Magnetic Resonance Imaging of the Dorsal Proximal Synovial Plica of the Equine Metacarpo-/Metatarsophalangeal Joint.

This study aims to examine and describe the location of the synovial plica, a structure found near a horse’s fetlock joint, using Magnetic Resonance Imaging (MRI). The findings indicate that the physical characteristics and position of the synovial plica changes during hyperextension of the joint, which suggests its potential role in the interaction between the first phalanx (P1) bone and the metacarpal/metatarsal bone.

Research Methodology

• For this research, the investigators utilized 20 cadaver limbs collected from five Warmblood horses.
• They conducted Magnetic Resonance Imaging (MRI) of the fetlock joint. More specifically, they studied an area found at the dorsal proximal part of the joint called the synovial plica. This structure is present in all animals and humans and is part of the synovial membrane, which lines joint cavities.
• An important part of their methodology was the induction of hyperextension in the joint – an unusual extension of the joint beyond its normal range of motion. During this induced hyperextension, they carefully observed and described the position and behavior of the synovial plica.

Findings and Observations

• The researchers noted differences in the dorsal (backside) length of the synovial plica between the front and hind limbs and between the medial (towards the middle) and lateral (away from the middle) aspects of the joint.
• Four distinct positions of the synovial plica were observed during the study: shortened with the tip curved towards the palmar/plantar (palm/sole); projecting distally (away from the center); projecting towards the dorsal; and projecting distally with the tip positioned between P1 and the condyle (the round prominence at the end of a bone).
• While the synovial plica was in close proximity to P1 and the condyle during the induced hyperextension, its position varied, indicating that it could be a contact interface between P1 and the metacarpal/metatarsal bone.

Conclusions

• Despite the observed close interaction and variable positioning of the synovial plica during joint hyperextension, the study found that the plica doesn’t consistently act as a cushioning surface.
• This might have implications for understanding the precise function of the synovial plica in horse’s fetlocks and potentially pave the way for future studies investigating the role of synovial structures in joint health and disease.