Abstract
Trapeziometacarpal joint instability is a well-recognised but under-diagnosed cause of basal thumb pain. A systematic approach with sound understanding of anatomy and clinico-pathological correlation is required to make a diagnosis. We discuss an overview of the principles of diagnosis and management of basal thumb joint instability. An evaluation algorithm for Eaton’s injury of the thumb is proposed for clinical application with evidence in literature.
Keywords: Thumb, Thumb carpometacarpal joint instability, Anterior-oblique ligament, Radiology, Eaton-littler ligament reconstruction
1. Introduction
The management of Trapeziometacarpal joint instability (TMCJ) can be assisted by having a good understanding of the anatomy, clinical history and examination of thumb. Complementary imaging and investigations can then help to treat TMCJ instability effectively.
The TMCJ is a saddle shaped, biconcave-convex joint. TMCJ stability is provided by five main ligamentous structures during static pinch and grasp, (1) The anterior oblique ligament, (2) the ulnar collateral ligament, (3) the first intermetacarpal ligament, (4) the posterior oblique ligament, and (5) the dorso-radial ligament.1,2 The anterior oblique ligament also known as volar/beak ligament is traditionally described as the primary static stabilizer and prevents radio-dorsal translation of thumb metacarpal during key pinch.3,4 However anatomical and biomechanical studies have debated this in current literature with considerable support for the dorso-radial ligament.5,6 Injuries to the thumb TMCJ ligaments leads to varying degrees of instability from a dislocated thumb with complete rupture to a partial rupture.1,2,5,7 Persistent instability has been reported in patients following closed reduction and percutaneous Kirschner wire fixation of acute CMC dislocations and have significantly better results with early ligament reconstruction.7,8 Eaton-Littler9 and Brunelli10 have described the common techniques for ligament reconstruction of the thumb. Modified technique of well-established Eaton-Littler’s ligament reconstruction has shown to restore global stability of the thumb addressing both the volar beak and the dorso-radial ligament components.11
1.1. Evaluation of Eaton’s injury
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A)
Clinical evaluation
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B)
Radiological evaluation
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C)
Arthroscopy
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D)
Examination under anaesthesia.
1.1.1. Clinical evaluation
-
i
History: A searching history is crucial. Presentation is often delayed due to a missed diagnosis. Patients typically present with pain at the base of the thumb especially when pushing up from a flat surface, for example when raising oneself from a chair. Commonest mechanism of injury is usually the result of axial loading in flexion.12
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ii
Palpation: isolates tenderness especially at the volar aspect of the trapeziometacarpal joint.
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iii
Provocative Tests
Eaton and Littler described a ‘Torque test’ which involves axial rotation of a distracted thumb to evaluate instability. This test is mentioned to be more specific for synovitis.3
Takwale et al. have described a two -step clinical provocative test to detect instability. The thumb is first abducted in a palmar direction and pronated. The second step involves gradual abduction, supination of the retro pulsed thumb reproducing symptoms of instability in the patient.13
The ‘Grind test’ (axial loading of the TMCJ with simultaneous rotation) and ‘Crank test’ (axial loading of the TMCJ with passive flexion and extension) are provocative tests to assess TMCJ. Tests are positive if pain and crepitus are produced and suggest arthritis with or without instability.
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iv
Movement Available active and passive range of movement at IP, MCP and TMCJ are recorded. Pinch and Grip strengths are measured with validated tools (e.g. Jamar hand dynamometer).
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v
Lignocaine Test Abolition of pain by injection of local anaesthetic at the TMCJ can be used as an aid to diagnosis and can be carried out in a hand clinic set-up.
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vi.
Differential diagnosis
In addition to the assessment of the TMCJ, associated hand and wrist conditions presenting as thumb pain are evaluated e.g. ganglia communicating with basal thumb joint. The wrist is carefully evaluated to rule out scapho-lunate ligament injuries, scaphoid fractures and chronic ulnar collateral injuries presenting as thumb pain. Common associated conditions include DeQuervain’s tenosynovitis, scaphotrapeziotrapezoid (STT) joint arthritis and carpal tunnel syndrome. Superficial radial nerve neuroma following previous surgery (e.g. trapeziectomy) may present as thumb pain.
1.1.2. Radiological evaluation
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i.
Plain radiographs: In patients with classic post-traumatic instability, plain radiographs are usually negative and predominantly help in ruling out radiological evidence of arthritis and associated fractures. Stress views are complementary and have been used to diagnose instability of the TMCJ by comparing the mobility of the injured metacarpal in relation to the trapezium with that on the uninjured side.14 Plain radiographs are undertaken to exclude any degeneration of the TMCJ joint. After excluding other non-articular conditions e.g. De Quervain’s, Neuroma, painful ganglion etc as a deferential diagnosis by clinical tests, we can confirm the clinical diagnosis and also assess the degree of instability by the stability tests to conclude a TMCJ injury.
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ii
Ultrasonography: Teixeria et al. feel ultrasound evaluation of the anterior oblique ligament of the trapeziometacarpal joint is feasible with state of the art equipment and a thorough knowledge of the complex anatomy of this region.15 Chivaras et al. suggest high resolution ultrasound imaging can depict volar translation of the metacarpal, which may facilitate diagnosis of ligamentous injury.16
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iii
Magnetic Resonance Imaging: Magnetic Resonance Imaging (MRI) and Magnetic Resonance Arthrography are being increasingly used in assessing TMCJ pathologies and instability. Following their study, Connell et al.17 recommend coronal and axial imaging with fat suppression and a coronal Short-TI Inversion Recovery (STIR) sequence to assess the integrity of stabilizing ligaments. Cardoso et al.18 have found MR arthrography further improves visualization and provides detailed information about the anatomy of the ligaments around the trapeziometacarpal joint.
