Sports-Related Extensor Carpi Ulnaris Pathology
Sports-Related Extensor Carpi Ulnaris Pathology
ECU is a long thin muscle located on the ulnar aspect of the forearm. It arises from the lateral epicondyle of the distal humerus and inserts at the fifth metacarpal base (figure 1). The muscle's actions vary dependent on the position of forearm rotation.
(Enlarge Image)
Figure 1.
Extensor carpi ulnaris muscle seen on the ulnar side of both of this golfer's wrists.
The ECU tendon passes through a fibro-osseous tunnel (the sixth extensor compartment) as it leaves the forearm, lying within a bony groove on the dorsal surface of the ulna. It is maintained within this groove by a retinaculum and subsheath. The structural integrity of the tendon and the fibro-osseous tunnel are essential for normal wrist mechanics and function.
The retinaculum is an extension of the dorsal retinaculum covering the other five extensor compartments but has no attachment to the ulna. The retinaculum principally prevents bowstringing of the tendon across the wrist during muscle contraction. The ECU subsheath lies deep in the retinaculum and is anchored to the distal ulna.
The ECU muscle provides a variable contribution to wrist flexion and extension dependant on forearm position. In full supination, the ECU tendon lies in a dorsal position relative to the flexion/extension axis of motion, resulting in a greater contribution to true wrist extension. In forearm pronation, the ECU tendon lies more in the palmar and ulnar positions, diminishing its contribution to wrist extension. Tendon tracking studies have shown that the excursion of ECU during extension diminishes by 60% when the forearm is positioned in neutral rotation or pronation.
This variation in position of the ECU tendon not only impacts its function, but also its relative stability. In full pronation, the ECU tendon exits the wrist in a straight direction. In forearm supination, the tendon exits the sixth compartment at an angle of approximately 30° (figure 2). Tension on the ECU retinaculum and subsheath is therefore greater during activities involving forearm supination—especially when this position is combined with wrist flexion and ulnar deviation. This combination of positions occurs particularly when holding an object tightly and close to the chest (Figure 3).
(Enlarge Image)
Figure 2.
Diagrammatic representation of the change of position of the extensor carpi ulnaris tendon between pronation and supination. There is an angulation of the tendon as it exits the subsheath in supination and flexion.
(Enlarge Image)
Figure 3.
The vulnerable extensor carpi ulnaris tendon in supination, flexion and ulnar deviation in a rugby player.
Anatomy and Function
ECU is a long thin muscle located on the ulnar aspect of the forearm. It arises from the lateral epicondyle of the distal humerus and inserts at the fifth metacarpal base (figure 1). The muscle's actions vary dependent on the position of forearm rotation.
(Enlarge Image)
Figure 1.
Extensor carpi ulnaris muscle seen on the ulnar side of both of this golfer's wrists.
The ECU tendon passes through a fibro-osseous tunnel (the sixth extensor compartment) as it leaves the forearm, lying within a bony groove on the dorsal surface of the ulna. It is maintained within this groove by a retinaculum and subsheath. The structural integrity of the tendon and the fibro-osseous tunnel are essential for normal wrist mechanics and function.
The retinaculum is an extension of the dorsal retinaculum covering the other five extensor compartments but has no attachment to the ulna. The retinaculum principally prevents bowstringing of the tendon across the wrist during muscle contraction. The ECU subsheath lies deep in the retinaculum and is anchored to the distal ulna.
The ECU muscle provides a variable contribution to wrist flexion and extension dependant on forearm position. In full supination, the ECU tendon lies in a dorsal position relative to the flexion/extension axis of motion, resulting in a greater contribution to true wrist extension. In forearm pronation, the ECU tendon lies more in the palmar and ulnar positions, diminishing its contribution to wrist extension. Tendon tracking studies have shown that the excursion of ECU during extension diminishes by 60% when the forearm is positioned in neutral rotation or pronation.
This variation in position of the ECU tendon not only impacts its function, but also its relative stability. In full pronation, the ECU tendon exits the wrist in a straight direction. In forearm supination, the tendon exits the sixth compartment at an angle of approximately 30° (figure 2). Tension on the ECU retinaculum and subsheath is therefore greater during activities involving forearm supination—especially when this position is combined with wrist flexion and ulnar deviation. This combination of positions occurs particularly when holding an object tightly and close to the chest (Figure 3).
(Enlarge Image)
Figure 2.
Diagrammatic representation of the change of position of the extensor carpi ulnaris tendon between pronation and supination. There is an angulation of the tendon as it exits the subsheath in supination and flexion.
(Enlarge Image)
Figure 3.
The vulnerable extensor carpi ulnaris tendon in supination, flexion and ulnar deviation in a rugby player.