Role of the extensor carpi ulnaris and its sheath on dynamic carpal stability

Abstract

Ten cadaveric forearms were tested using a wrist testing apparatus specifically designed to investigate the mechanisms of muscle stabilization of the wrist. The specimens were set in a jig allowing the distal row to migrate proximally and rotate around the axis of pronosupination. The extensor carpi ulnaris (ECU) was loaded with specific weights. Reactive rotations of the scaphoid, triquetrum, and capitate were measured by an electromagnetic motion tracking device. Loading the ECU caused pronation of both proximal and distal rows. After sectioning its sheath, the overall direction of the movement remained unchanged, but there was a 40% and 50% decrease of the pronation power over the distal and proximal carpal row, respectively. In addition to stabilizing the distal radiolunar joint, the ECU is an important structure that contributes to the dynamic stability of the wrist. Furthermore, its sheath plays a crucial role in maintaining the effect of the ECU muscle on the carpus.

Assessment and Treatment of Extensor Carpi Ulnaris Tendon Pathology

“…Salva-Coll et al found that the extensor carpi ulnaris also pronates the scaphoid, triquetrum, and capitate bones when it is activated 6 . This pronation was reduced when the extensor carpi ulnaris subsheath was sectioned (p , 0.01), implying that the extensor carpi ulnaris in its intact sheath acts as an important antagonist to carpal supinators (namely, the flexor carpi ulnaris, the extensor carpi radialis longus, and the abductor pollicis brevis) 6 .…”

Demystifying Palmar Midcarpal Instability

“…34 It is based on the theory that a loss of mechanoreceptors within damaged ligaments leads to deactivation of secondary muscular support, which then manifest as carpal instability. 42 The aim of these treatments is to activate extrinsic stabilizers to substitute for the lax ligaments. Proprioceptive training involves joint position and motion sensing exercises and mirror therapy.…”

“…Neuromuscular rehabilitation targets flexor and extensor carpi ulnaris and hypothenar muscles cocontractions to drive the pisiform dorsally, and to pronate and extend the proximal carpal row reducing the palmar sag. 16,34,[42][43][44]…”

Scapholunate Instability: Proprioception and Neuromuscular Control

“…We have recently shown in a cadaver model that the APL, the extensor carpi radialis longus (ECRL), and the FCU are intracarpal supinators and protect the carpus from excessive pronation, while the FCR and the ECU are distal row pronators. [23][24][25] The balance between these stabilizes the carpus.…”

“…We also analyzed the muscular effects on the threedimensional alignment of specific carpal bones in normal cadaver wrists as well as in wrists with a complete SL dissociation. [23][24][25] In such cases, the scaphoid behaves as if it were a distal-row bone when loaded. When the ECU muscle contracts, both the distal row and the scaphoid rotate into extreme pronation.…”