Hind End Hitch


While there are any number of ailments and injuries that can cause a horse to “go off” behind, some neurological and mechanical problems create specific abnormalities of movement you can learn to distinguish – if you know what to look for. The following guide will help you recognize the abnormalities caused by three ailments often mistaken for one another: upward fixation of the patella (UFP), shivers, and stringhalt. I’ve even included video links so that you can check out the differences for yourself!

UPWARD FIXATION OF THE PATELLA

Incidence: Fairly common
Etiology: Mechanical, possibly linked to conformation in some cases
Breeds affected: Any

What it is: When in a standing position, the horse has the ability to temporarily “lock” or fixate its stifle joints, allowing the horse to stand and even sleep standing up with minimal muscular exertion.  The joint locks when the patella (knee cap) slides into the upward position, and the medial patellar ligament  (MPL) shifts slightly to the inside and hooks over a notch in the medial femoral trochlea, a knob-like structure located at the bottom end of the femur.  The patella is then fixed in its upward position, keeping the limb extended. Fixation only becomes a problem when the locking mechanism doesn’t release properly when the limb needs to flex.   
There are a variety of factors that may contribute to UFP, but one of the most common is thought to be a lack of tone or condition in the muscles and ligaments in the stifle area In the most extreme cases of UFP, the horse is completely unable to flex the affected leg without assistance.  In the mildest cases of UFP, there is only a brief delay in flexion, without any actual locking of the limb. Horses with UFP may  fall anywhere in between mild and severe. Locking or less severe “catching” may be intermittent. 
UFP is usually present in both stifles, though symptoms are generally seen only on one side.  Examination most often shows that the other side is strongly predisposed to develop the problem, and it is not unusual for the “good” side to become symptomatic after treatment of the initially affected side. 

             What it looks like: The most severe cases of UFP are easy to distinguish: the “locked” leg will hyperextend (stick out behind the horse), and cannot release forward. In moderate cases where the leg “catches” noticeably at times but releases on its own, the leg will remain extended behind the horse for longer than normal, then “pop” out of the locked position, often with exaggerated flexion of the hock. There may actually be an audible pop or click when this occurs. Very mild cases can easily go undetected, as there may not be any observable abnormality in the gait. What you may notice instead is that the horse is reluctant to perform movements that require it to push off with or increase flexion of the affected limb. Whatever the severity, it is quite common for signs of UFP to come and go.
              Because of its variability, some cases of UFP can be difficult to diagnose. “The most common way UFP is identified is by manually pushing the patella up into the fixed position and then having the horse take a step forward,” says equine surgeon and lameness expert, Dr. Dennis Meagher, DVM, PhD, Dipl. ACVS, Professor Emeritus at UC Davis. “If the horse is normal, the patella will unlock once the horse takes a step forward.  But if they are having problems with it catching intermittently, you can usually make it catch manually.  In some cases, it is also possible to feel sort of a clicking or catching if you keep your hand on the area as the horse is walked forward.”
              Prognosis: The prognosis in most cases of UFP is very good. Mild to moderate cases can often be improved with a program of specific exercises, and if that doesn’t work, success is often achieved with counterirritant injections or acupuncture. Severe cases or those that don’t respond to conservative treatment can usually be corrected with a simple, minimally invasive surgery known as ultrasound guided splitting of the medial patellar ligament. This surgery is a great improvement over the older method of desmotomy, which cuts the ligament entirely and has the potential for serious complications down the line.
              Most often confused with: Moderate cases of UFP are often confused with stringhalt (see below), as the hyperextension of the limb can release into hyperflexion, which looks somewhat similar to the hyperflexion caused by stringhalt.

Video links: https://www.youtube.com/watch?v=A8uloBlHDZ8  (moderate)
                      https://www.youtube.com/watch?v=VmEMdcMyGr4 (more severe)

SHIVERS

Incidence: Fairly uncommon
Etiology: Unknown, possibly neurological
Breeds affected: Mainly draft horses, but can occur in QHs, warmbloods, TBs

            What it is: There are several theories as to what type of ailment shivers is. While it is generally categorized as a neuromuscular problem, the cause has yet to be determined. Some researchers believe neuropathy is involved, while others are exploring possibilities such as myopathy (muscle disease), genetic and metabolic disorders
What it looks like: According to a 2006 review by the AAEP, “Shivers is characterized by periodic, involuntary spasms of the muscles in the pelvic region, pelvic limbs, and tail. Mildly affected horses show a tenseness or trembling of the hind limbs and sudden jerky extensor movements of the tail that cause it to elevate.  The degree of tail elevation varies considerably in different cases.” In more severe cases, backing up causes the hind limb to raise suddenly upwards and to the side, and the hoof is held in the air for up to several minutes. The raised limb will tremble, and the tail will usually elevate and tremble as well. The horse may exhibit symptoms in one or both legs. More rarely, shivers can affect the front legs, neck, trunk or facial muscles.
             Prognosis: Horses with mild cases of shivers may perform well for years, though the disease is typically progressive, with spasms occurring more often and with greater severity over time. Muscle atrophy and weakness of the hind end is an almost universal consequence as the disease progresses. There is no known treatment or cure, though anecdotal evidence suggests that a low-carb, high fat diet may help some horses.
              Most often confused with: The sudden raising of the limb caused by shivers can resemble stringhalt (see below), but horses with stringhalt do not hold the limb in suspension as horses with shivers do. Stringhalt also does not affect that tail, which is a characteristic sign of shivers.

