In 1984, Watson and Ballet12 identified scapholunate advanced collapse as being the most significant cause of posttraumatic arthritis in the adult wrist. Linscheid et al4 postulated that the loss of integrity of the scapholunate interval permitted palmar flexion and dorsal subluxation of the scaphoid resulting in radioscaphoid arthritis. Simultaneously, the lunate dorsiflexes in its relationship to the capitate resulting in midcarpal incongruity and capitolunate arthritis.4 Berger1 elucidated the components of the scapholunate ligament and its histologic and biomechanical properties. He concluded that the dorsal component of the ligament was the thickest and provided the greatest biomechanical stability to the articulation.1
To identify the structures that must be injured to result in radiographic evidence of ligamentous injury, sequential sectioning studies of cadaveric wrists were done. Initial evidence pointed to the role of the palmar extrinsic ligaments in stabilizing the scapholunate interval.6 Meade et al7 sequentially sectioned the palmar extrinsic ligaments and the palmar and dorsal components of the scapholunate ligament and concluded that radiographic instability was not produced until the scapholunate interosseous and the palmar radioscapholunate and radial collateral ligaments were sectioned. Ruby et al8 emphasized the significance of the dorsal component of the scapholunate interosseous ligament with specific focus on its attachment to the dorsum of the lunate. Viegas et al11 shifted attention to the dorsal ligamentous structures and postulated that the attachments of the dorsal intercarpal ligament and the dorsal radiolunotriquetral ligament to the scaphoid and lunate, respectively, additionally stabilize the interval.
Our cadaveric study examined the role of the dorsal capsuloligamentous structures in preventing scapholunate instability.
MATERIALS AND METHODS
All human cadaveric material was approved by our institutional review board before start of this study. Fresh-frozen cadaveric upper extremities (n = 14) including the glenohumeral articulation were studied. All cadaveric wrists were evaluated arthroscopically before ligament sectioning to confirm the absence of peripheral triangular fibrocartilage complex tears, scapholunate tears, lunotriquetral tears, or dorsal capsular tears. Each wrist was placed in a quadrangular external fixator device with two pins in the radius and two pins in the ulna. Both sets of pins were attached to longitudinal graphite bars. A transfixing threaded rod was placed through the base of the index, long, and ring metacarpals and was attached to a traction bow. A removable 30-lb weight was attached to the traction bow to permit loading across the wrist (Fig 1). We used this external fixation device for distraction for arthroscopy, compression, and positioning to induce scaphoid flexion and diastasis and carpal collapse, radiographic study, and stabilization during dissection.
Radiographs obtained before sectioning revealed no deformities of the distal radius specimens. Portals radial to the sixth extensor dorsal compartment and between the third and fourth dorsal compartments (6-R, 3–4), and ulnar midcarpal portals were created in all wrists. A curved 4-mm arthroscopic blade was used for the ligament sectioning. The arthroscope permitted complete observation of the individual radiocarpal ligaments and the central, volar, and dorsal components of the scapholunate ligament as described by Berger.1 Resection of the cut ligament was done using 3.0-mm arthroscopic forceps to permit observation and verification of complete ligament transection. The ligaments were sectioned (Fig 2) at their origin on the radius in the following order: (1) radioscaphocapitate, (2) long radiolunate, (3) radioscapholunate, (4) short radiolunate, (5) central and proximal portions of the scapholunate interosseous ligament, (6) palmar portion of the scapholunate interosseous ligament, (7) dorsal portion of the scapholunate interosseous ligament, (8) dorsal capsular insertion on the scaphoid with the scapholunate ligament removed, and (9) dorsal intercarpal ligament insertion on the lunate.
Arthroscopic sectioning was used to preserve the integrity of the dorsal intercarpal ligament and dorsal capsule on the scaphoid and the dorsal radiocarpal ligament on the lunate. The arthroscope was directed distally at the insertion of the dorsal intercarpal ligament on the scaphoid and scapholunate interval and the dorsal radiocarpal insertion on the lunate. Finally, with the arthroscope in the ulnar midcarpal portal and the blade in the 3–4 portal, the insertion of the dorsal radiolunotriquetral ligament on the dorsum of the lunate was sectioned under direct observation (Fig 3). At the end of each experiment, each wrist was inspected through a dorsal midline incision to confirm that each of the ligaments had been transected completely.
