Equine Gait Abnormalities as a Diagnostic Tool
Stringhalt (seen here) often develops secondary to lateral digital extensor tendon. Scarring of that tendon can interfere with proper sensory input from the area, essentially telling the horse's body to put more force behind each step than it needs.
Photo: Peter Huntington
Some gait abnormalities are obvious, while others are hardly noticeable. Either way, they can indicate a variety of equine disorders. At the 2012 Western Veterinary Conference, held Feb. 19-23 in Las Vegas, Nev., one veterinarian discussed how some gait abnormalities can point to specific health problems.
"Evaluating how a lame horse moves may not reveal the specific source of lameness for every problem, but several disorders produce a characteristic stride pattern that should not be mistaken," said Robert L. Linford, DVM, PhD, Dipl. ACVS, a professor in the Department of Clinical Sciences at the Mississippi State University College of Veterinary Medicine.
Using a case study approach, Linford took the veterinary audience through these characteristic gait abnormalities.
Case 1--Linford described one case involving a horse seen playing in his pasture before turning up lame shortly after. He had no outward evidence of trauma but showed significant lameness in the left foreleg, and his left shoulder appeared to rotate when bearing weight on that leg. What's wrong with this horse?
After some guesses from the audience, Linford revealed that this gait abnormality is characteristic of a suprascapular nerve injury. This type of injury occurs when the suprascapular nerve is crushed against the edge of the scapula (shoulder blade), often via trauma when a horse's shoulder collides with a gate post or other solid object, he said. Muscle paralysis (which later becomes visible as atrophy) at the sight of the injury renders the shoulder unstable, resulting in a characteristic shoulder roll during weight bearing.
Linford explained that if these cases are caught quickly, veterinarians can inject steroids where the nerve crosses the front edge of the scapula, sometimes bringing horses back to normal. If a steroid injection isn't successful in treating the nerve damage, the owner should maintain the horse on stall rest to reduce movement (sometimes for up to 12 months): "The nerve is reinjured every time it's stretched," Linford noted.
Linford said that on average, about two-thirds of affected horses return to soundness with an average of six months stall confinement. If horses do not become sound enough for work after 12 months confinement, they're usually sound enough to be comfortable in pasture, he noted.
Case 2--Linford's next case involved a horse that recovered from general anesthesia (for an unrelated procedure) with a nonweight-bearing lameness in a foreleg. He noted the horse wasn't able to extend his elbow or use his triceps muscles in the affected leg. What's wrong with this horse?
"This is a bad injury if it happens," Linford relayed when he identified the problem as radial nerve paralysis. When radial nerve paralysis follows general anesthesia, it's likely incurred due to improper positing of the horse (with the down leg pulled well forward of the rib cage) or padded while in lateral recumbency (positioned on his side). As a result, the radial nerve can become pinched between the humerus and the rib cage.
Corticosteroid injections might help reduce local inflammation, Linford explained, and veterinarians can use a sling to support the horse's weight if it's well tolerated. Proper nerve function can take months recover, he added.
"The outcome is typically poor if nerve function fails to redevelop in six weeks," Linford said. "There typically isn't a good prognosis."
Case 3--The third case Linford discussed involved another horse recovering from general anesthesia with a different gait abnormality. This horse was unable to extend his hind limbs fully after recovery and couldn't support the weight of his hind end, Linford explained, which resulted in a crouched stance. What's wrong with this horse?
Similar to the previous case, a nerve injury was the root of this horse's issues. This characteristic abnormality is caused by femoral nerve damage. Linford explained that this occurs when the horse is positioned lying on his back with the hind limbs remaining fully extended during general anesthesia. (To prevent the problem, he said, ensure the horse's hind legs remain flexed or are periodically flexed when the horse is positioned in dorsal recumbency.)
Unlike radial nerve paralysis, femoral nerve damage is relatively transient and typically doesn't leave any lasting damage, Linford said. He suggested sedating or reanesthetizing the horse until nerve function returns, usually within two to three hours, and treating the animal with corticosteroids to aid in recovery.
"They typically come back from this," he said. "But it's scary when it happens."
Case 4--Before introducing attendees to Case 4, Linford described a case in which a horse's owner called a veterinarian, complaining that the horse wasn't able to extend his hind leg out backwards when his stifle was flexed. What's wrong with this horse?
Absolutely nothing; the horse was perfectly healthy.
As Linford explained, horses' hind legs include a reciprocal and a stay apparatus, which allows them to essentially lock their leg in place to rest. Due to ligamentous connections, movements of the stifle and hock joints are synchronous. So when the stifle is flexed, it is impossible to extend the hock, unless one of the ligamentous connections is damaged.
Keeping that in mind, attendees listened as Linford described a horse that presented with acute lameness following an injury and the ability to extend the hock with the stifle flexed. What's wrong with this horse?
Linford relayed this horse had a peroneus tertius tendon rupture. The peroneus tertius tendon causes the hock to flex when the stifle flexes and is part of the reciprocal apparatus. This tendon is commonly injured when a horse's hind limb is put in a full cast to treat another condition, he noted, or during traumatic hind limb entanglements.
This particular injury has a relatively good prognosis, he said. Most horses require stall rest for about three months and then a very gradual return to work. On average, these horses are out of strenuous work for 10 to 12 months.
