The STAY-APPARATUS of the Pelvic Limb

Pelvic Stay-Apparatus

What comprises the STAY-APPARATUS?

The pelvic limb stay-apparatus has three essential elements:

1. The first component involves the stifle-locking mechanism (illustrated in GREEN). This mechanism, when engaged, enables the horse to rest its caudal body weight on the "locked" stifle joint.

2. The second element, the reciprocal mechanism (illustrated in DARK RED), ensures that the stifle and hock joints work in unison with one-another. This mechanism allows the horse to navigate the pelvic limb in a smooth and coordinated manner.

The first and second elements operate conjunctively.

3. The third element (illustrated in YELLOW) involves other ligaments/ tendons in the pelvic distal limb. These structures conduct the effects of the preceding elements to the distal pelvic limb.

What is the FUNCTION of the STAY-APPARATUS?

By employing its pelvic limb stay-apparatus, the horse is able to support its caudal body weight in the absence of appreciable muscle exertion. This mechanism is generally associated with "resting" of the hind limb(s) while in the standing position (such as when the horse is sleeping), although it is also an integral part of normal pelvic limb movement and function during exercise. Effort of the intrinsic pelvic limb muscles is reduced during engagement of the stay-apparatus, which allows the horse to move efficiently and with normal stride length and metricity (height of stride). Since tendons and ligaments do not "tire" with exercise, their engagement enhances pelvic limb stamina as well as movement.

The Atlanta Equine Clinic - 2012
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