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Although the suspensory is considered a ligament, it is appropriate to discuss this structure in our tendon series since technically it is a vestigial ("existing as a rudimentary structure") tendon. To review the anatomy, the suspensory originates high on the limb near the top of the cannon bone and travels about two-thirds of the way down to the fetlock as a single structure. In the lower one-third, it splits into a lateral (outer) and medial (inner) branch that attaches to the top of the sesamoid bones. On the bottom of the sesamoids, the distal (lower) sesamoidian ligaments originate and travel distally, attaching to the pastern bone. This suspensory apparatus (the whole system described above) is vital to the support of the fetlock; abnormalities with the suspensory ligament often are associated with a "dropping" of the fetlock.
The suspensory ligament is subject to desmitis as described in the first part of this series. There often is a suspensory desmitis associated with "splints" or the fracture of a splint bone. In addition, there can be a primary desmitis associated with either the "body" of the suspensory or either of its two branches resulting from excessive stress on the ligament. This is more common in Standardbred racehorses where it has been shown that they have extra stresses placed on the suspensory ligament due to their gait. Also, several predisposing conformational factors can contribute to the stresses incurred by the suspensory; horses with long sloping pasterns and "coon-footed" conformation are generally thought to be predisposed. The term "coon-footed" refers to a broken forward axis at the coronary band. A line drawn from the fetlock down to the toe should be straight.
Another significant and frustrating problem affecting the suspensory ligament is called "degenerative suspensory ligament desmitis." This condition most commonly is seen in Peruvian Paso and Peruvian Paso crosses, but also has been observed in Arabian, American Saddlebred, National Show Horse, and American Quarter Horse breeds. I also have seen this condition in several aged Thoroughbreds, and it probably occurs sporadically in other breeds as well.
A case series describing this condition was reported in a 1993 issue of Hoofcare & Lameness, by Janice H. Young, DVM and farrier, of Cave Creek, Ariz. Young presented 12 cases of chronic suspensory desmitis that had been followed for up to five years. There were four Peruvian Pasos (two full sisters), three Peruvian Paso/Paso Fino crosses, two Arabians, one Quarter Horse, one Saddlebred, and one National Show Horse. The average age of these horses was nine years old, and ranged from five to 15. The treatment protocol used for these cases consisted of stall confinement for six to 12 months. For horses which had hind limb involvement, the hoof angle was raised with the use of "Patten" bar shoes, wedge pads, or other means. Pain relief was said to be "immediate" in these horses following this manner of shoeing. The horses with affected forelimbs had large egg bar shoes placed on the front feet. The use of elastic "sports medicine boots" also is reported to provide temporary relief when used for short periods of time.
The results of this study indicated that five (three Peruvian Pasos, two Peruvian Paso/Paso Finos) of the 12 horses were euthanized; four (two Arabians, one Saddlebred, one Quarter Horse) were pasture comfortable; one (Peruvian Paso/Paso Fino) was very lame; and one (National Show Horse) was progressing at the time of publication. One Peruvian Paso/Paso Fino cross was sound and is being used as a saddle horse.
As can be seen by Young's study, the Peruvian Paso and Peruvian Paso/Paso Fino cross had the worst outcome. This appears to support many anecdotal reports regarding the severity of this problem in these breeds. The pathology also appears to be consistent in these cases with the finding of "islands" of cartilage growing within the deteriorating ligament structure.
This condition strikes a personal note with me as my wife's horse, a 26-year-old Arabian, currently is developing this affliction. We now can sympathize and empathize with those who own or have owned horses thus affected.
Our horse is boarded at Cornell University's Equine Research Park. One night about a month ago, the director of the park contacted me with suspicions that our Arabian was acting strange--perhaps colic-like, but not really. After a physical examination, there was nothing specific regarding the abdomen, but he was depressed and had been off feed throughout the day. He would alternate lifting each hind leg, and hold it up for half a minute or so,acting like he was kicking at his belly. When walked, the horse would move very stiff behind, almost like he was tying up, but the muscles of his hind end were very supple and non-painful when palpated. Finally, when palpating his hind legs, we noted that the tendons, and in particular the suspensory ligament of both hind legs, were very sore. We thought that maybe the old guy just had had a little too much fun in the pasture and "strained" his tendons and ligaments, so we gave him some phenylbutazone and waited.
For the following three days his attitude and appetite were improved, but he still acted "funny" in his hind legs. We also noted that his hind fetlocks were getting closer to the ground. Over a period of approximately three weeks, his hind fetlocks "dropped" to the degree shown in the accompanying photographs. During that time, he required daily administration of phenylbutazone for pain control, and he was often seen "sitting" on his water bucket or feed manger in what appeared to be an attempt to reduce the weight his legs had to support. After several months of stall confinement, his comfort level improved significantly, and we moved him to a small paddock. After several more months, he is now in a large pasture and considered to be "pasture-sound." He actually is a quite-active member of the herd.
So if you have an older horse, especially of one of the breeds or crosses described above, watch for these signs. This condition does not have to be a death sentence for your horse, but he will require intense management to survive and be comfortable.
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