Operative Management of Carpal Malunions and Nonunions

Comprehensive Introduction and Patho-Epidemiology

The management of malunited fractures and established nonunions of the carpal bones presents a formidable, multifaceted challenge to the orthopedic hand and upper extremity surgeon. As established in foundational operative orthopedics, surgical intervention for carpal malunion is rarely, if ever, justified merely to restore radiographic alignment. The intricate kinematic tolerances and complex spatial geometry of the carpus dictate that by the time a malunion or nonunion is clinically recognized and symptomatic, it is almost invariably accompanied by secondary, irreversible derangements. These include chronic perilunate instability, adaptive ligamentous contractures, and advanced, predictable patterns of degenerative arthrosis.

Scaphoid fractures account for the vast majority of carpal injuries, representing up to 70% of all carpal fractures. Due to the tenuous, retrograde intraosseous blood supply derived primarily from the dorsal carpal branch of the radial artery, the proximal pole of the scaphoid is highly susceptible to avascular necrosis and nonunion. Epidemiologically, these injuries predominantly affect young, active males following a high-energy fall on an outstretched hand (FOOSH) with the wrist in forced hyperextension and ulnar deviation. Unfortunately, up to 20% of scaphoid fractures are missed at initial presentation, leading to a high incidence of delayed diagnosis.

Because the carpal bones function as a highly synchronized intercalated segment without direct tendinous insertions, their dynamic stability relies entirely on complex intrinsic and extrinsic ligamentous constraints coupled with precise articular congruity. A malunion—most commonly presenting as a "humpback" flexion deformity of the scaphoid—profoundly alters the transmission of axial and shear forces across the radiocarpal and midcarpal joints. This mechanical uncoupling inevitably leads to predictable, progressive patterns of cartilage wear, universally recognized as Scaphoid Nonunion Advanced Collapse (SNAC) or Scapholunate Advanced Collapse (SLAC).

In the early stages of nonunion without arthrosis, anatomic reconstruction via corrective osteotomy and vascularized bone grafting remains the gold standard. However, once the irreversible cascade of articular degeneration initiates, reconstructive osteotomies become entirely futile and frequently exacerbate symptomatology. At this critical juncture, the surgical algorithm definitively shifts toward salvage procedures. The primary goals of salvage surgery—specifically the excision of one or more carpal bones (Proximal Row Carpectomy) or partial/total arthrodesis of the wrist—are the eradication of pain, the provision of a stable carpus, and, when possible, the preservation of functional range of motion.

Detailed Surgical Anatomy and Biomechanics

To master the operative management of carpal salvage, the surgeon must possess a profound understanding of the complex osseous architecture, ligamentous restraints, and biomechanical collapse mechanisms that necessitate these interventions. The human carpus is not a rigid block but rather a dynamic, adaptable universal joint composed of two distinct rows. The distal row (trapezium, trapezoid, capitate, hamate) functions as a relatively rigid unit tightly bound to the metacarpal bases, moving synchronously with the hand. The proximal row (scaphoid, lunate, triquetrum) functions as an intercalated segment, mechanically bridging the radius and the distal carpal row.

Osseous and Ligamentous Architecture

The stability of the intercalated proximal row is entirely dependent on its ligamentous tethers. The intrinsic ligaments, notably the scapholunate (SL) and lunotriquetral (LT) interosseous ligaments, are critical for maintaining proximal row synchrony. The extrinsic ligaments, particularly the stout volar radiocarpal ligaments (radioscaphocapitate [RSC], long radiolunate [LRL], and short radiolunate [SRL]), act as critical check-reins. The RSC ligament is of paramount surgical importance during a Proximal Row Carpectomy; it forms a robust sling across the volar waist of the scaphoid to insert on the capitate, preventing ulnar translation of the carpus. Disruption of the RSC during scaphoid excision is a catastrophic technical error leading to immediate failure of the salvage procedure.

The Intercalated Segment and Biomechanical Collapse

Under normal axial loading, the scaphoid, due to its oblique orientation bridging the midcarpal joint, naturally tends to flex. Conversely, the triquetrum, driven by its articulation with the hamate, naturally tends to extend. The lunate, securely bound to both via the SL and LT ligaments, acts as the central balancing keystone, neutralizing these opposing rotational moments.

