Scapholunate Dissociation

Anatomy

• Metacarpals
• Hamate
• Capitate
• Trapezoid
• Trapezium
• Pisiform
• Triquetrium
• Lunate
• Scaphoid
• Ulna
• Radius

Epidemiology

• Scaphoid is most commonly fractured carpal bone with tenuous blood supply leading to increased post-injury risks
• Lunate injury can lead to Kienbock Disease
• SL is most common form of Traumatic Carpal Instability
• SL frequently overlooked condition which are associated with TFCC tears
• Dorsal Intercalated Segment Instability (DISI)
• ScaphoLunate Advanced Collapse (SLAC)

Pathomechanics

• ScaphoLunate ligament is weaker dorsally while it is stronger volarly causing volar tilt of the scaphoid against the lunate
• Unopposed extension forces on the Lunate by Triquetrium could lead to DISI
• Abnormal Scaphoid motion and dorsal subluxation onto the radial fossa on wrist flexion lead to wrist arthritis
• Migration of capitate can lead to SLAC (on dorsiflexion or extension)

Range of Motion

Wrist (Radiocarpal) Range of Motion

Flexion (Palmar Flexion) =80 Degrees
Extension (Dorsi Flexion) =70 Degrees
Abduction (Radial Deviation) =20 Degrees
Adduction (Ulnar Deviation) =30 Degrees

Clinical Exams

The patient should point to the most painful area and indicate where the pain radiates. 

Special tests can help support specific diagnoses e.g. :

Finkelstein’s test	Fovea sign
Lunotriquetral ballottement	Grind test
Lunotriquetral shear test	McMurray’s test
Pisotriquetral grind test	Piano-key test
Shuck test	Supination lift test
Ulnar snuffbox test	Watson’s test 1 & 2

Diagnostic Studies

Imaging

Radiographs
PA, Lateral, and Gripping Views should be obtained
The following items should be examined:

• Scapholunate Angle: 46◦ is Normal; > 60 degrees is abnormally elevated
• ScaphoLunate Gap: > 2mm is abnormal
• “Signet Ring” sign: as scaphoid flexes, distal pole will appear as ring on PA view
• Radiolunate Angle: >15◦ dorsal indicates DISI deformity
• Disruption of Gilula Lines
• Gripping Views may show SLIL changes

Arthrograms

• Arthrograms were initially the definitive tests, but have shown to have a very high rate of false positives and a non-negligible rate of false negatives.
• MRI has been suggested to examine wrist ligaments but rarely allow a definitive judgment to be made.

Surgical Evaluation

Arthroscopy

• Allows for direct inspection of SLIL ligament and supporting structures
• Helps determine changes in Ulnar Variance
• Helps inspect for TFCC tears
• Physical examination, though, should prevail

Treatment

Acute

• Open Repair
• Pin Acute Lesions
• Cast Immobilization

Chronic (static or dynamic)

Current Techniques include:

• Dorsal capsulodesis or tenodesis:to prevent static or dynamic flexion
• Brunelli Procedure: uses a strip of flexor carpi radialis through distal scaphoid and distal radius to limit scaphoid flexion and stabilize SLIL and STIL ligaments
• Ligament Reconstruction: Attempts using bone-ligament-bone constructs from carpus, foot, and extensor retinaculum
• Arthrodesis: Scaphotrapezial or Scaphocapitate arthrodesis

Chronic (with Arthritis)

Current Techniques include:

• STT fusion with radial styloidectomy
• Scaphocapitate Fusion with radial styloidectomy
• Four Corner Fusion or Proximal Row Carpectomy
• Total Wrist Fusion
• Total Wrist Arthroplasty

References

• J. Liberman(ed), S. Moran, M. Rizzo, A. Shin. Chapter 50: Hand & Wrist Fractures and Disclocations, including carpal instability. AAOS Comprehensive Review. (2009 edition).
• J Hand Surg [Am]. 2009 May 29. Treatment of Traumatic Scapholunate Dissociation. Kalainov DM, Cohen MS.
• Tech Hand Up Extrem Surg. 2009 Mar;13(1):54-8. Three-corner midcarpal arthrodesis and scaphoidectomy: a simplified volar approach. Dutly-Guinand M, von Schroeder HP
• Nelson, DL: The importance of the physical examination. Hand. Clin. 1997, Feb; 13(1):13-15. PMID: 9048179
• J Hand Surg Am. 2001 Jul;26(4):749-54. Static scapholunate dissociation: a new reconstruction technique using a volar and dorsal approach in a cadaver model. Dunn MJ, Johnson C. Department of Orthopaedic Surgery, Monmouth Medical Center, Longbranch, NJ, USA.
• J Hand Surg Br. 2000 Apr;25(2):188-92. Scapholunate ligament repair using the Mitek bone anchor. Bickert B, Sauerbier M, Germann G. Department of Plastic and Hand Surgery/Burn Centre, University of Heidelberg, Ludwigshafen, Germany.
• Arthroscopy. 1993;9(1):109-13. Pull-out strength of five suture anchors. Carpenter JE, Fish DN, Huston LJ, Goldstein SA. Orthopaedic Research Laboratories, University of Michigan, Ann Arbor.
• Eplasty. 2009;9:e7. Epub 2009 Jan 29. Reduction and maintenance of scapholunate dissociation using the TwinFix screw.Opreanu RC, Baulch M, Katranji A.