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Lunate Instability


Original Editor - William Silvestri and Jamie Keller as part of the Temple University EBP Project

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Introduction

Lunate instability refers to the lunate bone losing normal alignment with its surrounding carpal bones. Carpal dislocations are uncommon, but often as a result of high impact injuries.[1] Scapholunate dissociation is the most common location of carpal instability within the wrist.[1] Perilunate dislocations are more rare, making up less than 10% of all wrist injuries.[2] Lunotriquetral ligament injuries are relatively common cause of ulnar-sided wrist pain.[3]

If left untreated, lunate instability may progress to osteoarthritis and progressive carpal collapse, or scapholunate advanced collapse (SLAC).[4] Thus, it is very important to correctly diagnose and treat lunate instabilities in the acute phase for best prognosis.[4]

Clinically Relevant Anatomy

The lunate is one of the eight carpal bones located in the wrist.[5] These eight bones are arranged into two rows with four bones in each row.[5] They are connected together by intrinsic and extrinsic ligaments .

  • The proximal row, laterally to medially:

Scaphoid, lunate, triquetrum and pisiform.

  • The distal row, laterally to medially:

Trapezium, trapezoid, capitate and hamate.

The lunate articulates laterally with the scaphoid, medially with the triquetrum, and distally with the capitate and hamate.

There are several ligaments that attach to the dorsal and palmar surfaces of the carpal bones and hold them together and provide stability in the wrist. Most of the ligaments are named with respect to the two bones they connect.[1]

Illustration of scapholunate interosseous ligament anatomy. The drawing depicts a slightly oblique, coronal view of the distal radius (R), scaphoid (S) and lunate (L). The scapholunate ligament has been transected to demonstrate its three distinct parts, which include the dorsal region (arrowhead), palmer region (white arrow) and proximal region (black arrow) components. Note that the dorsal component is the thickest.

Mechanism of Injury

Lunate instability most frequently occurs due to high-energy trauma, such as when a person experiences a fall onto an outstretched hand (FOOSH) with the wrist positioned in extension, ulnar deviation, and intercarpal supination.[1][6][7]

Scapholunate instability is considered to be present if at least two of the following three ligaments are injured: palmar radioscapholunate ligament, scapholunate interosseous ligament, and dorsal scapholunate ligament.[8] With this pattern of injury, the progression of ligament injury starts from radial to ulnar.[8] If left untreated, dynamic scapholunate instability can progress to rotatory subluxation of scaphoid, lunate subluxation anteriorly, scapholunate dissociation, dorsal intercalated segment instability, and then scapholunate advanced collapse.[8]

If the injury occurred when the intercarpal bones were in pronation, forces are transmitted from ulnar to radial, which would cause the lunate to dislocate dorsally.[1] However, carpal dislocations are uncommon.[6] The lunate is more suspected to dislocate palmarly as a final stage of perilunar injury.[1]

Lunotriquetral injuries typically occur as a result of a backwards FOOSH with the arm in external rotation and the wrist in radial deviation and extension.[3] This causes the triquetrum, but not the lunate, to translate dorsally.[3] Atraumatic lunotriquetral injuries are typically as result of arthritis.[3]

Clinical Presentation

A patient presenting with lunate instability will most likely have a history of trauma to the wrist that has resulted in a lesion to the stabilising ligaments of the carpal bones.[6] Additionally, a patient with a history of certain degenerative inflammatory diseases such as chondrocalcinosis, gout, aseptic bone necrosis of the scaphoid or lunate bones, or Madelung deformity (a form of misalignment) may be more susceptible to carpal instability.[9]

The patient will have complaints of pain in the involved wrist, specifically around the scaphoid and lunate bones in scapholunate injuries or the lunate and triquetrum in lunotriquetral injury.[3][5] Lunotriquetral instability will present with pain on the ulnar side of the wrist, and can be difficult to differentiate from other causes of wrist pain.[10] The presentation can be chronic or acute as well as traumatic or atraumatic.[5] The pain is typically exacerbated by weightbearing activities, such as push-ups, overuse activities, such as typing on a computer, or gripping.[5] The patient may deny clicking in the wrist, but report a feeling of instability with some activities.[5]

Diagnostic Procedures

Physical Exam

The wrist will most likely have diffuse soft tissue swelling.[5] A tender dorsal scapholunate interval may be evident but it may appear normal in radiographs. The scaphoid shift test may be positive in cases of scapholunate instability.[5][11] Decreased range of motion and grip strength along with crepitation may be observed.[3]

Palpation of Scapholunate Articulation

The scapholunate articulation can be palpated by first palpating Lister’s tubercle on the distal radius and then moving slightly distal to the tubercle to find the scapholunate joint.

