Midcarpal Instability

MCI is uncommon, accounting for a small minority of carpal instabilities, and is widely regarded as under-diagnosed - many patients are initially labelled with wrist "sprain", ganglion, or TFCC pathology, with diagnostic delays often measured in many months. There is a clear female predominance (around 4:1) and a young age at presentation (second to fourth decades). Generalised ligamentous laxity (positive Beighton score) is present in 60-70%, and a subset have bilateral symptoms, supporting a constitutional rather than purely traumatic aetiology. A discrete antecedent injury (dorsiflexion / ulnar-deviation loading) is reported in a minority. Untreated, the course is typically chronic with mechanical pain, clunking and grip weakness; progression to frank midcarpal arthritis is less frequent than after dissociative instabilities such as scapholunate dissociation. Spontaneous resolution is rare in adults but may occur in adolescents with maturity.

Two-Row Carpal System

The proximal row (scaphoid, lunate, triquetrum) is an intercalated segment with no direct tendon attachments - its position is controlled entirely by ligamentous balance between the radius and the distal row (trapezium, trapezoid, capitate, hamate). In normal kinematics the proximal row extends with radial deviation and flexes (palmar-flexes) with ulnar deviation, a smooth transition governed by the palmar and dorsal carpal ligaments.

Key Stabilisers

The palmar midcarpal ligaments - principally the triquetrohamate-capitate ligament (ulnar arm of the arcuate/deltoid ligament) and the scaphotrapeziotrapezoid (STT) complex - act as a sling from the distal row to the proximal row, restraining excessive palmar flexion. The dorsal radiocarpal (DRC) ligament provides important secondary restraint, and DRC insufficiency is increasingly recognised as a driver of palmar MCI.

The Catch-Up Clunk Explained

1. At rest the lax palmar midcarpal ligaments allow the proximal row to drop into VISI (palmar flexion).
2. As the wrist moves from radial toward ulnar deviation under load, force builds across the midcarpal joint.
3. The lax ligaments eventually yield and the proximal row suddenly "catches up" - snapping from VISI to neutral/slight extension with reduction of the palmarly subluxed capitate.
4. This abrupt shift is the audible/palpable clunk that reproduces the patient's symptoms.

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Lichtman Classification of Palmar Midcarpal Instability

The Lichtman system, based on the degree and reducibility of VISI, remains the most widely cited framework.

Anatomic and Functional Subtypes

• Palmar MCI (80-90%) - palmar midcarpal / DRC ligament laxity producing reducible VISI. The classic clunking presentation.
• Dorsal MCI (rare, under 10%) - dorsal capsular laxity allowing the capitate to sublux dorsally out of the lunate (the "chronic capitolunate instability" described by Johnson and Carrera), tending toward a DISI-type attitude.
• Combined / global - both directions, typically in severe constitutional laxity.
• Extrinsic vs intrinsic - radiocarpal (extrinsic) vs midcarpal (intrinsic) ligament laxity; mostly combined in practice, so the distinction is largely conceptual. Hargreaves has proposed a functional staging scheme (graded by the extent of palmar translation of the distal row on stress testing) as an alternative that better reflects the dynamic nature of the disorder.

History

Patients describe ulnar-sided wrist pain, often with an audible or palpable clunk/snap and a sense of the wrist "giving way". Symptoms are mechanical and activity-related, provoked by forceful grip with ulnar deviation (racquet sports, golf, weight-bearing through the hand, push-ups) and by repetitive loading (gymnasts, yoga). Daily tasks such as opening jars, lifting and pushing up from a chair are affected. A subset can voluntarily reproduce the clunk.

Examination

• Inspection / palpation: usually minimal swelling; dorsal and palmar midcarpal tenderness; a dorsal capitate prominence may be felt in the VISI position.
• Range of motion: typically full; grip strength is commonly reduced relative to the contralateral side.
• Generalised laxity: formal Beighton score (thumb-to-forearm, fifth-MCP and elbow/knee hyperextension, forward flexion).
• Midcarpal shift test (Lichtman) - the key manoeuvre: with the forearm pronated and stabilised, the examiner applies a palmar-directed (volar) force on the dorsal capitate while axially loading and ulnarly deviating the wrist; reproduction of the painful clunk is positive.
• Adjuncts: the catch-up clunk on passive radial-to-ulnar deviation; the supination lift test (pain/giving-way lifting against resistance with the forearm supinated); a dorsal-palmar shear test across the midcarpal joint.

