Management of injuries to the superficial flexor tendons of racehorses has long been one of the greatest challenges to be presented to equine veterinary surgeons. We all know that it is better to try and prevent injuries in the first place by carefully monitoring tendon health, training on optimal gallop surfaces and not racing on firm ground. That said, however careful we are, the horse’s flexor tendons are working close to their elastic limit, most of the time and so overstretching and tearing of tendon fibres is going to happen. Any amount of fibre damage is significant, as even a small tear represents a weakness which is only going to get worse if the horse keeps galloping. So we have to take the horse out of training and divise a program of rest, repair and rehabilitation. The big question is, can we return a tendon to the level of strength and elasticity that it had pre-injury and then can we prevent the same injury process recurring?
An tendon injury left to it’s own devices will inevitably end up with an amount of less elastic fibrous scar tissue, making re-injury quite likely. So the holy grail of tendon repair is to be able to regenerate healthy, elastic tendon tissue at the injury site with the fibres fully aligned with the rest of the tendon. For the last twenty years, bone marrow derived stem cells have been available as a treatment option for tendon repair. In this author’s opinion, the launch of and early usage of stem cells in racehorses could have been handled much better and would have achieved a much higher success rate. The racing industry became rather disillusioned with the treatment due to re-injury occurring. This happened because horses were generally returned to work far too quickly, partly due to the fact that the scan images showed rapid healing of damaged areas but also because the rehab program recommended at the time suggested that horses were able to resume canter work after as little as six months. Initial tendon fibre repair contains large amounts of type 3 collagen whereas the majority of the healthy tendon is composed of stronger type 1 collagen. There is little good histological work to follow the repair process in healing thoroughbred tendon, so we really don’t know with certainty how long we should leave a tendon to repair. All experienced racehorse trainers will tell you that long periods of rest, such as a year or eighteen months have generally yielded the lowest re-injury rates in horses and that shorter recovery periods usually end in disaster. So is it any wonder that stem cells coupled with inappropriate rehab programs didn’t yield the best results? My message is that we need to keep these cases in controlled walking exercise for 12 months before gradually increasing the tempo and monitoring the tendon with the scanner as the faster work is introduced.
The images below show an injury to a five year old national hunt horse that had adipose derived stem cells implanted four weeks ago. These cells were harvested from subcutaneous fat located to the side of the tail base. This tissue yields far higher numbers of mesenchymal cells than bone marrow and they can be multiplied in the lab much quicker. As you can see the injury has filled in extremely well in a short time. Luckily this horse has a very patient owner who is prepared to give the mare a slow, controlled rehab program which should return her to the track.
Ultrasound scan showing damage to the superficial flexor tendon.
Four weeks post implantation of stem cells showing dramatic improvement in fibre pattern.