Scapholunate instability

1. High-Yield Summary

• Core Kinematic Decoupling: Scapholunate (SL) interosseous ligament dissociation represents the most prevalent form of carpal instability (CID: Carpal Instability Dissociative). Complete disruption uncouples the scaphoid (which flexes, pronates, and translates radially under distal row axial loads) from the lunate (which extends with the triquetrum under proximal row forces), culminating in dorsal intercalated segment instability (DISI).
• Mayfield Perilunate Progression and Anatomy: Represents Stage I of Mayfield progressive perilunate instability. The dorsal band of the SL interosseous ligament (SLIL) is the primary mechanical restraint (yield load approximately 300 N; 2 to 3 mm thickness). Static carpal dissociation requires concurrent disruption or plastic attenuation of secondary extrinsic stabilizers, particularly the dorsal intercarpal (DIC) and scaphotrapeziotrapezoid (STT) ligaments.
• Diagnostic Benchmarks: Physical examination hallmark is focal tenderness over the dorsal SL interval (1 cm distal to Lister’s tubercle) and a positive Watson scaphoid shift test. Radiographic diagnostic thresholds include a static SL interval > 3 mm (Terry Thomas sign; > 4 mm is pathognomonic), cortical “ring sign” of the hyperflexed scaphoid on posteroanterior (PA) projection, SL angle > 60° (normal 30° to 60°), and radiolunate angle > 10° of extension on true lateral projection. Dynamic diastasis is accentuated on bilateral clenched-fist PA stress radiographs.
• Natural History and SLAC Wrist: Untreated dissociation inevitably leads to Scapholunate Advanced Collapse (SLAC) over 10 to 20 years, progressing predictably through Stage I (radial styloid beaking), Stage II (pan-scaphoid fossa chondromalacia), and Stage III (capitolunate joint arthrosis). The radiolunate articulation is characteristically preserved due to spherical joint congruence and purely compressive loading.
• Stage-Specific Management: Governed by the Garcia-Elias staging algorithm. Acute injuries (< 6 weeks) with repairable tissue undergo direct open repair with dorsal capsulodesis or suture tape internal bracing. Chronic reducible dissociation with preserved cartilage warrants soft-tissue reconstruction (e.g., Three-Ligament Tenodesis / modified Brunelli). Chronic irreducible or arthritic wrists require motion-preserving salvage: proximal row carpectomy (PRC, requiring pristine capitate head cartilage) or four-corner arthrodesis (4CA, when capitolunate arthrosis is present).

2. Anatomy

The scapholunate interosseous ligament (SLIL) is a true intra-articular C-shaped (horseshoe) fibrocartilaginous and ligamentous complex binding the proximal articular contours of the scaphoid and lunate. Anatomically and functionally, the SLIL is divided into three distinct subregions: dorsal, membranous (proximal), and volar.

Scapholunate Interosseous Ligament Subregions

• Dorsal Subregion: The biomechanical keystone of carpal stability. Composed of densely packed, transversely oriented, true collagenous fascicles measuring 2 to 3 mm in thickness. Possesses the highest ultimate tensile strength (yield load approximately 260 to 300 N) and highest stiffness of the three subregions. It directly resists scaphoid flexion, rotatory subluxation, and distraction during axial loading. Disruption of this component is mandatory for pathological carpal translation.
• Volar Subregion: Composed of obliquely oriented collagen fibers measuring approximately 1 mm in thickness, providing an ultimate tensile yield load of roughly 120 to 150 N. Functions primarily to constrain external rotation of the scaphoid and control rotational congruency during radiocarpal extension and ulnar deviation.
• Membranous (Proximal) Subregion: A thin, triangular, avascular fibrocartilaginous sheet lining the proximal articular margin between the radiocarpal and midcarpal spaces. Possesses negligible mechanical tensile strength (yield load approximately 25 to 50 N). Serves predominantly as a synovial barrier and fluid seal. Isolated degeneration or perforation of the membranous band is commonly observed as an asymptomatic age-related finding and does not produce clinical or radiographic instability.

Secondary Extrinsic Ligamentous Stabilizers

Static carpal dissociation cannot occur through isolated complete rupture of the intrinsic SLIL alone. Maintenance of dynamic stability or progression to static collapse depends on the integrity of surrounding secondary extrinsic ligaments:

• Dorsal Extrinsic Complex: The dorsal intercarpal (DIC) ligament originates from the dorsal triquetrum and spans transversely to insert onto the dorsal ridge of the scaphoid, trapezoid, and lunate. Working in synergy with the dorsal radiocarpal (DRC) ligament, the DIC acts as a critical dorsal restraint preventing scaphoid flexion and dorsal subluxation. Attenuation or traumatic disruption of the DIC in conjunction with dorsal SLIL failure is the essential biomechanical prerequisite for static rotatory subluxation of the scaphoid.
• Volar Extrinsic Complex: The radioscaphocapitate (RSC) ligament originates from the radial styloid and courses across the waist of the scaphoid to insert onto the capitate, forming a structural sling supporting the scaphoid waist. The long radiolunate (LRL) ligament stabilizes the volar pole of the lunate against dorsal tilt. The scaphotrapeziotrapezoid (STT) ligament complex anchors the distal pole of the scaphoid, coupling distal carpal row translation to scaphoid flexion. The radioscapholunate (RSL) ligament (ligament of Testut and Kuenz) is not a true mechanical stabilizer but a neurovascular bundle carrying sensory nerve endings and vascular supply to the SL interval.

