Corpus: Suspensory ligament

In clinical parlance, fetlock pastern refers to the sinewy interosseus medius muscle on the horse's forelimbs or hind limbs.

The interosseus medius muscle is referred to as the fetlock pastern because, as part of the fetlock supporting apparatus, it plays a key role in stabilising the fetlock joint.

Due to its course and its tendinous nature, the fetlock support keeps the joint in its physiological extension position, while at the same time acting as a brake on any hyperextension that goes beyond this.

The interosseus medius muscle is functionally supplemented distal to the fetlock joint by the ligamenta sesamoidea obliqua and the ligamentum sesamoideum rectum to form the so-called fetlock support apparatus.

The interosseus medius muscle originates proximally on the cannon bone (os metacarpale teritum or metatarsale teritum) and on the ligamentum carpi radiatum. It then runs as a strong tendon between the two grip bones to approximately the distal third of the metacarpus or metatarsus. In this area, the strong tendon splits into two legs, which split again.

The first split inserts on each side of the proximal sesamoid bone (Os sesamoideum proximale), while the second split runs dorsally. There they run as a supporting branch to the common extensor tendon (extensor digitalis communis muscle) to finally merge with it.

The static function of the fetlock support can be significantly impaired by various diseases and injuries. Important diseases are

• Pastern desmitis: Acute inflammatory injury to the tendon with associated lameness.
• Degenerative pastern desmitis: Chronic inflammation of the tendon leading to loss of elasticity. The lack of support in the fetlock joint leads to chronic hyperextension and ultimately to a breakdown (fetlock joint approaches the ground).

The fetlock joint can also be injured directly or indirectly by external traumatic effects. In the case of fractures of the pastern bones, an ultrasound examination of the pastern must therefore always be carried out in order to recognise and treat possible lesions at an early stage.

• Baxter GM. 2011 Adams and Stashak's Lameness In Horses. Sixth edition. Wiley-Blackwell Publishing, Ltd. ISBN: 978-0-8138-1549-7/2011.
• Salomon FV, Geyer H, Gille U (eds.). 2008. anatomy for veterinary medicine. 2nd, updated and expanded edition. Stuttgart: Enke Verlag in MVS Medizinverlage Stuttgart GmbH & Co. KG. ISBN: 978-3-8304-1075-1