220 LAMENESS OF THE HORSE 



Open Stifle Joint. 



Anatomy of the Joint Capsule. — This joint capsule is thin 

 and very capacious. On the patella it is attached around the 

 margin of the articular surface, but on the femur the line of 

 attachment is at a varying distance from the articular surface. 

 On the medial side it is an inch or more from the articular car- 

 tilage; on the lateral side and above, about half an inch. It 

 pouches upward under the quadriceps femoris for a distance of 

 two or three inches, a pad of fat separating the capsule from the 

 muscle. Below the patella it is separated from the patellar liga- 

 ments by a thick pad of fat, but interiorly it is in contact with 

 the femerotibial capsules. The joint cavity is the most extensive 

 in the body. It usually communicates v.-ith the medial sac of 

 the femerotibial joint cavity by a slit-like opening situated at 

 the lowest part of the medial ridge of the trochlea. A similar, 

 usually smaller, communication with the lateral sac of the fe- 

 merotibial capsule is often found at the lowest part of the lat- 

 eral ridge. (Sisson's Anatomy.) 



Thus it is seen that because of its frequent communication 

 with the other parts of this large synovial membrane, a wound 

 which opens the external portion of the femerotibial capsule 

 may be the cause of contamination and resultant infectious ar- 

 thritis of the whole stifle joint. Because of the distance between 

 the most dependent part of the femerotibial articulatioii and 

 the summit of the patella, one may misjudge the exact location 

 of the lowermost part of this portion of the capsular ligament 

 of the stifle joint and thereby fail at once to appreciate the seri- 

 ousness of calk wounds in this region. 



Etiology and Occurrence. — AVounds to the patellar region 

 are of rather frequent occurrence, and because of the compara- 

 tively unprotected position of these structures, the capsular liga- 

 ments of the stifle joint may be perforated as a result of violence 

 in some form. Calk wounds which penetrate the tissues in the 

 immediate region of the lower portion of the external part of 

 the femerotibial capsule sometimes result in open joint because 

 of tissue necrosis resulting from the introduction of infection. 

 Contused wounds sometimes destroy the skin and fascia over 



