Superficial Digital Flexor Tendon
The SDFT is the most commonly damaged tendon in the forelimb. Damage is usually the result of long-term overstretching of the tendon causing “wear and tear” to the fibrils (long fibres that are bundled together to make up the tendon). An acute rupture then occurs, most commonly in the mid-cannon area of the tendon, although severe injuries can occur that involve nearly the entire length of the cannon bone. When the injured area repairs it does so with scar tissue that is less elastic than normal tendon tissue.
Recuperation must focus on:
- Minimising the area affected (preventing it spreading with swelling)
- Ensuring the fibrils being laid down as part of the repair are aligned in the direction of forces applied when the horse is active. This ensures the tendon is in the best position to withstand future workload and avoid re-injury.
Several techniques exist to help improve the quality of tendon repair. Needle puncture of the injured site to release pressure and prevent spread to the surrounding tendon fibrils (unaffected by the original injury) is one technique. Another approach is the collection of stem cells from the sternum of the affected horse which are cultured and then injected into the site of injury.
Most important is a consistent and disciplined regime of box rest and walking out. Commencing as soon after the injury occurs as possible, walking out is performed for gradually increasing periods of time. In most cases after 6 weeks or so the horse should be walking out for a total of 60 minutes daily. The walking out should be carried out on a hard flat surface at a constant pace. It should be dynamic enough that the repairing fibrils are stimulated to align vertically, but gentle enough that they are not ruptured by the exercise.
Assessment of the repair progress is best made by regular ultrasound scanning. In most cases, after about 12 weeks walking out, a horse can be “turned away”. Turn-out should first be on a small level paddock before progressing to full-field. After a further 6 months or so the horse is reassessed before a gradual return to successful active work.
The Check (Accessory) Ligament
The check ligament runs between the back of the knee and the Deep Digital Flexor Tendon (DDFT). It merges with the DDFT at the level of the lower third of the cannon bone. The role of the check ligament is to support the DDFT. If excessive forces are applied to the DDFT, the check ligament will be the structure that sustains damage first leading to an acute injury. Since the check ligament acts like a “safety valve” for the tendon, injuries to the DDFT in the region of the cannon are extremely rare. If a check ligament becomes injured it is almost always in the front leg.
Most usually, an injured check ligament first presents with an acutely lame horse. Close inspection of the affected limb will show a swelling on the outside of the limb, just below the knee. This swelling will be sore when touched. Diagnosis is confirmed by an ultrasound scan.
Management of a check ligament injury is very similar to that of a SDFT injury. However repair is generally much swifter than a tendon and a return to full work should be achieved within 6 months. Box rest with a carefully controlled walking out programme is essential for successful repair. Generally an ascending exercise programme from the box is performed for around 10 weeks. This is then followed by turnout in a small level paddock and then eventually full field turnout. Ridden exercise recommences about 4 months after injury and is built up gradually.
Poor foot balance can play an important role in causing check ligament injury. Remedial farriery of the front feet can be fundamental in preventing recurrence of the injury.
Injuries of the suspensory ligaments of both front and hind limbs are very common. The suspensory ligament arises at the top of the cannon bone and runs down the back of the cannon before attaching to the fetlock. The ligament gets its name because it “suspends” the fetlock. The suspensory ligament can be damaged either through long term “wear and tear” or from an acute over-extension of the fetlock. Injuries in the front limb are most common in horses performing fast work and jumping. Injuries in the hind limb are seen mainly in dressage horses.
A Suspensory ligament injury presents as lameness in the affected limb. The lameness can be subtle (especially in the hind limbs) or pronounced. Many owners of horses with SL injuries are unaware their horse is lame. Instead, their findings are varied e.g.
- He is less forward going
- He feels better on one rein than another
- His transitions are less smooth
- He is lacking impulsion from behind
Injury to the suspensory ligament is usually confirmed by a Vet performing “nerve blocks” to isolate the source of the lameness. It is then confirmed with an ultrasound scan.
In the front limb, suspensory ligament injuries are treated with box rest allied to regimented exercise of twice daily walking out on a hard flat surface. The exercise is gradually increased so that after 6 weeks the horse should be walking for a total of 1 hour daily. After around 3 months the horse can progress to turn-out in a small level paddock. Return to work is usually about 6 months after treatment started. The procedure of Shock wave therapy also can also be performed on suspensory injuries of the front limb, further improving the quality of ligament repair. Recovery from SL injury of the front limb is usually very good with an estimated 92% of horses returning to full work.
Injury to the suspensory ligament of the hind limb can be more problematic. The lameness is less likely to respond to the rest/walking out and Shockwave programme. Most Vets will first attempt the programme however and, if unsuccessful, will recommend an operation, called a fasciotomy/neurectomy. The operation is to section the nerve and decompress the ligament near its origin at the back of the cannon. The horse then undergoes a recuperation programme. Most horses undergoing this operation respond very well with an estimate of just fewer than 80% returning to full work.