Perilunate Dislocation

Perilunate dislocation is a dislocation of the carpus around the lunate, which stays in the lunate fossa of the radius. The capitate and the rest of the carpus move dorsally in most cases. It is a high energy injury of young adults, usually men, after a fall from height, a road traffic collision or a sporting collision.

About a quarter are missed at the first presentation. The injury lies on a spectrum from scapholunate dissociation to lunate dislocation, and it is often a fracture dislocation. The greater arc pattern passes through bone (transscaphoid perilunate fracture dislocation is the most common variant), and the lesser arc pattern passes through ligaments.

The Mayfield stages describe the progressive ligament failure around the lunate. Stage I is scapholunate disruption, stage II is capitolunate disruption (perilunate dislocation), stage III is lunotriquetral disruption, and stage IV is the lunate dislocated volarly out of its fossa.

Complications are acute carpal tunnel syndrome and median neuropathy, avascular necrosis of the lunate or proximal scaphoid, scapholunate instability, post-traumatic arthritis with carpal collapse, stiffness, complex regional pain syndrome, and tendon rupture.

Pathophysiology.

The mechanism is an axial load on a hyperextended, ulnar deviated and supinated wrist. The force passes through the radial side of the carpus, tears or fractures the scaphoid and the scapholunate ligament, then the capitolunate articulation, and finally the lunotriquetral ligament.

The volar capsule ligaments keep the lunate seated in the radius. When the lunate is stripped of them it can lose its blood supply, which produces the avascular necrosis risk.

Severe wrist pain, swelling and deformity, with loss of movement and a stiff, flexed finger posture. Numbness in the median nerve territory, thenar weakness and rising pain suggest acute carpal tunnel syndrome. Examine the skin for open wounds, and check pulses and capillary refill.

Look for other injuries in the same limb (distal radius, forearm, elbow), the spine and other high energy injuries.

• Radiographs: posteroanterior and lateral wrist. On the posteroanterior view the carpal rows overlap, the Gilula arcs are broken and a scaphoid fracture may be visible. On the lateral view the capitate lies dorsal to the lunate while the lunate stays in the radial fossa.
• CT to define scaphoid and other carpal fractures and the radius. MRI for ligament injury when the diagnosis is uncertain.
• A scapholunate gap of over 3 mm and a scapholunate angle of over 70 degrees show instability on the lateral view.
• Test median nerve function before and after reduction.

Differential diagnosis.

• Lunate dislocation (the lunate leaves the fossa).
• Scaphoid fracture and scapholunate dissociation.
• Radiocarpal dislocation and Barton fracture.
• Chauffeur fracture and Kienböck disease.

Emergency reduction. Reduce under regional block or general anaesthesia as soon as possible. Apply longitudinal traction with finger traps for about 10 minutes, extend the wrist, then press the capitate volarly while flexing the wrist (Tavernier method). Immobilise in a long arm splint with the wrist neutral. Check the median nerve and repeat radiographs.

Definitive treatment. Closed reduction alone fails to hold, so open reduction and ligament repair are needed, ideally within 7 days.

• Combined dorsal and volar approaches. Reduce and fix the scaphoid fracture with a headless compression screw (greater arc injury).
• Repair the scapholunate and lunotriquetral ligaments with suture anchors, and pin the scapholunate and lunotriquetral joints with 1.6 mm Kirschner wires.
• Decompress the carpal tunnel when there is median neuropathy or an acute carpal tunnel syndrome.
• Immobilise for 6 to 8 weeks. Remove the wires at 8 to 10 weeks, then start movement and strengthening. Heavy use is allowed at 4 to 6 months.
• Chronic injuries (over 6 weeks): proximal row carpectomy or partial wrist fusion.

Open injury.

• Give intravenous co-amoxiclav 1.2 g every 8 hours (or cefazolin 2 g every 8 hours) within 1 hour of injury.
• Continue until 24 hours after wound closure for types I and II. For type III, continue until 72 hours or 24 hours after soft tissue cover, whichever is earlier.
• Co-amoxiclav maximum is 3.6 g daily. Give every 12 hours at creatinine clearance 10 to 30 mL/min. Check liver tests in courses over 7 days.

For heavy contamination or soft tissue loss add gentamicin 5 mg/kg intravenously once daily for up to 72 hours. Check creatinine daily and a level before the second dose. Avoid it, or extend the interval, at eGFR under 60 mL/min/1.73 m2.

With severe penicillin allergy use clindamycin 600 mg intravenously every 8 hours (maximum 2.7 g daily) with gentamicin.

Give a tetanus booster 0.5 mL intramuscularly if the last dose was over 10 years ago. Add tetanus immunoglobulin 250 units intramuscularly (500 units if over 24 hours since injury or heavily contaminated) when immunisation is incomplete or unknown. Debride and stabilise within 24 hours.

Analgesia.

• Paracetamol 1 g orally every 6 hours as needed for up to 5 to 7 days (maximum 4 g daily; 3 g daily when weight is under 50 kg, with chronic alcohol use or hepatic impairment).
• Ibuprofen 400 mg orally every 8 hours with food for up to 5 days (maximum 1200 mg daily); avoid with eGFR under 30 mL/min/1.73 m2, peptic ulcer, heart failure or anticoagulant use.
• Oral morphine 5 to 10 mg every 4 hours as needed for severe pain for up to 3 days. Start 2.5 to 5 mg with age over 75 or eGFR under 30 mL/min/1.73 m2. Avoid exceeding 60 mg in 24 hours without senior review. Monitor sedation and respiration and prescribe a laxative.

Operative antibiotic prophylaxis. Give cefazolin 2 g intravenously (3 g when weight is 120 kg or over) within 60 minutes before incision as a single dose. Repeat after 4 hours or blood loss over 1500 mL. With severe penicillin allergy, give vancomycin 15 mg/kg intravenously starting 90 to 120 minutes before incision as a single dose, with levels and creatinine checked in prolonged cases.

Monitoring. Median nerve function and perfusion hourly in the first 24 hours. Radiographs at 1 week, 2 weeks, 6 weeks, 3 months, 6 months and 12 months. Carpal alignment (scapholunate gap and angle) and signs of lunate or scaphoid avascular necrosis at 3 to 12 months. Wire sites and wrist range at each visit.

Referral and escalation. Emergency referral to orthopaedics or hand surgery on diagnosis. Immediate escalation for acute carpal tunnel syndrome, open injury, skin tenting or vascular compromise.

Special groups.

• Older adults: lower energy injuries occur with osteoporosis, and bone health assessment follows.
• Multiple trauma: reduce and splint early, then fix once the patient is stable.
• Kidney impairment: avoid ibuprofen, reduce morphine doses and extend gentamicin intervals.
• Region specific: late presentation after traditional bone setting is common, and chronic injuries need salvage procedures.