Always compare with the asymptomatic contralateral wrist, since baseline laxity is common.

The midcarpal shift is the headline manoeuvre, but the topic names two further adjuncts - the supination lift test and the dorsal-palmar shear test - that are often left undefined. They are performed and interpreted together, always against the asymptomatic side, because no single test is diagnostic.

Supination Lift Test

With the forearm fully supinated and the hands placed flat beneath a fixed table, the patient is asked to push up against the undersurface of the table (or lift a heavy fixed object) so the extended wrist loads against resistance. Reproduction of dorsal/ulnar-sided wrist pain or a sense of the wrist giving way is positive; it stresses the ulnar midcarpal and ulnocarpal region under supinated load. Importantly it is not specific to MCI - it is also positive in TFCC and distal radioulnar joint pathology - so it supports rather than makes the diagnosis.

Dorsal-Palmar Shear (Shuck) Test

The examiner stabilises the distal row/capitate and translates it dorsally and palmarly relative to the fixed proximal row and radius. Excessive translation, a painful clunk, or apprehension indicates midcarpal laxity. It is the clinical analogue of the arthroscopic midcarpal "bounce"/trampoline assessment.

Grading and Interpretation

Provocative manoeuvres are judged by the magnitude of the shift and - decisively - whether a painful clunk that reproduces the patient's symptoms is elicited. A small, painless shift is common in lax but asymptomatic wrists and does not constitute pathology.

Radiographs

Standard PA, lateral and oblique views are frequently normal. The lateral may show VISI - capitolunate angle over 15 degrees with palmar lunate tilt and scapholunate angle under 30 degrees - but only if the wrist is genuinely relaxed and neutral; inadvertent radial deviation masks it. Reference angles: capitolunate normally under 15 degrees, scapholunate normally 30-60 degrees, radiolunate around 0 degrees.

Dynamic Video Fluoroscopy (Key Confirmatory Test)

Real-time imaging through full radial-to-ulnar deviation under load captures the catch-up clunk as the proximal row shifts abruptly from VISI to neutral. It also demonstrates reducibility, the feature that separates MCI from fixed dissociative VISI. Side-by-side comparison with the opposite wrist aids interpretation in subtle cases. 4D (dynamic) CT has been described as an emerging adjunct, characterising lunate triggering and capitate subluxation along the radius-lunate-capitate axis.

MRI and Arthroscopy

MRI is usually normal in isolated MCI because the lesion is ligamentous attenuation, not rupture; its main value is excluding TFCC tears, lunotriquetral dissociation and occult fracture. Arthroscopy allows direct grading of midcarpal laxity (a "trampoline"/bounce assessment with the probe) and identification of associated pathology, and can be therapeutic (capsular shrinkage). However, neither MRI nor arthroscopy reliably confirms MCI on its own - the diagnosis remains clinical and fluoroscopic.

The differential for ulnar-sided wrist pain with mechanical symptoms is wide; the table below highlights the discriminators most often tested.

After Soft-Tissue Stabilisation

• Recurrent instability - the most frequent problem, more likely with severe generalised laxity or premature return to loaded ulnar deviation; manage by re-confirming the diagnosis, excluding missed pathology, and considering revision reefing, ligament augmentation or salvage fusion.
• Stiffness - some loss of flexion-extension (around 10-20 degrees) is expected and generally well tolerated; excessive stiffness needs directed therapy.
• Persistent pain - suggests inadequate correction, an unrecognised co-existing lesion (TFCC, LT), or progression to arthritis.
• Dorsal ganglion at the capsulodesis site, often asymptomatic.
• Neurovascular injury - dorsal sensory branches of the radial and ulnar nerves are at risk during dorsal exposure; protect them. Wound infection is uncommon.

After Limited Fusion

Non-union, hardware prominence/loosening, dorsal impingement and adjacent (radiolunate) degeneration, in addition to the inherent and substantial loss of motion.

Outcomes and Prognosis

Outcomes are variable and grade-dependent, and the evidence is Level IV throughout. Limited midcarpal fusion is the most reliable operation for pain relief but costs motion; soft-tissue stabilisation preserves motion but historically carries meaningful recurrence (Lichtman: 6 of 9 soft-tissue reconstructions failed; Wright: only 56% good/excellent overall with no surgical advantage). Modern minimally-invasive approaches report encouraging early results in small series but lack long-term and comparative data. Poor-prognosis markers: severe generalised laxity (Beighton over 7), workers' compensation/litigation, bilateral disease, high-demand sport, and unrealistic expectations.