Lister's Tubercle

Scaphoid Shift Test (Watson Test)

The scaphoid shift test assesses dynamic scapholunate instability by applying stress to the scaphoid as the wrist moves from ulnar to radial deviation.[6] The test is positive if a clunk is produced or the patient's symptoms are reproduced when the compression is released.[5][6]

[12]

Diagnostic Exam

The scapholunate interval measurement is the distance between the proximal medial corner of the lunate and the proximal lateral corner of the scaphoid.[5] A separation of greater than 3 mm may be indicative of scapholunate instability and it is referred to as the “Terry Thomas sign”, while a gap of 4-5mm is more definitive.[13] This can be measured through radiographs and should be compared with the patient’s uninvolved side. A “clenched-fist” view in a radiograph may help accentuate the space between the two bones.[13]

With lunotriquetral ligament injuries, standard radiography is typically normal.[3] It can be helpful to have radiographs taken with the wrist in ulnar and radial deviation as there may be a lunotriquetral angle decrease with ligament injury.[3]

Dorsal View
Dorsal View- Radiograph

Outcome Measures

Potential self-report measures for individuals presenting with wrist pain are listed below.

Management / Interventions

Conservative

Conservative treatment is utilised for partial ligament tears.[4] Immobilisation of the wrist is beneficial to allow for healing and to decrease symptoms.[4] Nonsteroidal anti-inflammatories and therapy are also beneficial at this stage.[4] Strengthening dynamic stabilising muscles of the wrist, such as extensor carpi radialis longus and brevis, flexor carpi ulnaris, and abductor pollicis is helpful to provide stability to the wrist and improve function.[4] Corticosteroid injections are also an option to help control pain and inflammation.[3][10] If a patient fails conservative therapy, arthroscopic debridement may be an option to maximise function and decrease pain.[4]

Image:Long_Opp..jpg Wrist Control.jpg

Physical Therapy Management

Physical therapy focuses on maximising patient function. If the patient is immobilised, maintaining and improving shoulder, elbow, and finger mobility and strength is helpful. Targeting the forearm, wrist, and hand musculature that surrounds the affected ligaments of the lunate will help to provide dynamic stability.[4][14] NMES can be a useful tool to support functional recovery of these stabilising muscles.[14] Wrist mobilisation with an oblique line of force can help to regain mobility lost during injury or immobilisation.[15] Training proprioception, as one would for a lower extremity, is important to decrease future instability.[16] This can be completed with joint position sense training, mirror training, or motor imagery.[16][17] Improving neuromuscular function and joint stability through balancing exercises, ball toss, or racket taps can also help maximise a patient's level of function.[16][17]

Surgical

Surgery is recommended if there is a significant degree of injury to the ligaments in question or if conservative interventions fail.[4][18] Surgery can be performed to repair the damaged ligaments that are causing instability or to fixate or fuse the carpal bones.[4][10][18][19] Acuity of injury plays a role in which surgery is selected, with surgeries performed within 6 weeks of injury having improved prognoses.[4][20] In acute cases, anatomic repairs tend to be the preference with satisfactory outcomes.[20] If static malalignment of carpal bones is present in more chronic cases, prognosis tends to be inferior as compared to more acute cases or cases without static malalignment.[20] Surgical techniques vary for chronic cases, but most are trying to replicate an anatomical reconstruction in order to maximise post-operative range of motion and grip strength as compared to the contralateral side.[20]

Post-Surgical Management

Post-surgical rehabilitation is dependent on the surgery performed. However, immobilisation or restricted mobility with a custom orthotic is common to restrict stress to the repaired structures.[16] Protected range of motion through combined radial deviation and extension to ulnar deviation and flexion is utilised to maintain and improve mobility without negatively affecting surgical site in acute phases of healing.[16]

Following the acute phase of healing, it is important to strengthen wrist musculature as they provide dynamic stability to the carpal bones.[16] Strengthening programme should include extensor carpi ulnaris and pronator quadratus for ulnar side carpal instability and abductor pollicis longus, extensor carpi radialis longus, flexor carpi radialis, and pronator quadratus for radial side carpal instability.[17] Strengthening in to functional tasks required by the patient is important to maximi se function post-operatively.[17] Proprioceptive exercises and neuromuscular facilitation techniques can also be added in later stages of healing. [17]

Differential Diagnosis

Other conditions to be aware of when evaluating a patient with wrist pain are:

Summary

While lunate instability is uncommon, early treatment is important in regards to prognosis.[1] The most common mechanism of injury is from a high energy fall, such as a FOOSH.[6] The wrist is typically painful laterally over the scaphoid and lunate with generalized oedema.[5] Conservative treatment for partial ligament tears includes immobilisation, medication, and therapy emphasizing strengthening lateral wrist musculature to provide support.[4] Surgery is reserved for complete tears or those who fail conservative methods.[4] Surgery is dependent on the chronicity and degree of instability.[4]

