Intersection Syndrome

Intersection syndrome is an uncommon overuse disorder of the forearm.
 
==Aetiopathophysiology==
Intersection syndrome is an overuse injury caused by repetitive wrist extension. There are two forms - the more common proximal form, and less common distal form.
Proximal Intersection Syndrome
In the proximal form the affected location is where the musculotendinous junctions of the first compartment containing abductor pollicis longus (APL) and extensor pollicis brevis (EPB) cross over the tendons of the second compartment containing extensor carpi radialis longus (ECRL) and extensor carpi radialis brevis (ECRB). These two compartments intersect at an angle of approximately 60 degrees located 4-8cm proximal to Lister's tubercle. 
One theory is that the syndrome is caused by frictions between the muscle bellies of first compartment cross over the tendons of the second compartment. A second theory is that there is entrapment of muscles in the second compartment secondary to stenosis - a "stenosing tenosynovitis". 
Distal Intersection Syndrome 
There is a rarer distal intersection site that has been much more recently described than the proximal form. In the distal form the affected site is where the third extensor compartment tendon intersects with the second extensor compartment tendons. It is hypothesised that this form is related to the "biomechanical pulley effect" that Lister's tubercle has on the EPL tendon.
==Epidemiology and Risk Factors==
The condition is considered to be rare. For example in a study of 1,131 patients referred for wrist ultrasound, intersection syndrome was only identified in 21 cases (1.9%). In another study of 1,815 MRI examinations of the wrist and forearm, intersection syndrome was only identified in 3 cases (0.2%). In a prospective study of 8080 patients with arm or hand pain in Thailand, intersection syndrome was found in 30 patients (0.37%).
Most patients are male, in contrast to de Quervains. In sport-people common culprits are heavy lifting, rowing, skiing, and racket sports. The highest risk is when beginning a new sport. The dominant hand is more commonly affected. It can also occur occupationally for example in typists and carpenters.
==Clinical Features==
===History===
The pain is located radially but is slightly more proximal and dorsal than de Quervains. They will typically also report a "squeaking" sensation with wrist and thumb movement. In the prospective study where 30 patients were identified, symptoms were swelling (73.3%), crepitus (40%), pain with radial deviation (46.7%), pain with pulling (13.3%), and pain with a combination of hand movements (40%). Patients tend to present acutely.
===Examination===
Swelling and redness may be noted compared to the contralateral side. Pay careful attention to the location of tenderness to avoid misdiagnosis as de quervains - they should not be tender over the radial styloid. More prominent movement of the thumb is required to reproduce the pain in comparison to de quervains. Wrist extension and radial deviation may reproduce pain. Squeaking or crepitus may be noted at the site. Auscultation can be performed over the area of pain while the patient flexes and extends their wrist.
==Investigations==
Ultrasound and/or MRI can confirm the diagnosis.
In proximal intersection syndrome there is an effusion within the second extensor compartment tendon sheath and occasionally also within the first osseofibrous tunnel sheath. Less frequently there is oedema or a bursitis between the two tendon groups. In distal intersection syndrome common findings are tenosynovitis, soft tissue oedema, and bursitis. MRI shows peritendinous oedema.
==Diagnosis==
The diagnosis is made on clinical features, however imaging can be supportive. Some clinicians prefer confirmation on imaging due to the low prevalence.
==Differential Diagnosis==
==Treatment==
* Rest - The condition is commonly self-limited.
* Activity modification
* Bracing (wrist splint in 15 degrees extension)
* Stretching
* NSAIDs
* Injections - Corticosteroid injection into the tendon sheath of the second compartment at the area of maximal tenderness. Prolotherapy has also been described.
* Surgery. This involves release of the second extensor compartment. This is only very rarely required. In the prospective study of 30 patients, none required surgery.
==Follow Up and Prognosis==
The prognosis is generally good.
==References==
Category:Tendinopathies
Category:Hand and Wrist Conditions