Intersection synrome is a painful condition that affects the thumb side of the forearm when inflammation occurs at the intersection of the muscle bellies of the abductor pollicis longus and extensor pollicis brevis cross over the extensor carpi radialis longus and the extensor carpi radialis brevis. The mechanism of injury is usually repetitive resisted extension, as with rowing, weight lifting, or pulling. Intersection syndrome is often confused with another condition called DeQuervain's syndrome, which is an irritation of the upper set of tendons at the wrist.