When the scaphoid fractures and heals in a "humpback" malunion (characterized by volar flexion and dorsal foreshortening) or progresses to a frank nonunion, this delicate mechanical linkage is abruptly lost. Uncoupled from the volar-flexing force of the scaphoid, the lunate is left entirely under the influence of the extending force of the triquetrum. This results in the classic Dorsal Intercalated Segment Instability (DISI) deformity, characterized radiographically by a radiolunate angle exceeding 15 degrees of extension and a scapholunate angle greater than 60 degrees.

Pathoanatomy of SNAC and SLAC

The biomechanical uncoupling of the scaphoid initiates a highly predictable cascade of osteoarthritis. In a scaphoid nonunion, the distal scaphoid fragment flexes and rotates, causing abnormal point-loading against the radial styloid.
* Stage I: Arthrosis is confined to the radial styloid and the distal scaphoid pole.
* Stage II: Arthrosis progresses to involve the entire radioscaphoid fossa.
* Stage III: The proximal scaphoid fragment and lunate migrate, causing proximal migration of the capitate and subsequent arthrosis of the capitolunate joint.
* Stage IV: Pan-carpal arthrosis involving the radiolunate joint (rare in standard SLAC/SNAC but occurs in severe trauma or inflammatory arthropathies).

The radiolunate joint is uniquely spared in both SLAC and SNAC Stage I-III wrists due to the concentric, spherical nature of the lunate fossa and the robust tethering of the short radiolunate ligament, which prevents abnormal translational wear. This anatomical preservation is the fundamental cornerstone that permits motion-preserving salvage procedures, specifically the Four-Corner Fusion.

Exhaustive Indications and Contraindications

Surgical decision-making in the setting of carpal malunions and nonunions is highly nuanced. The surgeon must carefully weigh the patient's physiological age, functional demands, occupation, and the exact radiographic stage of arthrosis. Intervention is broadly indicated when the patient experiences intractable, activity-limiting wrist pain that is refractory to conservative measures, including prolonged splinting, non-steroidal anti-inflammatory drugs (NSAIDs), activity modification, and fluoroscopically guided intra-articular corticosteroid injections.

The choice between Proximal Row Carpectomy (PRC), Four-Corner Fusion (4CF), and Total Wrist Arthrodesis (TWA) depends heavily on the status of the capitate head and the lunate fossa. PRC requires a pristine capitate head and lunate fossa, as these two surfaces will form the new radiocarpal articulation. 4CF requires a pristine radiolunate joint but is utilized when the capitate head is arthritic. TWA is the definitive salvage when pan-carpal arthrosis is present, or when the patient is a heavy manual laborer who prioritizes absolute stability and pain relief over range of motion.

Indications and Contraindications Matrix

Pre-Operative Planning, Templating, and Patient Positioning

Thorough preoperative planning is the linchpin of successful carpal reconstructive and salvage surgery. The clinical evaluation must rigorously assess the exact location of point tenderness, the presence of a positive Watson scaphoid shift test, baseline grip strength (measured via Jamar dynamometer and compared to the contralateral extremity), and precise active and passive range of motion arcs.

Advanced Imaging Protocols

1. Standard Radiographs: A complete wrist series is mandatory. This includes a zero-rotation posteroanterior (PA) view to assess ulnar variance and carpal height ratio, a true lateral view to measure the radiolunate and scapholunate angles (identifying DISI or VISI deformities), and specific scaphoid views (PA with ulnar deviation and 30 degrees of tube angulation). A clenched-fist PA view is critical to dynamically unmask scapholunate dissociation and dynamic carpal collapse.
2. Computed Tomography (CT): A fine-cut (sub-millimeter) CT scan with multiplanar sagittal and coronal reconstructions is the modern gold standard. It allows for the precise volumetric assessment of carpal bone stock, exact geometric mapping of a malunion, and the definitive identification of subtle midcarpal or radiocarpal osteophytes and subchondral cysts that may preclude a PRC.
3. Magnetic Resonance Imaging (MRI): While plain films and CT are paramount for osseous architecture, MRI is highly sensitive for assessing the vascularity of the proximal scaphoid pole (evaluating for avascular necrosis via T1-weighted signal loss) and the integrity of the interosseous ligaments.

