Discussion

This presentation will focus on those cases of lameness which have been localised to the femorotibial joints by diagnostic local analgesia and in which there are minimal radiographic findings and mild or equivocal ultrasonographic findings. Thus obvious fractures and subchondral cystic lesions are excluded and this represents a common scenario in sport horse practice in cases which block to the stifle, with no obvious findings on diagnostic imaging. Some of these may have an acute history suggestive of trauma and in others there can be an insidious onset of lameness. Magnetic resonance imaging and CT examination of the stifle is still limited in the horse and arthroscopy is therefore often used for diagnostic evaluation of the joint. Ultrasonographic examination can be complimentary in that the areas of the menisci that cannot be visualised very well arthroscopically are those which are most amenable to ultrasonographic examination.
A number of different approaches can be used for evaluation of the femorotibial joints. I prefer the lateral approach to the medial femorotibial joint as this offers the best operative positioning. My technique is to place the ingress cannula into the cranial aspect of the joint in a flexed position. While the landmarks are still palpable I will pass the scope into the caudal pouch of the medial femorotibial joint. Once this has been evaluated I will return to the cranial aspect and make a cranial instrument portal for full evaluation of the medial femorotibial joint. I will then withdraw the scope slightly and pass a second ingress cannula into the lateral femorotibial joint through the cranial portal and evaluate the lateral femorotibial joint in this fashion. Once the femorotibial joints have been evaluated the leg is moved into extension for evaluation of the femoropatellar joint using a standard craniolateral portal.
Meniscal lesions are the most commonly diagnosed abnormities of the menisci and associated ligaments (Walmsley 2003). Injuries are most commonly identified in the cranial aspect of the medial femorotibial joint. Tears are removed using a combination of sharp instruments and motorised equipment aiming to leave a clean edge of healthy meniscus. Excessive
meniscal resection runs the risk of destabilising the joint but some horses appear to be quite tolerant of relatively radical surgery. The cranial and caudal cruciate ligaments can be damaged, with the former being the most commonly injured. Again, treatment is currently limited to debridement of torn and fibrillated tissue. This does seem to reduce the lameness, presumably by reducing the inflammatory stimulus of the torn tissues. The prognosis for return to function for moderate-severity cruciate injuries is approximately 50%. The overall prognosis for meniscal injuries is around 50% return to function with the actual prognosis being greater or lesser depending on the severity of the injury. Biological products such as A-Cell, PRP, Irap and stem cells are now being employed in an attempt to improve the outcome, although evidence-based medicine is currently lacking on the benefits these treatments provide. Horses may have mild residual lameness after their rehabilitation which may respond to medication with corticosteroids once the horse comes back into work.
Lesions of the articular cartilage can also be found, most commonly on the medial femorotibial condyle. These are most commonly identifiable as fissuring, fibrillation or softening of the articular cartilage, often in a more axial position than a bone cyst would be found. Lesions in this area have been commonly identified in sport horses coming into work for the first time and histological examination has been suggestive of osteochondrosis (Bathe and Henson, unpublished data). Initial treatment involved debridement of these lesions and had a good success rate one year post operatively although by 3 years post operatively the success rate had decreased to 50% of horses in full work. A more conservative surgical approach with micro picking through the damaged cartilage is currently employed. Subjectively, post operative Irap seems to offer some benefit in this condition