Intersection Syndrome: A Review
Intersection syndrome is an uncommon overuse injury of the forearm. It is termed ‘intersection’ due the pathologic relationship at the intersection of the 1st dorsal compartment (containing the abductor pollicis longus [APL] and extensor pollicis brevis [EPB]) and the 2nd dorsal compartment (containing the ECRL, ECRB). This syndrome has also been referred to as crossover syndrome, peritendinitis crepitans, oarsmen’s wrist, squeaker’s wrist, Bugaboo forearm, adventitial bursitis, subcutaneous perimyositis, chronic synovial tendonitis, hydropsia of the tendon, and abductor pollicis longus syndrome .
Image 1. Muscles of the 1st and 2nd extensor compartments
Anatomy. Understanding the anatomy of the dorsal forearm is critical to diagnosing and managing intersection syndrome. The abductor pollicis longus (APL) muscle originates along the mid-proximal radius, ulna and interosseous membrane and inserts on the 1st metacarpal. The extensor pollicis brevis (EPB) muscle originates along the same distribution and attaches at the proximal phalanx of the thumb. Both muscles are innervated by the posterior interosseous nerve and are responsible for abduction and extension of the thumb. The two tendons form the first extensor compartment of the wrist. Note that these compartment can also cause de quervain’s tenosynovitis. The two tendons form the lateral border of the anatomical snuff box.
Epidemiology. This disease is commonly seen from repetitive microtrauma in athletes. Sports frequently implicated include rowers, weight lifters, racquet sports, canoeing. The epidemiology of this disease is poorly understood. Occupations associated with intersection syndrome include manual farming, landscaping, hammering, mechanical work .
Image 2. Illustration of the two dorsal compartments
Pathogenesis. The pathophysiology of intersection is not entirely clear. It represents a focal inflammatory process at the intersection of the two dorsal compartments. Two potential mechanisms have been proposed. The first involves friction between the two compartments with repeated use. The second postulates stenosis of the 2nd extensor compartment. The flexor retinaculum is also thought to play a role in the pathogenesis of this syndrome .
History. Patients with intersection syndrome typically report a profession or sport-related activity associated with repetitive wrist flexion and extension. Occasionally, direct trauma can also cause intersection syndrome. Patients will endorse forearm pain and tenderness at the junction of the two compartments along the dorsal forearm and wrist. There can be a history of swelling.
Physical Exam. Patients may have swelling along the dorsal radial forearm, roughly 4-6 cm or 2-3 fingerbreadths proximal to the joint. They may have crepitus over the area, especially with resisted wrist and thumb extension.
Differential Diagnosis. The differential diagnosis is fairly short and includes de quervain’s tenosynovitis, wrist ligament sprain, ganglion cyst, infection, soft tissue tumors, wartenberg’s syndrome (entrapment of the sensory branch of the radial nerve) and muscle sprain.
Image 3. Short axis ultrasound of the 2nd extensor compartment (courtesy of ultrasoundcases.info)
Image 4. Short axis cross section of MRI (courtesy of radsource.us)
Diagnostics. A combination of history and physical exam should raise suspicion for this clinical entity and narrow down the differential diagnosis. However patients with comorbidities, atypical presentations and because it is a rarely encountered disorder, clinical diagnosis can be challenging.
Management. In most cases, intersection syndrome resolves with the cessation of provocative activities and conservative management. Usually this occurs along side immobilization of the wrist, typically with splinting at 20 degrees of extension, along with NSAID administration. One study suggested that 60% of patients responded to this management within 2-3 weeks .
Summary. Intersection is a rarely encountered cause of dorsal wrist pain usually caused by friction of the 1st and 2nd dorsal compartments. Diagnosis is usually made with a combination of clinical exam and ultrasound, and in some cases MRI as well. Treatment in most cases involves conservative management, notably discontinuation of the offending activities.