Surgical Corridors and Internervous Plane

Open surgical exposure of the scapholunate interval is achieved through a dorsal approach exploiting the internervous interval between the third and fourth extensor compartments. Dissection proceeds between the extensor pollicis longus (EPL, innervated by the posterior interosseous nerve [PIN]) in the third compartment and the extensor digitorum communis (EDC) and extensor indicis proprius (EIP, both innervated by the PIN) in the fourth compartment. While both compartments share radial nerve innervation, entering between their distinct fibrous sheaths minimizes intramuscular dissection and avoids denervation.

Dorsal capsulotomy is performed utilizing the ligament-sparing Berger technique. An inverted V-shaped or chevron incision is created along the longitudinal axes of the DRC and DIC ligaments, with the apex directed towards the triquetrum. This configuration preserves the vascularity of the dorsal carpus, maintains the integrity of the extrinsic ligamentous restraints, and permits anatomic closure without inducing postoperative extension stiffness.

Neurovascular Danger Zones

• Posterior Interosseous Nerve (PIN): Courses along the floor of the fourth extensor compartment adjacent to the dorsal radius. The terminal sensory branch innervates the dorsal radiocarpal and midcarpal capsule. During dorsal exposure, a 1.5 to 2 cm segment of the terminal PIN is routinely identified and resected (partial wrist denervation) to provide postoperative analgesia, taking care to avoid indiscriminate proximal dissection.
• Anterior Interosseous Nerve (AIN): Runs along the volar wrist capsule deep to the pronator quadratus. Provides articular sensation to the volar radiocarpal joint; at risk during volar portal placement or volar scaphoid harvesting.
• Superficial Branch of the Radial Nerve (SBRN): Traverses the subcutaneous tissue overlying the first and second extensor compartments. Longitudinal sensory branches cross the anatomical snuffbox within 2 to 5 mm of dorsal radial wrist portals (1-2 and 3-4 portals). Iatrogenic laceration or traction injury results in refractory neuroma formation and intractable neuropathic pain.
• Radial Artery: Winds through the floor of the anatomical snuffbox, passing deep to the abductor pollicis longus and extensor pollicis brevis tendons and directly over the scaphoid waist and trapezium. Vulnerable during radical radial styloidectomy, mobilization of the distal scaphoid pole, and placement of distal tenodesis bone anchors.

3. Pathogenesis

Scapholunate dissociation is primarily traumatic in origin, precipitated by high-energy loading of the carpus. The classical mechanism of injury is a fall onto an outstretched hand (FOOSH) with the wrist forced into hyperextension (> 95°), ulnar deviation, and intercarpal supination. This creates an intense traction and shearing moment centered on the radial carpal column.

Mayfield Progressive Perilunate Instability (Stage I)

In 1980, Mayfield and colleagues characterized the pathomechanics of progressive perilunate dislocation as a sequential, four-stage circular disruption propagating around the lunate from radial to ulnar:

• Stage I (Scapholunate Dissociation): The carpal disruption initiates on the radial aspect. Hyperextension and ulnar deviation force the scaphoid into hyperflexion while the capitate wedges into the scapholunate interval. This results in progressive tensile rupture of the radioscapholunate ligament, followed by the volar SLIL, membranous SLIL, and finally the thick dorsal SLIL.
• Stage II (Capitolunate Dislocation): The traumatic vector propagates through the space of Poirier (an inherently weak, ligament-free zone between the volar radiocapitate and radiolunate ligaments), dissociating the capitate from the lunate.
• Stage III (Lunotriquetral Dissociation): The force vectors tear the lunotriquetral interosseous ligament and dorsal radiocarpal ligament, freeing the lunate from its carpal attachments.
• Stage IV (Lunate Dislocation): Complete ligamentous avulsion allows the capitate to drive the lunate out of the lunate fossa of the radius, displacing it volarly into the carpal tunnel.

Scapholunate instability thus represents an arrested or isolated Mayfield Stage I perilunate injury.

Biomechanical Decoupling and DISI Deformity

In the native wrist, the proximal carpal row functions as an intercalated segment lacking direct tendon insertions. The kinematic behavior of the proximal row is dictated by reciprocal antagonist moments:

• Scaphoid Flexion Moment: The scaphoid is oriented obliquely across the radiocarpal and midcarpal joints. Under axial load transmitted from the distal row via the STT joint, the scaphoid possesses an intrinsic tendency to flex and pronate.
• Triquetrum Extension Moment: The triquetrum articulates with the helicoidal facet of the hamate. Under axial load, the hamate drives the triquetrum into extension and supination.
• The Lunate Intercalated Pivot: In the healthy wrist, the lunate is coupled to the scaphoid via the SLIL and to the triquetrum via the lunotriquetral (LT) ligament. The lunate balances these opposing vectors, maintaining collinear alignment with the radius and capitate in neutral wrist position.