Before and after each ligament was sectioned, anteroposterior (AP) and lateral static radiographs were obtained. A 30-lb load was applied to the wrist using a traction bow, and fluoroscopy was used to determine the view that provided the maximal gap on the AP view and a true lateral view in the lateral plane. After these planes were identified, AP and lateral views of each wrist were obtained with the 30-lb load in place.
Each radiograph was analyzed by two authors, and the following measurements were recorded: (1) the congruity of Gilula’s lines; (2) the maximum scapholunate gap on the AP plane; (3) the lateral scapholunate angle; and (4) the lateral capitolunate angle. Measurements were recorded to the nearest degree, and discrepancies between the two observers were averaged. The congruity of Gilula’s arcs was determined by superimposing the preinjury radiograph on the sectioning AP view. Incongruity was defined by a disruption of either the proximal carpal arc or midcarpal arc. All measurements were recorded as increases above the preoperative radiographic values (Table 1).
Mean values, standard deviations, and ranges were analyzed for the scapholunate gap, scapholunate angle, capitolunate angle, and the congruity of Gilula’s lines. Analysis of variance and covariance with repeated measures were used to analyze the data. Adjusted means from repeated measures’ analyses of variance were obtained. Pairwise comparisons were done using Bonferroni’s method.
Our presection measurements showed that the mean value for the scapholunate gap was 3.1 ± 1.1 mm, the mean scapholunate angle was 48.4° ± 5.0°, and the mean lateral capitolunate angle was 3.5° ± 2.2°.
After serial sectioning of the palmar extrinsic ligaments (Fig 2A) in the order of their origin on the palmar surface of the radius, there was no appreciable change in the radiographic appearance of the wrists. Specifically, sectioning of the radioscaphocapitate, long radiolunate, short radiolunate, and radioscapholunate resulted in a mean scapholunate gap of 3.4 ± 1.1 mm, a mean scapholunate angle of 47.4° ± 4.6°, and a mean capitolunate angle of 2.8° ± 2.0°. There was no statistical difference when the postsectioning measurements were compared with the presectioning measurements.
After sectioning the palmar extrinsic ligaments, additional sequential sectioning of the three components of the scapholunate interosseous ligament (Fig 2B) did not result in statistically significant changes from presectioning measurements. The mean values after all three components sectioned were: AP gap, 3.3 ± 1.2 mm; scapholunate angle, 49.8° ± 5.6°; and capitolunate angle, 1.9° ± 2.2°.
When the dorsal intercarpal ligament insertion on the scaphoid was divided in addition to the volar extrinsics and scapholunate interosseous (Fig 2C), a flexion deformity of the scaphoid occurred. After sectioning of these ligaments (scapholunate interosseous, volar extrinsics, and dorsal intercarpal), there was a significant increase (p = 0.0001) in the mean lateral scapholunate angle from 50° to 66°. The capitolunate angle as a measure of lunate dorsiflexion remained neutral (mean, 4.3°). Likewise, there was no significant change in the AP gap (mean, 3.7 ± 1.5 mm). Despite the palmar flexion of the scaphoid, Gilula’s arc was not disrupted in any specimen.
Complete sectioning of the palmer extrinsics, scapholunate interosseous ligament, the dorsal intercarpal ligament and the dorsal radiolunotriquetral ligament resulted in a static dorsal intercalated scapholunate instability collapse pattern (Fig 2D). The scaphoid palmar flexed, and the lateral scapholunate angle increased to a mean of 71.4° ± 6.1°; this change was not statically significant. The most significant change occurred in the posture of the lunate. The sectioning of the dorsal capsuloligamentous structures from the lunate resulted in a significant increase (p = 0.0001) in the lateral capitolunate angle from a mean of 4.3° to a mean of 24°. Finally, the AP gap increased to a mean of 6.0 mm, and Gilula’s lines were incongruous in all specimens (p < 0.005).
