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Scapholunate Dissociation

Original Editors - Brenda Walk, Liz Record, James Passmore, Jeremy Brady, & Thomas Albaugh as part of the Texas State University Evidence-based Practice Project

Top Contributors - Manisha Shrestha, Jess Bell, Kim Jackson, Paul Trevino and Tarina van der Stockt  

Introduction

Scapholunate ligament (SLL) injury is the most frequent cause of carpal instability.[1][2][3] Scapholunate dissociation results from injury to the scapholunate ligament, causing malalignment between the scaphoid and lunate bones that appears radiographically as a widened gap.[1]

Clinically Relevant Anatomy

The scapholunate ligament, also known as the scapholunate interosseous ligament (SLIL), consists of three regions arranged in a C-shaped configuration: dorsal, membranous, and volar. The dorsal region is the strongest component and serves as the primary stabiliser, withstanding loads of up to 260 N. The central membranous region is avascular and provides minimal resistance to laxity (63 N). The volar region contributes primarily to rotational control and resists forces of 118 N.[4]

The scapholunate ligament sits between the two major load-transmitting articulations of the proximal carpal row: the radioscaphoid joint (bearing 50% of axial load) and the radiolunate joint (bearing 35%). This anatomical position makes the ligament particularly susceptible to destabilising forces.[2]


The secondary stabilisers of the scapholunate joint are the scaphotrapeziotrapezoid, scaphocapitate, radioscaphocapitate and dorsal intercarpal ligaments.[5][2] The dynamic muscle stabilisers include extensor carpi radialis longus and abductor pollicis longus.[2] The radial artery provides the principal blood supply to the scapholunate ligament, though overall vascularisation is poor.[4]

Epidemiology/Aetiology

Scapholunate injuries are common after wrist trauma.[6] The primary mechanism is an axial load applied to the wrist in extension and ulnar deviation (e.g., falling onto an outstretched hand (FOOSH injury).[1]

The incidence of scapholunate ligament injury remains unknown, as these injuries are often overlooked when more obvious fractures are present, such as distal radius fractures from falls onto outstretched hands.[7]

Scapholunate ligament tears occur in approximately 5% of wrist sprains and in 13.4% of distal radius fractures. In isolated radial styloid fractures (Chauffeur's fracture), scapholunate injury is present in 60% of cases, with 20% requiring surgical stabilisation.[4][8]

Characteristics/Clinical Presentation

Patients with a scapholunate ligament injury typically present with a clear history of wrist trauma involving a fall onto an extended, ulnarly deviated wrist (FOOSH injury), or repetitive trauma whilst the wrist is in extension. Tenderness is present over the dorsoradial aspect of the wrist, often in the anatomic snuffbox or over the palmar scaphoid tuberosity. Patients may report a sensation of 'clicking' or 'giving way' on the dorsoradial aspect of the wrist, accompanied by swelling and limited grip strength and range of movement.[2][4][9]

Special Radiographic Views for Scapholunate Dissociation: Clenched Fist
Special Radiographic Views for Scapholunate Dissociation: Clenched Fist

Classification

Watson et al. proposed a four-stage classification system for scapholunate ligament injury based on radiographic findings: predynamic instability (occult), dynamic instability, static scapholunate dissociation, and scapholunate advanced collapse (SLAC).[2]

Radiographic Findings

On posteroanterior radiographs, the scapholunate interval is measured at the midpoint between the bones. Normal scapholunate spacing is less than 2mm. A gap of 3mm or greater (Terry-Thomas sign) is generally considered diagnostic of scapholunate dissociation, though some sources use 4-5mm as the threshold. Comparing sides is essential as asymmetry is a key diagnostic finding. Lateral radiographs show the scapholunate angle, which is normally 30-60°. Angles greater than 70° indicate dissociation.[10][11]

Radiolograph showing the gap between scaphoid and lunate.
Radiolograph showing the gap between scaphoid and lunate.

Dynamic instability typically develops gradually over 3-12 months as secondary ligamentous stabilisers progressively stretch or tear. Clenched-fist or ulnar-deviation radiographs can reveal scapholunate angles exceeding 60° and gaps greater than 3mm.[4]

Scapholunate advanced collapse progresses through four stages. Degenerative changes first appear at the radial styloid (Stage I), progress to involve the radioscaphoid joint (Stage II), then extend to the capitolunate joint (Stage III), and finally affect the entire radiocarpal and midcarpal joints (Stage IV).[2]

Arthroscopic Findings

The Geissler classification grades scapholunate ligament injuries based on arthroscopic findings.