When the dorsal SLIL and secondary dorsal stabilizers rupture, the balance is severed. Unshackled from the lunate, the scaphoid collapses into pathological hyperflexion, pronation, and radial translation (rotary subluxation of the scaphoid). Concurrently, the intact LT ligament allows the triquetrum’s extension moment to pull the lunate unchecked into pathologic extension. This reciprocal malalignment constitutes the Dorsal Intercalated Segment Instability (DISI) deformity, characterized by an increased scapholunate angle (> 60°) and abnormal radiolunate extension (> 10°).

4. Natural History

The natural history of untreated complete scapholunate dissociation is inexorable progression toward degenerative carpal collapse, designated Scapholunate Advanced Collapse (SLAC) wrist. First classified by Watson and Ballet in 1984, the SLAC pattern represents the most frequent cause of non-inflammatory wrist arthritis.

Progression of SLAC Arthropathy

Because the scaphoid is abnormally flexed and rotated, contact pressures between the articular cartilage of the scaphoid and the distal radius become concentrated over small, non-physiological contact areas. Over 10 to 20 years, predictable cartilage wear advances through sequential anatomic zones:

• Stage I (Radial Styloid Chondrosis): Excessive shear and localized mechanical loading between the radial styloid and the distal articular facet of the rotarily subluxated scaphoid produce point contact wear. Radiographs demonstrate radial styloid sharpening, sclerosis, and joint space narrowing isolated to the radioscaphoid tip.
• Stage II (Pan-Scaphoid Fossa Chondrosis): Cartilage loss and eburnation extend across the entire scaphoid fossa of the distal radius. The proximal scaphoid facet is completely denuded. The articular cartilage of the adjacent lunate fossa remains entirely normal.
• Stage III (Capitolunate Joint Arthrosis): As the scaphoid subluxates further dorsally and radially, the capitate loses its normal midcarpal seat and migrates proximally into the widened scapholunate interval. High contact stresses between the rounded head of the capitate and the extended, dorsally tilted lunate produce joint space narrowing, subchondral sclerosis, and cystic changes at the capitolunate articulation.
• Stage IV (Pan-Carpal Collapse): Advanced midcarpal and radiocarpal wear with proximal migration of the capitate. Crucially, even in end-stage disease, the radiolunate joint is characteristically spared. The spherical, concentric geometry of the lunate seated within the concave lunate fossa of the distal radius generates purely compressive axial forces without eccentric shear, preserving the radiolunate articular cartilage. This anatomical phenomenon provides the biomechanical foundation for motion-preserving salvage procedures such as four-corner arthrodesis and proximal row carpectomy.

Epidemiology and Clinical Burden

Scapholunate ligament disruption is the most common form of carpal instability, estimated to occur in up to 5% of all wrist sprains evaluated in emergency departments. Concomitant SLIL injury is highly prevalent in distal radius fractures, occurring in 13% to 30% of high-energy intra-articular fractures (particularly AO Type B and C injuries). The demographic distribution displays a bimodal pattern: young active males (aged 20 to 45 years) sustaining high-energy trauma (motor vehicle collisions, contact sports, falls from height), and older adults (aged > 60 years) sustaining low-energy domestic falls onto osteopenic wrists with pre-existing attritional ligament degeneration.

5. Clinical Presentation

History

Patients typically present with pain localized to the dorsal and radial aspects of the wrist. The clinical onset may be acute following a traumatic fall, or insidious after a remote “sprain” that failed to resolve over weeks to months. Key clinical inquiries include:

• Mechanical Symptoms: Patients frequently report painful clicking, snapping, or a sensation of the carpus “giving way” or “clunking” during active wrist motion, particularly when transitioning from ulnar to radial deviation.
• Aggravating Activities: Symptoms are exacerbated by axial load applied across an extended wrist, such as pushing up from a seated position, performing push-ups, weightlifting, or opening heavy doors.
• Functional Deficits: Loss of grip strength and subjective wrist fatigue are universal complaints, reflecting dynamic carpal collapse and secondary muscular inhibition.

Physical Examination

Physical examination begins with bilateral inspection for dorsal carpal fullness or localized swelling over the radiocarpal joint. Palpation elicits well-demarcated tenderness over the scapholunate interval, situated approximately 1 cm distal to Lister’s tubercle on the dorsal radius, immediately between the extensor carpi radialis brevis (ECRB) and extensor digitorum communis (EDC) tendons.

Specialized provocative physical examination maneuvers must be methodically executed:

