Diagnosis of digital flexor tendon sheath conditions in the horse

The digital flexor tendon sheath (DFTS) is a synovial cavity occupying the distal third of the palmar metacarpus/plantar metatarsus and the palmar/plantar pastern, to the level of the middle phalanx. It contains the digital flexor tendons and helps to lubricate and stabilise their passage through the highly mobile fetlock canal and the pastern region. The proximal sheath is defined by a reflection of the sheath's synovial membrane at the junction between the middle and distal third of the metacarpus/tarsus. The dorsal sheath effaces the suspensory ligament branches, the proximal scutum and the distal sesamoidean ligaments. The distal sheath is defined by the T-ligament that borders the distal interphalangeal (DIP) joint dorsally and the navicular bursa palmarly/plantarly.

Proximal to the fetlock canal, the lateral and medial margins of the superficial digital flexor tendon (SDFT) are attached to a thin collar of tendinous tissue that wraps around the deep digital flexor tendon (DDFT), known as the manica flexoria (Findley et al, 2017) (Figure 1). The manica flexoria helps to stabilise the flexor tendons in alignment as they traverse this location. At the mid-proximal phalanx, the digital manica connects the branches of the SDFT, between the dorsal sheath wall and the DDFT (Jordana et al, 2017).