Evaluation of the passive function of the biceps brachii muscle-tendon unit in limitation of shoulder and elbow joint ranges of motion in horses.

This research examines the passive role of the biceps brachii muscle-tendon unit in limiting the range of motion in the shoulder and elbow joints of horses. It finds that this muscle-tendon unit restricts the extension of the elbow joint during the flexion of the shoulder joint and any excess extension may indicate a biceps brachii injury.

Methodology

• The research was conducted on right forelimb specimens from six Thoroughbred cadavers. These specimens included the scapula, humerus, radius-ulna, biceps brachii muscle-tendon unit, and the stabilizers of the shoulder and elbow joints.
• These specimens were mounted on a rigid board using transfixation pins through the humerus and were adjusted for mechanical manipulation. The set up also enabled the measurement of joint angle and load.
• The limits of the flexion and extension range of motion in the shoulder and elbow joints were measured individually, with the other joint being fixed to isolate movement. Measurements were made both before and after the transection of the biceps brachii muscle-tendon unit.

Findings

• Results showed that the biceps brachii muscle-tendon unit restrains the extension of the elbow joint when the shoulder joint is fixed in a flexion state, indicating that this unit plays a significant role in limiting movement.
• Similarly, this unit also limited shoulder joint flexion when the elbow joint was fixed in extension.
• It was also found that the biceps brachii muscle-tendon unit moderately inhibited shoulder joint extension when the elbow joint was fixed at mid-range angles of 75 to 90 degrees.

Conclusions

• The findings suggest that if during clinical manipulation of the horse’s joint, the elbow joint hyperextends during the flexion of the shoulder joint, it could indicate an injury in the biceps brachii muscle-tendon unit.
• This signifies the vital function of the biceps brachii muscle-tendon unit in stabilizing and limiting joint motion in horses, and its role in potential injuries.