Arthroscopic visualisation of the third metacarpal and metatarsal condyles in the horse

Arthroscopy of the fetlock joints is a routine surgical procedure in the horse. It is unclear how much of the articular surface of the condyles of the metacarpal (MCIII)/metatarsal (MTIII) bone can be visualised using either the dorsal or palmar/plantar arthroscopic approach.

To investigate which part of the articular surface of the MCIII/MTIII condyles of the fetlock joints can be evaluated arthroscopically using: 1) dorsal approach in combination with flexion; 2) standard palmar/plantar approach; or 3) additional portal at the base of the sesamoid bone with joint extension.

All 3 arthroscopic approaches were performed on 20 fore- and 20 hindlimbs of 14 cadavers. For each approach, a curette was inserted ipsilaterally to create a lesion at the most distal part of the condyle that could be seen. After disarticulation and placement of a nail in each lesion, the maximally reachable angle was calculated on a perfect lateromedial radiograph. The 0 degrees angle was determined as the distal crossing of the best fitting circle around the condyle with a line parallel to the dorsal MCIII/MTIII bone running through the circle centre (positive angle dorsal to 0 degrees, negative palmar/plantar to 0 degrees).

Using the dorsal approach with flexion, a significantly larger area of visualisation was present in the hind- (-23.4 degrees) compared to the forelimb (+2.7 degrees). Using the palmar/plantar approach (fore: -60.4 degrees; hind: -70.7 degrees) and the approach at the base of the sesamoid bone (fore: -36.3 degrees; hind: -47.6 degrees) more cartilage could be seen in the fore- compared to the hindlimb. When combining the 3 approaches, the remaining nonvisible part measured 38.9 degrees in the fore- and 24.2 degrees in the hindlimb, both located palmaro/plantarodistally.

The use of dorsal and palmar/plantar arthroscopic approaches in combination with flexion and extension of the fetlock joint allows visualisation of the majority of the cartilage of the MCIII/MTIII condyles. The nonvisible section is smaller in the hindlimb compared to the forelimb.

Knowledge of the specific areas of visualisation of the condyles on arthroscopy is important for both diagnostic and therapeutic planning of fetlock disorders.