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.