Scapholunate dissociation is the most common carpal instability. Scapholunate instability is associated with increased scaphoid flexion and pronation with associated lunate extension. The abnormal kinematics lead to a decrease in surface area contact at the radioscaphoid joint. This abnormal articulation causes an increased concentration of load, leading to the development of degenerative arthritis. Watson and coworkers described the typical pattern of wrist arthritis related to scapholunate instability, which has been termed scapholunate advanced collapse SLAC wrist. The goals of the surgical reconstructions for a scapholunate dissociation are to relieve the symptoms associated with the instability, maintain motion, and prevent the development of degenerative arthritis.
Acute Scapholunate dissociation
Acute static scapholunate dissociation, which may occur as an isolated entity or as a late sequela of a perilunate dislocation, results from injury to the scapholunate interosseous and palmar radioscaphoid ligaments. Depending on the extent of ligamentous injury, there is either diffuse tenderness of the carpus or point tenderness over the scapholunate interval.
Which specific ligaments must be injured to cause a scapholunate dissociation is controversial. Several studies have shown that disruption of the scapholunate interosseous ligament changes carpal motion. According to Mayfield, a partial injury of the anterior aspect of the scapholunate interosseous ligament could result in scapholunate instability. Ruby et al. consider the posterior aspect of the scapholunate interosseous ligament as the important mechanical component. Berger et al., on the other hand, suggested that there were no alterations in scaphoid motion with scapholunate interosseous ligament sectioning. Others have proposed that the palmar scaphotrapezoid ligament prevents rotatory subluxation of the scaphoid . Taleisnik noted that the radioscapholunate and radioscaphocapitate ligaments prevent the instability. More recently, Berger and Landsmeer have shown that the radioscapholunate ligament plays less of a role in stabilizing the wrist; its significance may be related to the vascular and neural structures that lie within the ligament. This controversy, as well as the technical difficulties in ligament repair and reconstruction, has led to the numerous procedures described for the treatment of this carpal instability.
The patient may give a history of clicking and clunking of the wrist.
On examination, there is tenderness about the scapholunate interval, which lies just distal to the Lister tubercle. Provocative maneuvers for scapholunate instability, such as the scaphoid shift test, may be positive and there is often associated grip strength weakness.
Radiographs reveal key features of rotatory subluxation of the scaphoid.
Treatment (acute injuries)
Ligamentous repair within three weeks after the injury is preferred. Delayed repair can be carried out as long as four to six months from the time of the injury.
Neither closed reduction alone nor closed reduction and percutaneous pin fixation is uniformly successful in maintaining carpal alignment and in achieving satisfactory long-term outcomes in wrists with acute scapholunate instability. The preferred method of treatment is open reduction of the carpus through a dorsal approach, pinning of the scaphoid to the lunate and to the capitate with two 1.2mm Kirschner wires, and direct repair of the scapholunate ligament. Ligament repair is carried out either with direct suture for ligaments torn in their midsubstance or with pull-out sutures or suture anchors for ligaments avulsed from bone. The wrist is immobilized in neutral position in an above elbow thumb spica cast for eight weeks, following which time the pins are removed and active motion is initiated
Several factors govern the feasibility of delayed ligamentous repair (repair later than three weeks after the time of the injury):
Chronic Scapholunate Dissociation
For wrists in which the scapholunate interosseous ligament cannot be repaired primarily several reconstructive options exist:
Factors affecting choice of reconstruction:
Blatt reported good results in his series of 12 patients treated with dorsal capsulodesis for scapholunate dissociation. His singular criterion for the
procedure was the ability to anatomically reduce the scaphoid at the time of
surgery. He noted a recovery of 80% of grip strength and loss of no more than
20° of wrist flexion.
Deshmukh et al. reviewed their experience in treating 44 cases of chronic scapholunate dissociation treated by Blatt capsulodesis. They reported only 24
of 44 (55%) patients with a good or excellent result. There was a decrease in
grip strength and a loss of wrist motion, specifically wrist flexion and radial
deviation. The authors found no statistically significant change in the
scapholunate angle, scapholunate gap or carpal height at follow-up. They noted
several reasons for the less favourable results. There was a long time interval
from injury to surgery, with patients waiting on average 58 months. In addition,
39% of the patients were involved in workers' compensation. They recommended
that the procedure not be performed on a routine basis except in a select group.
The goal in the treatment of scapholunate dissociation is to stabilize the carpus in the appropriate alignment in addition to maintaining wrist range of motion. The optimal method of attaining these goals is currently controversial. Dorsal capsulodesis is a reconstructive surgical option that acts as a check rein to correct the abnormal alignment of the scaphoid that occurs with scapholunate instability. The procedure does not anatomically reconstruct the scapholunate ligament. It maintains carpal motion but leads to some limitation of wrist flexion. The results of the procedure reported in the literature are conflicting. It appears to provide the best results in patients with less significant static radiographic abnormalities such as in a dynamic instability. Unfortunately, the alternative surgical options are also not ideal, although recent advances in the reconstructive procedures such as the bone-ligament-bone grafts have great potential. At this time, dorsal capsulodesis is a reasonable procedure for dynamic scapholunate instability using appropriate selection criteria.
Dorsal capsulodesis surgical technique (click here)
GILULA, L A; MANN, F A; DOBYNS, J H; YIN, Y; IWIW TERMINOLOGY COMMITTEE WRIST TERMINOLOGY AS DEFINED BY THE INTERNATIONAL WRIST INVESTIGATORS' WORKSHOP (IWIW). Journal of Bone & Joint Surgery - American Volume. 84-A SUPPLEMENT 1:1-66, 2002.
Kaawach, Wael; Ecklund, Kirsten; Di Canzio, James; Zurakowski, David; Waters, Peter M. Normal Ranges of Scapholunate Distance in Children 6 to 14 Years Old. Journal of Pediatric Orthopedics. 21(4):464-467, July/August 2001.
GELBERMAN, RICHARD; COONEY, WILLIAM P. III; SZABO, ROBERT M.; - Carpal Instability. JBJS - A Vol. 82-A(4):578-594, April 2000
Last updated 16/09/2004