Intersection Syndrome: A Review
Introduction. 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 .
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.
The extensor carpi radialis longus (ECRL) muscle originates at the lateral supracondylar ridge of the humerus and attaches distally to the 2nd metacarpal. The extensor carpi radialis brevis (ECRB) originates at the lateral epicondyle and helps form the common extensor tendon and attaches distally to the 3rd metacarpal. Both muscles are innervated by the radial nerve and are responsible for abduction and extension of the hand. These two tendons form the second dorsal compartment of the wrist. Generally these two muscles share a common tendon sheath, although there is an anatomic variant where they each have their own tendon sheath.
The APL and EPB muscles sit deep within the forearm moving from the ulnar side along the dorsal forearm to become more superficial as the become tendinous and attach to the thumb. As this occurs, they cross over ECRL and ECRB tendon sheaths moving proximal to distal to forearm the second extensor compartment. This intersection of the two muscle groups typically occurs 4-8 cm proximal to lister's tubercle. At this point the two compartments are arranged at an angle of approximately 60 degrees.
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 .
The incidence and prevalence of intersection syndrome is poorly understood. This is due to multiple factors including distal forearm pain is a rare chief complaint, unrecognized or missed diagnosis, and most cases are self limited. In the general population, the prevalence varies between 0.20% and 0.37% . In one group of alpine skiers, the prevalence was estimated to be 21% . In a factory employing 12,000 people in 1951, the incidence was found to be 0.33% .
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 .
Two categories of intersection syndrome have been proposed. Proximal intersection syndrome represents the classical presentation with pain at the crossover point of the 1st and 2nd dorsal compartments. Distal intersection syndrome refers to tenosynovitis of the EPL tendon as it crosses the ECRL and ECRB tendons.
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.
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.
Radiographs are not indicated in the diagnosis of intersection syndrome but may be useful to evaluate for other etiologies of pain. Ultrasound is a safe, cheap and non-invasive method of evaluating the dorsal forearm and wrist in cases of suspected intersection syndrome and useful to exclude other pathology as well. Thus ultrasound will typically be performed first on patients when it is available. Ultrasound will show peritendinous edema and fluid within the tendon sheaths of the 1st and 2nd dorsal compartments. MRI remains the gold standard for diagnosis of this disease. Typically, this will reveal peritendinous edema or fluid within the 1st or 2nd extensor compartments.
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 .
Physical therapy is targeted at wrist range of motion and strengthening wrist extensors. Physical therapy should begin at completion of the healing process and removal of the splint. In refractory cases or in select cases of athletes looking to compete, anesthetic and steroids can be used to help alleviate symptoms. This is typically performed under ultrasound guidance and aimed at the 2nd extensor compartment. In one case series of 5 patients, kinesiology taping daily for 3 weeks improved symptoms and function for up to 1 year from initial consultation .
Surgical release is rarely indicated and only when conservative therapy fails. Surgical management involves tenosynovectomy aka release of the 2nd dorsal compartment approximately 6 cm proximal to radial styloid. Fasciotomy of the abductor pollicis longus muscle can also be performed.
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.
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