Video link: https://www.youtube.com/watch?v=2l90K9NoZ6s (moderate)

STRINGHALT

Incidence: Rare in North America, very rare in Canada
Etiology: Neurological, some cases thought to be caused by ingestion of toxic plants
Breeds affected: Any

            What it is: Explains Andrea Finnen DVM, DES, MSc, Diplomate ACVIM, a specialist in equine neurology at the Caledon Equine Hospital in Ontario, “'Stringhalt' is the lay term for equine reflex hypertonia. There are two forms of the disease; idiopathic and acquired. In idiopathic disease, signs are usually asymmetric with one hind limb affected only whereas in acquired (also known as Australian stringhalt) disease, both hind limbs are affected and a toxic plant etiology is suspected.”
            What it looks like: Stringhalt is characterized by spasmodic, rapid and excessive flexion (lifting) of one or both hind limbs when attempting to move, most often seen at the walk, when turning or when backing. Says Finnen, “The flexion can be so severe that the horse's hoof hits the abdomen.”  In mild cases or in the early stages of disease, symptoms may be hard to spot. Severely affected horses, however, will exhibit obviously abnormal movement, with the legs jerking upwards hard and fast, and possibly a plunging or hopping gait. Hind limb muscle atrophy is present in some cases, and laryngeal paralysis (roaring) is sometimes an accompanying symptom in Australian stringhalt. Symptoms may appear and disappear intermittently.
            Prognosis: Some cases of stringhalt will resolve spontaneously, but others will progress over time. “It is difficult to predict if a horse will respond to treatment and what the prognosis is,” says Finnen. “Some cases will take a long time to recover and may never regain 100% function. There are reports of clinical improvement with conservative treatment such as anti-inflammatory and anti-oxidant medications. In severe cases, myotenectomy can be performed to relieve the tension on the flexor tendon to prevent the mechanical movement of the limb.”
            Most often confused with: The hyperflexion that is the characteristic symptom of stringhalt is most often confused with shivers, but can also be taken for UFP, especially in less severe instances.
            
 Video link: https://www.youtube.com/watch?v=Cii3DVIxp7w

Popular posts from this blog

CONFORMATION FAULT: Three Common Knee Problems

Image
No Perfect Horse: Three Knee Problems As we mentioned in the last installment in this series, the knee of the horse is a complex structure that is subject to a great variety of conformation faults. Today we’ll take a look at three knee deviations, all of which are best observed from a lateral (side) view. Back at the Knee (aka calf or sheep knee) This is a serious fault in which there is a slight to marked ‘bowing’ backwards of the leg from a lateral view. A plumb line would fall closer to the front of the knee and further behind the heel bulb. This puts similar strain on the limb as if the horse were continually traveling downhill. Such conformation can put excess strain on various parts of the limb, including the flexor tendons, inferior check ligament, and suspensory ligament.  Horses with this fault may not move well and may be prone to stumbling, as well as bone chips in the knees and soft-tissue injuries such as bowed tendons. Working these horses in deep foo...
Read more

CONFORMATION FAULT: Sickle Hocks

Image
For this installment of our new series on conformation faults, we spoke to Charles Hutton, PhD, an instructor in breeding management at Murray State University in Kentucky, and owner of Nu Chex To Cash, an NRHA Million Dollar Sire, Multiple World Champion and World Champion Sire. Dr. Hutton has a particular interest in applied equine genetics and conformation.             Small hock angles, also known as sickle hocks, is a conformation fault in which the point of the hock lines up under the buttock correctly, but the canon bone angles forward so that the horse is standing under from the hock down. In profile, the leg appears to curve forward, giving it some resemblance to a sickle. This conformation places the plantar (rear) aspect of the hock under great stress, predisposing the horse to sprain and strain of the soft tissue structures that support the back part of the hock. Most experts agree that any horse with hock angles of less than 53 deg...
Read more

CONFORMATION FAULT: Downhill Balance

Image
Downhill Balance: The Bottom Line on the Topline This horse demonstrates downhill conformation, which can appear in any breed, but which is particularly common among the stock horse breeds.              Many growing horses, especially those in the stock horse breeds, go through phases where the top of the croup is taller than the highest point of the withers. In many cases, the front end eventually catches up, but when this build persists into adulthood, it is generally considered a conformation fault. Variously termed as being “downhill”, “bum high” or having “downhill balance”, such horses are said to be more prone to front end lameness and back problems, as well as to have more difficulty performing athletic endeavors.   However, there is little in the way of scientific evidence to support the assertion of increased lameness risk, and some argue that downhill balance is not a fault at all.   There is even the perception in some circle...
Read more