Equine Health and Disease Management

By

Dr. Jack Sales, DVM

Copyright © July 2003

As we study Equine Health and Disease management in this course we will want to become familiar with the internal anatomy and functions of the horse as well as the external anatomy and functional parts of the body. In each section, become familiar with the area on the horse’s body that is involved in the disease process. This will make it much easier to understand and remember.

Lesson 1

Musculoskeletal System

The first system we are going to study is the musculo-skeletal system. This will include the main muscles and major bones of the body, with emphasis on the lower limbs. It is important to realize the front limbs of the horse carry the majority of the weight of the horse. The front limbs carry approximately 65 to 70% of the horse’s weight when standing and, at times, even more when in motion. For this reason we will find that the front limbs are the ones that seem to have more lameness problems in the average horse. Of course, depending on the use of the horse, there are times in which the hind legs are used more extensively, and in these cases we see a number of hind limb problems. Think of the reining horse and how much pressure is put on the hind limbs during different maneuvers.

In order to study the lameness conditions of the front and hind limbs, it is important the student have some knowledge of equine anatomy. As we study the different problems of the front and hind limbs, we will be referring to limb anatomy. It will be necessary for you to become familiar with the terms used as we study the particular area of the leg. There will be diagrams of limb anatomy throughout our discussions of lower limb lameness. It is important that as we identify some of the lameness problems of the front and hind limbs, you can relate each problem to the area of the anatomy that is affected.

When dealing with lameness problems in the horse, it is important that we categorize each lameness problem as either acute, meaning that it was a sudden lameness that came on very rapidly, or chronic, which would indicate a problem or lameness that had a gradual and usually progressive onset. For example, a sudden bone break or fracture would be considered an acute lameness whereas a condition such as ringbone is considered a chronic condition that comes on gradually over a period of months or years, and usually continues to get worse and worse.

Let’s start our study of lameness problems in the horse with the shoulder area of the horse’s front limb, and then continue downward toward the hoof. One thing to keep in mind regarding lameness in the horse is that most lameness is going to be seen in the lower limb area, from the knee down. But for continuity, we will start our study of front limb lameness in the shoulder.

Shoulder Sweeny

This is a condition of the shoulder that is characterized by atrophy (loss of muscle mass) over the shoulder blade. The muscles over the scapula will atrophy (shrink or disappear) due to an injury to the nerve that supplies these muscles. This nerve, the suprascapular nerve, is usually injured by a blow to the area around the point of the shoulder, and if the nerve is damaged severely enough, these muscles will lose the innervation from that nerve and begin to waste away. This will usually cause a mild lameness or funny way of going by the horse, but many times the horse will learn to compensate for this muscle loss and can be used for his intended purpose.

Looking at a horse with shoulder sweeny, you can easily tell that the shoulder on one side is not full in appearance, and if you look closer, you can even see that the skin is just covering the bone of the shoulder blade, with the spine of the scapula (the bony ridge of the center of the shoulder blade) very prominent. This is usually a permanent condition, in that this nerve, once damaged or severed, does not grow back.

Fracture of the Scapula

A fracture of the scapula or cracked scapula can occasionally occur and is usually caused by as severe blow or kick over the shoulder blade. All bone fractures show a sudden, usually severe lameness and it is usually evident from severe swelling, where the fracture is located.

A horse that sustains a fracture of the shoulder blade can usually be stall confined for a period if 3 to 6 months and healing will usually be complete. Unless the bone break extends into the shoulder joint area, the horse will normally heal without further lameness. A concept that you should keep in mind about fractures or broken bones is that any break that extends into a joint area will have the potential of causing a future arthritis of the affected joint after healing occurs. So any fracture that extends into a joint area, unless surgically plated or pinned by a veterinarian, will usually heal with continued future lameness in that horse because of the arthritis in that particular joint.

Bicipital Bursitis

This is a condition that causes a lameness of the shoulder area. The bicipital bursa is found on the front of the shoulder joint, and when there is a blow to this area or there is a strain to this area, the horse will show a short stride in the affected shoulder. You can usually make the horse flinch to pressure directly over the point of the shoulder from the front. Also if you pick up and extend the shoulder, the horse may elicit a pain response.