Surgical Templating

For Total Wrist Arthrodesis, digital templating is essential. The surgeon must pre-select the appropriate dorsal spanning plate, ensuring the distal footprint accommodates the third metacarpal without impinging on the metacarpophalangeal (MCP) joint, and the proximal footprint allows for at least six cortices of robust fixation in the distal radius. The built-in extension angle of the plate (typically 10 to 15 degrees) must be verified to optimize postoperative grip biomechanics.

Patient Positioning and Setup

The patient is positioned supine on the operating table with the operative extremity extended onto a radiolucent hand table. A well-padded pneumatic tourniquet is applied to the proximal brachium. Following meticulous exsanguination with an Esmarch bandage, the tourniquet is inflated to 250 mm Hg (or 100 mm Hg above systolic blood pressure). Anesthesia typically consists of a regional brachial plexus block (supraclavicular or axillary approach) supplemented with intravenous sedation, though general anesthesia may be utilized based on patient preference or medical comorbidities. The mini-C-arm fluoroscopy unit is positioned perpendicular to the hand table, entering from the distal aspect to allow unobstructed imaging throughout the procedure.

Step-by-Step Surgical Approach and Fixation Technique

The surgical execution of carpal salvage requires meticulous soft tissue handling, precise osteotomies, and rigid internal fixation. The dorsal approach to the wrist is the universal utility approach for PRC, 4CF, and TWA.

The Universal Dorsal Approach and Neurectomy

1. Incision: A longitudinal dorsal incision is made, centered precisely over Lister's tubercle, extending proximally from the distal radius and distally to the base of the third metacarpal.
2. Extensor Retinaculum: The extensor retinaculum is exposed. The third extensor compartment is incised longitudinally, and the extensor pollicis longus (EPL) tendon is mobilized and transposed radially. The second compartment (ECRL, ECRB) and the fourth compartment (EDC, EIP) are elevated subperiosteally from the radius, preserving the integrity of the retinacular flaps for later repair.
3. PIN Neurectomy: The posterior interosseous nerve (PIN) is reliably identified at the ulnar floor of the fourth extensor compartment, lying directly on the interosseous membrane. A 1- to 2-cm segment of the nerve is sharply excised and the proximal stump is buried into the pronator quadratus muscle belly. This prophylactic partial denervation of the dorsal wrist capsule significantly mitigates postoperative pain without compromising motor function.
4. Capsulotomy: A ligament-sparing dorsal capsulotomy is performed. The Berger (dorsal radiocarpal and dorsal intercarpal ligament-splitting) or a standard Mayo (radially based flap) approach is utilized to widely expose the radiocarpal and midcarpal joints, ensuring the capsular flaps are preserved for robust closure to prevent postoperative carpal subluxation.

Proximal Row Carpectomy (PRC) Technique

1. Scaphoid Excision: The scaphoid is approached first. In the setting of chronic nonunion, it is often fragmented and sclerotic. It is excised piecemeal using a rongeur, osteotomes, or a high-speed burr. Crucial Technical Point: The surgeon must exercise extreme caution during the volar dissection of the scaphoid waist to avoid violating the robust radioscaphocapitate (RSC) ligament. Disruption of the RSC will lead to catastrophic ulnar translation of the capitate off the lunate fossa.
2. Lunate and Triquetrum Excision: A threaded Steinmann pin or a towel clip is inserted into the lunate to serve as a joystick. Sharp dissection with a #15 blade releases the robust volar radiolunate ligaments. The triquetrum is similarly excised, taking care to protect the ulnar neurovascular bundle and the triangular fibrocartilage complex (TFCC).
3. Articular Assessment: The capitate head and the lunate fossa of the radius are meticulously inspected under direct vision. If the capitate head demonstrates severe eburnation or exposed subchondral bone, PRC is strictly contraindicated. The surgeon must intraoperatively abort the PRC and convert to a Four-Corner Fusion, Total Wrist Arthrodesis, or utilize a capitate resurfacing implant (e.g., RCPI).
4. Closure: The capitate is allowed to seat naturally into the lunate fossa. The dorsal capsule is meticulously repaired with heavy non-absorbable sutures (e.g., 2-0 Ethibond) to prevent dorsal subluxation of the capitate. The extensor retinaculum is repaired over the EDC tendons, leaving the EPL transposed subcutaneously.