Modified Geissler Classification[12][13]
Grade I SLL attenuation and haemorrhage; no intercarpal incongruency
Grade II SLL attenuation and intercarpal incongruency; a 1mm probe can be passed but not rotated through the carpal gap
Grade III SLL attenuation and intercarpal incongruency; a 1mm probe can be passed and rotated through the carpal gap from the midcarpal space to the radiocarpal space, but cannot pass a 2.7 mm arthroscope
Grade IV Drive-through sign with 2.7 mm scope (i.e., an arthroscope can drive through from the midcarpal joint to the radiocarpal joint)

Complications

Scapholunate advanced collapse (SLAC), the most common pattern of wrist osteoarthritis, commonly develops from untreated scapholunate dissociation. Cartilage degeneration follows a predictable pattern, beginning at the radial styloid, progressing to the radioscaphoid joint, and eventually affecting the midcarpal joints.[4]

Examination

Palpation

Palpation of the wrist anatomic landmarks may elicit informative tenderness. There may be pain in the anatomic snuffbox or the palmar scaphoid on palpation.

Special Tests

Scapholunate Ballottement Test: the therapist stabilises the lunate between thumb and index finger while moving the scaphoid dorsal-palmar direction with the other hand. The test is positive if it produces pain or increased laxity compared to the opposite side.[14]

Watson's Test (Scaphoid Shift Test): The therapist places one thumb on the palmar side of the scaphoid, with their other fingers wrapped around the dorsum of the wrist to provide a counterpressure. They hold the patient's metacarpals with their other hand. They apply a dorsally directed pressure to the scaphoid and bring the patient's wrist into radial deviation and slight flexion. The test is positive if the scaphoid subluxes over the dorsal rim of the radius, causing pain. The scaphoid self-reduces with a painful clunk when the pressure is removed.[15][16]

Watson's Test

Used with permission. November 2011.

Imaging

Relevant views are posteroanterior, lateral, and stress views (clenched fist, ulnar deviation) are obtained.[11][17] Key radiographic findings are described in the Classification section above.

Differential Diagnosis

Scapholunate ligament injury should be differentiated from other causes of dorsoradial wrist pain following trauma, including the following.[18]

  • Scaphoid fracture
  • Distal radius fracture (particularly radial styloid)
  • Scaphoid impaction syndrome
  • De Quervain's tenosynovitis
  • Dorsal wrist ganglion
  • Posterior interosseous nerve compression

Outcome Measures

Surgical Management

There are a range of surgical options for scapholunate ligament injuries. Surgical treatment is tailored to injury severity and timing. Options include ligament repair for acute injuries, reconstructive procedures for chronic instability without arthritis, and fusion operations for advanced degenerative changes. Currently, there's no gold standard approach, and treatment selection typically depends on individual patient factors and surgeon experience.[9][11][13]

Rehabilitation Management

Rehabilitation evidence for scapholunate injuries is emerging. Currently, it seems that a combination of physiotherapy, proprioceptive, and neuromuscular training produce the greatest improvements in terms of joint stability and sensorimotor control, but further research is required.[13] Post-operative protocols are procedure-specific and require close collaboration with the treating surgeon.[19][4]

Acute Phase

After ruling out more serious injuries, acute scapholunate ligament injuries of lesser severity (i.e., without static dissociation/partial ligament injury) may be managed conservatively. Treatment may include initial immobilisation, followed by progressive loading and strengthening. Rehabilitation emphasises proprioceptive training and selective muscle strengthening (particularly flexor carpi radialis for dynamic scaphoid stabilisation). Patients should be educated on activity modification and symptom management strategies.[13][20]

Chronic Phase

Rehabilitation in the chronic phase focuses on restoring range of motion, improving grip strength, and managing pain. Flexor carpi radialis strengthening may be beneficial,[21] as cadaveric studies have demonstrated its role in providing dynamic scaphoid stabilisation during wrist movement. Patients should avoid or modify activities that place increased stress on their wrist. Heating or cooling modalities and NSAIDs may be used for symptom control during flare-ups.[22] In addition, splints may be used to limit the movement of the involved joints.[22]

Post-Surgical Rehabilitation

Post-operative protocols vary significantly based on the surgeon's protocol. Immobilisation periods depend on the technique used. Following cast removal, rehabilitation addresses range of motion deficits, grip strength impairments, and proprioceptive loss. It has been suggested that rehabilitation following a major reconstruction surgery can take 4-6 months until return to activity and 12-15 months until full recovery.[23] Long-term use of orthoses during high-demand activities may be recommended.[23]

Specific Rehabilitation Exercises

Progressive strengthening exercises may include:

  • Re-education of the flexor carpi radialis (FCR)[4]
  • Resisted wrist flexion/extension with a handheld weight
  • Resisted ulnar/radial deviation
  • Passive self-stretch with elbow extended into flexion/extension
  • Isometric strengthening of the wrist extensors/flexors
  • Prayer stretch with palms together and fingers extended
  • Wrist extension self mobilisation in a prayer position
  • Concentric/eccentric wrist flexor/extensor strengthening using a resistance band
  • Pronation/supination exercises using a hammer or cane (adjusting hand position to modify resistance)
  • Progressive grip strengthening using a dynamometer (dosed relative to contralateral side or percentage of one-repetition maximum)
  • Dart throwers motion (caution required)[24]

