Intersection Syndrome

Inflammation and friction at the point on the dorsoradial forearm where the muscle bellies of abductor pollicis longus and extensor pollicis brevis (first dorsal compartment) cross over the tendons of extensor carpi radialis longus and brevis (second dorsal compartment). The crossing point lies about 4 to 8 cm proximal to the radiocarpal joint.

• The primary lesion is probably tenosynovitis or peritendinitis of the second compartment tendons, with oedema of the overlying muscle bellies producing a swollen, creaking area.
• It follows repetitive wrist extension and flexion against resistance: rowing and canoeing (the classic cause, hence "oarsman's wrist"), weightlifting, racket sports, skiing with pole use, horse riding, cycling, and manual work such as hammering, painting, and prolonged keyboard or tool use.
• It is much less common than de Quervain tenosynovitis. It affects men and women, usually in the third to fifth decades, and is more frequent after a sudden increase in training load or new equipment.
• Most cases settle with rest and splinting within 4 to 6 weeks.

• Pain, swelling and tenderness on the radial dorsal forearm, 4 to 8 cm proximal to the wrist, aggravated by resisted wrist extension, thumb movement, gripping and repetitive wrist motion.
• Palpable or audible crepitus (a creaking, "squeaky leather" sensation) on moving the wrist and thumb, which is the hallmark sign. Visible swelling and local warmth may be present.
• Pain does not centre on the radial styloid, and the test of ulnar deviation with the thumb flexed in the fist (pain at the radial styloid) is usually negative.
• Differential diagnosis: de Quervain tenosynovitis (first dorsal compartment, at the radial styloid), superficial radial nerve neuropraxia (numbness over the dorsum of the thumb and index finger, a positive tap test), extensor carpi radialis tendinopathy, scaphoid fracture, scapholunate ligament injury, thumb carpometacarpal osteoarthritis, lateral epicondylalgia, cervical radiculopathy (C6), septic tenosynovitis, rheumatoid tenosynovitis and gout.
• Red flags: fever, marked warmth and spreading erythema (infection), a history of trauma with snuffbox tenderness, neurological deficit, and persistent swelling with systemic features (inflammatory arthritis).
• Complications: chronic tenosynovitis, loss of grip strength, tendon rupture (rare), and recurrence with return to the provoking activity.

• Clinical, based on the site of tenderness, the crepitus and the activity history.
• X-ray of the wrist if trauma, a scaphoid injury or arthritis is possible.
• Ultrasound shows peritendinous fluid, tendon sheath thickening and increased Doppler signal at the crossing point, and confirms the diagnosis dynamically. MRI shows oedema in and between the muscle bellies and tendon sheaths, and is used when the diagnosis is uncertain.
• CRP, ESR, urate and rheumatoid serology if the swelling is persistent, bilateral or accompanied by other joint symptoms.

• Relative rest from the provoking activity for 2 to 4 weeks, and correction of technique and equipment (rowing grip and feathering, oar handle size, tool grip, keyboard and mouse set up).
• Splinting: a wrist splint holding the wrist in about 15 to 20 degrees of extension, worn day and night for 2 to 3 weeks, then during activity for a further 2 to 4 weeks. Thumb is left free.
• Ice for 10 to 15 minutes, 3 times daily, in the first days.
• Analgesia: paracetamol 1 g orally 6 hourly. Ibuprofen 400 mg orally 8 hourly with food (or naproxen 500 mg 12 hourly) for 1 to 2 weeks if no contraindication. Topical diclofenac 1% gel 2 to 4 g 3 to 4 times daily to the dorsal forearm.
• Physiotherapy after pain settles: gentle active wrist movement, then progressive wrist extensor and forearm strengthening, stretching, and graded return to activity over 3 to 6 weeks.
• Corticosteroid injection for pain that persists after 3 to 4 weeks of splinting: triamcinolone acetonide 10 to 20 mg (or methylprednisolone acetate 20 mg) with lidocaine 1% 1 to 2 mL, injected into the second compartment tendon sheath at the point of maximal tenderness, ideally under ultrasound guidance. Relief is usually rapid and often lasts months. Do not inject into the tendon substance. Limit to 1 to 2 injections. Warn about skin atrophy, depigmentation (especially in dark skin) and a rise in glucose for 3 to 5 days in diabetes.
• Surgery for failure after 3 to 6 months of well delivered conservative treatment: release of the fascia of the second extensor compartment with tenosynovectomy and decompression of the muscle bellies, with good results in most patients. Rehabilitation takes 4 to 8 weeks.
• Septic tenosynovitis: needs urgent surgical drainage and IV antibiotics.
• Special groups:
  • Athletes: graded return when pain free with full grip strength, with technique correction and strengthening before return to rowing or racket sports.
  • Pregnancy: splint, ice, paracetamol and positioning. Avoid NSAIDs after 20 weeks.
  • Diabetes: monitor glucose after injection.
  • Renal impairment and gastrointestinal disease: avoid oral NSAIDs and use topical agents.
• Follow up: review at 2 to 3 weeks and at 6 weeks. Refer to hand surgery or sports medicine for no improvement after 6 to 12 weeks, recurrent episodes, or diagnostic doubt.