• Watson Scaphoid Shift Test: The examiner sits facing the patient, stabilizes the patient’s distal forearm with one hand, and applies direct dorsal pressure with the thumb over the volar prominence of the scaphoid tuberosity. The patient’s wrist is moved passively from full ulnar deviation and slight extension into radial deviation and slight flexion. In the normal wrist, the scaphoid naturally flexes; however, the examiner’s thumb blocks this motion. In the SL-deficient wrist, blocking scaphoid flexion forces the proximal pole of the scaphoid to subluxate dorsally over the posterior lip of the radial scaphoid fossa. Upon releasing thumb pressure, the scaphoid snaps back into the scaphoid fossa with an audible or palpable painful clunk -> Positive Finding: Dorsal subluxation followed by painful reduction clunk [Sensitivity: 69-89%, Specificity: 64-98%]. Note: A positive Watson test can occur in up to 20% to 30% of asymptomatic hypermobile individuals; therefore, bilateral comparison is mandatory.
• Scapholunate Ballottement / Shear Test (Kleinman): The examiner stabilizes the lunate between the thumb and index finger of one hand, and grasps the scaphoid with the contralateral hand. Direct anteroposterior shear stress is applied across the scapholunate articulation -> Positive Finding: Pain, crepitation, and pathological excessive translation relative to the uninjured contralateral wrist [Sensitivity: 68-75%, Specificity: 82-88%].
• Dorsal SL Interval Palpation Sign: Direct focal digital pressure applied into the dorsal depression immediately distal to Lister’s tubercle while passively flexing the wrist -> Positive Finding: Exquisite, localized tenderness concordant with patient’s baseline symptoms [Sensitivity: 85-92%, Specificity: 60-72%].

6. Imaging and Diagnostic Studies

Evaluation of scapholunate instability follows a structured diagnostic hierarchy, beginning with standard and dynamic stress plain radiography, progressing to cross-sectional arthrography, and culminating in wrist arthroscopy as the definitive gold standard.

Standard and Dynamic Plain Radiography

Standard radiocarpal imaging requires a zero-rotation posteroanterior (PA) view (shoulder abducted 90°, elbow flexed 90°, forearm in neutral rotation) and a true lateral projection. In the early or dynamic stages of dissociation, static views may appear entirely normal.

• Terry Thomas Sign (Scapholunate Interval Diastasis): Widening of the parallel joint space between the scaphoid and lunate on the neutral PA view. A gap exceeding 3 mm is considered abnormal, while a diastasis > 4 mm is pathognomonic of complete disruption of both intrinsic and extrinsic dorsal restraints. Comparison with the uninjured contralateral wrist is mandatory, as physiologic symmetry can exhibit baseline gaps up to 3 mm in hyperlax individuals.
• Cortical Ring Sign (Signet Ring Sign): When the scaphoid flexes pathologically into the coronal plane, its distal tuberosity rotates volarly and is projected end-on on the PA radiograph, producing an abnormal dense circular cortical ring in the distal scaphoid body. Concurrently, the scaphoid appears foreshortened, with a reduced distance (< 7 mm) between the ring and the proximal scaphoid pole.
• Scapholunate Angle (Lateral View): Measured between the long axis of the scaphoid (connecting the midpoints of the proximal and distal convex poles) and the long axis of the lunate (perpendicular to a line connecting its anterior and posterior horn apices). Normal range is 30° to 60° (mean: 47°). An SL angle > 60° (often reaching 70° to 90°) signifies abnormal scaphoid hyperflexion and diagnostic DISI deformity.
• Radiolunate Angle (Lateral View): Measured between the longitudinal axis of the radius and the axis of the lunate. Normal range is -15° (volar tilt) to +15° (dorsal tilt). A radiolunate extension angle > 10° of dorsal tilt confirms dorsal intercalated segment instability (DISI).
• Capitolunate Angle (Lateral View): Measured between the long axis of the capitate and the long axis of the lunate. Normal is 0° (collinear, ±15°). An angle > 15° reflects midcarpal zigzag collapse.
• Clenched-Fist Stress PA Views: Clenching the fist contracts the long flexor tendons and drives the wedge-shaped proximal pole of the capitate proximally into the carpal mortise between the scaphoid and lunate. This dynamic maneuver accentuates occult diastasis, converting a latent dynamic lesion into an overt radiographic gap (> 3 mm). Dedicated pencil-grip or traction views provide complementary dynamic assessment.

Advanced Cross-Sectional Imaging

• Magnetic Resonance Imaging (MRI) and MR Arthrography (MRA): Standard non-contrast 1.5T or 3.0T MRI achieves moderate sensitivity (60% to 75%) and high specificity (85% to 90%) for complete dorsal SLIL tears, but frequently fails to distinguish partial from full-thickness perforations. Magnetic resonance arthrography (MRA)—incorporating fluoroscopically guided radiocarpal or triple-compartment gadolinium injection—substantially enhances diagnostic accuracy, yielding a sensitivity of 85% to 95% and specificity of 95% to 98% for dorsal band disruption. High-resolution coronal proton density (PD) and T2-weighted fat-suppressed sequences demonstrate fluid extravasation, contour blunting, or complete absence of the dorsal collagen bundle.
• Computed Tomography Arthrography (CTA): Triple-compartment CTA represents an exceptional high-resolution alternative, particularly in patients with indwelling metal hardware or MRI contraindications. It provides superior spatial resolution (sub-millimeter slice thickness) to evaluate subtle chondral thinning, subchondral cysts, and step-offs at the scaphoid fossa and capitolunate joint.

