Scaphoid excision and four-corner fusion (4CF) is a motion-preserving limited wrist arthrodesis performed for advanced carpal collapse secondary to scapholunate ligament insufficiency (SLAC wrist) or scaphoid nonunion (SNAC wrist). The procedure involves excising the scaphoid and fusing the capitate, lunate, hamate, and triquetrum into a single bony mass that articulates with the radius at the preserved radiolunate joint.

The concept was developed from the observation by Watson and Ballet (1984) that wrist arthritis follows predictable patterns. In SLAC wrist, the radiolunate joint is preserved until very late, meaning the lunate fossa of the radius and the proximal pole of the lunate remain healthy even as the scaphoid and its surrounding articulations degenerate. By excising the arthritic scaphoid and stabilising the remaining carpus, pain is relieved while a functional arc of motion is maintained.

Fundamental principle: the scaphoid is the mechanical keystone linking the proximal and distal carpal rows. When the scapholunate ligament fails or the scaphoid does not unite, the scaphoid flexes and collapses into a vertical position, the lunate extends into dorsiflexed intercalated segment instability (DISI), and the carpus collapses in a predictable proximal migration pattern. Removing the scaphoid eliminates the pain source; fusing the four corners stabilises the remaining carpus.

Indications:

• SLAC wrist stages I and II with preserved radiolunate joint and intact lunocapitate cartilage
• SNAC wrist with arthritis confined to the scaphoid articulations and preserved radiolunate joint
• Chronic scapholunate instability with secondary degenerative changes, unsuitable for ligament reconstruction
• Scaphoid nonunion with secondary arthritis and a viable proximal pole that is unsalvageable
• Patient who desires motion preservation and understands the expected functional outcomes
• Patient willing to comply with prolonged immobilisation and rehabilitation (6-12 weeks protected mobilisation)

Relative indications:

• Kienbock disease (late stage) with carpal collapse where radiolunate preservation is possible
• Preiser disease (avascular necrosis of the scaphoid) with secondary arthritis

Carpal kinematics relevant to four-corner fusion:

• The wrist functions as two carpal rows. The proximal row (scaphoid, lunate, triquetrum) acts as an intercalated segment with no direct tendon insertions, moving passively in response to forces transmitted through the distal row. The distal row (trapezium, trapezoid, capitate, hamate) is rigidly interconnected and moves as a unit.
• The scaphoid is the critical mechanical link between the two rows. It bridges the proximal and distal carpal rows and prevents the lunate from extending into a DISI position. When the scapholunate ligament ruptures or the scaphoid fractures and does not unite, this mechanical link is lost and the lunate extends (DISI), the capitate migrates proximally, and the carpus collapses.
• In SLAC wrist, the pattern of degeneration follows the loss of scaphoid support. The scaphoid rotates into flexion and the increased contact pressures at the styloscaphoid and radioscaphoid joints cause progressive arthritis. The radiolunate joint is biomechanically spared because the lunate remains congruent within the lunate fossa even as it extends into DISI.

The lunate and its fossa:

• The lunate fossa of the radius is a concave, spherical articulation that matches the proximal convexity of the lunate. This joint has a large contact area and low contact pressure, which explains why it is preserved in SLAC wrist until very late.
• After 4CF, the radiolunate joint becomes the sole remaining articulation between the forearm and the carpus. The fused capitate-lunate-hamate-triquetrum mass transmits loads through the lunate into the lunate fossa.

The four corners:

• Capitate: the largest carpal bone, centred in the distal row. Its proximal pole articulates with the lunate (the lunocapitate joint). After 4CF, the capitolunate interface must fuse for the procedure to succeed.
• Lunate: the keystone of the proximal row. Its proximal surface articulates with the radius (preserved) and its distal surface with the capitate (must fuse).
• Hamate: articulates with the triquetrum and the capitate. Inclusion in the fusion mass provides lateral stability and increases the surface area for fusion.
• Tiquetrum: articulates with the lunate and hamate. Some surgeons exclude the triquetrum (three-corner fusion) but including it adds stability and does not significantly reduce motion.

