Overview
They are two fibrous bands that tie the digital flexor tendons to the skeleton of the thoracic limb. By fixing the tendon below the muscle belly, the horse's weight tenses the tendon without the muscle having to contract.
- Accessory ligament of the superficial digital flexor (radial or "superior" check ligament): arises from the caudomedial surface of the distal radius and joins the superficial digital flexor tendon above the carpus.
- Accessory ligament of the deep digital flexor (carpal or "inferior" check ligament): continues the palmar carpal ligament and joins the deep digital flexor tendon at about mid-cannon.
In the pelvic limb the superficial digital flexor has no accessory ligament and that of the deep flexor is thin or absent.
Origin
- Proximal: caudomedial surface of the distal radius.
- Distal: palmar carpal ligament.
Insertion
- Proximal: superficial digital flexor tendon, proximal to the carpus.
- Distal: deep digital flexor tendon, at about mid-metacarpus.
Action
They passively transfer the load on the fetlock to the radius and carpus, and limit stretching of the muscle bellies.
Innervation
They are ligaments: they have no motor innervation.
Clinical relevance
- With the digital flexors and the interosseus medius they form the stay apparatus of the thoracic limb, which lets the horse stand for hours with little muscular effort.
- Desmitis of the accessory ligament of the deep digital flexor causes swelling at the back of the proximal third of the cannon. It is more common in ponies and older horses and is diagnosed by ultrasonography.
- Desmotomy of either ligament is used to treat flexural deformities in foals: the distal one for "club foot" and the proximal one for some fetlock deformities.