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15Joint 5 Dental Surgery Equipment & Instrumentation Examination and Surgery of the Meniscus www.vetinst.com Diagnosis Meniscal damage may be suspected in a stifle which seems significantly more painful than might be expected with cruciate rupture alone. Some patients may exhibit an audible and palpable click on walking. This occurs as the femur rolls over a detached meniscus which has folded over. MRI in larger patients may suggest a meniscal injury. Introduction Menisci contribute greatly to the normal function of the stifle joint. The stifle joint is not a simple hinge as knee replacements in both man and dogs which were based on the hinge premise have discovered. The menisci are the interface between the two articular surfaces. They transmit load, absorb energy and lubricate the joint. Importantly they contribute to joint stability to both shear and rotational forces. A definitive diagnosis is provided by examination of the meniscus either by direct visualisation via arthotomy or by arthroscopy. The caudal horn is not easy to expose regardless of technique.Veterinary Instrumentation offers a substantial range of instruments designed to make exposure easier. Caudal detachments, longitudinal and bucket handle tears may be difficult to identify without detailed probing of the surface of the meniscus. The detached areas often fall back into position when not loaded. When the cranial cruciate ligament fails the menisci become vulnerable to damage as the femur is free to move relative to the tibia creating excessive crushing and shearing forces. The lateral meniscus is relatively securely attached to the femur so moves with it avoiding injury. The medial meniscus is, however, firmly attached to the tibia and subject to repetitive trauma. Injuries to the lateral meniscus are uncommon whereas medial injuries are common. The incidence and severity of meniscal injuries are related to the weight of the dog and the duration of the injury. Surgical Management of Meniscal Injuries The poor healing characteristics of the meniscus leaves removal of the damaged area as the only real surgical option. The damaged areas are made slippery by synovial fluid and are difficult to grasp and cut without dedicated instruments. Typically, damaged areas are grasped and retracted as far as they can be and detached from their remaining attachments using knives of various designs. Arthroscopic punches may be used to ‘tidy up’ less distinct areas of damage in both open and arthroscopic approaches. Meniscal Release This procedure remains contentious. Recognising the important function of the meniscus anti-release surgeons seek to preserve as much intact meniscus as possible. However, all the tibial plateau levelling techniques leave the stifle unstable in certain circumstances leaving the meniscus vulnerable to injury from the resulting crushing and shearing forces. Pro-release surgeons argue that releasing the meniscus removes it from harm by the femur and that no meniscus is better than a damaged one. It is certainly the case that meniscal release reduces the incidence of late meniscal injury which might be linked to the initial injury. Longer term outcomes in terms of the development of degenerative joint disease (DJD) are less predictable. The meniscus is avascular except around the periphery and generally does not heal. Despite active research in man to find repair and replacement techniques these are not readily applicable to the canine patient. Ultimately the evidence is unclear so surgeons must make their own decision. Classification of Meniscal Injuries Meniscal release is performed by transecting the medial horn by a radial cut just caudal to the medial colateral ligament at ‘x’.(illustrated). The caudal horn of the medial meniscus will rotate caudally into the caudal compartment of the joint capsule. If the meniscus does not move significantly it has not been released. Alternatively the meniscus may be released by transection of the meniscotibial ligament ‘y’. The crushing and shearing forces resulting from a cruciate deficient stifle create a number of relatively specific meniscal injuries. These were classified by Bennett and May in 1991 into seven types. 1. Caudal detachment with folded caudal horn 2. Longitudinal tear 3. Multiple longitudinal tears 4. Fibrillation/tearing of the surface ­Photo: Geoff Robins 5. Axial fringe tear Video 6. B  ucket handle tear (similar to type 2 or 3 but inner concave portion, or portion between two longitudinal tears, of meniscus becomes lax and displaced from the tibial surface give the appearance of a bucket handle) Geoff Robins has created a video illustrating a number of meniscal surgery procedures. It is available free of charge on the VI cruciate DVD or as a download from www.vetinst.com 7. Transverse tear 150