Complete transection of the scapholunate interosseous ligament and the palmar extrinsic ligaments did not result in flexion deformity of the scaphoid as long as the dorsal capsuloligamentous insertions onto the scapholunate ligament and dorsum of the scaphoid remained intact. Our study suggests the role of the dorsal and palmar radial extrinsic ligaments and the scapholunate interosseous ligament in prevention of scapholunate instability. The role of the scapholunate ligament in preventing rotatory subluxation of the scaphoid and dorsiflexion of the intercalated segment has been analyzed. Berger1characterized the scapholunate interosseous ligament as consisting of central, dorsal, and palmar components with the proximal portion composed primarily of fibrocartilage, whereas the thick dorsal region is composed of transversely oriented collagen fibers. Our study showed that isolated injury to the central fibrocartilaginous portion of the scapholunate ligament does not result in radiographically or arthroscopically evident instability. Review of the clinical literature indicates that debridement of torn central fibrocartilaginous portions of the scapholunate interosseous ligament does not result in radiographically evident static or dynamic instability.9,13 Weiss et al13 reported that debridement of arthroscopically documented complete scapholunate tears provided complete relief in 66% of patients. Clinical studies have had 85–92% good and excellent results after debridement of incomplete scapholunate and lunotriquetral ligament injuries with no patients showing a change in the scapholunate or capitolunate angle at a 2- year followup.9,13
The importance of the dorsal intercarpal ligament in stabilizing the scaphoid and the scapholunate interosseous ligament is emphasized by the results of our study. The dorsal portion of the scapholunate ligament consists of thick, transversely oriented collagen fibers. The dorsal capsule and dorsal intercarpal ligament complex inserts on the scaphoid and the scapholunate ligament. After disruption of the scapholunate interosseous ligament, the dorsal intercarpal ligament and the dorsal capsular attachments to the scaphoid act as a tether to prevent rotatory subluxation of the scaphoid. With the dorsal intercarpal ligament and dorsal capsule intact in the cadaveric specimens, palmar flexion of the scaphoid could not be produced. However, after these structures were dissected free from the scapholunate interosseous ligament and the waist of the scaphoid, the distal pole showed no restriction to palmar flexion with loading. Although the lateral scapholunate angle increased from 50° to 66°, the increased angle resulted from palmar flexion of the scaphoid and not from dorsiflexion of the lunate as evidenced by the lack of change at the capitolunate angle. Therefore, injury to the scapholunate interosseous ligament and the dorsal capsule results in rotatory instability of the scaphoid and an increase in the scapholunate interosseous angle without an obvious radiographically documented dorsal intercalated scapholunate instability collapse pattern. Such an injury represents rotatory instability of the scaphoid alone and may explain the successful results of some patients with scapholunate ligament injuries after dorsal capsulodesis.14
The dorsal radiolunotriquetral ligament has been shown to play a major role in stabilizing the lunate and preventing volar intercalated segmental instability collapse.10 This ligament passes dorsally from the distal radius across the dorsal lip of the lunate to insert on the triquetrum and serves as the dorsal tether to dorsiflexion of the lunate. With avulsion of this ligament from the lunate, the lunate is unleashed dorsally. A cadaveric sectioning study showed that injury to the lunotriquetral ligament and the ulnocarpal ligaments will not produce a volar intercalated segmental instability collapse.10 It is not until the lunate is destabilized by sectioning of the dorsal radiocarpal ligament that palmar flexion of the lunate may occur. Similarly, the results of our study indicate that, despite complete sectioning of the scapholunate interosseous ligament, the palmar extrinsic ligaments, and the dorsal intercarpal ligament, dorsiflexion of the lunate will not occur until the lunate is released from the dorsal radiocarpal tether.
Perhaps one reason for the relative lack of attention given to the dorsal capsuloligamentous structures in previous studies is related to the open technique of ligament sectioning that was used. Previous ligament sectioning studies used dorsal approaches to elevate soft tissue flaps for observation of the intrinsic ligaments and palmar extrinsic ligaments. However, this technique results in disruption of the dorsal capsule and the dorsal radiolunotriquetral ligament. Under such circumstances, the significance of these structures was not recognized. Sequential arthroscopic sectioning in the current study permitted the transection of specific structures without injury to associated capsuloligamentous soft tissue, and the use of wrist arthroscopy techniques allowed the dorsal capsuloligamentous structures to be described and evaluated while maintaining their integrity.