Linford stressed that if a horse with an injury of this nature isn't confined, the lesion will eventually turn chronic. At that point, there is little to no chance of the tendon healing properly.
Case 5--Conversely, Linford's next case wasn't able to extend his hock following an injury, even when his stifle was properly extended. He was nonweight-bearing lame on the affected leg, he added. What's wrong with this horse?
This display is characteristic of a superficial digital flexor tendon (which forms part of the Achilles tendon along the back of the gaskin, before running distantly along the back of the cannon bone) or gastrocnemius tendon (which also forms part of the Achilles tendon) rupture, he said.
Foals have a fair prognosis for recovery, Linford said, but mature horses have a "grave" prognosis, because the ends of the torn tendons are pulled further apart every time the horse bears weight on the limb. For the ruptured tendons to heal, the hock must be stabilized in extension or horse must be kept from bearing weight on the affected limb. Tendon healing takes several months, he explained, and while some horses can rely on a sling to help them heal, many don't tolerate the sling or other methods of supporting the hind limb very well; thus, the prognosis is poor.
Case 6--Next Linford discussed a case in which a horse was confined to a stall to rehabilitate a forelimb injury. Once the animal was released from stall rest, his owners noted lameness in his hind limb. His stifle and hock appeared to temporarily lock in extension and then his stifle seemed to "pop" and his leg "flicked" up with each step. What's wrong with this horse?
Attendees correctly diagnosed the animal with intermittent upward fixation of the patella. Three large ligaments, which are several inches long, run in a vertical direction connecting the lower aspect of the patella to the tibia. Sometimes the inside (medial) ligament gets hooked over a knob on the end of the femur. When this happens the leg locks in extension and is dragged behind the horse with the toe facing downward as the horse tries to move forward. When the ligament suddenly slips off into a normal position, the patella pops forward and the leg immediately jerks into flexion.
Several treatment options are available for this condition, Linford said:
- Some horses will respond well to simple exercises, Linford said. He suggested trotting the horse up hills or in soft footing for 15 to 20 minutes, twice daily, for several weeks. This will help "tone up" the ligaments in the stifle that are often stretched or lax in affected horses, he added;
- In conjunction with the exercise, a counter irritant injection can help thicken and strengthen the medial ligament, which is often stretched or lax when a horse suffers from the condition; and
- Medial patellar ligament desmoplasty is a procedure in which numerous small longitudinal stab incisions are made in the medial ligament of the patella (similar to what is done during tendon splitting); this procedure has been shown to thicken and strengthen the ligament. Again, he suggested using this treatment concurrently with exercise.
Linford stressed that medial patellar desmotomy is no longer advocated, except as a very last resort. During this surgery the medial patellar ligament is completely cut near its attachment to the tibia. The procedure was once routinely recommended, he explained, but has been shown to produce fragmentation of the patella at the middle ligament attachment, which causes a prominent lameness in a significant percentage of performance horses.
Case 7--Linford then discussed a horse that presented with an unusual hind limb gait in which he repeatedly overflexed the hock and stifle, essentially giving the appearance he was always stepping over something. What's wrong with this horse?
Attendees quickly diagnosed this horse with stringhalt. Linford explained that there are two common causes of stringhalt:
- In many cases the disorder develops secondary to lateral digital extensor tendon (located in the gaskin) injury. He explained that scarring of the tendon can interfere with proper sensory input from the area, essentially telling the horse's body to put more force behind each step than it needs. Linford recommends treating these horses with a myotenectomy (surgical resection of part of the affected muscle and the tendon of insertion) of the lateral digital extensor to improve the gait. The prognosis the horse will return to normal is fair, he said.
- Conversely, stringhalt can also results from ingesting Hypochoeris radicata, also known as false dandelion, Linford said. In these cases multiple horses turned out in the same field are often affected, and the condition often affects both hind legs. Although it might take several months for horses to recover from this type of stringhalt, removing the offending plant from the animals' diet often does the trick. Linford said that 15 to 25 mg/kg of phenytoin administered orally once or twice daily might help the recovery process along.
Case 8--The final case Linford discussed involved a horse that, six months prior to presentation, had been severely entangled in a rope. The horse exhibited lameness for two months prior to presentation. What's wrong with this horse?
Linford relayed this horse was suffering from fibrotic myopathy, which occurs when a restrictive scar develops in the musculature and/or the fascia in the rear thigh (the fascia is a single structural entity that extends from the tip of the horse's ears to his feet and supports and envelops every organ of the body).
For horses with mild scarring, Linford estimated a 70% success rate for treating the disorder by cutting the scarred tendon. With excessive scarring, he noted, there is minimal chance the lameness will improve.
As Linford noted, not every gait abnormality or lameness is indicative of a specific problem. However, knowing which abnormalities are characteristic of specific problems can aid in implementing treatment early. It's advisable to contact a veterinarian if a horse develops a gait abnormality, as Linford pointed out some lamenesses can indicate a serious condition.
About the Author
Erica Larson, news editor, holds a degree in journalism with an external specialty in equine science from Michigan State University in East Lansing. A Massachusetts native, she grew up in the saddle and has dabbled in a variety of disciplines including foxhunting, saddle seat, and mounted games. Currently, Erica competes in three-day eventing with her OTTB, Dorado.