Intersection syndrome (tenosynovitis of the radial wrist extensors) is a cause of radial-sided wrist and forearm pain. Multiple conditions can cause radial-sided wrist and forearm pain; the most common are de Quervain tenosynovitis and thumb carpometacarpal (CMC) arthritis.
Intersection syndrome is tenosynovitis of the radial wrist extensors, extensor carpi radialis longus (ECRL), and extensor carpi radialis brevis (ECRB). The condition also affects the extensor pollicis brevis (EPB) and the abductor pollicis longus (APL), causing pain and swelling of these muscle bellies. Intersection syndrome is characterized by pain and swelling in the distal dorsoradial forearm. [1, 2]
Intersection syndrome is much less common than de Quervain tenosynovitis, the syndrome with which it is most easily confused. Draghi and Bortolotto reported that intersection syndrome was identified in 1.9% of 1,131 hand and wrist ultrasound examinations. 
Intersection syndrome can be caused by direct trauma to the second extensor compartment. It is more commonly brought on by activities that require repetitive wrist flexion and extension.  Weightlifters, rowers, and other athletes are particularly prone to this condition. [5, 6, 7]
While this condition occurs at the intersection of the first and second extensor compartments, many contend that the condition is a tenosynovitis of the extensor carpi radialis longus (ECRL) and extensor carpi radialis brevis (ECRB) tendons. However, the condition has long been held to be caused by friction from the overlying extensor pollicis brevis (EPB) and abductor pollicis longus (APL) tendons.  Tensile and shearing stresses in the tendons and peritendinous tissues may lead to thickening, adhesions, and cellular proliferation. Subsequent swelling and proliferation of tenosynovium may cause pain, as these tissues are compressed within the unyielding second extensor compartment.
Patients with intersection syndrome complain of radial wrist or forearm pain. Symptoms may be exacerbated by repetitive wrist flexion and extension.
On examination, discrete swelling at this area of intersection often is present. Active or passive wrist motion produces a characteristic "wet leather" crepitus. The examiner must exclude other causes of radial forearm pain, such as the following:
de Quervain tenosynovitis
Thumb CMC arthritis
Radial sensory nerve irritation (Wartenberg syndrome)
Extensor pollicis longus (EPL) tendinitis
Surgery is only rarely required, when symptoms persist despite an adequate course of conservative treatment (including activity modification).
The dorsal wrist and dorsal distal forearm are divided into six extensor compartments. Intersection syndrome involves the first two compartments. The tendons of the first compartment, the abductor pollicis longus (APL) and extensor pollicis brevis (EPB), pass obliquely over (dorsal to) the extensor carpi radialis longus (ECRL) and extensor carpi radialis brevis (ECRB) in the second compartment, approximately at their musculotendinous junction. This intersection occurs dorsoradially at the junction of the middle and distal thirds of the forearm, just proximal to the extensor retinaculum.
The radial wrist extensors continue distally through the second compartment, the boundaries of which are the distal radius, two vertical septal walls, and the overlying extensor retinaculum. The ECRL and ECRB pass over the dorsal wrist capsule before inserting into the base of the index and long finger metacarpals, respectively.
Surgery is contraindicated in patients with vague nonspecific complaints or in those patients who have not received or been compliant with recommended nonoperative measures.
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