Intersection syndrome presents with pain, swelling, and distinct crepitus in the distal dorsal forearm. This is caused by mechanical friction where the muscle bellies of the first dorsal extensor compartment cross directly over the tendons of which other compartment?

Explanation:
The correct option is a. Intersection syndrome is an overuse tenosynovitis often seen in rowers, weightlifters, and racquet sport athletes. It occurs at the 'intersection' located approximately 4 cm to 6 cm proximal to the radiocarpal joint (Lister's tubercle), where the muscle bellies of the first dorsal compartment (Abductor Pollicis Longus and Extensor Pollicis Brevis) obliquely cross over the bare tendons of the second dorsal compartment (Extensor Carpi Radialis Longus and Extensor Carpi Radialis Brevis). This location clearly distinguishes it clinically from De Quervain's tenosynovitis, which occurs precisely at the radial styloid. Reference: Campbell's Operative Orthopaedics.