Anti-inflammatory therapy (refer to the upper and lower leg therapy section in this lesson) is helpful for this problem, and if severe, a veterinarian can administer local injections ( refer to Injectable therapy in lesson 2) to help resolve the problem.

Fracture of the humerus

A bone break of the humerus is a very serious injury. Oftentimes it is considered a life threatening injury.

Because the horse has numerous large bones making up the front and hind limbs, we will talk about fractures of the major bones of the horse’s limbs as a general subject.

All that will be discussed on this subject applies to all the major bones of the horse’s limbs. The following is a summary of most major bone fractures in the horse.

Fractures in the Major bones of Horses

Fracture = Broken Bone = Broken Leg

Types Of Fractures

n Simple Fractures

n No displacement of bone ends.

n Only one fracture line

n Compound Fractures

n Broken piece of bone breaks through skin

n More serious because of introduction of infection.

n Comminuted Fractures

n More than one fracture line in a single bone.

n More than two pieces of bone make up the fracture

Other Types of Fractures

n Compound comminuted fractures
Most devastating type
Most difficult to repair with good outcome

n Incomplete Fractures

n Fracture line doesn’t go all the way through bone

n Hairline fractures

n Less serious

n Usually only show mild lameness

n Can warm out of lameness

n Can turn into devastating complete, compound, comminuted fracture if horse continues work.

Prognosis ( Outcome)

n Large bone fractures (Humerus,Radius, Femur, Tibia).

n Very serious, possibly life threatening

n Extreme swelling, and pain

n Usually poor outcome

n Medical advances still lagging behind

n Fracture lines extending into joint

n Secondary arthritis very possible after complete healing

n Future soundness unlikely

n Economics

n Great expense involved in attempts to repair

n Horse’s weight a factor

n Adult horses weigh so much, often will founder in opposite leg

n Horse’s temperament a factor

n May have to spend time in a sling

Osteochondritis Dissecans (OCD)

OCD is a disease condition in the horse that can be found in nearly any major joint of the horse’s limbs.

We will discuss it here at the shoulder joint and what you learn here will apply to OCD as seen in any other joint of the front or hind limb.

OCD is a condition that is seen as it develops in young growing horses. It is associated with the areas of growth of the long bones and the long bones grow at the ends of the bones close to the joints. Although the exact cause has not been determined, research indicates that either a nutritional imbalance or a change in the rate of growth (too rapid growth) could be the main cause. An area in or around the joint loses blood supply and the area necrosis (dies), which leaves bone chips, or cartilage flaps or bone cysts (holes in the bone) in and around the joint. This causes the horse joint pain, which leads to lameness, especially if the horse has started into training.

X-rays are normally diagnostic to identify the problem and arthroscopic surgery may be indicated to remove bone chips, spurs or bone cysts. The success of the surgery is dependent on the amount of damage and the length of time the condition has been there. Some horses respond to treatment well, some never fully recover, developing a long-term joint arthritis that will plague the horse for his lifetime.

Fractures of the Radius or Ulna

Refer to fractures of major bones above

Hygroma of the Elbow (Capped Elbow or Shoe Boil)

This is a condition caused by a blow or irritation to the point of the elbow. Can often be seen in horse’s that lay on hard ground with their elbows directly on the hard surface, or their heel or heel of the shoe putting pressure on their point of the elbow. There is normally a swelling on the point of the elbow that is slightly painful and full of fluid. It normally does not cause lameness. This condition can become chronic where scar tissue is formed over the elbow and it does not go away. In the acute case, a veterinarian can be called out to drain and possibly inject the shoe boil, hopefully bringing the swelling down The swelling may or may not return.

To prevent this from occurring in horses prone to banging their elbow, a donut, which is a foam piece attached around the pastern by Velcro or a buckle, provides a cushion which prevents the heel from making contact with the point of the elbow.

