Scapholunate Ligament Injury

Scapholunate Ligament Injury. Chapter 76 Essential Orthopaedics (Miller, MD; Hart, et al.).

[Audio] The scapholunate ligament is the most frequently injured carpal ligament. Its dorsal portion is the primary restraint against instability. When the SLL is torn, the scaphoid tends to flex and the lunate extends, creating a dorsal intercalated segment instability (DISI) deformity. This malalignment alters wrist kinematics and overloads the articular cartilage. Over years, this progresses to scapholunate advanced collapse (SLAC), a predictable pattern of arthritis starting between the radial styloid and scaphoid, then involving the entire radioscaphoid joint, and finally the capitolunate joint. Early recognition is crucial to prevent irreversible damage..

[Audio] Many patients with SLL injury do not seek immediate care, dismissing it as a simple wrist sprain. Watson's maneuver is the key provocative test: the examiner places thumb pressure on the scaphoid tubercle while passively moving the wrist from ulnar to radial deviation. In a positive test, the proximal pole of the scaphoid subluxates over the dorsal rim of the radius, producing a painful clunk. This test must be compared to the uninjured side, as some individuals have a nontender, bilateral clunk. Pain during the maneuver not just the clunk indicates pathology. Always perform a full neurovascular exam of the upper extremity to exclude associated injuries..

[Audio] Staging guides treatment. In predynamic instability, the ligament is attenuated but intact, so standard and stress radiographs are normal. Diagnosis often requires arthroscopy. Dynamic instability means the ligament is completely torn but the carpus reduces under no load; stress views (clenched‑fist) reveal widening. Static instability indicates that even without loading, the scaphoid and lunate are separated, and a DISI deformity is present. Once arthritis develops (SLAC wrist), treatment shifts from ligament reconstruction to salvage procedures like proximal row carpectomy or fusion. Understanding these stages helps determine prognosis and surgical timing..

[Audio] On a posteroanterior radiograph, the normal scapholunate interval should not exceed 2–3 mm. A gap wider than 5 mm is diagnostic of dissociation the Terry Thomas sign. As the scaphoid flexes, its distal pole tilts, creating a ring‑shaped shadow (the ring sign) over the proximal scaphoid. Measuring the scapholunate angle on lateral view is critical: the long axes of the scaphoid and lunate normally form an angle between 30 and 60 degrees. In DISI, the lunate extends, increasing this angle beyond 70 degrees. These measurements are essential for confirming static instability and planning surgical correction..

[Audio] SLAC wrist is the most common pattern of degenerative arthritis in the wrist. It progresses in a predictable sequence because the altered mechanics concentrate stress on specific areas. Initially, the radial styloid and distal scaphoid wear down (Stage I). As the scaphoid continues to collapse, the entire radioscaphoid articulation erodes (Stage II). The capitate then migrates proximally, wearing against the lunate (Stage III). Finally, the entire wrist becomes arthritic (Stage IV). Interestingly, the radiolunate joint is spared until late, which is why radiolunate fusion can sometimes preserve motion while relieving pain..

[Audio] Treatment depends entirely on stage and chronicity. Early, partial injuries (predynamic) often heal with immobilization. Complete tears (dynamic/static) in young or active patients require early referral for surgical repair or reconstruction to prevent SLAC. In established SLAC, surgery aims to relieve pain options include proximal row carpectomy (preserves motion) or partial wrist fusion (preserves some motion while eliminating painful articulation). Total wrist fusion is a last resort for severe panarthritis. MRI with gadolinium can help confirm tears but is operator‑dependent; arthroscopy remains the gold standard for both diagnosis and treatment..