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Proceedings: Functions of the menisci. A preliminary study.

There are reasons to believe that one of the most important functions is load-bearing, and this paper presents experimental evidence to demonstrate this and to quantitate the fraction carried by the menisci of the load acting on the joint. Experiments were carried out on young cadaveric knees, at full extension. First the knee was compressed in a universal Instron machine, and the approximation of the condyles, on both sides, was measured. For this two displacement transducers were employed, one on each side of the knee. The armature of the transducer was attached to the femur and the cam to the tibia. Two x y plotters were used to record the load displacement curves on both sides. The load that was applied on the knee was slowly increased by 2 kg. to 100 hg. The menisci were then made redundant by dividing their anterior attachments to the tibiaand the experimentwas repeated. Oncomparing the load displacement curves before and after dividing the meniscal attachments, it was possible to determine the load carried by the menisci. The results showed that they carry a considerable share, the lateral meniscus 70 per cent and the medial meniscus 50 per cent of the load acting on the respective sides of the joint. As a result, the stresses occurring in the knee are low and comparable with those occurring in the hip under the similar conditions of loading. The fact that the menisci have a load-bearing function has other implications. The congruity they add to the joint increases the time of approach of the condylar surfaces to 30 to 60 times its value, based on the assumption that they do not carry load. Previous work has shown this value to be 90 seconds. This means that the bearing surfaces of the joint will not come into contact after long periods ofstandstill. This is a desirable situation as it is known that wear in lubricated bearings takes place during the starting phase, when the surfaces are in contact, and ceases during the running phase, in which the surfaces are separated by a lubricant film. Discussion DR. A. J. PALFREY (London) In my experience there is a good deal of variation in the area of the lateral meniscus. Have you related this to the load transmitted through the meniscus in the individual specimen? Secondly, would you agree that the menisci are virtually inextensible along their length? Thirdly, the surface of the meniscus in a histological preparation is much less smooth than the surface of articular cartilage: is this partly responsible for the long squeeze-ffilm time?