Tenoscopic-assisted subcutaneous approach to a plantar annular ligament desmotomy in a horse with severe constriction of the fetlock canal

The desmotomy of the palmar/plantar annular ligament (PAL) is recommended when it hinders the sliding motion of the flexor tendons in the sesamoidean canal, leading to persistent lameness that often does not improve with conservative treatment. Tenoscopic-assisted PAL desmotomy can be accomplished with various instruments via an intrathecal approach. However, severe constriction or adhesions within the fetlock canal can restrict manoeuvrability and access of instruments within the sheath, preventing safe and effective transection of the ligament. This case report describes the successful use of a hook knife via a subcutaneous approach to safely transect the PAL under tenoscopic visualisation in a horse where severe constriction of the fetlock canal prohibited the standard intrathecal approach. In similar chronic tenosynovitis cases, a subcutaneous approach to PAL transection at the start of the tenoscopic examination of the digital flexor tendon sheath may minimise iatrogenic injury to intrathecal structures.