Biomechanical evaluation of ligamentous stabilizers of the scaphoid and lunate

This study evaluated the effects of sectioning the scapholunate interosseous ligament, radioscaphocapitate ligament, and scaphotrapezial ligament on the kinematics of the scaphoid and lunate. Eight cadaver upper extremities were placed in a wrist joint simulator and moved in continuous cycles of flexion-extension and radial-ulnar deviation. Positional data of the scaphoid and lunate were obtained in the intact state, after the scapholunate ligament was cut; after the scapholunate and scaphotrapezial ligaments were cut; after the scapholunate, scaphotrapezial, and radioscaphocapitate ligaments were cut; and after all 3 ligaments were cut and the specimen was placed through an additional 1,000 cycles of flexion-extension. Cutting the scapholunate ligament caused changes in scaphoid and lunate motion during flexion-extension, but not radial-ulnar deviation. Additional sectioning of the scaphotrapezial ligament followed by the radioscaphocapitate ligament caused further kinematic changes in these carpal bones. One thousand cycles of motion after all 3 ligaments were sectioned caused additional kinematic changes in the scaphoid and lunate. The scapholunate ligament appears to be the primary stabilizer between the scaphoid and lunate. The radioscaphocapitate and scaphotrapezial ligaments are secondary restraints. Repetitive cyclic motion after ligament sectioning appears to have additional deleterious effects on carpal kinematics.     

Biomechanical evaluation of the ligamentous stabilizers of the scaphoid and lunate: part III

PURPOSE: This study continued our previous investigations of the ligaments stabilizing the scaphoid and lunate in which we examined the scapholunate interosseous ligament, the radioscaphocapitate, and the scaphotrapezial ligament. In this current study, we examined the effects of sectioning the dorsal radiocarpal ligament, dorsal intercarpal ligament, scapholunate interosseous ligament, radioscaphocapitate, and scaphotrapezial ligaments. In the current study, the scapholunate interosseous ligament, radioscaphocapitate, and scaphotrapezial ligaments were sectioned in a different order than performed previously. METHODS: Three sets of 8 cadaver wrists were tested in a wrist joint motion simulator. In each set of wrists, only 3 of the 5 ligaments were cut in specific sequences. Each wrist was moved in continuous cycles of flexion-extension and radial-ulnar deviation. Kinematic data for the scaphoid and lunate were recorded for each wrist in the intact state, after the 3 ligaments were sectioned in various sequences and after the wrist was moved through 1,000 cycles of motion. RESULTS: Dividing the dorsal intercarpal or scaphotrapezial ligaments did not alter the motion of the scaphoid or lunate. Dividing the dorsal radiocarpal ligament alone caused a slight statistical increase in lunate radial deviation. Dividing the scapholunate interosseous ligament after first dividing the dorsal intercarpal, dorsal radiocarpal, or scaphotrapezial ligaments caused large increases in scaphoid flexion and lunate extension. CONCLUSIONS: Based on these findings, we concluded that the scapholunate interosseous ligament is the primary stabilizer and that the other ligaments are secondary stabilizers of the scapholunate articulation. Dividing the dorsal radiocarpal, dorsal intercarpal, or scaphotrapezial ligaments after cutting the scapholunate interosseous ligament produces further changes in scapholunate instability or results in changes in the kinematics for a larger portion of the wrist motion cycle.     

Palmar dislocation of the scaphoid and lunate

A case of palmar dislocation of the scaphoid and lunate was complicated by a delay in the diagnosis and avascular necrosis of the lunate. Anatomic reduction was obtained 34 days after the injury. At 2 1/2 years follow-up the patient had good return of hand function and radiologic evidence of resolution of the avascular necrosis without evidence of collapse or intercarpal arthritis.     

Palmar-divergent dislocation of the scaphoid and the lunate

We describe a patient with palmar-divergent dislocation of the scaphoid and lunate. After successful closed reduction, the scapholunate and lunotriquetral ligaments were sutured through the dorsal approach, and the anterior capsule was sutured through the palmar approach. The scapholunate and lunotriquetral joints were fixed with Kirschner wires for 7 weeks. At the 1-year follow-up, magnetic resonance imaging showed no evidence of avascular necrosis of the scaphoid or lunate, and radiographs showed no evidence of the dorsal and volar intercalated segment instability patterns associated with carpal instability. However, flexion of the scaphoid and a break in Gilula’s line remained. To our knowledge, this is the first report showing treatment of palmar-divergent dislocation of the scaphoid and lunate by suturing the carpal interosseous ligaments.     

Coexisting avascular necrosis of the scaphoid and lunate

Reports of coexisting avascular necrosis of more than one carpal bone are rare. We report coexisting avascular necrosis of the scaphoid and lunate in a 56-year-old woman with no history of using steroids or injury. We treated her with a radioscapholunate fusion with two angled 2.4 mm distal radius plates to stabilise the locking plate. At her 12-month follow up there was no evidence of non-union.     

