The stifle of the horse is the largest joint, the most complex and often the most difficult to manage when there is a problem within that joint. The stifle joint of the horse is anatomically comparable to the knee joint of a human.

The stifle joint is comprised of 4 bones: the femur, tibia, patella and fibula. The joint space itself is between two large, cartilage covered, smooth surfaces – the distal end of the femur and the proximal end of the tibia. They are anchored to each other across the joint by several large, thick ligaments and the joint capsule. The large quadriceps muscles above the joint come down the front of the leg into a large thick tendon, in which the patella is embedded. There is also a vestigial bone, the fibula, which runs down the outside of the tibia and is not a weight bearing bone, so is not important in the actual function of the stifle joint.

There are two major classes of stifle problems in the horse – those that affect the weight bearing surfaces, or inside of the joint, and those that affect the ligaments and muscles surrounding the stifle joint.

The biggest problem we have with managing stifle joint disease inside the joint is not just the sheer size of the joint, but also the size of the weight bearing surfaces. The stifle joint is not a joint that can be “fused” like a lower hock joint or middle pastern joint. The bones need to be able to slide over each other smoothly in order to function correctly. Lesions like OCD flaps and cysts, and also flattening and DJD of the weight bearing cartilage surfaces – even if they are small – can cause significant pain and lameness in a horse.

Diagnostics like radiographs can be used to image the bones and cartilage surfaces to look for OCD flaps, cysts or other DJD (arthritic) changes in the joint space. New technology in digital radiology machines, and the power of the portable machines, has made the diagnosis of even the tiniest of these lesions much more feasible now. Even 15 years ago, it was very difficult to find a portable machine that had the power to “get through” the thick stifle joint in order to produce a diagnostic picture.

Some of the OCD lesions can be surgically removed, getting the debris out of the way so the joint surfaces can slide smoothly. There are also several techniques now being used for cyst-type lesions, like drilling and packing, which also help improve lameness when the stifle is weight bearing. It is commonly known that once a horse with an OCD lesion becomes lame, it becomes more difficult to manage the lameness, even with surgical interventions. This is one place where it may be of benefit to radiograph the stifles of yearlings before they are put into work, or if any type of swelling is noticed in the stifle joint at all, even if there is no lameness. The sooner these are operated on, the better the recoveries for athletic soundness. Stifle joints can also be injected with hyaluronic acid and/or corticosteroids to help manage inflammation. Care should be taken in using steroids, because they can be detrimental to the health of the cartilage and cause more DJD problems to occur.

The second type of stifle disease involves the ligaments and musculature surrounding the stifle joint. You may know this as “loose stifles”. What it means is that the muscles and ligaments surrounding the joint appear to be wiggly or loose – you can take the patella and move it medially and/or laterally in your hand. Horses also may appear to have a wobble in their stride when they are walked or trotted.

The key in managing loose stifles is in strengthening the muscles that surround and support the joint space. Over the years, veterinarians and horsemen have tried different techniques to “tighten” the ligaments surrounding the stifle – like injecting iodine in almond oil over the ligaments or applying blistering agents like dish soap to the skin over the stifle – but the reality is these don’t really do anything to the ligaments themselves. What they do accomplish is making the horse want to avoid flexing the stifle joint because of the discomfort, so they lift and swing from the hip and hindquarters. Inadvertently, the horse is strengthening the quadriceps muscles which in turn provides more support to a wobbly joint and “fixes” the problem.

The same kind of quadriceps strengthening can be accomplished without blistering by long trotting horses over poles or up and down hills, which makes the horse engage the hindquarter and strengthen the necessary muscles.

Tanis MacDonald Walker, DVM graduated from the Atlantic Veterinary College on Prince Edward Island and currently practices both small animal emergency and equine medicine in Delaware. You can email her at tanis_macdonald@hotmail.com or visit her at www.drtanis.com. You can also write to her in care of InStride Edition.