Evaluation of the passive function of the biceps brachii muscle-tendon unit in limitation of shoulder and elbow joint ranges of motion in horses.
OBJECTIVE
To quantify the passive contribution of the biceps brachii muscle-tendon unit to the limits of elbow joint extension during shoulder joint flexion in horses.


METHODS
Normal right forelimb specimens from 6 Thoroughbred cadavers.


METHODS
Specimens included the scapula, humerus, radius-ulna, biceps brachii muscle-tendon unit, and stabilizers of the shoulder and elbow joints. Specimens were mounted to a rigid board by transfixation pins through the humerus and instrumented for mechanical manipulation of the limb and joint angle and load measurements. Flexion and extension limits of shoulder and elbow joint ranges of motion were measured in each joint separately, while the other joint was fixed. Measurements were made before and after transection of the biceps brachii muscle-tendon unit.


RESULTS
The biceps brachii muscle-tendon unit limited elbow joint extension when the shoulder joint was fixed in flexion, limited shoulder joint flexion when the elbow joint was fixed in extension, and inhibited shoulder joint extension to a lesser degree when the elbow joint was fixed at midrange angles of 75 degrees to 90 degrees.


CONCLUSIONS
Clinical manipulation of the elbow joint into hyperextension during shoulder joint flexion is indicative of biceps brachii injury.
Nevens
Amy L
AL
JD Wheat Veterinary Orthopedic Research Laboratory, Department of Anatomy, Physiology, and Cell Biology, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
Stover
Susan M
SM
Hawkins
David A
DA
D000818:Animals; D001696:Biomechanical Phenomena; D005552:Forelimb / Q000502:physiology*; D006736:Horses / Q000502:physiology*; D007596:Joints / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology*; D012785:Shoulder Joint / Q000502:physiology*; D013710:Tendons / Q000502:physiology*