Three-dimensional description of ligamentous attachments around the lunate

PURPOSE: To detail the location and area of specific ligament attachments on the 3-dimensional (3-D) surface morphology of the individual carpal bones. METHODS: We describe the attachment regions of both extrinsic and intrinsic intercarpal ligaments by using a combination of detailed dissection, computed tomography imaging, and a 3-D digitization technique and provide detailed information about ligament attachments around the lunate. RESULTS: The length, width, and thickness of each ligament are described in millimeters and its area of attachment is given in square millimeters and as a percentage of the bone surface and/or total ligament attachment area. The attachment sites of the ligaments also are shown visually on 3-D images of the bones. CONCLUSIONS: This study improves the knowledge and understanding of carpal ligament anatomy, which can result in better intraoperative assessment of ligament integrity/disruption and allow more accurate and anatomic repair, reattachment, and/or reconstruction of carpal ligaments for the treatment of carpal instability.     

Coexisting avascular necrosis of the scaphoid and lunate

Abstract

Reports of coexisting avascular necrosis of more than one carpal bone are rare. We report coexisting avascular necrosis of the scaphoid and lunate in a 56-year-old woman with no history of using steroids or injury. We treated her with a radioscapholunate fusion with two angled 2.4 mm distal radius plates to stabilise the locking plate. At her 12-month follow up there was no evidence of non-union.     

Influence of lunate type on scaphoid kinematics

PURPOSE: To assess the influence of lunate type on scaphoid kinematics. METHODS: One hundred normal wrists had fluoroscopic assessment of the wrist in maximal radial, neutral, and ulnar deviation. The shortest distance in a neutral position between the capitate and triquetrum, C-T distance, determined lunate type. A type I lunate had a C-T distance of < or =2 mm, a type II lunate > or =4 mm, and an intermediate group lay between these values. Scaphoid flexion and translation in radial and ulna deviation was measured. RESULTS: There were 18 subjects with a type I lunate, 19 with an intermediate lunate, and 63 with a type II lunate. There was no statistically significant difference between lunate type, subject age, or hand dominance. There was a statistically significant higher proportion of women with a type I lunate. Subjects with a type II lunate had a statistically greater amount of flexion during radioulnar deviation as determined by CR index (0.79 vs 0.91) and scaphoid flexion index (0.21 vs 0.09). Subjects with a type II lunate had statistically less translation during radioulnar deviation as determined by translation ratio (0.22 vs 0.31) and scaphoid inclination index (0.18 vs 0.23). The average scaphoid kinematic index in subjects with a type II lunate was 1.24, intermediate 0.86, and type I 0.42. A scaphoid kinematic index of greater than 1 indicates the scaphoid has more flexion during radioulnar deviation than translation. CONCLUSIONS: Wrists with a type I lunate show statistically greater scaphoid translation with radial deviation. Wrists with a type II lunate show statistically greater scaphoid flexion with radial deviation. Intermediate lunates have intermediate scaphoid mechanics. This allows the surgeon to determine the likely wrist scaphoid mechanics based on the lunate type determined from a single posterior-anterior x-ray.     

Unusual case of isolated lunate fracture without ligamentous injury

Fractures of the lunate are rare injuries that usually result from high-energy trauma and are typically associated with other carpal and ligamentous injuries. The incidence of lunate fractures has been cited as 0.5% to 6.5% of all carpal fractures. These fractures are not frequently reported in the literature, and no consensus exists on the treatment of these injuries in the acute and chronic setting. The mechanism typically producing this fracture is a loading force applied to a dorsiflexed, ulnarly deviated wrist such that the capitate is driven downward into the lunate.No prior reports exist in the literature of an isolated fracture of the lunate without perilunate dislocation or ligament disruption. This article reports a case of an isolated displaced transverse shear fracture of the lunate seen 3 months after initial injury, which was successfully treated using a volar and dorsal combined approach and open reduction and internal fixation using microscrews. Bony union across the fracture site was obtained by 7-week follow-up and continued to show improved consolidation through 10-month follow-up. The patient had decreased pain, normal range of motion, and no radiographic evidence of lunate osteonecrosis on most recent follow-up despite the delayed presentation and degree of fracture displacement. This case demonstrates a previously unreported type of wrist injury.     

Unusual combined scaphoid and lunate fracture of the wrist: a case report

All perilunate fracture-dislocations combine ligament ruptures, bone avulsions, and fractures in a variety of clinical forms. The most frequent is the dorsal trans-scaphoid perilunate dislocation. In rare cases, however, these dislocations also have been associated with capitate fractures, triquetral fractures, or lunate fracture. We report a combined scaphoid and lunate fracture of the wrist that was not associated with perilunate dislocation.     

Palmar dislocation of scaphoid and lunate as a unit

A case of closed palmar dislocation of the scaphoid and lunate as a unit is described. This was treated by closed reduction and resulted in a good functional result as assessed at 1-year follow-up. No aseptic necrosis of the lunate or of the scaphoid developed. The only residual abnormality was an asymptomatic x-ray VISI pattern of the lunate. This is attributed to the disruption of the lunotriquetral joint. A functional analysis of the x-ray films with the wrist in radial and ulnar deviation indicated a normal arthrokinematic pattern.     

Dislocation of the scaphoid and lunate bones without fracture: a case report

A patient with a dislocation of both lunate and scaphoid bones is described. The position of the hand at the moment of injury seems to have been dorsiflexion and radial deviation. A mechanism for this injury is proposed. Internal fixation in severe carpal injuries is advised.