Current conceptScapholunate Instability: Current Concepts in Diagnosis and Management
Section snippets
Anatomy
The clustering of the 8 small carpal bones into proximal and distal carpal rows has been widely accepted, based on their kinematic behavior during global wrist motion. The 4 bones of the distal carpal row (trapezium, trapezoid, capitate, and hamate) are tightly bound to one another via stout intercarpal ligaments, and motion between them can be considered negligible. Similarly, the nearly rigid ligamentous connection of the trapezium and capitate to the index and middle metacarpals and lack of
Wrist Mechanics
As the anterior cruciate ligament is considered the primary stabilizer of the knee, so too can the SLIL be considered the primary stabilizer of the scapholunate joint, if not the entire carpus. It is surrounded in turn by several secondary stabilizers, each insufficient to cause instability after isolated disruption, but each important in the maintenance of normal scapholunate kinematics, and vulnerable to attritional wear after complete disruption of the SLIL. On the volar-radial side are the
Definition
Classically, the diagnosis of scapholunate instability was predicated on abnormal scaphoid or lunate alignment as seen on static radiographs (Fig. 5).23 This definition, however, was not inclusive enough to explain the often disabling symptoms of pain with mechanical loading or sudden shifts or “clunks” that were noted among some injured patients with normal radiographs. The concept of dynamic scapholunate instability was proposed to describe abnormal carpal positioning that required special
Classification (Table 1)51
The mildest form of scapholunate instability, or occult instability, is usually initiated by a fall on the outstretched hand that may only cause a tear or attenuation of a portion of the scapholunate interosseous ligament, with or without a disruption of the ligament of Testut.27 Patients with this injury may not seek treatment initially, have no abnormalities of scaphoid or lunate posture on static or stress radiographs, and have wrist pain or dysfunction with mechanical loading. Fluoroscopic
Dorsal Intercalated Segment Instability
Massive ligament disruption at the time of injury, as may occur in perilunate or lunate dislocations, or gradual attrition of the secondary extrinsic stabilizers leads to abnormal extension of the lunate and carpal collapse after scapholunate dissociation. The combined effects of an extension moment transmitted through the intact triquetrolunate ligament and coupled dorsal translation of the capitate force the lunate into extension and exacerbate the abnormal posture of the scapholunate joint.
Scapholunate Advanced Collapse Wrist
In the earliest stage of the SLAC wrist deformity, degenerative changes are limited to an area of abnormal contact between the abnormally rotated scaphoid and the radial styloid. Radial styloidectomy will not alter the progression of the degenerative process at this stage, and any degree of pain relief is generally regarded as temporary. The scaphoid remains rotated into palmar flexion and its contact area with the radius remains reduced and shifted dorsally. Persistent abnormal load transfer
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