01/09/2021
Equine Lameness
Brian S. Burks, DVM, Dipl. ABVP
Board Certified in Equine Practice
The equine foot is a unique structure that takes a tremendous amount of force and stress when moving. It is the foundation of the horse. There is an old adage “No Foot, No Horse” as the horse is not stable without its foundation. Forelimb lameness is more common due to 65% of the horse’s weight being carried in front. The foot is the most common part of the forelimb to be affected because of the stress is takes; 80% of forelimb lameness originates from the foot. It is necessary to have knowledge of the foot, clinical conditions associated with the foot and ways to avoid and treat the more common foot problems.
There are three bones that comprise the foot: the third phalanx or coffin bone, the second phalanx or short pastern bone and the distal sesamoid or navicular bone. The short pastern and coffin bones support weight while the navicular bone serves as a fulcrum for the deep digital flexor tendon. The joint between the first and second phalanges is the proximal interphalangeal or pastern joint, and the joint between the second and third phalanges is the distal interphalangeal or coffin joint.
There are numerous soft tissue structures within the foot. The deep digital flexor tendon runs down the back of the leg to curve around the navicular bursa and bone. The navicular bursa is a fluid-filled pouch that sits between the navicular bone and the deep digital flexor tendon and helps cushion and protect the bone and tendon. The navicular bone also has three ligaments attaching it to the second and third phalanges. There are two large collateral ligaments attaching the second and third phalanges.
External structures of the foot include the coronet, where skin intersects with the hoof wall, and is the area from which the hoof grows at about 0.25 inches each month. The ground surface of the foot includes the sole, frog, white line and bars.
Foot conformation is important to maintenance of hoof health and soundness of the horse. The front foot should be large and round; the hind hoof is more elongated, though similar in size. The sole should be concave, not flat, to allow for expansion and absorption of force when the foot contacts the ground. The foot should land heel first, and the heel bulbs should expand. Pressure moves to the walls and frog, absorbing the concussive force and pumping blood through the foot.
Although the hoof-pastern axis is ideally considered to be ideal when the hoof and pastern all line up perfectly, some horses do not have this angle, being more upright or sloping. These angles may not need to be changed, and doing so may cause more harm than good.
Proper foot care ensures that the foundation can maintain soundness. A good farrier is a must. The foot should be trimmed to the widest part of the frog, have a good angle, and be balanced inside and outside. Shoes should be made to fit the foot, not the foot to the shoe. It should be wider than the hoof at the heels, and nails should be set forward. This allows for improved hoof expansion and absorption of force.
Horse lameness is a condition that occurs when a horse is unable to move normally. While the majority of horse lameness is related to the foot, this condition may be caused by problems in a horse’s bones, muscles, nerves, tendons or ligaments. Repetitive injuries, infection, poor nutrition, laminitis are the primary causes for horse lameness. It may occur gradually over time or suddenly with little warning. In few cases, lameness may resolve itself; however, veterinary intervention is often required to proactively treat this condition and prevent additional health problems.
Lameness is the most common cause of poor performance in sport horses. Diseases or injuries to the musculoskeletal system are a major cause for poor athletic performance. The age, breed and gender of a horse are also important. Certain causes for lameness are more likely to affect certain breeds and ages of horses. Past medical history is also important in a lameness evaluation.
An equine veterinarian is trained to diagnose and evaluate lameness in a horse. The more severely lame a horse is, the more noticeable this lameness will be in the horse’s walk. A horse will be evaluated at a trot (jog), which is the optimal gait for detecting lameness. A horse will be observed from both the front and the back while the horse is moving to detect lameness.
A veterinarian will evaluate the following:
• Amount of weight bearing
• Length of stride
• Flight and landing of feet
• Carriage of the head and neck
The American Association of Equine Practitioners rates horses on the following scale for lameness:
0: Not detectable under any circumstances
1: Difficult to observe and not consistently apparent
2: Difficult to observe at a walk or when trotting in a straight line, but noticeable under certain circumstances (e.g., circling, inclines, weight carrying)
3: Consistently observable at a trot under all circumstances.
4. Lameness is obvious at a walk.
5. Lameness produces minimal weight bearing in motion and/or at rest or a complete inability to move
The lameness is localized via the use of local anesthesia around nerves or within joints. The horse does not have muscle below the carpus or tarsus (knee and hock, but the use of knee is incorrect, as the homologous joint to humans is the stifle) so that the nerves do not control function and are only sensory.
Many different diagnostic modalities are use. These include nuclear scintigraphy, CT and MRI, but the most common imaging modalities are radiography and ultrasonography. It is critical that good, detailed, comprehensive radiographic studies be performed. When radiographing the foot, a minimum of five views should be taken to allow for a complete evaluation of all of the bony structures within the foot.
Once a horse’s lameness has been localized, the most effective treatment options can be chosen to directly target the underlying cause for lameness. In general, this means reducing exercise and the weight of the horse. Checking the horse’s conformation and correcting faults, where possible, is paramount. Farriery can be used to treat many problems of the equine foot, when lameness is detected and diagnosed early. Medications for horse lameness are non-steroidal anti-inflammatory medications that fight pain and improve joint mobility. Some injectable medications are also available to protect joint cartilage and support normal joint fluid. Hoof supplements that contain biotin, zinc, copper, complete proteins, and Omega 3 fatty acids may also be beneficial, depending on the cause for lameness. Extra Corporeal Shock Wave Therapy is useful for some fractures of the coffin bone, and for many soft tissue injuries of the lower limb. Sometimes surgery may be necessary to remove a bone chip or repair a fracture, or to help restore tendon function.
Fox Run Equine Center
www.foxrunequine.com
(724) 727-3481
Experienced. Dedicated. Focused on the Horse.
