The fifth compartment is located above the distal radioulnar joint and houses the extensor digiti minimi tendon (usually comprised of two slips). The fourth compartment is quite wide and contains the extensor digitorum tendons and, deep to it, the extensor indicis tendon. This represents the second intersection between the deep and superficial extensor layers. Second compartment by Lister’s tubercle, contains the extensor pollicis longus tendon before it crosses over the tendons of the second compartment en route to its final attachment site on the thumb. The third compartment, separated from the The second compartment contains the extensor carpi radialis longus and extensor carpi radialis brevis tendons.
At the junction of Zones VII and VIII, the first compartment tendons cross over those of the second compartment, forming the first intersection between the deep and superficial extensor layers ( Fig. In Zone VIII, the first extensor compartment tendons reside in a position ulnar to the tendons of the second extensor compartment. The first compartment contains the abductor pollicis longus and extensor pollicis brevis tendons with the floor comprised of the radial styloid process and insertion of the brachioradialis muscle.
The tendons are lined by a synovial sheath allowing them to glide easily within their respective compartments. The infratendinous layer is limited to the most ulnar area, whereas the supratendinous layer forms six septa that insert onto the radius producing the extensor compartments. This retinaculum is derived from the deep parts of the antebrachial fascia and consists of a supra- and infratendinous layer. In Zone VII, the wrist extensor compartments are six in number with their corresponding tendons invested within the extensor retinaculum, a strong fascial envelope derived from the antebrachial fascia that anchors the tendons in place and restricts their motion ( Fig.
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