Biomechanical outcome of 4CF:

• Flexion-extension arc is reduced to approximately 50-60% of normal (approximately 40-60 degrees total arc). This is because midcarpal motion is eliminated (the midcarpal joint is fused) and only radiolunate motion remains.
• Radioulnar deviation is reduced to approximately 50% of normal.
• Grip strength typically returns to approximately 65-80% of the contralateral side, which is often better than PRC in comparative studies.
• The fused carpal mass acts as a single block that pivots on the radiolunate joint, providing a stable but mobile wrist.

Dorsal approach to the wrist (standard for 4CF):

• Incision: longitudinal dorsal skin incision centred over Lister tubercle, extending approximately 6-8 cm from the distal radius to the midcarpal region.
• Interval: the approach is developed between the third (extensor pollicis longus) and fourth (extensor digitorum communis / extensor indicis proprius) dorsal compartments. The EPL is identified at its oblique course around Lister tubercle and retracted radially. The EDC/EIP tendons are retracted ulnarly.
• The posterior interosseous nerve (PIN) terminal branch is identified on the floor of the fourth compartment and sacrificed (neurectomy) to provide partial wrist denervation as part of the pain-relief strategy. A 1-2 cm segment is resected to prevent neuroma formation at the resection site.
• The dorsal wrist capsule is incised longitudinally, and the capsular flaps are elevated to expose the carpus from the distal radius to the midcarpal row.

Structures encountered:

• Lister tubercle - the key landmark on the dorsal radius, between the second and third compartments
• Extensor pollicis longus (EPL) - crosses obliquely in the third compartment; must be identified and protected
• Extensor digitorum communis (EDC) and extensor indicis proprius (EIP) - fourth compartment; retracted ulnarly
• Extensor carpi radialis brevis (ECRB) and longus (ECRL) - deep to the second compartment, radial side; may be retracted radially
• Dorsal radiocarpal ligament and dorsal intercarpal ligament - divided to access the carpus; some surgeons attempt repair at closure
• Posterior interosseous nerve - terminal branch on the floor of the fourth compartment; sacrificed for denervation

Alternative approaches:

• Radial styloidectomy extension: the incision can be extended radially to allow access to the radial styloid for styloidectomy, performed to prevent radial impingement on the fused carpus during radial deviation.
• Some surgeons use a separate radial incision for the styloidectomy to avoid extensive dorsal dissection.

• Position: supine with the arm extended on a hand table. A padded tourniquet is applied to the upper arm. The arm is draped free to allow full wrist flexion, extension, and rotation.
• Anaesthesia: general or regional (brachial plexus block - axillary or supraclavicular). Regional anaesthesia provides excellent post-operative analgesia and allows early mobilisation of the fingers.
• Tourniquet: exsanguination and inflation to approximately 250 mmHg. The tourniquet should be released before closure to assess haemostasis, particularly around the dorsal radial artery branches.
• Fluoroscopy: essential. The image intensifier is positioned to obtain PA, lateral, and oblique views of the wrist. Intra-operative imaging confirms scaphoid excision completeness, correction of lunate alignment (reduction of DISI), hardware position, and adequacy of styloidectomy.
• Instrumentation: standard hand surgery tray, osteotomes, rongeurs, K-wires (0.045 and 0.062 inch), and the chosen fixation device (circular plate set, headless compression screws, or K-wires alone).
• Bone graft: autologous cancellous bone graft from the distal radius (via the same dorsal incision or a separate radial styloid window) or from the excised scaphoid (the healthy portions of the scaphoid provide excellent local autograft). Some surgeons use bone substitute or allograft.

Four-corner fusion has a significant complication profile. The overall complication rate ranges from approximately 10-30% in published series, with reoperation rates of approximately 10-20%.

