Perilunate Injuries and Carpal Dislocations

Perilunate dislocations are high-energy injuries at the most severe end of the carpal instability spectrum. Clinically the injury is usually not subtle; the subtlety is that the radiographs are often misread, and up to 25% are not diagnosed at first presentation.

Mechanism. High-energy hyperextension of the wrist. Force transmitted through the palm makes the ligaments fail in sequence, or in greater-arc injuries fractures through bone, and the energy needed to do either means these are not minor injuries.

• Motor vehicle accidents
• Falls from height
• Industrial injuries
• Sports injuries: a fall on the outstretched hand with significant force

The carpal rows. The proximal row is the scaphoid, lunate and triquetrum, with the pisiform; the distal row is the trapezium, trapezoid, capitate and hamate. The lunate is the central keystone and articulates with the radius, and the head of the capitate articulates with the lunate's concavity.

The ligaments. The scapholunate (SL) ligament connects scaphoid to lunate, and its dorsal portion is the strongest. The lunotriquetral (LT) ligament connects lunate to triquetrum. Between the lunate and the capitate, on the volar side, lies the space of Poirier, a weak area.

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Carpal malalignment. Measured on the true lateral, the normal angles are:

• Scapholunate angle about 30-60 degrees (mean ~47)
• Capitolunate angle under about 30 degrees
• Radiolunate angle under about 15 degrees

DISI (dorsal intercalated segment instability) follows scapholunate dissociation. The unrestrained lunate extends (dorsiflexes) and the scaphoid flexes, so the scapholunate angle exceeds 70 degrees, the radiolunate angle is over 15 degrees dorsal and the capitolunate angle increases. This is the pattern that follows a perilunate or SL injury.

VISI (volar intercalated segment instability) typically accompanies lunotriquetral dissociation. The lunate flexes (volarflexes), the scapholunate angle is low, under about 30 degrees, and the radiolunate tilt is volar.

Assessment must document mechanism, timing, median nerve function, skin condition and associated carpal fractures, before and after reduction.

The median nerve. Acute carpal tunnel syndrome occurs in up to 25% of cases. The dislocated carpal bones compress the median nerve in the carpal tunnel, which makes this an urgent indication for reduction, and delay risks permanent nerve damage.

Radiographs. Request PA, true lateral and oblique wrist radiographs immediately. The injury is subtle on the PA view and the diagnosis depends on sagittal carpal alignment, so do not accept a poor lateral film. If the mechanism is high energy or the radiograph shows any carpal crowding, add CT of the wrist to define greater-arc fractures and plan fixation.

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Gilula's lines. Three smooth arcs traced on the PA film. Disruption indicates carpal instability or dislocation.

• Arc 1: the proximal surface of the proximal carpal row
• Arc 2: the distal surface of the proximal carpal row
• Arc 3: the proximal surfaces of the capitate and hamate

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Algorithm

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Reduce urgently. Closed reduction is indicated for every perilunate and lunate dislocation and may be done in the emergency department under sedation. Before it, record the median nerve, skin integrity and associated injuries, and have adequate PA and lateral films.

1. Finger-trap traction for 10-15 minutes
2. Extend the wrist while applying pressure to the carpus
3. For a lunate dislocation, press directly on the dislocated lunate from the palmar side
4. Flex the wrist to lock the reduction
5. Confirm with a radiograph
6. Splint the wrist in neutral to slight flexion

After reduction, re-examine the median nerve and arrange definitive surgery.

Who needs surgery. Essentially all perilunate and lunate dislocations, even after a successful closed reduction, because closed reduction alone has unacceptable outcomes. The goals are anatomic reduction, ligament repair, fixation of any greater-arc fracture, and fixation stable enough to allow early motion. Surgery is an emergency for:

• An unreducible dislocation
• Median nerve symptoms persisting after reduction
• An open injury

The approach. Most surgeons prefer a combined dorsal and volar approach. The dorsal limb serves ligament repair (SL, LT), assessment of carpal reduction and K-wire stabilisation; the volar limb gives carpal tunnel release where needed, direct visualisation of the lunate and capitate reduction, and assessment and repair of the volar ligaments. A dorsal approach alone may be adequate for lesser-arc injuries and some surgeons use it in selected cases, but it must still achieve an adequate reduction.