Diagnostic Wrist Arthroscopy

Diagnostic wrist arthroscopy remains the undisputed gold standard for the diagnosis, dynamic grading, and staging of scapholunate instability. Utilizing standard 3-4 and 4-5 radiocarpal portals alongside midcarpal radial (MCR) and midcarpal ulnar (MCU) portals, arthroscopy uniquely permits direct visual inspection and dynamic mechanical probing:

• Radiocarpal Space Evaluation: Direct visualization of the proximal membranous and volar portions of the SLIL. Probe palpation assesses tissue elasticity, tearing, or avulsion from the scaphoid or lunate articular footprints.
• Midcarpal Space Evaluation: Crucial for assessing functional competence. The midcarpal space affords direct visualization of the dorsal SLIL band. A 1.0 mm blunt probe is introduced between the scaphoid and lunate to test rotational stability, joint step-off, and joint congruency under dynamic loading.

7. Classification

Two validated, universally recognized classification systems dictate the diagnostic assessment and surgical decision-making for scapholunate instability: the Geissler Arthroscopic Classification and the Garcia-Elias 6-Stage Algorithm.

Geissler Arthroscopic Classification

Originally described in 1996, the Geissler classification categorizes carpal interosseous ligament tears based on arthroscopic visualization and mechanical probe displacement from both radiocarpal and midcarpal portals:

Garcia-Elias 6-Stage Clinical Algorithm

Published in 2006, the Garcia-Elias algorithm guides surgical decision-making by evaluating five sequential clinical, radiographic, and arthroscopic questions:

• 1. Is the dorsal SL ligament intact?
• 2. Does the dorsal SL ligament possess sufficient tissue quality for direct suture anchor repair?
• 3. Is the scaphoid alignment normal on static non-stress radiographs?
• 4. Is the abnormal carpal alignment passively reducible under fluoroscopy?
• 5. Is the articular cartilage of the radiocarpal and midcarpal joints preserved?

8. Treatment

Medical / Nonoperative

Nonoperative management is strictly indicated for Geissler Grade I partial tears, asymptomatic dynamic instability in low-demand or elderly patients, or acute mild carpal sprains where static and stress radiographs demonstrate normal carpal architecture without diastasis (< 2 mm).

• Immobilization Protocol: Short-arm thumb-spica cast or rigid wrist orthosis maintaining the wrist in neutral to 10° of extension for 4 to 6 weeks, immobilizing the first metacarpal to relax the dynamic traction moment of the abductor pollicis longus across the distal scaphoid.
• Neuromuscular Re-Education and Proprioception: Following immobilization, specialized hand therapy focuses on dynamic carpal stabilization. Rehabilitation selectively recruits dynamic pronator and carpal stabilizers—specifically the flexor carpi radialis (FCR), abductor pollicis longus (APL), and extensor carpi radialis longus (ECRL)—which generate an extension and supination moment on the scaphoid, counteracting rotatory subluxation. Unconstrained contraction of the extensor carpi ulnaris (ECU) is discouraged during early rehab, as it accentuates scaphoid flexion.
• Objective Failure Criteria: Persistent dorsal radial wrist pain beyond 6 to 12 weeks of structured therapy, worsening subjective grip weakness, or radiographic progression to static diastasis (> 3 mm) mandates surgical evaluation.

Operative

The primary goals of operative intervention are to anatomically restore the scapholunate relationship, re-establish congruent load transmission across the radiocarpal and midcarpal joints, relieve pain, and halt the progression to SLAC wrist. Surgical strategy is stratified by chronicity, ligament tissue quality, reducibility, and chondral status.

1. Acute Dissociation (< 6 Weeks, Garcia-Elias Stage 2):

• Direct Open Repair and Dorsal Augmentation: Performed through a dorsal approach between the 3rd and 4th extensor compartments utilizing a Berger ligament-sparing capsulotomy. The ruptured dorsal SLIL footprint is debrided down to a bleeding bony bed on the dorsal rim of both the scaphoid and lunate. Miniature suture anchors (1.3 to 1.8 mm) loaded with braided nonabsorbable sutures are placed into the respective footprints. Sutures are passed in a horizontal mattress fashion.
• Capsulodesis or Suture Tape Augmentation (InternalBrace): To protect the primary repair, a dorsal capsulodesis (Blatt modification using a proximal-based strip of dorsal capsule anchored to the distal scaphoid, or Berger DIC capsulodesis) is performed. Alternatively, contemporary internal brace augmentation utilizing ultra-high-molecular-weight polyethylene (UHMWPE) suture tape anchored across the scaphoid and lunate footprints provides immediate biomechanical strength, offloading the biological repair.
• Temporary Kirschner-Wire Transfixation: Two smooth K-wires (0.045-inch or 0.062-inch) are placed under fluoroscopic guidance: one transfixing the reduced scaphoid to the capitate (scaphocapitate wire) and one transfixing the scaphoid to the lunate (scapholunate wire). K-wires are maintained for 8 to 10 weeks to protect soft-tissue healing.