The conservative programme repeatedly invokes dart-thrower's-motion retraining, but the concept is the biomechanical foundation of motion-preserving care in MCI and deserves explanation.

The dart-thrower's motion (DTM) is the oblique, diagonal wrist arc running from radial deviation with extension to ulnar deviation with flexion - the plane used to throw a dart, swing a hammer or pour from a jug, and the plane of most functional daily tasks. In-vivo kinematic studies show that during DTM the proximal carpal row (scaphoid and lunate) moves remarkably little relative to the radius, with the majority of the excursion occurring at the midcarpal joint through the distal row.

Relevance to MCI: the symptom-generating movement in palmar MCI is loaded pure coronal-plane radial-to-ulnar deviation with the wrist near neutral flexion - exactly the arc that lets the VISI-postured proximal row abruptly "catch up". Because DTM couples ulnar excursion with flexion, functional loading can be retrained through this diagonal plane while avoiding the terminal coronal ulnar-deviation-under-load position that triggers the clunk. DTM drills are combined with co-contraction training of the dynamic stabilisers (extensor carpi ulnaris, flexor carpi ulnaris, hypothenar muscles) to actively control the proximal row, progressing from unloaded proprioceptive work to closed-chain and sport-specific loading. The goal is a stable, pain-free functional arc, not restoration of full coronal deviation.

There are no dedicated society guidelines for MCI (AAOS, BOA/BSSH, AO, EFORT, ASSH) given its rarity and the absence of high-level evidence - practice is built on expert case series and review (Lichtman; Wright; Hargreaves). The points below summarise the global, society-agnostic consensus and where practice genuinely varies.

Global epidemiology: a rare, under-recognised instability with consistent reports of female predominance (around 4:1), young age, and generalised laxity in 60-70%. High- vs limited-resource settings: in well-resourced units, dynamic fluoroscopy, wrist arthroscopy and certified hand therapy are routine, enabling motion-preserving surgery; in limited-resource settings the diagnosis is often missed or made clinically, conservative care predominates, and surgical management - if undertaken - is more likely to be a definitive fusion than a technically demanding soft-tissue reconstruction. No implant registry captures MCI procedures specifically, reflecting the predominance of soft-tissue rather than arthroplasty surgery.

• What is the primary lesion? Historically attributed to triquetrohamate / ulnar arcuate ligament laxity, but contemporary work implicates dorsal radiocarpal (DRC) ligament insufficiency as a key driver of palmar MCI - which is why DRC tensioning features in modern procedures. The true biomechanical culprit remains debated.
• Which classification? The radiograph-based Lichtman grades coexist with Hargreaves' functional staging; because MCI is a functional instability often with normal static films, no single system is universally accepted.
• Does dynamic instability need surgery at all? A positive midcarpal shift occurs in many asymptomatic hypermobile people, so the threshold for intervention - and the reliability of provocative tests - is contested.
• Soft tissue vs fusion. Soft-tissue stabilisation preserves motion but is historically unreliable; fusion is reliable but sacrifices motion. There are no comparative or randomised trials to adjudicate, and choice is individualised.
• Role of arthroscopic thermal shrinkage. Once popular, then questioned for durability and chondral/capsular safety; newer combined techniques (shrinkage + DRC tensioning) report better early results but need validation.

Midcarpal instability (MCI) is a non-dissociative carpal instability (CIND) in which the intrinsic interosseous ligaments are intact but abnormal motion occurs between the proximal and distal carpal rows. The hallmark is a painful catch-up clunk during ulnar deviation, caused by the lax palmar midcarpal ligaments failing to control the proximal row, which sits in VISI (volar intercalated segment instability) at rest and then snaps to neutral as the wrist is loaded. Most patients are young women with generalised ligamentous laxity, and a minority have a clear post-traumatic onset. Diagnosis is primarily clinical (Lichtman midcarpal shift test) confirmed by dynamic video fluoroscopy; static radiographs are frequently normal, and arthroscopy/MRI mainly exclude other pathology. The evidence base is uniformly Level IV - there are no comparative or randomised trials. Management begins with proprioceptive rehabilitation and splinting; refractory cases are treated with soft-tissue stabilisation (dorsal capsulodesis, ligament reefing, thermal shrinkage) or, with established arthritis, limited (e.g. four-corner) fusion.