The inferior check ligament, also known as the accessory ligament of the deep digital flexor tendon, is an interesting and important soft-tissue structure in the equine athlete.
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Injury occurs most often in the front limbs from overextension because of excessive twisting or pivoting on the leg. Injuries to the inferior check ligament do not get the attention that other injuries in this area tend to get, such as those to the suspensory ligament and flexor tendons, as they occur less often. However, for a dressage horse an injured inferior check ligament can be performance-limiting. The inferior check ligament runs from the carpus (knee) on the back of the leg and attaches to the deep digital flexor tendon approximately one-third of the way down on the third metacarpal (cannon) bone. Its function is to help the deep flexor tendon with shock absorption and prevent excessive lengthening of the tendon. A horse who has a tear of the inferior check ligament will show a variable degree of lameness. However, if the ligament is only mildly strained or inflamed, lameness will often not be present. Careful regular examination and palpation of the back of the cannon bone, including the tendons and ligaments, will reveal a focal area of swelling laterally and/or medially in the upper third of the cannon bone. Any time you notice swelling in that area—even without visible lameness—you should have the leg examined. In some cases, there is only fluid buildup or edema. In that case, you can manage the swelling with cold therapy (icing the leg) and stall rest to try to avoid developing a real tear. Once you have a real tear, the horse will become lame though the duration of lameness is variable. If the tear is severe enough, the horse will become severely lame.
Managing a horse with a torn inferior check ligament can be tricky as the ligament is short, wide and snug between the deep digital flexor tendon and suspensory ligament. Based on its location, a tear of the inferior check ligament can also affect both the deep and superficial digital flexor tendons in the short and long term. If the swelling persists after the icing treatments, the horse should get an ultrasound. The check ligament is structured in a way that can make it look normal although it is damaged and vice versa. For this reason, it is important that a veterinarian experienced in ultrasound do the evaluation. In addition, it is important to compare the injured check ligament to that of the other leg to have an objective measure.
Within four to six weeks, a horse with only fluid buildup or edema of the inferior check ligament will be fine. If you have a real tear, rehabilitation takes about six to eight months, and the ligament's condition should be monitored via ultrasound by an experienced veterinarian every six to eight weeks in order to make more accurate rehabilitation recommendations. Management options of tears within this ligament are similar to those in others such as stall rest, icing, controlled rehabilitation exercise, the use of biologics such as PRP (platelet rich plasma) and stem cells, shockwave and therapeutic ultrasound. These therapies allow new fibers to grow within the lesion that are as similar as possible to those prior to the injury. Some veterinarians recommend cutting the inferior check ligament to release it when there is a significant enough tear. However, in my experience this is often unrewarding, resulting in chronic lameness.
José M. Garcia-López, VMD, is a Diplomate of the American College of Veterinary Surgeons, a Diplomate of the American College of Veterinary Sports Medicine and Rehabilitation, an associate professor of large animal surgery and the director of equine sports medicine at the Cummings School of Veterinary Medicine at Tufts University in North Grafton, Massachussetts.