1.1.3. Arthroscopy
-
i.
Thumb CMC joint arthroscopy is gaining popularity for evaluation, diagnosis and treatment of TMCJ pathologies. Arthroscopy is a less invasive method of examining joint surfaces and ligament integrity. It also allows debridement of synovitis.
-
ii
Senior author’s preferred technique: With the patient in supine position and a tourniquet applied, a counter-traction strap is applied around the arm and table, while a single finger trap for the thumb is used to apply 5 lbs–7 lbs of vertical traction over a wrist tract tower. Commonly two arthroscopic portals are used. The first radial (1-R) portal is located just volar to the APL tendon. The first ulnar (1-U) portal is just ulnar to the EPB tendon.19 We use the thermal capsular shrinkage to treat the attenuated (partially torn) ligament (e.g. Smith & Nephew MICROBLATOR™ 30 Radiofrequency probe). Post-operatively the thumb is immobilised in the Plaster of Paris Spica for 6–8 weeks. The torn ligament cases required reconstruction.
1.1.4. Examination under anaesthesia
-
i
EUA: This is an important adjunct in re-enforcing the findings of Lignocaine test and complementary investigations i.e. MR imaging/TMCJ arthroscopy since is conducted in a controlled atmosphere under adequate anaesthesia usually in operating theatre. Amount of displacement of thumb metacarpal is compared with opposite un-injured side and recorded.
1.2. Decision making
1.2.1. Non-operative treatment
A pain free and stable thumb is a prerequisite for good hand function. Mechanical instability of the TMCJ of the thumb interferes with normal function of the hand and may lead to articular degeneration of the joint.20
Common methods of conservative intervention for TMCJ instability include splinting, pain control, hand therapy, use of non-steroidal anti-inflammatory drugs and corticosteroid injections. Splinting provides extrinsic support to the TMCJ helping to reduce pain, improve function with a predominant aim to prevent subluxation. However, splinting does not address the inherent instability of the CMC joint; which is typically caused by an intrinsic weakness of the capsule-ligamentous structures.21
1.2.2. Operative treatment
In the young the instability is usually secondary to trauma. The anterior oblique ligament is the key primary stabilizer of the TMCJ. Rupture of the anterior oblique ligament leads to traumatic mechanical instability of the TMCJ and requires surgical reconstruction of the ligament to avoid any compromise to the function of the thumb.
A variety of ligamentoplasty techniques to stabilise the TMCJ have been described. This involves substituting either the anterior oblique ligament or the dorso-radial ligament or the intermetacarpal ligament.
1.2.2.1. The anterior oblique ligament substitution
Eaton-Littler have described the classic procedure of ligament reconstruction using a harvested portion of flexor carpi radialis as a substitute for the anterior oblique ligament.3,9 This had the advantage of reconstructing the joint in two planes, reconstituting the volar ligament and also creating a new ligament radially in a part of the joint capsule which was weak. Other authors7,13,22 have also found this technique reliable, reproducible and retards future joint degeneration. However proponents of dorso-radial ligament as the main restraint to dorsal dislocation have undertaken reconstruction of dorsoradial ligament complex in their patients.23,24 These patients did have an underlying dislocation of the TMCJ as well. To address the reservation that traditional Eaton-Littler does not provide adequate dorsal stability, a modified Eaton-Littler’s procedure has been described11 which restores global stability of the thumb addressing re-enforcement of the volar beak and the dorso-radial ligament.
1.2.2.2. The intermetacarpal ligament substitution
Brunelli et al., Eggers and Slocum have described techniques which substitute the intermetacarpal ligament b using harvested slips of abductor pollicis longus, extensor carpi radialis longus and palmaris longus respectively.10,25,26
1.2.2.3. Arthroscopic electro-thermal shrinkage
In patients with symptomatic basal thumb instability, with features of partial or attenuated ligaments, thermal shrinkage of the beak ligament has been undertaken arthroscopically with encouraging results. Chu PJ et al. describe a method of arthroscopic electro thermal shrinkage of the volar ligaments and joint capsule in patients with symptomatic thumb basal joint instability.27 Arthroscopic thermal capsular shrinkage + Plaster of Paris treatment option is useful for the attenuated/partially torn ligament.
2. Conclusion
High index of suspicion, good clinical history and clinical examination are keys to a correct diagnosis of trapeziometacarpal joint instability. Complementary investigations are helpful in ruling out associated injuries with similar presentation and mechanism of injury. Early surgical reconstruction of the ligament (can) restore (s) thumb stability and pain free thumb function.
We propose an algorithm (Fig. 1) for reaching a diagnosis of Eaton’s injury of the thumb with management options, which may provide a planning guideline for treating clinicians.
Contributors
KPI provided the idea and conceptualization of the article, wrote the Manuscript and flow diagram. DVS was involved in collecting references for the article. WYL the senior author helped design the algorithm and edited the final draft.
Ethical approval
The study protocol was approved by the local research and clinical effectiveness audit department.
Statement of location
The study carried out in the department of Trauma & Orthopaedics at Southport & Ormskirk Hospital NHS Trust, Southport, United Kingdom.
Funding statement
The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Patient consent for publication
Not required.
Declaration of competing interest
KPI, DVS, WYL as authors haves nothing to declare.
Contributor Information
Karthikeyan Iyengar, Email: kartikp31@hotmail.com.
Deepak V. Sree, Email: drdeepakvs@gmail.com.
William Y.C. Loh, Email: william.loh@nhs.net.
Appendix.
Fig. 1.
Algorithm for Eaton’s injury of the thumb.
Abbreviations: MR: Magnetic Resonance; TMCJ: Trapeziometacarpal joint.
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