There are a number of tendons that pass across the back (dorsal aspect) of the wrist. These tendons connect the forearm muscles to the hand bones and help to control wrist and hand movements. Each tendon passes through one of six tunnels, known as the “extensor compartments”. Intersection syndrome occurs at the junction of 2 of these compartments. The extensor compartments, from the radial (thumb) side to ulnar (pinky) side of the wrist, are made up of: Compartment 1: Abductor pollicis longus tendon (APL) and extensor pollicis brevis tendon (EPB) Compartment 2: extensor carpi radialis longus tendon (ECRL) and extensor carpi radialis brevis tendon (ECRB) Compartment 3: extensor pollicis longus tendon (EPL) Compartment 4: extensor indices tendon (EI) and extensor digitorum tendon (ED) Compartment 5: extensor digiti minimi tendon (EDM) Compartment 6: extensor carpi ulnaris tendon (ECU)