rehabilitation protocol is dictated by the specific procedure performed.

Proximal Row Carpectomy (PRC)

• Weeks 0-2: Immobilization in a bulky dressing and volar plaster splint. Elevation and digital range of motion (ROM) are encouraged immediately.
• Weeks 2-4: Sutures are removed. The patient is transitioned to a removable thermoplastic wrist splint. Gentle active ROM of the wrist is initiated.
• Weeks 4-8: Passive ROM and progressive strengthening begin. Splint use is discontinued during the day.
• Months 3+: Return to heavy manual labor or sports is permitted once painless, functional ROM and grip strength are achieved.

Four-Corner Fusion and Total Wrist Arthrodesis

• Weeks 0-2: Immobilization in a short-arm cast or rigid splint.
• Weeks 2-6: Transition to a short-arm cast. Digital ROM is strictly enforced to prevent tendon adhesions.
• Weeks 6-8: Radiographs are obtained to assess bony consolidation. If bridging trabeculae are visible, the patient is transitioned to a removable splint, and active ROM (for 4CF) is initiated.
• Weeks 8-12: Progressive strengthening. For total wrist fusion, therapy focuses entirely on digital dexterity, grip strength, and compensatory forearm rotation.

COMPLICATIONS AND MANAGEMENT

1. Nonunion (Pseudarthrosis): Most common in Four-Corner Fusions (up to 5-10%). If symptomatic, revision bone grafting and rigid internal fixation are required. If revision fails, conversion to a total wrist arthrodesis is indicated.
2. Hardware Prominence/Tendon Irritation: Dorsal plates used in total wrist fusion can irritate the extensor tendons, occasionally leading to rupture. Plate removal may be considered after 12-18 months if solid clinical and radiographic fusion is confirmed.
3. Progressive Arthrosis: Following a PRC, progressive radiocapitate arthritis may occur over a 10- to 15-year horizon. Management involves conversion to a total wrist arthrodesis.
4. Infection: Deep surgical site infections are rare but devastating. Management requires aggressive surgical debridement, hardware removal (if stability can be maintained externally), and culture-directed intravenous antibiotic therapy.

CONCLUSION

The surgical management of carpal malunions and nonunions requires a profound understanding of wrist kinematics and a pragmatic approach to patient expectations. Because restoring native anatomy is rarely feasible in the setting of chronic deformity and established arthrosis, the surgeon must adeptly employ salvage procedures. Whether utilizing a Proximal Row Carpectomy for motion preservation or a Total Wrist Arthrodesis for definitive stability, meticulous surgical technique, rigid fixation, and structured rehabilitation are paramount to restoring a functional, painless upper extremity.