Clinical Features and Diagnosis of Musculus Interosseus Medius Injury

There are three interossei muscles (medialis, medius and lateralis) and it is the musculus interosseus medius that has developed significantly in the horse to become the better know suspensory ligament. The medialis and lateralis muscles arise from the corresponding small metacarpal / metatarsal bones and continue distally to blend with the fascia around the metacarpophalangeal / metatarsophalangeal joints. The majority of the suspensory ligament arises from the proximopalmar/proximoplantar aspect of the third metacarpal / metatarsal bone. However, there are proximopalmar/proximoplantar attachments to C3, C4 in the forelimb and via the accessory suspensory ligament to T4 and the calcaneous in the HL and via the distal plantar ligament to T1, T3 and the sustentaculum tali in the hind limb. At the origin the fore limb proximal suspensory ligament is obviously bilobar. In the hind limb, the origin is also bilobar but the lobes are asymmetrical with a larger lateral lobe and a smaller medial lobe. The lobes in the hind limb fuse very quickly to become one structure after a very short distance. In addition to these main attachments there is now evidence of loose connective tissue attachments that exist between both the proximal and distal aspects of the suspensory ligament and the plantar aspect of the third metacarpal / metatarsal bone, between the suspensory ligament and the accessory ligament of the deep digital flexor tendon. The suspensory apparatus is divided into three parts: proximal / mid-body and the branches. The distal sesamoidean ligaments are a continuation of the suspensory apparatus distal to the level of the fetlock joint. The proximal aspect of the suspensory ligament will be discussed here. [...]