Releasing the carpal tunnel: the evidence. A 2025 review devoted to this question surveyed the small literature on median neuropathy complicating perilunate dislocation and concluded that the treatment of acute median nerve compression in this setting is controversial, proposing a treatment algorithm precisely because the indication is unsettled (DOI). In many patients median symptoms settle once the carpus is reduced, which is why routine release in every case has never become doctrine.

The discriminator is what the nerve does after reduction. Document the nerve, reduce urgently, then examine it again. Symptoms that improve tell you the reduction itself was the decompression. Symptoms that persist or progress after an adequate reduction earn a formal release, and they earn it urgently. Release is also indicated when reduction cannot relieve the compression and when an open injury needs exploration.

The two errors are not symmetrical. Leaving an established, non-resolving compression undecompressed risks permanent median nerve injury, and that is the graver error; it is the one an examiner is testing when they tell you the numbness is worse the next morning. Calling release mandatory in every perilunate injury has its own cost: it commits you to a volar incision you may not need, and shows you have memorised a slogan rather than the decision. Most surgeons release routinely when they use the volar approach, so with a combined approach practice and principle often coincide without the principle being universal.

Post-traumatic arthritis is the most significant long-term complication. It affects the radiocarpal and midcarpal joints, develops despite optimal treatment and may progress despite a good initial result, although in the longest follow-up its clinical and functional impact appeared low. Treatment is activity modification and fusion procedures.

Carpal instability. The SL ligament heals poorly, and chronic SL dissociation may persist despite repair. It leads to a DISI pattern and a SLAC wrist, and may need late reconstruction or fusion.

Median nerve injury. Acute compression usually resolves with reduction. Delayed treatment carries a higher risk of permanent deficit, which may need neurolysis or secondary procedures.

Late collapse: SLAC and SNAC. The late sequel of the perilunate or SL injury is a SLAC (scapholunate advanced collapse) wrist, staged I-III. SNAC (scaphoid nonunion advanced collapse) is the analogous cascade after scaphoid nonunion, relevant to the trans-scaphoid greater-arc injury, and is staged the same way around the nonunion. The radiolunate joint is characteristically spared even in advanced disease.

Why the stage chooses the salvage. Motion-preserving salvage relies on the load-bearing radiolunate joint and the proximal capitate and lunate cartilage. PRC needs a healthy capitate head and lunate fossa, so it fails, and is contraindicated, once the capitolunate joint is arthritic. Four-corner fusion excises the scaphoid and fuses the capitate, lunate, hamate and triquetrum, and is preferred when the capitolunate joint is involved but the radiolunate joint is spared.

Principles. Fingers move from day one to prevent stiffness, and protected wrist motion starts at 2 weeks. K-wires are typically left for 8-12 weeks to allow ligament healing, the SL ligament being particularly slow to heal; they come out once adequate healing is confirmed, and before aggressive range of motion begins.

Recovery. Grip strength takes 6-12 months to recover, and the wrist needs long-term monitoring for arthritis.

Even with optimal treatment, outcomes are guarded. Counsel patients that long-term problems may develop even after good initial treatment.

The arc and prognosis. Greater-arc injuries may have better long-term outcomes than lesser-arc injuries, because bone heals better than ligament. The scaphoid fracture, once healed, provides stability; in a lesser-arc injury the SL ligament rarely heals to normal strength, and the lesser arc has historically carried the worse prognosis.

The arc is not the whole story. In Herzberg's multicentre series, open injury and delayed treatment adversely affected results.

Global epidemiology (PubMed-verifiable):

There is no orthopaedic device registry that tracks perilunate dislocation outcomes, because management relies on K-wires, screws and ligament repair rather than registered implants. Arthroplasty registries (AOANJRR in Australia, NJR in England/Wales, AJRR in the USA) therefore do not capture this injury. Evidence is confined to retrospective single-centre and multicentre series; there are no randomised trials.

Side-by-side guidance and society position (global):

Practical management across health systems: These high-energy injuries should be managed in centres with hand-surgery capability. Urgent closed reduction should be performed at the presenting centre to decompress the median nerve before transfer for definitive fixation. For any open component, antibiotic prophylaxis follows standard open-wound antimicrobial guidelines.