Midcarpal Instability

Midcarpal instability (MCI) is a non-dissociative or combined carpal instability pattern in which symptoms arise from abnormal motion between the proximal and distal carpal rows. A painful catch-up clunk during loaded deviation is characteristic, but only when it reproduces the patient's symptoms. Painless midcarpal shifting can occur in hypermobile people, and laxity alone is not disease.

Making the diagnosis. Static radiographs and MRI may be normal. The diagnosis integrates symptom reproduction, carpal alignment, dynamic imaging when useful and the exclusion of competing ulnar-sided wrist pathology: TFCC, ECU, intrinsic-ligament and DRUJ disorders. Surgery is kept for persistent, disabling, well-characterised instability.

MCI is uncommon and under-recognised. Constitutional hypermobility is common in reported cohorts, but the exact female-predominance and generalised-laxity percentages come from small referral series and vary from series to series. Some patients report trauma, and some have bilateral findings.

Natural history is heterogeneous. Progression to arthritis is not inevitable.

Two rows. The proximal row is an intercalated segment whose position reflects ligament balance, contact forces and distal-row motion. During normal radial-ulnar deviation and dart-thrower's motion, the scaphoid, lunate and triquetrum rotate and translate in coupled but non-identical patterns.

The stabilisers. The palmar midcarpal, dorsal radiocarpal, dorsal intercarpal and ulnocarpal ligaments all contribute to row-to-row stability, and the status of both the intrinsic and the extrinsic restraints is assessed rather than assumed. MCI is heterogeneous, so avoid attributing every symptomatic clunk to a single arcuate-ligament lesion.

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The catch-up shift. A symptomatic shift may occur when the proximal row moves abruptly during loaded deviation. The starting posture, direction and ligament contribution vary among palmar, dorsal and combined phenotypes, so the clunk should not be described as one universal VISI-to-neutral mechanism.

Lichtman. The Lichtman framework is a historical description of palmar MCI by severity and reducibility, and should not be treated as a validated treatment ladder. It runs from Grade I (dynamic: VISI only with provocation) through Grade II (static reducible: VISI at rest that corrects with radial deviation) and Grade III (static irreducible: persistent VISI) to Grade IV (midcarpal arthritis). The table sets out four descriptive phenotypes.

Hargreaves. Hargreaves proposed a functional staging, based on the extent of palmar translation of the distal row, as better suited to a functional instability.

Direction and function. Palmar, dorsal and combined midcarpal shifts have been described, and extrinsic and intrinsic restraint abnormalities often overlap. Direction, reducibility, symptom reproduction and cartilage status are more useful than a rigid percentage distribution of subtypes.

History. Patients describe ulnar-sided wrist pain, often with an audible or palpable clunk or 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, and a subset of patients can reproduce the clunk voluntarily.

Examination. Swelling is usually minimal. There is dorsal and palmar midcarpal tenderness, and a dorsal capitate prominence may be felt in the VISI position. Range of motion is typically full, while grip strength is commonly reduced relative to the contralateral side.

Generalised laxity. Record a formal Beighton score: thumb-to-forearm, fifth-MCP and elbow/knee hyperextension, and forward flexion. Generalised laxity is a modifier, not a diagnosis.

No single test is diagnostic. The midcarpal shift test is the headline manoeuvre and the others are adjuncts; they are performed and interpreted together, always against the asymptomatic contralateral wrist, because baseline laxity is common.

Midcarpal shift test (Lichtman). With the forearm pronated and stabilised, the examiner applies a palmar-directed force on the dorsal capitate while axially loading and ulnarly deviating the wrist. Reproduction of the painful clunk is positive. The catch-up clunk can also be sought on passive radial-to-ulnar deviation.

Supination lift test. With the forearm fully supinated and the hands flat beneath a fixed table, the patient pushes up against its undersurface, or lifts a heavy fixed object, so that the extended wrist loads against resistance. Dorsal or ulnar-sided wrist pain, or a sense of the wrist giving way, is positive; the test stresses the ulnar midcarpal and ulnocarpal region under supinated load. It is also positive in TFCC and distal radioulnar joint pathology, so it supports the diagnosis rather than makes it.

Dorsal-palmar shear (shuck) test. The examiner stabilises the distal row and capitate and translates it dorsally and palmarly across the midcarpal joint, 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" or trampoline assessment.

Reading the result. Each manoeuvre is judged by the magnitude of the shift and, decisively, by whether it elicits a painful clunk that reproduces the patient's symptoms.

Radiographs. Static PA, lateral and oblique views may be normal. On the PA, the Gilula arcs screen row congruity but may remain normal in dynamic instability. On a true lateral, evaluate radius-lunate-capitate alignment and the scapholunate and capitolunate relationships without relying on one angle in isolation; a well-positioned normal lateral is the reference.

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Dynamic imaging. Video fluoroscopy or 4D CT may demonstrate the symptomatic shift and its reducibility when the clinical diagnosis remains uncertain. Comparison with the opposite wrist helps, but constitutional bilateral laxity can limit it. Dynamic analysis measures lunate rotation and translation relative to the radius rather than relying on one static angle.

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MRI evaluates the intrinsic ligaments, TFCC, cartilage, occult fracture and other causes, but may not show dynamic laxity. Like arthroscopy, it is not diagnostic without clinical correlation.

Arthroscopy directly examines the intervals, including their congruity and probe passage, together with the cartilage and any associated ligament lesions. It is also the route for thermal capsular shrinkage (see Management).