Cellulitis

This condition can occur on the front or hind leg, but I will discuss it here because it is commonly found in the forearm area. It is an extensive infection usually caused by a puncture wound in the forearm area. The puncture causes the infection to build and fester in the deep tissues of the forearm and usually it will suddenly blow up (swell excessively) overnight. It is hot to the touch and painful and usually causes a mild lameness or tenderness of the leg.

If you can find the area of initial penetration of the wound, make sure there is good drainage (sometimes the wound is scabbed over and this traps the infection.)

Clean the area with disinfectant soap and water and establish good drainage. The horse will need a tetanus booster and normally your vet will recommend daily antibiotics until the infection is under control.

Degenerative Joint disease (DJD) (Osteoarthritis)

This is a condition that can affect many of the lower limb joints, and we will discuss it here as we begin to discuss the carpus or knee of the horse. What we say here will apply to other joint areas of the horse’s limb that are affected by DJD.

DJD as associated with the knee joint of the horse refers to the every day wear and tear that joints undergo, eventually resulting in mild to severe arthritic changes within a joint. We are normally talking about older horses when we talk about DJD, but it is important to realize that this wear and tear starts early in the athletic horse’s career and minor sprains and strains of joints in the early years can result in the start of DJD. The problem may become severe enough to end the young horse’s career.

Small chips in the knee joints can be removed arthroscopically and the horse will normally recover to compete another day, but the damage that is done is never fully healed and eventually more joint damage occurs which becomes additive. This process of additive repeated damage to the joints is what is referred to as DJD in all its stages. Refer to anti-inflammatory therapy and lower leg therapy for details on treatment of the different stages of DJD.

Hygroma of the carpus

A blow to the front of the knee can occasionally occur that can cause a large fluid filled swelling on the surface of the knee. It is usually not painful, but can be unsightly and cause a restriction of knee movement. It is necessary to contact a Veterinarian who will normally drain the fluid off and inject with an appropriate anti-inflammatory medication and recommend that the horse be stall confined with pressure wraps over the knee until the skin attaches smoothly over the front of the knee.

If exercise continues, the fluid will usually build back up due to action of the knee.

Epiphysitis

This is a condition seen in the young growing horse usually between six months and 2 years of age. Although it can be seen in the knee, ankle (fetlock), or hock areas, it is normally a problem in the knee area. The distal radial epiphysis (directly above the knee joint) becomes inflamed due to imbalanced nutrition or excessively rapid growth spurts. There can be some mild lameness.

There is normally an enlargement of the area involved. This must be corrected by balancing the diet and/or slowing the growth rate by cutting back on energy feeds such as grain and supplements. It is wise to notify a veterinarian to help you manage this condition so no permanent growth abnormalities occur at the epiphysis.

Moving down to below the knee we should keep in mind that the anatomy in this area should be very familiar to us. If we are not knowledgeable of this lower limb anatomy please take some time to become very familiar with it. From the knee down, the anatomical structures are the same as from the hock down. There is no muscle found below the knee or below the hock. It should also be kept in mind that the blood supply to the tissues and bone structure below the knee and hock is not very good which means that healing of wounds or injuries is not very good either.

Bucked Shins (Shin Bucked)

This condition is seen in young horses in early training, especially race training. The shin or cannon bone undergoes slow strengthening as the horse gets heavier and heavier into training, adapting to the extra concussion it is exposed to during this training process. Sometimes the training can get ahead of the strengthening of the cannon bone and soreness and inflammation of the front of the cannon bone occurs. The horse will be sore to the touch, and heat and some swelling may be evident on the front of the shins. This usually shows up initially as an acute condition, but if it is not resolved it can turn into a continuous or chronic condition plaguing the horse during much of his early career.

Therapy to relieve the heat, pain and swelling is in order (refer to lower leg therapies) and controlled exercise is also important to allow the cannon bone strength to catch up with the training regime.