References

  1. ↑ 1.0 1.1 1.2 Duke Orthopaedics: Wheeless' Textbook of Orthopaedics. http://www.wheelessonline.com/ortho/scapholunate_instability (accessed 15 October 2011).
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 Konopka G, Chim H. Optimal management of scapholunate ligament injuries. Orthopedic research and reviews. 2018;10:41.
  3. ↑ Kitay A, Wolfe SW. Scapholunate instability: current concepts in diagnosis and management. J Hand Surg Am. 2012 Oct;37(10):2175-96.
  4. ↑ 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 Andersson JK. Treatment of scapholunate ligament injury: current concepts. EFORT open reviews. 2017 Sep;2(9):382-93.
  5. ↑ Van Overstraeten L, Camus EJ, Wahegaonkar A, Messina J, Tandara AA, Binder AC, Mathoulin CL. Anatomical description of the dorsal capsulo-scapholunate septum (DCSS)—arthroscopic staging of scapholunate instability after DCSS sectioning. Journal of wrist surgery. 2013 May;2(02):149-54.
  6. ↑ Goelz L, Kim S, Güthoff C, Eichenauer F, Eisenschenk A, Mutze S, Asmus A. ACTION trial: a prospective study on diagnostic Accuracy of 4D CT for diagnosing Instable ScaphOlunate DissociatioN. BMC Musculoskelet Disord. 2021 Jan 15;22(1):84.
  7. ↑ Tomas A. Scapholunate Dissociation. Journal of Orthopaedic & Sports Physical Therapy. 2018 Mar;48(3):225-.
  8. ↑ Lee B, Gilpin B, Bindra R. Should all isolated radial styloid fractures be assessed arthroscopically for concomitant scapholunate ligament injury? Orthopaedic Proceedings. 2023;105-B:35-35.
  9. ↑ 9.0 9.1 Lau S, Swarna SS, Tamvakopoulos GS. Scapholunate dissociation: an overview of the clinical entity and current treatment options. European Journal of Orthopaedic Surgery & Traumatology. 2009 Aug 1;19(6):377-85.
  10. ↑ Bajwa A, Bajwa A. Terry Thomas sign and the ring sign of scapholunate instability. South African Journal of Radiology. 2007;11:106.
  11. ↑ 11.0 11.1 11.2 Bloom HT, Freeland AE, Bowen V, Mrkonjic L. The Treatment of Chronic Scapholunate Dissociation: An Evidence-Based Assessment of the Literature. Orthopedics. 2003;26(2):195-203
  12. ↑ Andersson JK. Treatment of scapholunate ligament injury: current concepts. EFORT open reviews. 2017 Sep;2(9):382-93.
  13. ↑ 13.0 13.1 13.2 13.3 Zhou JY, Jodah R, Joseph LP, Yao J. Scapholunate ligament injuries. J Hand Surg Glob Online. 2024 Apr 1;6(3):245-267.
  14. ↑ Opreanu RC, Baulch M, Katranji A. Reduction and maintenance of scapholunate dissociation using the TwinFix screw. Eplasty. 2009;9.
  15. ↑ Duke Orthopaedics: Wheeless' Textbook of Orthopaedics. http://www.wheelessonline.com/ortho/scapholunate_advanced_collapse_slac. (Accesed 15 October 2011).
  16. ↑ Watson's Test. http://en.wikipedia.org/wiki/Watson%27s_test. (accessed 24 October 2011).
  17. ↑ Imada AO, Welch K, Mlady G, Moneim MSA. The tangential view described by Moneim to demonstrate scapholunate dissociation: an update. Eur J Orthop Surg Traumatol. 2022.
  18. ↑ Jacobson MD, Plancher KD. Evaluation of hand and wrist injuriesin athletes. Operative Techniques in Sports Medicine. 1996 Oct 1;4(4):210-26.
  19. ↑ Wolff AL, Wolfe SW. Rehabilitation for scapholunate injury: application of scientific and clinical evidence to practice. Journal of Hand Therapy. 2016 Apr 1;29(2):146-53.
  20. ↑ Holmes MK, Miller C, Mansfield M. Rehabilitation of stage-one scapholunate instability (ReSOS): An online survey of UK practice. Hand Ther. 2024 Dec;29(4):175-187.
  21. ↑ Salvà-Coll G, Garcia-Elias M, Llusá-Pérez M, Rodríguez-Baeza A. The role of the flexor carpi radialis muscle in scapholunate instability. The Journal of hand surgery. 2011 Jan 1;36(1):31-6.
  22. ↑ 22.0 22.1 Capele A, et al. Mayo Clinic Health Letter - Tools for Healthier Lives. 2011;29(1):1-3. Mayo Foundation for Medical Education and Research, 200 first St. SW, Rochester, MN 55905
  23. ↑ 23.0 23.1 Goldberg SH, Strauch RE, Rosenwasser MP. Scapholunate and lunotriquetral instability in the athlete: Diagnosis and management. Operative Techniques in Sports Medicine. 2006 Apr 1;14(2):108-21
  24. ↑ Bergner JL, Farrar JQ, Coronado RA. Dart thrower's motion and the injured scapholunate interosseous ligament: A scoping review of studies examining motion, orthoses, and rehabilitation. J Hand Ther. 2020 Jan-Mar;33(1):45-59.
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