Comparison of magnetic resonance contrast arthrography and arthroscopic anatomy of the equine palmar lateral outpouching of the middle carpal joint.

The objective of this report was to provide an anatomic description of the equine palmar lateral outpouching of the middle carpal joint by comparing its arthroscopic and magnetic resonance (MR) contrast arthrography appearance and to define the structures within the palmar lateral outpouching of the middle carpal joint that can be assessed arthroscopically. MR contrast arthrography was performed on seven cadaveric limbs; images were compared with those obtained during arthroscopic exploration of the palmar lateral outpouching of the middle carpal joint. Gross dissection was performed to confirm identification of intra-articular structures. The MR images compared well with the arthroscopic and gross appearance of the palmar lateral outpouching of the middle carpal joint. Portions of the ulnar carpal bone, fourth carpal bone, fourth metacarpal bone, lateral palmar intercarpal ligament, and lateral collateral ligament of the carpus were identified within the palmar lateral outpouching of the middle carpal joint in all limbs. In addition, in three limbs areas of the third carpal bone and intermediate carpal bone could be seen. MR arthrography was a useful tool for helping to define the anatomy of the palmar lateral outpouching of the middle carpal joint. The arthroscopic approach to the palmar lateral outpouching of the middle carpal joint is technically easy, but the intra-articular anatomy can be confusing. Use of a motorized arthroscopic blade to remove excess synovial tissue is necessary to view all of the structures within the palmar lateral outpouching of the middle carpal joint. Arthroscopic removal of osteochondral fragments from this location may be facilitated by the information obtained from this study.