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

First line for every grade. Conservative care is first-line for all grades and may be definitive in dynamic (Grade I) and static reducible (Grade II) disease. The core is a structured hand-therapy programme:

• Dynamic stabilisers: strengthening and co-contraction training of extensor carpi ulnaris, flexor carpi ulnaris and the hypothenar muscles, to control the proximal row actively
• Proprioceptive and dart-thrower's-motion retraining, progressed from unloaded proprioceptive work to closed-chain and sport-specific loading
• Orthoses that block terminal palmar flexion and ulnar deviation, holding a slight radial-deviation and extension posture, reduce provocation; a custom "ulnar boost" orthosis that supports the pisotriquetral complex has been described specifically for CIND
• Activity modification to avoid loaded ulnar deviation

NSAIDs give only short-term relief. Corticosteroid injection has no role and may weaken already-attenuated ligaments.

The dart-thrower's plane. The dart-thrower's motion (DTM) is the oblique arc 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 row (scaphoid and lunate) moves remarkably little relative to the radius, behaving as a near-stationary intercalated segment, and most of the excursion occurs at the midcarpal joint through the distal row.

Why it protects. 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 the diagonal plane while avoiding the terminal coronal ulnar-deviation-under-load position that triggers the clunk. The goal is a stable, pain-free functional arc, not restoration of full coronal deviation.

When to operate. Surgery is considered when a genuine, supervised conservative trial fails, symptoms meaningfully limit function or sport, and dynamic imaging confirms reducible instability. The trial typically runs 3-6 months, although its duration and progression follow the patient's response rather than a fixed calendar. Counsel candidly: the literature is Level IV and soft-tissue procedures have historically been unreliable.

Relative contraindications. Very severe generalised laxity (e.g. Beighton over 7) predicts recurrence. Active workers' compensation or litigation, psychiatric comorbidity and unrealistic expectations all predict poorer outcomes.

Soft-tissue stabilisation. The shared aim is to limit excessive palmar flexion of the proximal row while preserving motion. Dorsal capsulodesis advances a distally based dorsal capsular flap and reefs the dorsal restraints. Described variants tension the dorsal radiocarpal ligament, advance the ulnar arm of the arcuate (triquetrohamate-capitate) ligament, or both; arcuate advancement was the most successful soft-tissue option in Lichtman's original series.

What it costs. Roughly 10-20 degrees of flexion-extension is traded for stability, and recurrence is well recognised, particularly in markedly lax wrists.

Salvage arthrodesis. Four-corner fusion, usually with scaphoid excision, is reserved for Grade IV MCI with established midcarpal arthritis or for failed stabilisation, and its stability is durable. Total wrist arthrodesis is the last resort for pan-carpal arthritis or repeated failures, eliminating motion but providing a stable, pain-free wrist.

1. Confirm symptomatic instability. Reproduce the patient's pain and clunk, assess both wrists and exclude TFCC, ECU, DRUJ, intrinsic-ligament and neurological causes. Use dynamic imaging when it will resolve uncertainty.
2. Individual rehabilitation trial. Education, load modification, an activity-blocking orthosis when useful, and proprioceptive and dynamic-stabiliser retraining.
3. Persistent reducible instability. Confirm the dominant direction and the deficient restraints before considering arthroscopic or open soft-tissue stabilisation. The evidence does not establish one preferred procedure.
4. Fixed malalignment, arthritis or failed stabilisation. Reassess the cartilage and the complete instability pattern; a selected limited fusion or other salvage may trade pain relief for motion.

After soft-tissue stabilisation.

• Recurrent instability is the most frequent problem, more likely with severe generalised laxity or a premature return to loaded ulnar deviation. Re-confirm the diagnosis, exclude missed pathology, and consider revision reefing, ligament augmentation or salvage fusion.
• Stiffness: the expected loss of flexion-extension is generally well tolerated; excessive stiffness needs directed therapy.
• Persistent pain suggests inadequate correction, an unrecognised coexisting lesion (TFCC, LT) or progression to arthritis.
• Dorsal ganglion at the capsulodesis site, often asymptomatic.
• Neurovascular injury: the dorsal sensory branches of the radial and ulnar nerves are at risk during dorsal exposure and must be protected. Wound infection is uncommon.

After limited fusion. On top of the inherent and substantial loss of motion, the complications are non-union, hardware prominence or loosening, dorsal impingement and adjacent (radiolunate) degeneration.

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: in Lichtman's series 6 of 9 soft-tissue reconstructions failed, and Wright reported only 56% good or excellent results overall, with no surgical advantage.

Newer techniques. Modern minimally invasive approaches report encouraging early results in small series but lack long-term and comparative data.

Prognosis. Severe generalised laxity, workers' compensation or litigation, bilateral disease, high-demand sport and unrealistic expectations all mark a poorer prognosis.

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? MCI was historically attributed to triquetrohamate or 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? Because MCI is a functional instability, often with normal static films, neither the radiograph-based Lichtman grades nor Hargreaves' functional staging 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 the provocative tests, are contested.

Soft tissue or fusion? There are no comparative or randomised trials to adjudicate between motion-preserving but historically unreliable soft-tissue stabilisation and reliable but motion-sacrificing fusion, and the choice is individualised.

Arthroscopic thermal shrinkage. Once popular, it was then questioned for durability and for chondral and capsular safety. Newer combined techniques (shrinkage with DRC tensioning) report better early results but need validation.