2. Chronic Reducible Dissociation (> 6 Weeks, Garcia-Elias Stage 3 and 4, Preserved Cartilage):

• Three-Ligament Tenodesis (3LT / Modified Brunelli Technique): The workhorse reconstructive procedure for chronic reducible dissociation. A distally based split strip of the flexor carpi radialis (FCR) tendon (approximately one-third to one-half width, 10 cm length) is harvested volarly, leaving its distal insertion on the base of the second metacarpal intact. The tendon strip is passed dorsally through an oblique osseous tunnel drilled through the distal scaphoid pole (entering volar-distal and exiting dorsal-proximal at the anatomical dorsal SLIL insertion). The graft is pulled firmly to reduce the flexed scaphoid, routed across the dorsal lunate surface to replicate the dorsal SLIL, secured to the lunate with an anchor or bone tunnel, and finally sutured under tension to the dorsal radiocarpal (DRC) ligament or dorsal radial rim to replicate the DIC ligament. This construct simultaneously addresses three restraints: the distal rotatory STT restraint, the dorsal SLIL, and the secondary DIC tether.
• All-Dorsal Anatomical Reconstructions: Contemporary variants (such as the Corella technique, RASL [reduction and association of the scaphoid and lunate], and tendon graft reconstructions through dual scaphoid and lunate tunnels) reconstruct both dorsal and volar constraints using free tendon grafts (palmaris longus) secured with biotenodesis screws.

3. Chronic Irreducible or Arthritic Collapse (SLAC Wrist, Garcia-Elias Stage 6):

• Proximal Row Carpectomy (PRC): Excision of the entire scaphoid, lunate, and triquetrum, allowing the convex head of the capitate to articulate directly within the concave lunate facet of the distal radius. PRC is an elegant, non-fusion, motion-preserving procedure that requires no internal hardware and eliminates the risk of nonunion. Absolute prerequisite: The articular cartilage of the capitate head and the radial lunate facet must be completely pristine (Outerbridge Grade 0 or 1). Indicated for SLAC Stage I and II. Contraindicated if capitolunate arthrosis (SLAC Stage III) is present.
• Four-Corner Arthrodesis (4CA) with Scaphoid Excision: Complete excision of the arthritic scaphoid followed by rigid intercarpal fusion of the four remaining central carpal bones: capitate, hamate, lunate, and triquetrum. Fixation is achieved using a circular multi-hole locking plate, headless compression screws, or crossed K-wires with autologous local bone graft (harvested from the excised scaphoid or distal radius). Indicated for SLAC Stage III (where capitate chondrosis precludes PRC), or in young, heavy manual laborers requiring greater structural stability. Crucial prerequisite: The radiolunate joint must have pristine articular cartilage.
• Total Wrist Arthrodesis: Rigid fusion from the distal radius to the third metacarpal shaft utilizing a pre-contoured dorsal locking plate. Reserved as a final salvage procedure for end-stage pan-carpal collapse (SLAC Stage IV) or failed motion-preserving salvage procedures.

Indications and Contraindications

• Primary Direct Repair: Indicated for acute injuries ( 3 mm, SL angle > 60°, and robust, reparable residual ligament tissue. Contraindicated in chronic injuries (> 6 weeks) with tissue attenuation, fixed irreducible carpal collapse, or existing chondrosis.
• Three-Ligament Tenodesis (3LT): Indicated for chronic reducible scapholunate dissociation without articular cartilage wear (SLAC Stage 0). Contraindicated if the scaphoid cannot be fully reduced into anatomical alignment under fluoroscopy, or if joint space narrowing (< 2 mm) or subchondral sclerosis is noted at the radioscaphoid or capitolunate joints.
• Proximal Row Carpectomy (PRC): Indicated for SLAC Stage I and II with isolated radioscaphoid wear. Absolutely contraindicated if there is chondromalacia or eburnation involving the capitate head or the lunate facet of the distal radius.
• Four-Corner Arthrodesis (4CA): Indicated for SLAC Stage II and III, especially with capitolunate arthrosis. Absolutely contraindicated if active radiolunate joint chondrosis or pan-carpal arthrosis is present.

9. Outcome

Clinical outcomes following intervention for scapholunate instability correlate closely with diagnostic timeliness, the degree of pre-existing carpal collapse, and the specific surgical technique employed. Validated patient-reported outcome measures (PROMs) including the Patient-Rated Wrist Evaluation (PRWE), Disabilities of the Arm, Shoulder, and Hand (DASH/QuickDASH), and the Mayo Wrist Score demonstrate significant functional improvements compared to preoperative baseline, though near-normal wrist biomechanics are rarely fully restored.

Functional Recovery and Range of Motion

• Acute Direct Repair with Dorsal Augmentation: Achieves the most favorable functional restoration. Patients typically regain 75% to 85% of contralateral flexion-extension arc (mean arc approximately 110° to 125°) and 80% to 90% of contralateral grip strength. PRWE scores average 15 to 25 points at 2-year follow-up.
• Three-Ligament Tenodesis (3LT / Modified Brunelli): Consistently provides pain relief and carpal stabilization. Systematic reviews demonstrate an average postoperative flexion-extension arc of 90° to 105° (approximately 65% to 75% of the uninjured contralateral wrist). A permanent 20% to 30% reduction in wrist flexion is anticipated and clinically accepted, representing the intentional tethering effect required to restrain scaphoid collapse. Grip strength recovers to 75% to 85% of the contralateral limb. QuickDASH scores average 18 to 28 points.
• Proximal Row Carpectomy (PRC): Yields a reliable, durable motion-preserving outcome. Mean postoperative flexion-extension arc ranges from 70° to 85° (approximately 60% to 65% of the contralateral limb), with grip strength reaching 70% to 80% of normal. Mayo Wrist Scores demonstrate 75% to 85% good-to-excellent results at 10-year follow-up.
• Four-Corner Arthrodesis (4CA): Provides a rigid, stable wrist capable of sustained heavy load transmission. Flexion-extension arc averages 60° to 75° (approximately 50% to 55% of the contralateral limb), with an expected loss of 40% to 50% of wrist flexion. Grip strength is reliably preserved at 75% to 80% of the contralateral side, comparable to or slightly exceeding PRC in heavy manual laborers.