Splints

This is a similar condition seen in young horses in training, and is caused by a strain of the ligament that attached the splint bone to the cannon bone. The splint is usually seen high on the cannon bone between the attachment of the splint bone and the cannon bone on the side of the leg (inside or outside). It is painful when pressed on and usually warm to the touch. Some firm swelling will also usually be found. As this splint heals, calcium will fill in the area between the splint bone and the cannon bone, making it stronger and able to withstand the strain. This may leave a hard knot that is not sore or inflamed and this is also referred to as a splint , but technically would be called a dead (healed) splint as opposed to a green (fresh or acute and sore) splint. Refer to lower leg therapies for treatment protocols.

Fracture of splint bones

Occasionally the ends of the splint bones ( the lower inch or so) will break off or fracture. This will cause a mild lameness initially, along with signs of inflammation (heat, pain and swelling). These can be diagnosed by x-ray and the veterinarian will normally recommend they be removed surgically. This is not a major surgery and the horse will usually be able to return to training within a week or so. If they are not surgically removed, a calcium bump usually forms in the area of the fracture and may only slightly bother the horse, usually not causing a noticeable lameness.

Bowed Tendon

The back of the cannon bone anatomy consists of the superficial and deep flexor tendon, as well as the suspensory ligament and the inferior check ligament. When the Superficial and/or deep flexor tendon is strained or sprained or sometimes even ruptured due to excess stretching, we refer to the swelling in this area as a bowed tendon. Bowed tendons can be mild to severe and involve a small area or a very large area. They are usually caused by excessive stretching of the superficial and/or deep flexor oftentimes because of tendon fatigue coupled with continuous work.

Initially this is an acute injury with all the signs of inflammation (heat, pain and swelling) and should be treated as an emergency. (Refer to lower leg therapies). Depending on the amount of involvement of the tendons, the horse usually needs from 3 to 12 months rest for healing to occur. If there has been a substantial amount of tendon fibers involved in the injury, the tendon usually heals with much scar tissue and the horse is left with a larger, thicker tendon area (bowed tendon). This healed tendon would be referred to as a chronic bowed tendon. The tendon is never as strong or resistant to stretching as it once was, and is prone to re-injury more easily, although with controlled training and exercise, many horses with chronic bows can be very useful for certain endeavors.

Suspensory Ligament Desmitis (desmitis refers to inflammation of a ligament)

This injury would be very similar to the bowed tendon, in that the fibers of the suspensory ligament have undergone excessive strain or sprain or rupture. A ligament has less ability to stretch than a tendon, so it can be more easily injured with overstretching. The suspensory ligament is found beneath the flexor tendons, just behind the cannon bone, and attaches to the top of the sesamoid bones. It can be injured anywhere along its length. Refer to lower limb therapies for treatment protocols.

Check Ligament Desmitis (inferior check ligament)

This is an inflammatory condition caused by a strain or sprain to the inferior check ligament which is located directly behind the cannon bone in the upper part of the cannon bone. It is between the cannon bone and the deep flexor tendon. This can be a difficult problem to find because it is deep in this area.

Conditions and lameness from the fetlock (ankle) down to the hoof all are associated with excessive concussion causing an inflammatory process in the area of involvement. These conditions can be aggravated by poor conformation causing excessive concussive forces in a certain area of the anatomy. The following is a summary of the conditions and the anatomical area of involvement. Keep in mind that the conditions discussed from below the knee down to the hoof are normally seen in the front limbs, and are not seen as often involving the lower structures of the hind limbs. As stated earlier, this is due to the fact the front limbs carry 65 –70% of the weight of the horse and therefore absorb the most concussion. All of the conditions below will be helped by referring to lower leg therapies and anti-inflammatory treatments.

Osselets – refers to inflammatory changes occurring over the dorsal and lateral and medial areas of the fetlock due to excessive strain.

Sesamoiditis – refers to inflammatory changes in and around the proximal sesamoids due to excessive strain of the area.

Ringbone – Calcification or new bone growth on the first, second, or third phalanx caused by excessive strain or injury to this area. High ringbone refers to P1 or upper P2, Low ringbone refers to lower P2 and/or upper P3. Articular ringbone refers to new bone growth within the articulation (joint) whereas non-articular ringbone refers to new bone growth not involving the joint surfaces.

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