Tendonitis

Tendonitis (tendon inflammation) is a common debilitating injuries seen in all types of performance horses. While healing does occur, it can take months and the injury recurrence rate is high.

Pathology

Tendon inflammation is referred to as tendonitis. Ligamentous inflammation is referred to as desmitis. Injury occurs when the elastic forces of the tendon/ligament are overcome or the vascular supply is overstretched. Healing requires repair and realignment of fibers. Tendon healing requires approximately 6 months while ligamentous healing takes approximately 9 months. [Learning hint:the number of letters = months of healing. Bone heals in ~ 4 months, tendons in ~ 6 months and ligaments in ~ 8-9 months.]

In racehorses, event horses and showjumpers, the superficial digital flexor tendon (SDFT) is most commonly injured tendon. Most SDF tendon injuries are in the forelimb and in mid-metacarpal region. This region has the smallest cross-sectional area and may be stressed to a greater extent at this level.

The deep digital flexor tendon (DDFT) is most often affected near the insertion of the distal check ligament or within the tendon sheath adjacent to or below the fetlock.

Clinical signs of superficial digital flexor tendonitis (bowed tendons)

Initially,  the cardinal signs of inflammation are observed both on physical exam and ultrasonographically.

The damaged tendon is warm, painful and often swollen.  This swelling is referred to as a bowed tendon because the palmar surface of the tendon “bows” out.  The horse is lame initially but this typically improves rapidly.

On ultrasound, tendon fibers are often disrupted and hemorrhage and/or edema is present (separating the fibers and creating enlargement of the tendon).

Clinical signs of deep flexor tendonitis (tenosynovitis)

Because the deep flexor tendon is most often affected within the deep flexor tendon sheath, the primary clinical sign is effusion (extra fluid) within the tendon sheath due to the local inflammation. The combination of tendon inflammation and secondary tendon sheath inflammation is termed tenosynovitis.

Over time, the tendon stays swollen but the signs of inflammation resolve. The area may no longer be painful on palpation and the horse may be sound at a walk. However, tendon damage may still exist and be evident on ultrasound.

In the future, MRI and/or CT may be more commonly used to evaluate tendon damage and healing.

General therapy

Because these are inflammation (-itis),  medical treatment initially includes anti-inflammatory agents, cold therapy, physical support/compression (wraps or casts keep the swelling down and permit safe transport if needed) and complete rest until the initial inflammation resolves. Other agents may be given to increase blood supply to the area to speed healing (the rationale behind therapeutic ultrasound and the previous use of ‘firing’).

McCarthy and coworkers recently demonstrated the combination of compression and cold therapy was more effective at limb cooling than ice boots without compression (February 2025, Veterinary Surgery 54(3)).

While steroids are useful for controlling acute inflammation in tendon sheaths and bursae, their usefulness in other tendonitis cases is not verified in horses. Side effects do exist, including the risk of tendinopathy (tendon break down). Currently, the recommendation is to stick to other anti-inflammatory agents for tendon injections.

For chronic lesions, controlled exercise is the key component of therapy.  Controlled exercise is needed to stimulate healing and realignment of fibers along the lines of stress.

Exercise protocols are designed to stimulate fiber alignment without overuse and re-tearing. Controlled exercise is key. Horses are NOT turned out as this would immediately result in reinjury. Complete stall rest is contraindicated as this doesn’t provide enough force for proper fiber alignment. Once a horse is sound at a walk without NSAID administration, horses are allowed to walk in hand (under control) for increasing amounts of time.  If ultrasound reevaluation shows improvement, trotting is started at low levels (2 minutes per day). Exercise is gradually increased as long as the horse stays sound. Ultrasound rechecks are essential to detect early damage. If the tendon shows signs of worsening on ultrasound (more damage), the training program is slowed and more time taken to move to the next level. Horses should still be on stall rest during this process. Turnout is not advised until the horse is cantering for ~10 minutes/day without reinjury.

Advanced therapy

If healing is not progressing, other techniques may be used to minimize scar tissue and maximize collagen structure and alignment. Hyaluronic acid has been injected in the area in an attempt to prevent adhesions but has not been very effective. Polysulfonated glycosaminoglycan (PSGAGs) injections (IM) did help healing in experimental studies. Shockwave therapy is most likely useful at bone-tendon junctions and unlikely to be useful in the middle of a tendon (despite its widespread use).  High energy lasers may also be used to “restart” healing. Various stem cells and stem-cell types have been injected in the region with varying results. The most promising include platelet rich plasma and stem cells of various sources; however, better controlled clinical studies are still needed. High frequency ultrasound energy (Tenex) can be used to break down and remove degenerate tendon injury and is minimally invasive. Its use is expanding in equine medicine but research on the technique is still limited.

Previously, surgical treatment has been considered only when horses do not respond to medical therapy and exercise or if they plateau (no further improvement). A recent retrospective study suggested that racehorses have a better chance of returning to the track with intralesional bone marrow injections and superficial check desmotomy than if just treated conservatively. Cutting the proximal check releases the pull of the inflexible ligament on the SDFT leaving only the more flexible SDF muscle belly to “pull” on the tendon. In a more recent retrospective study, racehorses did better if the proximal check ligament was transected. However, the procedure can also lead to higher risk of suspensory ligament damage. Another option is “tendon splitting”. A scalpel is used to cut through the nonhealing region in order to increase blood supply to the area. It is most useful for core (central) lesions that aren’t healing with medical treatment.

If the tendon is swollen in the area of the fetlock, the palmar annular ligament may be cut to reduce pressure on the tendon. Finally, in one study, cutting the proximal check ligament aided in preventing recurrence of the tendonitis, not by increasing strength of the repair but by increasing the elasticity of the entire tendon unit.

Basically, non-healing tendon lesions should be referred to a specialist as the field is challenging and rapidly changing.

Bandage bows

A bandage bow is damage to the peritendinous structures leading to inflammation and swelling that looks like a bowed tendon. Luckily the tendon itself is not involved but you can’t tell that by appearance. Ultrasound is typically needed to differentiate tendinous swelling (real tendonitis) from peritendinous swelling (bandage bows).

Bandage bows often occur due to a bandage being too tight or too loose (sliding down and constricting). Bandage bows respond to anti-inflammatory treatm

ent (cold therapy and NSAIDs). The horse should be stall rested until ultrasound can be performed to confirm the tendon is okay.

This sort of bandage on a horse is likely to cause damage at the edges -it can be pretty tight and put pressure on the soft tissue structures and tendons. Bandages should extend from the carpus to below the fetlock and NOT stop in the middle of the tendon.

Resources

Tendon sheaths and tenosynovitis-chapter

Current Practices and Considerations in Therapeutic Farriery for Equine Tendon and Ligament Injuries. Vet Clin Equine 41 (2025) 443–451

Diagnosis and Minimally Invasive Surgical Treatment for Enhancing Intrathecal/ Intrasynovial Tendon Injuries,.Vet Clin Equine 41 (2025) 299 – 318

Treatment of tendinopathies -Equine Vet Educ. 2024;36:659–672. lovely review and includes what to do as well as why and how.

Palmar/plantar tenosynovitis – client education, AEC- nice explanation with images

Ultrasonography of the equine pastern region – UGA free ibook

Equine shock wave therapy – where are we now? Equine Vet J. 2023;55:593–606. extensive literature review

Current use of biologic therapies for musculoskeletal disease: A survey of board-certified equine specialists. Veterinary Surgery. 2022;51:557–567. – doesn’t mean they work….