• Nonunion - the most significant complication and the commonest reason for reoperation. Rates range from approximately 3% with K-wires to 15-30% with circular plates in some series. Risk factors include inadequate cartilage denudation, poor bone grafting, smoking, and insufficient fixation. Nonunion presents with persistent wrist pain and may require revision fusion or conversion to total wrist arthrodesis.
• Dorsal impingement - the fused carpal mass or prominent hardware impinges on the dorsal rim of the radius during wrist extension. This causes pain with terminal extension and is a common cause of persistent post-operative symptoms. Prevention includes adequate dorsal rim trimming, ensuring the lunate is reduced from DISI, and using low-profile fixation.
• Hardware complications - prominent dorsal hardware (especially circular plates) causes extensor tendon irritation, tenosynovitis, and rarely extensor tendon rupture. Hardware removal is required in approximately 10-30% of cases with circular plates. K-wires may back out or cause pin-tract infection.
• Radial styloid impingement - inadequate styloidectomy results in residual impingement between the radial styloid and the fused carpus during radial deviation. This presents as pain on radial deviation and may require revision styloidectomy.
• CRPS (complex regional pain syndrome) - reported in approximately 2-5% of cases. Early mobilisation of fingers, adequate analgesia, and early hand therapy are preventive.
• Infection - superficial wound infection in approximately 1-3%; deep infection requiring implant removal is rare.
• Residual stiffness - the expected motion after 4CF is approximately 40-60 degrees of flexion-extension (roughly 50-60% of normal). Patients who expect full motion will be disappointed. Pre-operative counselling is essential.
• Extensor tendon adhesion or rupture - dorsal dissection and hardware can cause adhesions limiting finger and wrist extension. EPL rupture has been reported with prominent hardware.
• Progressive radiolunate arthritis - although the radiolunate joint is preserved at surgery, it may degenerate over time (approximately 10-15% at long-term follow-up), eventually requiring conversion to total wrist arthrodesis.
• Superficial radial nerve neuroma - the dorsal approach puts the superficial radial nerve branches at risk; neuroma formation causes dorsal wrist and hand dysesthesia.

There is no single universal guideline for four-corner fusion; practice follows evidence-based principles of carpal arthritis staging and motion-preserving surgery. Several international hand surgery societies have published consensus statements and recommendations:

Key guidance principles:

• ASSH (American Society for Surgery of the Hand): four-corner fusion and PRC are both recognised as motion-preserving options for SLAC/SNAC wrist stages I-II. The choice depends on the condition of the radiolunate and capitate head cartilage, patient demands, and surgeon experience.
• BSSH (British Society for Surgery of the Hand): guidelines support limited wrist arthrodesis as a motion-preserving alternative to total wrist fusion in appropriately selected patients with SLAC/SNAC arthritis. Patient counselling about expected motion and grip strength outcomes is emphasised.
• FESSH (Federation of European Societies for Surgery of the Hand): European practice generally favours four-corner fusion over PRC for patients with high functional demands, reflecting a preference for retaining the lunocapitate articulation. However, the evidence does not strongly favour one over the other.

Registry and outcomes data:

• Large institutional series from the Mayo Clinic, Virginia Hand Center, and European centres confirm approximately 85-95% union rates with K-wire fixation and approximately 70-80% union rates with circular plates.
• Conversion to total wrist arthrodesis after failed 4CF is reported at approximately 10-15% at 10 years in most series, comparable to PRC conversion rates.
• Patient satisfaction scores are generally high (approximately 75-90% satisfied or very satisfied) in patients who achieve union.

Global practice variation:

• European hand surgeons have historically been more aggressive in performing limited wrist fusions compared with North American surgeons, who have tended toward PRC as the simpler first-line option for SLAC/SNAC wrist. This gap is narrowing as evidence accumulates.
• Japanese hand surgery literature has contributed significantly to understanding carpal kinematics after limited fusion, with several biomechanical studies from Japanese centres.
• In low- and middle-income settings, both PRC and K-wire four-corner fusion are valued as reliable, low-cost procedures that avoid the need for expensive implants.
• The trend away from circular plates toward K-wires or headless compression screws is now widespread in high-volume hand surgery centres globally, driven by the higher complication rates of dorsal plating.

4CF vs PRC - the ongoing debate:

• The choice between 4CF and PRC remains one of the most debated topics in hand surgery. Neither procedure has been shown to be clearly superior in high-quality randomised trials.
• PRC is simpler, faster, has a lower complication rate, and provides slightly better motion. 4CF may provide marginally better grip strength by retaining the native lunocapitate joint.
• Most surgeons now select based on: (1) radiolunate joint status (if arthritic, PRC or TWA), (2) capitate head cartilage (if arthritic, 4CF rather than PRC), (3) patient demands and expectations, and (4) surgeon experience and comfort with each technique.