Long-Term Survivorship and Failure Modes

Long-term registry and cohort analyses reveal that tenodesis procedures (including 3LT) experience a gradual loss of radiographic correction over 5 to 10 years in approximately 15% to 25% of patients. Progressive stretching of the tendon autograft under continuous physiological cyclic loads allows recurrent scaphoid flexion and gradual widening of the SL interval; however, clinical pain scores often remain significantly improved despite radiographic relapse. For salvage procedures (PRC and 4CA), long-term survivorship without conversion to total wrist arthrodesis exceeds 85% to 92% at 10 to 15 years. Secondary conversion to complete fusion is driven primarily by progressive neochondrosis (capitate-radius wear after PRC) or painful nonunion (after 4CA).

10. Complications

Complications following operative reconstruction for scapholunate instability are categorized based on their temporal occurrence into immediate intraoperative, early postoperative, and late postoperative events:

11. Pearls and Pitfalls

• Dynamic Contralateral Fluoroscopy: Never evaluate carpal angles or scapholunate gaps in isolation. Always obtain comparative bilateral clenched-fist PA radiographs and lateral fluoroscopy. Up to 30% of healthy individuals exhibit asymptomatic physiologic laxity with SL gaps approaching 3 mm and positive Watson tests. Pathological instability requires asymmetric diastasis, rotatory scaphoid subluxation, and symptom concordance.
• The Scaphoid Drill Tunnel Vector (3LT Pearl): When performing a modified Brunelli / 3-ligament tenodesis, drill the scaphoid tunnel starting from the distovolar scaphoid tubercle and aiming toward the proximodorsal footprint of the dorsal SLIL. Avoid an eccentric dorsal exit: exiting too far distally fails to control the proximal pole, while exiting too close to the proximal articular cartilage risks cortical blowout, scaphoid fracture, or avascular necrosis. Use a 2.7 mm cannulated bit over a central guide wire verified on biplanar fluoroscopy.
• Anatomical Carpal Reduction Before Graft Tensioning: Never attempt to reduce the scaphoid using the tenodesis graft alone, which produces excessive graft tension, creep, and early construct stretching. Place a temporary 0.045-inch joystick K-wire into the scaphoid to extend and derotate it out of flexion, and a separate joystick wire into the lunate to correct its extension tilt. Secure the anatomical reduction with a temporary scaphocapitate K-wire first; only then tension and anchor the tendon graft into its neutral isometric bed.
• Diagnostic Snare of the “Simple Wrist Sprain”: A classic pitfall is misdiagnosing an acute complete SLIL tear as an uncomplicated sprain because initial static radiographs appear entirely normal. If localized tenderness over the SL interval (1 cm distal to Lister’s tubercle) or a positive Watson test persists beyond 2 to 3 weeks, dynamic clenched-fist radiographs and MR arthrography or diagnostic arthroscopy are mandatory before the window for acute primary repair closes.
• Avoid Soft-Tissue Reconstruction in Fixed Carpal Collapse: Attempting a ligament repair or tenodesis in the setting of fixed, irreducible DISI deformity or established cartilage wear (SLAC Stage I-III) is doomed to rapid failure. Soft-tissue grafts cannot maintain reduction against chronic intercarpal contracture. In irreducible wrists with preserved cartilage, intercarpal arthrodesis (SC or STT) is indicated; once chondrosis occurs, salvage procedures (PRC or 4CA) are mandatory.
• The Cartilage Checkpoint in PRC: During planned proximal row carpectomy, never excise the carpal bones until the proximal articular cartilage of the capitate head has been directly visualized and probed. If Outerbridge Grade 2 to 4 chondromalacia, eburnation, or subchondral cystic collapse is discovered on the capitate head, abandon PRC immediately and convert to a four-corner arthrodesis using the excised scaphoid for morselized bone graft.

12. Controversy

Proximal Row Carpectomy vs. Four-Corner Arthrodesis in SLAC Stage II

The choice of motion-preserving salvage for SLAC Stage II osteoarthritis remains one of the most vigorously debated topics in wrist surgery. Proximal row carpectomy (PRC) offers significant procedural advantages: it is technically simpler, requires no internal fixation hardware, avoids autologous bone grafting, eliminates the risk of nonunion, and permits early active mobilization at 2 to 3 weeks. Long-term studies indicate that PRC yields a slightly superior postoperative flexion-extension arc (approximately 65% of the contralateral wrist vs. 50% to 55% for 4CA). However, PRC fundamentally converts the wrist into a non-anatomic, non-congruent hemiarthroplasty between the capitate and lunate fossa, predisposing to late capitate neochondrosis, particularly in patients younger than 40 years or those who perform heavy manual labor.