The clinical significance of the dorsal capsuloligamentous insertions on the scaphoid has long been recognized. Blatt,2 Lavernia et al,3 and Wintman et al14 have showed the clinical success of the dorsal capsulodesis for prevention of rotatory subluxation of the scaphoid. The results of the current study support the reconstruction of a dorsally based capsuloligamentous tether to prevent palmar flexion of the distal pole.
Limitations of our study were the number of specimens that were available for sequencing of ligamentous injury and the order of ligamentous sectioning was not reversed or attempted in a different order. The rationale for the selection of the order in which the ligaments were sectioned was based on a previous study that defined the significance of the palmar extrinsic ligaments in perilunate instability5 and defined the current concept of perilunar instability as occurring progressively from the palmar extrinsic ligaments, through the scapholunate interosseous ligament and subsequently the capitolunate and lunotriquetral articulation.5 Although isolated injuries to the aforementioned structures may occur, sequential sectioning of all permutations of possible injuries in a cadaveric study would be prohibitive.
Although the results of this cadaveric study reinforce the importance of the dorsal intercarpal ligament and the dorsal radiolunotriquetral ligament in wrist stability, the study provides no data regarding the natural history of ligamentous wrist injuries which is another limitation of this study. An isolated scapholunate ligament injury may not result in immediate instability, but the question arises whether these secondary constraints are sufficient to withstand repetitive loading with time. This observation also may explain the clinical scenario in which a patient with a prior wrist injury presents with acute instability after a seemingly minor trauma. The origin of the instability may be only addressed by long-term followup studies of patients who had debridement for isolated scapholunate ligament injuries.
The central, palmar, and dorsal portions of the scapholunate interosseous ligament and the palmar extrinsic ligaments may be injured without altering radiographic parameters. The dorsal intercarpal ligament and capsule are important stabilizers in preventing rotatory subluxation of the scaphoid, thereby supporting the clinical role of dorsal capsular reimplantation. The dorsal radiolunotriquetral ligament is an important stabilizer preserving rotation of the lunate as evidenced by change in the capitolunate angle after its sectioning.
We thank the Orthopaedic Research Laboratory at Wake Forest University-School of Medicine for assistance with providing the cadaveric specimens.
1. Berger RA. The gross and histologic anatomy of the scapholunate interosseous ligament. J Hand Surg
2. Blatt G. Capsulodesis in reconstructive hand surgery: Dorsal capsulodesis for the unstable scaphoid and volar capsulodesis following excision of the distal ulna. Hand Clin
3. Lavernia CJ, Cohen MS, Taleisnik J. Treatment of scapholunate dissociation by ligamentous repair and capsulodesis. J Hand Surg
4. Linscheid RL, Dobyns JH, Beabout JW, et al. Traumatic instability of the wrist: Diagnosis, classification, and pathomechanics. J Bone Joint Surg
5. Mayfield JK. Mechanism of carpal injuries. Clin Orthop
6. Mayfield JK. Wrist ligamentous anatomy and pathogenesis of carpal instability. Orthop Clin North Am
7. Meade TD, Schneider LH, Cherry K. Radiographic analysis of selective ligament sectioning at the carpal scaphoid: A cadaveric study. J Hand Surg
8. Ruby LK, An KN, Linscheid RL, et al. The effect of scapholunate ligament section on scapholunate motion. J Hand Surg
9. Ruch DS, Poehling GG. Arthroscopic management of partial scapholunate and lunotriquetral injuries of the wrist. J Hand Surg
10. Viegas SF, Patterson RM, Peterson PD, et al. Ulnar-sided perilunate instability: An anatomic and biomechanic study. J Hand Surg
11. Viegas SF, Yamaguchi S, Boyd NL, et al. The dorsal ligaments of the wrist: Anatomy, mechanical properties, and function. J Hand Surg
12. Watson HK, Ballet FL. The SLAC wrist: Scapholunate advanced collapse pattern of degenerative arthritis. J Hand Surg
13. Weiss AP, Sachar K, Glowacki KA. Arthroscopic debridement alone for intercarpal ligament tears. J Hand Surg
14. Wintman BI, Gelberman RH, Katz JN. Dynamic scapholunate instability: Results of operative treatment with dorsal capsulodesis. J Hand Surg