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 Alonso-Tejero D, Luengo-Alonso G, Jiménez-Díaz V, García-Lamas L, Porras-Moreno MÁ, Cecilia-López D. Chronic isolated dorsal dislocation of the lunate. A rare presentation of carpal instability. Strategies in Trauma and Limb Reconstruction. 2022 Jan;17(1):59.
  2. ↑ Subramanian K, Arora B, Bhatnagar A, Jan I. Perilunate dislocation–case report and review of literature. Journal of clinical and diagnostic research: JCDR. 2017 Aug 1;11(8):RD06
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 Van de Grift TC, Ritt MJ. Management of lunotriquetral instability: a review of the literature. Journal of Hand Surgery (European Volume). 2016 Jan;41(1):72-85.
  4. ↑ 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 4.11 4.12 4.13 Wessel LE, Wolfe SW. Scapholunate Instability: Current Concepts in Diagnosis and Management Classification and Treatment ConsiderationsePart 2. The Journal of Hand Surgery. 2023.
  5. ↑ 5.00 5.01 5.02 5.03 5.04 5.05 5.06 5.07 5.08 5.09 5.10 Wessel LE, Wolfe SW. Scapholunate instability: diagnosis and management–anatomy, kinematics, and clinical assessment–part I. The Journal of Hand Surgery. 2023 Nov 1;48(11):1139-49.
  6. ↑ 6.0 6.1 6.2 6.3 6.4 6.5 Schmauss D, Pöhlmann S, Weinzierl A, Schmauss V, Moog P, Germann G, Bickert B, Megerle K. Relevance of the scaphoid shift test for the investigation of scapholunate ligament injuries. Journal of Clinical Medicine. 2022 Oct 26;11(21):6322.
  7. ↑ Mayfield JK, Johnson RP, Kilcoyne RK. Carpal dislocations: pathomechanics and progressive perilunar instability. J Hand Surg Am. 1980;5 (3): 226-41
  8. ↑ 8.0 8.1 8.2 Kitay A, Wolfe SW. Scapholunate instability: current concepts in diagnosis and management. The Journal of hand surgery. 2012 Oct 1;37(10):2175-96.
  9. ↑ Redeker J, Vogt PM. Carpal instability. Chirurg. 2011 Jan; 82(1):85-93.
  10. ↑ 10.0 10.1 10.2 Shin AY, Battaglia MJ, Bishop AT. Lunotriquetral instability: diagnosis and treatment. JAAOS-Journal of the American Academy of Orthopaedic Surgeons. 2000 May 1;8(3):170-9.
  11. ↑ Dyer GS. Predynamic scapholunate instability. J Hand Surg Am. 2010 Nov;35(11):1879-1880.
  12. ↑ CRTechnologies. Scaphoid Shift Test (CR). Available from: http://www.youtube.com/watch?v=DGH-pHmeLnQ [last accessed 12/10/17]
  13. ↑ 13.0 13.1 Avery III DM, Rodner CM, Edgar CM. Sports-related wrist and hand injuries: a review. Journal of orthopaedic surgery and research. 2016 Sep 16;11(1):99.
  14. ↑ 14.0 14.1 Dağ A, Ayık Ö, Fırat T, Şahinkaya T, Topuz S. The effectiveness of NMES-integrated therapy in scapholunate ligament injuries-a randomized controlled trial. BMC Sports Science, Medicine and Rehabilitation. 2025 Dec 2.
  15. ↑ Braidotti F, Atzei A, Fairplay T. Dart-Splint: an innovative orthosis that can be integrated into a scapho-lunate and palmar midcarpal instability re-education protocol. Journal of Hand Therapy. 2015 Jul 1;28(3):329-35.
  16. ↑ 16.0 16.1 16.2 16.3 16.4 16.5 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.
  17. ↑ 17.0 17.1 17.2 17.3 17.4 Cheuquelaf-Galaz C, Antúnez-Riveros MA, Lastra-Millán A, Canals A, Aguilera-Godoy A, Núñez-Cortés R. Exercise-based intervention as a nonsurgical treatment for patients with carpal instability: A case series. Journal of Hand Therapy. 2024 Jul 1;37(3):397-404.
  18. ↑ 18.0 18.1 Kitay A, Wolfe SW. Scapholunate instability: current concepts in diagnosis and management. The Journal of hand surgery. 2012 Oct 1;37(10):2175-96.
  19. ↑ Wheeless C. Lunotriquetral Dissociation. Duke Orthopaedics presents Wheeless' Textbook of Orthopaedics Web site. http://www.wheelessonline.com/ortho/lunotriquetral_dissociation. Accessed 03/02, 2011.
  20. ↑ 20.0 20.1 20.2 20.3 Pappou IP, Basel J, Deal DN. Scapholunate ligament injuries: a review of current concepts. Hand. 2013 Jun;8(2):146-56.
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