Proximal Suspensory Desmitis in a Horse

A 10 year-old warm-blood gelding presented to PHD veterinary services for the complaint of forelimb lameness. During the lameness exam, it was noted that the gelding was moderately lame in the right front limb and the lameness appeared worse when the horse was lunged at the trot in a circle to the left. Palpation of the limb noted only mild response to pressure over the proximal suspensory ligament (back side of the limb, just below the carpus). A series of nerve and joint blocks were performed to isolate the source of the lameness. Once the proximal suspensory ligament was "blocked" the horse's lameness improved significantly. Therefore, an ultrasound exam was performed of the soft tissue structures of the right limb with emphasis on the proximal suspensory ligament. Figures 1 and 2 correspond to the proximal suspensory ligament. The yellow line outlines the body of the proximal suspensory ligament in cross-section and the blue arrows a bright (hyperechoic) lesion within the suspensory ligament. The area of increased brightness or echogenicity is consistent with an enthysophyte. In addition, the enthysophyte was surrounded by an area of decreased echogenicity consistent with edema or active inflammation. An enthysophyte is a abnormal bony projections at the site of attachment between a tendon/ligament at bone. In this case, between the proximal suspensory ligament and the third metacarpus (cannon bone).

Figure1

Figure 2

In a similar case, the horse was subjected to a CT (computed tomography) exam and the enthysophytes appear as small, spikes (blue arrows) which are projecting into the body of the suspensory ligament (yellow outline). From this view is understanding why these horses have chronic and recurring forelimb lameness issues. The presence of enthysophytes tends to worsen the prognosis with regards to return to "full" work.

Figure3

The above mentioned gelding was treated with rest, multiple PRP (platelet rich plasma) injections, and shockwave treatment. He is currently sound however his prognosis remains guarded for full return to work and show.

Hind Limb Proximal Suspensory Ligament Desmitis in a Horse

A 15 year-old mare presented for a 3 week history of rear-limb lameness that was associated with a "drop" of the rear fetlock joint. On presentation there was moderate swelling of the lower limb, just below the hock joint and the mare was lame at the walk. In addition, there was a 90 degree drop of the fetlock/pastern axis as noted in Figure 1.

Figure 1

The primary mechanism involved in "suspending" the fetlock joint and maintaining the proper fetlock/pastern axis is the suspensory ligament (Figure 2). The suspensory ligament originates just below the hock (red arrow) and initially is one structure (body) that travels down the back of the lower limb (yellow arrow). Approximately half way down the canon bone the suspensory ligament splits into a medial (inside) and lateral (outside) branch. The suspensory branches attach to the sesamoid bones which are located just behind and below the fetlock joint. As such, the suspensory ligament helps "suspend" the fetlock joint and a  proper fetlock/pastern axis.

Figure 2

An ultrasound exam was performed to evaluate the entire suspensory ligament. The origin or proximal suspensory ligament is imaged in cross-section in Figures 3-6. The proximal suspensory ligament of the affected limb is grossly enlarged (yellow circle) and the fiber pattern is a mixed pattern with significant edema and evidence of active inflammation! There is a black and grey swirl pattern noted in the proximal suspensory ligament (tissue inside the yellow circle) of the affected limb which is indicative of severe changes.

Figure 3

Figure 4

 When compared to the normal limb, the significant increase in the size of the proximal suspensory ligament is evident. In this case the affected suspensory ligament was 2x the "normal" size. These ultrasound findings confirm the diagnosis of proximal suspensory desmitis of the hind limb. The prognosis for this injury is poor for return to riding and guarded for return to pasture soundness. Once the fetlock has "dropped" the physical changes to the suspensory ligament CANNOT be reversed!! Treatment is aimed at slowing the progress of the condition and attempting to provide pain relief to the horse. In my experience, corrective shoeing is the MOST important aspect of managing this condition.

Figure 5

  

Figure 6

A "fish tail" bar shoe is strongly recommended for this condition. The shoe should be set extra full such that approximately 1.5 to 2 inches of shoe extended BEHIND the heel bulb. Any kind of a wedge is CONTRAINDICATED in this condition! In addition, daily treatment with ice packs over the proximal suspensory ligament followed by topical Surpass cream are indicated to reduce inflammation and provide pain relief. With corrective shoeing, adequate pain relief, and supervised turn-out, these horses may return to pasture soundness however such a condition carries a guarded prognosis.

Figure 7

Proximal Suspensory Desmitis in a Horse

The ultrasound images below are from a teenage gelding that presented for a 3 month history of mild, forelimb lameness. The lameness would improve with rest but would return soon after the gelding was returned to work. On physical exam, the proximal suspensory palpated sensitive, just below the carpus (knee) of the right forelimb. The gelding was not lame in a straight line however when lunged in a circle to the left, a mild lameness (2/5) was noted in the right forelimb. The lameness improved approximately 50% after blocking the lower limb however when the proximal suspensory ligament was blocked, the gelding was sound. Ultrasound exam of the tendons and ligaments revealed a focal area of decreased echogenicity (dark spot) which was consistent with inflammation and edema within the proximal suspensory ligament. 

Figure 1

Figure 2

In Figure 1, there is a cross sectional image of the superficial flexor tendon (SDF), deep digital flexor tendon (DDF), distal check ligament, and the proximal suspensory ligament. This image was made approximately 10cm below the knee or carpus. In Figure 2, the same area is imaged in cross section and in longitudinal plane. The same lesion (dark spot) can be seen in both images which is consistent with a "real" lesion versus an artifact. In the longitudinal view (right image in Figure 2), the origin of the suspensory is highlighted by the blue arrows and the edema is noted by the dark fibers just above the blue arrows. In Figure 3, the cross sectional image is slightly obliqued to visualize the inside or medial aspect of the limb. The lesion within the suspensory ligament is more apparent in this image and is represented by the dark blue circle within the yellow circle (suspensory ligament) in Figure 3.

Figure 3

Figure 4

The history and lameness exam findings are "classic" for a forelimb proximal suspensory ligament injury. Often the lameness is most noticeable when the affected limb is on the outside of the circle and the lameness will improve temporarily with rest. The prognosis for this injury is "good" however will require rest, ice therapy, corrective shoeing and a specific rehabilatory program. Adjunct therapies include shockwave treatment and platelet rich plasma (PRP) injections.