Partial Wrist Arthrodesis: Four-Corner Fusion (4CF) Technique

1. Scaphoid Excision and Graft Harvest: The scaphoid is completely excised. Rather than discarding the bone, the excised scaphoid is meticulously debrided of cartilage and morselized to serve as high-quality autologous cancellous bone graft.
2. Joint Decortication: The articular surfaces between the lunate, capitate, hamate, and triquetrum are systematically decorticated down to bleeding, healthy cancellous bone using a high-speed burr and sharp osteotomes. The subchondral bone plate must be breached to facilitate robust osteogenesis.
3. Deformity Correction: The chronic DISI deformity of the lunate must be anatomically corrected prior to fixation. A 0.062-inch K-wire is driven dorsally into the lunate, serving as a joystick to volar-flex the lunate into a neutral alignment relative to the radius (restoring a collinear radiolunate axis on lateral fluoroscopy). The capitate is subsequently reduced onto the lunate, restoring carpal height.
4. Rigid Fixation: Fixation is achieved using a specialized dorsal circular locking plate (spider plate) or multiple headless compression screws. If utilizing a circular plate, a central reamer is used to create a recessed bed at the confluence of the four bones. The plate is applied, and locking screws are sequentially placed into the capitate, hamate, triquetrum, and lunate.
5. Bone Grafting: The morselized scaphoid autograft, supplemented with distal radius cancellous graft if necessary, is packed tightly into the decorticated interstices of the four bones prior to final compression.

Total Wrist Arthrodesis (TWA) Technique

1. Extensive Decortication: Following complete excision of the dorsal capsule, the articular cartilage is aggressively removed from the radiocarpal joint, the midcarpal joint, and the carpometacarpal (CMC) joint of the third digit. The distal radioulnar joint (DRUJ) is strictly avoided to preserve forearm rotation, unless a concurrent Darrach or Sauvé-Kapandji procedure is explicitly planned for DRUJ arthrosis.
2. Plate Contouring and Application: A pre-contoured, specialized dorsal wrist fusion plate is selected. The optimal position for wrist arthrodesis is 10 to 15 degrees of extension and neutral radioulnar deviation, which maximizes grip strength and facilitates activities of daily living.
3. Fixation Sequence: The plate is first secured distally to the diaphysis of the third metacarpal using standard cortical screws. The wrist is reduced, and the plate is secured proximally to the distal radius. A dedicated central compression screw is placed obliquely through the plate into the dense bone of the capitate, generating massive compression across the radiocarpal and midcarpal arthrodesis sites.
4. Bone Grafting: Copious cancellous autograft, harvested from the distal radius, proximal ulna, or iliac crest, is meticulously impacted into all decorticated joint spaces to ensure a solid, continuous fusion mass.

Complications, Incidence Rates, and Salvage Management

Despite meticulous surgical technique, salvage procedures of the carpus carry a significant risk of complications. The alteration of native kinematics, the reliance on bone healing in compromised vascular beds, and the proximity of prominent hardware to gliding tendinous structures all contribute to the complication profile.

Nonunion (pseudarthrosis) remains the most dreaded complication following Four-Corner Fusion and Total Wrist Arthrodesis. The incidence is notably higher in patients who actively smoke or have profound osteopenia. Hardware prominence is particularly common following TWA, as the dorsal plate sits directly beneath the thin dorsal skin and extensor tendons. Progressive radiocapitate arthrosis is the primary mode of long-term failure for Proximal Row Carpectomy, often presenting 10 to 15 years postoperatively as the non-congruent capitate head wears against the lunate fossa.

