Sprain

Modern day horse sports have great osseous, muscular, tendinous and ligamentous demands. Work intensity generates stress on these structures.

Anatomically, joints are complex structures composed of:

• At least two bones with a thin cartilage layer on the articular surfaces. Both rigid and deformable, cartilage allows an articular mobilisation without friction;

• A joint capsule, covered with a synovial membrane which produces the synovial fluid that lubricates and feeds the articulation;

• Collateral ligaments, intra or extra-articular, which are fibrous structures made with collagen and binding bones, limiting their movements.

During an exertion, some movements can exceed the physiological limits of the articulation (hyperflexion, hyperextension and/or rotation) and the ligaments can be overloaded. As a result, they can stretch or rupture, in whole or part, creating a desmitis.

Desmitis is qualified as «mild» if only some individual fibers are stretched or torn, as «moderate » if a part of the ligament is torn, and as « serious » if one of the ligament insertions has been torn or if a large portion of the ligament is stretched. Desmitis can be accompanied by an avulsion fracture if a fragment of bone is torn off by the ligament.

All articulations with ligaments may be affected, but in horses, fetlock articulation and interphalangeal articulations are the primary joints affected.

Most of the time, the main reason for a consultation is sudden lameness. A thickened articulation is often noticed during the static exam and pressure applied to the collateral ligament may induce a painful reaction. Flexion of the affected articulation generally induces pain.

The stability of the articulation suspected to be affected by a collateral ligament desmitis must be assessed by moving it in all planes of motion. If the desmitis is new, the articulation has good mobility, but if desmitis is advanced, the mobility may be reduced.

Lameness is the most obvious symptom, but the degree of lameness is not always linked to the severity of the lesions. To obtain a more precise diagnosis, a dynamic exam can be performed: the horse is lead to different gaits and the suspected articulations are flexed.  However, if clinical signs of desmitis are present or if the articulation is not stable enough, this exam is not recommended.

When they are practicable, flexion tests are often positive. Diagnostic anesthesia of the articulation is not recommended in order to avoid exacerbating the lesions.

If a collateral ligament desmitis is suspected, further imaging examinations can be conducted such as ultrasonography of the affected area, or radiographs if an avulsion fracture is suspected or if there is  joint laxity.

The main treatment consists of a rest period, sometimes for many months, in order to restrict the movement of the joint.

During the acute and inflammatory phase, we may use localized care on the affected areas such as cold therapy, hydrotherapy, clay or anti-inflammatories. But they must be carefully used: the numbness caused by the anti-inflammatories can lead to increased movement of the joint since the pain is dulled. When a serious desmitis is diagnosed, with ligament rupture and/or articulation laxity, a cast can be set for 4 to 6 weeks to achieve complete immobilisation.

After the inflammatory phase of moderate desmitis cases, regenerative therapies such as PRP (Platelet Rich Plasma) or stem cells injections can be used.  These therapies promote tissue healing. Shock wave therapy can also be used, although its efficacy is unproven.

Finally, a surgical arthroscopic treatment (insertion of appropriate tools and a camera into the joint) may be used in cases with very serious lesions or joint hemorrhaging.

After a rest period and good care, the horse may slowly return to work. A good walking warm up and work on a even ground is recommended. Throughout the rehabilitation period, transitional orthopedic shoes can be set. These horseshoes must be light. In the case of an asymmetric ligamentary lesion of a joint,  an asymmetric shoe with a wide branch on the side of the lesion may reduce foot sinking on this side.

The prognosis for collateral ligament desmitis varies widely. It depends on the location and severity of the lesions, as well the activity of the horse.

For a recent case of desmitis, prognosis depends on three essential factors:

• Lesion severity and articulation stability

• Early diagnosis, which allows a quick immobilisation of the affected articulation and the horse

• Associated lesions (avulsion fracture etc.)

Prognosis also depends on the activity level of the horse  and  the quality of the treatment.

For prolonged or chronic cases of desmitis, prognosis mainly depends on residual pain and articulation affection (fibrosis, lack of mobility).

The sudden appearance of collateral ligament desmitis makes it a condition feared by horse owners. Traumatic injuries to the joints can cause decreases in performance, early retirement, or temporary withdrawal during the competitive season. For these reasons, an early diagnosis is extremely important in order to quickly set a rest period and begin the appropriate care to reduce lesions and allow an early return to exercise.

Dr Perinne PIAT