Communications between the femoropatellar, medial femorotibial, and lateral femorotibial joints were studied, using fresh equine cadaver specimens. A total of 90 specimens from 45 horses were used. Horses were randomly assigned to 3 groups with 15 horses/group. Each group was assigned an injection site (femoropatellar joint, medial femorotibial joint, or lateral femorotibial joint), and red latex was injected into the respective location of each joint in each group. Immediately after injection, the joints were flexed and extended 100 times. The stifles were frozen in slight flexion, then cut into 1-cm sagittal sections. The communications between the femoropatellar and medial and lateral femorotibial joints were determined. None of the specimens in this study had communication between afl 3 joint compartments. When the femoropatellar joint was injected, 18 of 30 joints (60%) communicated with the medial femorotibial joint, and 1 of 30 (3%) communicated with the lateral femorotibial joint. Injection of the medial femorotibial joint revealed 24 of 30 (80%) joints that communicated with the femoropatellar joint, and 1 of 30 (3%) that communicated with the lateral femorotibial joint. Injection of the lateral femorotibial joint resulted in communication with the femoropatellar joint in 1 of 30 (3%) joints. Communication did not exist between the medial and lateral femorotibial joints.

To study communications and boundaries of the middle carpal and carpometacarpal joints of the horse, 50 forelimbs were obtained from fresh cadaver specimens. Blue latex solution (20 +/- 2.5 ml) was injected into the middle carpal joint, and the specimens were frozen in extension. Frozen specimens were cut into 1-cm sagittal sections from the middle of the radius to the middle of the metacarpus. The communications between the middle carpal and carpometacarpal joints and the presence, length, and position of the distopalmar outpouchings of the carpometacarpal joint were recorded. The middle carpal and carpometacarpal joints always communicated between os carpale III (C3) and os carpale IV (C4). An additional communication between the joints existed in 17 (34%) of the specimens, 10 on the palmar aspect of C4, and 3 on the palmar aspect of os carpale II (C2). When os carpale 1 (C1) was present (n = 5), communication between C1 and C2 was observed in 4 of the 5 specimens. In all specimens, medial and lateral distopalmar outpouchings of the carpometacarpal joint were observed and were located between the axial surface of os metacarpale II (MC2) and os metacarpale IV (MC4) and the abaxial surface of the suspensory ligament. There was no significant difference between the lengths of the lateral (2.3 +/- 0.54 cm) or medial (2.6 +/- 0.75 cm) distopalmar outpouchings. Small extensions from the distopalmar outpouchings were seen and extended axially into the fibers of the suspensory ligament or between the suspensory ligament and the distal accessory ligament of the deep digital flexor tendon. In one carpus, the middle carpal joint communicated with the antebrachiocarpal joint between the articulation of the os carpi intermedium (Ci) and the os carpi ulnare (Cu).