Conversely, four-corner arthrodesis (4CA) preserves the congruent, anatomically stable radiolunate articulation and provides greater structural stability for heavy grip and loaded labor. Nevertheless, 4CA is burdened by a 5% to 10% nonunion rate, hardware-related impingement or plate irritation requiring secondary removal in 10% to 15% of patients, longer postoperative cast immobilization (6 to 8 weeks), and greater loss of terminal wrist flexion. Current evidence suggests equivalent long-term pain relief and patient-reported satisfaction; thus, many surgeons favor PRC for patients aged > 45 to 50 years with lower physical demands, while reserving 4CA for younger high-demand laborers or whenever capitate cartilage integrity is questionable.

Tendon Reconstruction vs. Arthroscopic InternalBrace Augmentation

In chronic reducible scapholunate dissociation (Garcia-Elias Stage 3 and 4), open tenodesis procedures (such as the 3-ligament tenodesis / modified Brunelli) have long stood as the gold standard. However, open tenodesis entails extensive dorsal capsular dissection, dividing extrinsic stabilizers and frequently resulting in a permanent 25% to 35% loss of wrist flexion and grip fatigue. Furthermore, tendon autografts invariably suffer biological creep and stretching over 5 to 10 years, leading to a high rate of recurrent radiographic DISI deformity.

Recently, minimally invasive arthroscopic-assisted scapholunate ligament reconstruction and suture tape internal brace augmentation have emerged as alternatives. By placing high-strength UHMWPE suture tape anchored with biotenodesis screws across the dorsal SLIL footprint through minimal capsulotomy windows, this technique preserves the extrinsic capsular blood supply, minimizes postoperative arthrofibrosis, and provides immediate biomechanical strength that resists cyclic elongation. Proponents report faster rehabilitation and superior preservation of wrist flexion. However, critics argue that non-absorbable synthetic tapes cannot replicate the dynamic compliance of native ligaments, and long-term data (> 10 years) evaluating synthetic material creep, foreign-body synovitis, and scaphoid osteolysis remain limited compared to decades of clinical data supporting open tenodesis.

13. Evidence-Based Synthesis

Modern clinical decision-making is grounded in high-quality randomized controlled trials and prospective registry analyses, corroborated by seminal biomechanical and anatomical descriptions.

14. References

• Athlani L, Cholley-Roulleau M, Blum A et al. Intercarpal arthrodesis: A systematic review. Hand Surg Rehabil. 2023. doi:10.1016/j.hansur.2022.12.006 [Level I: Systematic Review / Meta-Analysis]
• Athlani L, Pauchard N, Detammaecker R et al. Treatment of chronic scapholunate dissociation with tenodesis: A systematic review. Hand Surg Rehabil. 2018. doi:10.1016/j.hansur.2017.12.001 [Level I: Systematic Review / Meta-Analysis]
• Naqui Z, Khor WS, Mishra A et al. The management of chronic non-arthritic scapholunate dissociation: a systematic review. J Hand Surg Eur Vol. 2018. doi:10.1177/1753193417734990 [Level I: Systematic Review / Meta-Analysis]
• Ronald L. Linscheid, James H. Dobyns, John W. Beabout et al. Traumatic Instability of the Wrist. Journal of Bone and Joint Surgery. 1972. doi:10.2106/00004623-197254080-00003 [Level IV (Prognostic / Case Series): Seminal Conceptual / Observational Study]
• Jack K. Mayfield, Roger Paul Johnson, Raphael K. Kilcoyne. Carpal dislocations: Pathomechanics and progressive perilunar instability. The Journal Of Hand Surgery. 1980. doi:10.1016/s0363-5023(80)80007-4 [Level IV (Prognostic / Case Series): Seminal Conceptual / Observational Study]

15. Master Class Pro-Tip

When performing a Three-Ligament Tenodesis (modified Brunelli) for chronic scapholunate dissociation, the most frequent mode of early construct failure is over-relying on the tendon autograft to pull the flexed scaphoid out of rotatory subluxation. Attempting to tension the graft against an unreduced carpus induces severe tendon shear, microtrauma, and inevitable graft creep. To achieve a durable anatomical reconstruction, the carpal reduction must be established and rigidly transfixed entirely independently of the graft before a single suture is tied. Insert two percutaneous 0.045-inch joystick K-wires: one into the dorsal distal scaphoid directed proximally, and one into the dorsal lunate directed distally. Under direct lateral fluoroscopy, simultaneously extend and supinator-derotate the scaphoid joystick while flexing the lunate joystick until the scapholunate angle is restored to exactly 45° to 50° and the radiolunate angle is 0°. Lock this reduction with a 0.045-inch trans-articular scaphocapitate K-wire and a separate scapholunate K-wire. Only after fluoroscopic confirmation of anatomic collinear alignment should you pass the FCR tendon strip through the central scaphoid tunnel, lay it across the dorsal lunate bed, and anchor it under resting physiological tension to the dorsal radiocarpal ligament. This two-phase discipline guarantees that the tendon graft heals in an isometric, non-strained environment without early elongation.

Master Class Surgical Pearl: Scapholunate Instability