Complications and Management Matrix

Phased Post-Operative Rehabilitation Protocols

The postoperative rehabilitation protocol must be rigidly tailored to the specific salvage procedure performed. The fundamental dichotomy lies between Proximal Row Carpectomy, which relies entirely on soft tissue healing and demands early motion to mold the new articulation, versus partial or total arthrodesis, which requires strict immobilization until definitive bony consolidation is achieved.

Proximal Row Carpectomy (PRC) Protocol

• Weeks 0-2: The wrist is immobilized in a bulky, compressive dressing and a rigid volar plaster splint in neutral position. Immediate active range of motion of the digits, elbow, and shoulder is heavily encouraged to prevent edema and tendon adhesions.
• Weeks 2-4: The postoperative dressings and sutures are removed. The patient is transitioned to a custom-molded, removable thermoplastic wrist splint. Gentle, gravity-assisted active range of motion (AROM) of the wrist is initiated under the supervision of a certified hand therapist.
• Weeks 4-8: Passive range of motion (PROM) and progressive isometric strengthening begin. Splint use is gradually discontinued during the day but maintained at night for protection.
• Months 3+: Progressive resistance exercises are advanced. Return to heavy manual labor, contact sports, or high-impact activities is permitted once painless, functional ROM and at least 70% of contralateral grip strength are achieved.

Four-Corner Fusion (4CF) and Total Wrist Arthrodesis (TWA) Protocol

• Weeks 0-2: The extremity is strictly immobilized in a short-arm cast or rigid postoperative splint. Digital ROM is strictly enforced.
• Weeks 2-6: Sutures are removed, and the patient is transitioned to a well-molded short-arm cast. Strict immobilization of the wrist is maintained to foster osteogenesis.
• Weeks 6-8: The cast is removed, and interval radiographs are obtained to assess for early bony consolidation and bridging trabeculae. If radiographic healing is progressing, the patient is transitioned to a removable splint. For 4CF, gentle AROM is initiated. For TWA, therapy focuses entirely on digital dexterity and compensatory forearm rotation.
• Weeks 8-12: Progressive strengthening is introduced. The splint is weaned as clinical and radiographic fusion solidifies. Full, unrestricted activity is typically delayed until 4 to 6 months postoperatively to ensure robust arthrodesis.

Summary of Landmark Literature and Clinical Guidelines

The evolution of carpal salvage surgery is deeply rooted in several landmark biomechanical and clinical studies that continue to dictate modern operative guidelines.

The fundamental understanding of carpal collapse was established by Watson and Ballet (1984), who first described the SLAC wrist pattern. Their seminal work demonstrated that the radiolunate joint is universally spared in the setting of scapholunate dissociation, providing the anatomical justification for the Four-Corner Fusion.

The debate between PRC and 4CF has been extensively studied. Krakauer et al. (1994) provided a critical comparative analysis, demonstrating that both procedures offer comparable pain relief and patient satisfaction. However, their data indicated that PRC generally yields a slightly greater postoperative range of motion, whereas 4CF better preserves grip strength and carpal height. This study remains the foundation for tailoring the procedure to the patient's specific functional demands.

Regarding definitive salvage, Weiss and Hastings (1995) published definitive guidelines on Total Wrist Arthrodesis utilizing the dorsal contoured plate. They established that fusing the wrist in 10 to 15 degrees of extension optimizes the mechanical advantage of the extrinsic digital flexors, maximizing postoperative grip strength while minimizing extensor tendon irritation.

Current clinical consensus guidelines, supported by the American Academy of Orthopaedic Surgeons (AAOS) and the American Society for Surgery of the Hand (ASSH), dictate that patient selection is the ultimate determinant of success. PRC is highly recommended for older, lower-demand patients due to its technical simplicity and early rehabilitation profile, provided the capitate is pristine. Conversely, 4CF is the procedure of choice for younger, high-demand laborers who require preserved grip strength and possess midcarpal arthrosis. Total Wrist Arthrodesis remains the uncompromising gold standard for pan-carpal arthrosis, failed partial fusions, and patients requiring absolute, lifelong stability.