Skier Thumb

Skier thumb is an acute injury to the ulnar collateral ligament of the metacarpophalangeal joint of the thumb, caused by forced abduction (radial deviation) of the thumb, classically a fall onto a ski pole handle, and also from ball sports (basketball, rugby, football, goalkeeping), falls onto an outstretched hand and combat sports.

• It is the second most common ligament injury in skiers (after the knee) and accounts for about 6 to 10% of skiing injuries. It is much more common than radial collateral ligament injury.
• The ligament tears from its distal attachment at the base of the proximal phalanx in most cases, and may take an avulsion fragment of bone (in about 20 to 30%). In about 64% of complete ruptures, the torn ligament end lies on top of (proximal to) the adductor pollicis aponeurosis, which then blocks healing (the interposition lesion). Surgery is needed in these patients.
• Early diagnosis matters, because acute repair gives the best result and chronic instability leads to weak pinch, pain and arthritis.
• Chronic or repetitive injury is called gamekeeper thumb.

• Pain, swelling and bruising on the ulnar (inner) side of the thumb metacarpophalangeal joint after a fall or radial deviation force, with tenderness over the ligament, weakness of pinch, and difficulty opening jars, turning keys and gripping.
• A palpable lump on the ulnar side (a displaced ligament end or the interposition lesion) suggests a complete tear with interposition.
• Stress testing (after X-ray excludes fracture): with the metacarpophalangeal joint in full extension and in 30 degrees of flexion, apply radial stress and compare with the other thumb. Laxity above 30 to 35 degrees in total, or above 15 degrees more than the opposite side, or no firm end point suggests a complete tear. Laxity in extension suggests injury to the accessory ligament and volar plate as well.
• Grades: grade 1 (sprain, no laxity), grade 2 (partial tear, laxity with a firm end point), grade 3 (complete tear, laxity with no end point).
• Differential diagnosis: avulsion fracture or fracture of the base of the proximal phalanx, radial collateral ligament injury, fracture of the first metacarpal base, carpometacarpal dislocation, extensor pollicis longus rupture, flexor tendon injury, scaphoid fracture and arthritis.
• Red flags: open wound, deformity, numbness, a displaced fracture and an unreduced dislocation.
• Complications: chronic instability, weak pinch, post-traumatic osteoarthritis, stiffness, scar neuroma and persistent pain.

• Clinical, with X-rays first (anteroposterior, lateral, and oblique of the thumb) to exclude a fracture, because stress testing a fracture can displace it. Look for an avulsion fragment and subluxation.
• Stress testing is done after the X-ray, using a local anaesthetic (lidocaine 1% 1 to 2 mL into the joint or a median and radial nerve block) if pain prevents it.
• Ultrasound identifies the torn ligament and interposition (the torn end proximal to the adductor aponeurosis, seen as a "yo yo on a string" appearance on MRI). MRI is the most accurate test, and is used when the examination is equivocal.
• Stress X-rays (radial deviation) show joint opening above 35 degrees or 15 degrees more than the other side.

• Initial care: protect the thumb in a splint, ice for 10 to 15 minutes several times daily, elevation, and paracetamol 1 g orally 6 hourly with ibuprofen 400 mg 8 hourly with food for 1 to 2 weeks.
• Grade 1 and 2 (stable partial tears and non-displaced avulsion fractures): a thumb spica cast or a custom thermoplastic splint, immobilising the metacarpophalangeal joint and leaving the interphalangeal joint free, for 4 to 6 weeks. Then start active range of movement, followed by strengthening at 6 weeks, and a protective splint for sport and heavy work for a further 4 to 6 weeks. Return to sport takes about 8 to 12 weeks.
• Grade 3 (complete tear) and unstable injuries: surgical repair, ideally within 2 to 3 weeks (up to 6 weeks), with the best results when done early:
  • Direct repair of the ligament to its insertion with suture anchors, or reattachment through bone tunnels, with removal of the interposed aponeurosis.
  • Displaced avulsion fractures (displacement above 2 mm, rotation above 30 degrees, or a fragment involving more than 20 to 25% of the articular surface) are reduced and fixed with a small screw, wire or anchor.
  • Protect with a thumb spica cast for 4 to 6 weeks, then therapy. Return to sport takes 3 to 4 months.
  • Complications: radial digital nerve injury and numbness, stiffness, scar tenderness, residual laxity and infection.
• Corticosteroid injection into the ligament is not advised.
• Late presentation (beyond 6 weeks) with instability: ligament reconstruction with a tendon graft (palmaris longus, or a strip of another tendon), and arthrodesis for painful arthritis of the joint.
• Special groups:
  • Athletes: tape or splint for return to sport, and graded return when pain free with stable examination and pinch strength at least 90% of the other side.
  • Children: a growth plate fracture (Salter-Harris type) is more likely than a ligament tear, so X-ray carefully and refer.
  • Elderly: assess for arthritis and osteoporotic fracture, and avoid prolonged immobilisation to prevent stiffness.
  • Pregnancy: splint and paracetamol. Avoid NSAIDs after 20 weeks.
  • Anticoagulation: surgery planning with the prescriber.
• Follow up: review at 1 week to confirm the diagnosis, then at 3 to 4 weeks and at 6 weeks. Refer urgently to hand surgery for any complete tear, a palpable ulnar lump, a displaced avulsion fracture, or instability.