Wrist Immobilization for Scapholunate Interval Injury
For immobilizing the scapholunate interval, use a thumb spica cast or splint that extends from just proximal to the metacarpophalangeal joints to approximately 5 cm distal to the elbow flexion crease, maintaining the wrist in neutral position.
Rationale for Immobilization Type
The scapholunate ligament is an intrinsic carpal ligament that requires adequate immobilization to prevent long-term complications such as osteoarthritis 1. Based on biomechanical principles and imaging evidence:
The immobilizer must restrict both wrist motion and forearm rotation to adequately protect the scapholunate interval, as dynamic instability can be missed without proper immobilization 1
Cast length directly correlates with restriction of forearm rotation: extending the cast to 5 cm distal to the elbow flexion crease reduces active forearm rotation by 50%, while shorter casts provide inadequate restriction 2
Plaster of Paris demonstrates superior wrist stabilization compared to fiberglass, Woodcast, X-lite, or 3D-printed materials in both volar and dorsal configurations 3
Specific Immobilization Protocol
Cast Configuration
Include the thumb in the immobilization (thumb spica design) to limit radial deviation and rotational forces on the scapholunate ligament 1
Extend proximally to 5 cm distal to the elbow flexion crease to adequately restrict forearm rotation without causing antecubital skin breakdown 2
Maintain wrist in neutral position rather than flexion or extension, as neutral positioning provides optimal ligament healing environment 4
Material Selection
Plaster of Paris is preferred over synthetic materials, demonstrating stiffness of 146 N/mm compared to ≤7.7 N/mm for alternatives, with superior resistance to both wrist flexion and extension 3
Volar plaster splints perform similarly to short arm casts in limiting flexion, extension, and radial deviation, while being easier to adjust during the acute inflammatory phase 5
Monitoring During Immobilization
Repeat radiographs at 10-14 days if initial imaging was equivocal, as this allows detection of occult fractures or ligament-associated injuries 1
Consider advanced imaging if symptoms persist: MRI has 65-89% sensitivity for scapholunate ligament tears at 3T, while MR arthrography may provide higher sensitivity for complete tears 1
Monitor for skin complications with regular assessments, particularly at pressure points and the antecubital fossa if the cast extends proximally 1
Critical Pitfalls to Avoid
Do not use below-ankle equivalents for the wrist (such as wrist cock-up splints alone or short volar splints ending at mid-forearm), as these provide inadequate immobilization of the diseased joints and limited restriction of forearm rotation 1, 2
Avoid removable splints in the acute phase unless cast application is contraindicated, as compliance issues may compromise healing 1
Do not extend the cast into the antecubital fossa, as this increases risk of skin breakdown without additional benefit 2