A bowed tendon is a strain injury to one of the flexor tendons running down the back of a horse’s lower leg, most commonly the superficial digital flexor tendon (SDFT). The name comes from the visible outward curve the leg takes on when the tendon swells, giving it a “bowed” appearance. It’s one of the most common soft tissue injuries in performance horses, and while it heals, the process is slow, often requiring six to twelve months of structured rehabilitation.
Which Tendon Is Affected
The superficial digital flexor tendon runs along the back of the cannon bone, connecting the muscle above the knee to the second pastern bone below. Its job is to flex the pastern and fetlock joints, absorbing enormous shock loads every time the horse’s hoof hits the ground at speed. Because of its position just beneath the skin, the SDFT is both vulnerable to direct trauma and highly susceptible to strain from overloading.
The deep digital flexor tendon, which sits behind the SDFT, can also bow, though this is less common. The swelling can appear anywhere from just below the knee (or hock, on the hind leg) down to the pastern region. Vets sometimes describe the location as a “high bow,” “mid bow,” or “low bow” depending on where the damage is concentrated, and location can influence both treatment and prognosis.
What Causes a Bowed Tendon
The core problem is mechanical overload. When a tendon absorbs more force than its fibers can handle, individual fibers tear. This can happen in a single dramatic moment, like a bad step on uneven footing at a gallop, or it can build gradually through repetitive stress. Fatigue plays a major role: a tired horse loses the muscular support that normally protects its tendons, leaving the SDFT to bear forces it wasn’t designed to handle alone.
Several factors raise the risk. Deep, heavy, or inconsistent footing forces the tendons to work harder to stabilize the leg. Horses that are asked to perform at high speeds, particularly racehorses, face the greatest exposure. Poor conditioning, returning to work too quickly after a layoff, and conformational flaws that place extra load on the back of the leg all contribute. Long toes with low heels, a common trimming issue, shift mechanical stress toward the flexor tendons and increase vulnerability.
Recognizing the Signs
In the acute phase, the back of the cannon bone area swells noticeably, creating that characteristic outward bow shape when viewed from the side. The area is warm to the touch and painful when pressed. Most horses show obvious lameness, though the degree varies with the severity of the tear. Some horses are only mildly off at the trot, while others refuse to bear full weight on the leg.
One tricky aspect of this injury is that early signs can fade quickly with rest and anti-inflammatory medication. The swelling goes down, the horse seems comfortable, and it’s tempting to assume the problem has resolved. It hasn’t. The underlying tendon damage remains, and swelling typically returns as soon as the horse goes back to work. This cycle of apparent recovery followed by relapse is one of the most common mistakes owners make with bowed tendons.
How Veterinarians Diagnose the Injury
Physical examination can identify a bow, but ultrasound is the standard tool for understanding how bad it is. Ultrasound lets the vet see the internal structure of the tendon in cross-section and along its length. They evaluate the size of the damaged area (called the lesion), how disrupted the fiber pattern is, and how much of the tendon’s cross-sectional area is involved. A small peripheral tear is a very different injury from a large core lesion that takes up half the tendon’s width.
This information directly shapes the rehabilitation plan and gives a realistic picture of recovery time. Repeat ultrasounds at regular intervals, typically every 60 to 90 days, track healing progress and help determine when it’s safe to increase the horse’s activity level.
Acute Treatment: The First Two Weeks
The immediate priority is controlling inflammation and preventing further fiber damage. Cold therapy is the single most important intervention in the first 24 to 48 hours. It is nearly impossible to overdo cooling on a fresh tendon injury. Apply cold wraps or ice boots as frequently as possible, recognizing that most cold therapy wraps only deliver reliable cooling for about 20 minutes per application. The more cooling sessions you can fit into a 24-hour period, the better the outcome.
Proper bandaging is equally critical. A correctly applied standing wrap controls swelling and provides stability to the injured tendon. The padding must lie flat without wrinkles or ridges, and pressure should be applied evenly with each turn. Start and end the wrap along the side of the cannon bone rather than directly over the tendons. Extend the bandage down under the sesamoid bones at the back of the fetlock to provide support, but don’t end it high on the fetlock where it could create a pressure point.
Stall rest begins immediately. The horse should not be turned out, lunged, or ridden during this phase. Your vet will likely recommend anti-inflammatory medication to manage pain and swelling during these initial days.
The Long Road of Rehabilitation
Tendon healing happens in distinct phases, and rushing any of them risks re-injury. The inflammatory phase lasts roughly the first two weeks, during which the body clears damaged tissue and begins laying down early repair material. During weeks two through eight, the proliferation phase, the body produces new connective tissue to fill the damaged area. This tissue is disorganized at first, more like scar tissue than functional tendon.
Controlled hand-walking typically begins during the proliferation phase, usually around two to four weeks after the injury depending on ultrasound findings. This gentle, straight-line movement provides mechanical stimulus that helps guide new fibers into alignment along the tendon’s natural axis. It’s a crucial step, because fibers that heal in a random pattern produce weaker scar tissue that’s prone to re-tearing.
The remodeling phase stretches over many months, during which the repair tissue gradually matures and strengthens. Activity increases in careful stages: from hand-walking, to turnout in a small paddock, to light riding at the walk, then trot, and eventually controlled canter work. Significant core lesions in the SDFT typically require six to twelve months of structured rehabilitation before return to full work. Each step up in activity should be guided by follow-up ultrasound exams confirming that the tendon is responding well.
Regenerative Therapies
Beyond the traditional approach of rest and controlled exercise, two regenerative treatments have shown promising results for tendon injuries in horses.
Platelet-rich plasma (PRP) involves drawing the horse’s own blood, concentrating the platelets to roughly eight times their normal level, and injecting that concentrate directly into the injured tendon. Platelets release growth factors that promote new blood vessel formation, attract healthy inflammatory cells, and stimulate connective tissue production. The goal is to push the repair process toward true tissue regeneration rather than disorganized scar formation. PRP works best on acute lesions, like a recent bow, and is less effective on chronic tendon problems. Research at UC Davis found that even Standardbred racehorses with career-threatening ligament injuries were able to return to racing after PRP treatment.
Stem cell therapy uses cells harvested from the horse’s bone marrow or other tissues, which are then injected into the injury site. Clinical trials at UC Davis have produced very promising results. In one case, a racehorse with a torn SDFT underwent stem cell treatment followed by a carefully controlled 18-month rehabilitation and returned to win his first race back. While not every case produces that dramatic an outcome, stem cell therapy represents a meaningful advance in tendon repair options.
Long-Term Prognosis
The tendon may never look completely normal again. A horse that has bowed will often retain some thickening along the back of the cannon bone permanently. But appearance and function are different things. Even horses with severe tendon injuries can fully recover, and once they’ve healed properly, the injury rarely limits future performance in most disciplines.
The key qualifier is “most disciplines.” Horses with a previously bowed tendon are generally sound enough for careers as hunters, jumpers, and dressage horses. However, high-speed sports like barrel racing or upper-level eventing put the greatest strain on soft tissue and carry a higher risk of re-injury. The severity and location of the original bow, the quality of the rehabilitation program, and the demands of the horse’s intended job all factor into the long-term outlook.
The biggest threat to a good outcome is impatience. Bringing a horse back to work before the tendon has fully remodeled is the most common cause of re-injury. Sticking to the rehabilitation timeline, even when the horse looks and feels sound months before the program is complete, gives the tendon its best chance at a durable repair.