Gross anatomy, computed tomographic contrast tenography, and needle endoscopy of the equine medial digital flexor tendon sheath.

Objective: To investigate the computed tomography (CT) and gross anatomy of the equine medial digital flexor tendon sheath (MDFTS), and the endoscopic anatomy and approach to the MDFTS.

Study design: Ex vivo experimental study and one clinical case.

Sample population: Twelve clinically normal cadaveric hindlimbs.

Methods: Dissection, native and contrast CT scans were conducted to evaluate the anatomy of the MDFTS. Based on these findings, the portal locations for the endoscopic approaches were determined. Six hindlimbs were used in the pilot phase and another six limbs were selected for the main study. Endoscopic images were reviewed by three observers for the quality of visualization of intrasynovial structures during endoscopy.

Results: Intrasynovial structures that could consistently be identified during dissection and CT examination included the mesotenon in the proximal recess and two synovial plicae surrounding the medial digital flexor tendon. Communication between MDFTS and tarsal sheath varied among individual horses. Two portals were necessary to visualize the complete length of the MDFTS. Endoscopic entry was possible with both a needle scope and a conventional arthroscope; however, endoscopic examination was only feasible with the needle scope. The aforementioned intrasynovial structures could also be visualized endoscopically. One clinical case is presented with septic tenosynovitis due to a laceration with penetration of the MDFTS.

Conclusion: Endoscopic examination of the MDFTS is possible with the use of a needle scope.

Clinical significance: Endoscopic lavage of the MDFTS might be indicated in cases of septic tenosynovitis of the MDFTS and/or tarsal sheath.