A well known osteopathic principle developed by the founder of osteopathy Andrew Tailor Still is “structure governs function” and so as an osteopath my starting point is always the function of the joint. Evolution has adapted body structure according to its function and therefore once the osteopath understands the joint's function, structure is simply an adaption to meet the demands of the environment. Furthermore, as an osteopath I consider how the patient uses his body, that is, what kind of environment do the joints have to cope with and how pathophysiology may be developing under the circumstances. The knee joint is one of the most interesting joints in the body since it has two mutually exclusive functions which it has to perform; motility and stability. Unlike the shoulder, the king of joint mobility, the knee is a weight bearing joint. Unlike the hip, the king of stability, the knee needs to be highly mobile. Therefore there are structures unique to these 2 joints that we do not see in the knee. However, the knee is similar to the shoulder in that it requires a degree of mobility and it is similar to the hip in that it requires stability and it shares some of the structural features common to both. The knee like the shoulder lacks congruity and so has muscle and ligamentous strength to support it. Just like the hip the knee propels the body forward and therefore has structures that increase its congruity providing stability with mobility.
So, the knee has multiple function, but probably the most obvious one is that of propelling the foot forward in order to make contact with the ground to allow the leg to propel the body forward.
If the knee were a regular hinge joint like the elbow, one can imagine how much trouble the leg would run into. Therefore unlike the elbow the knee allows for a degree of rotation in order to allow for uneven surfaces and pivoting.
If we appreciate for a moment the weight bearing function of the knee we will see that if all the ligaments and the muscles were removed from the knee joint it would essentially collapse in a medial direction. The reason for this is the q-angle. The femur which attaches to the pelvis extends laterally from the body in order to increase the range of movement of the hip. However, in order for the feet to face forwards the femoral condyles are more medial than the hip joint. The result of this is that most of the body weight is transferred to the medial aspect of the knee and therefore this has to be more stable than the lateral side.
The knee is split up into two compartments essentially. One compartment is designed for stability, that is the medial side of the bit – fem joint. It has a much wider surface area, it is much larger than the lateral side of the tibial plateau. The medial meniscus is much less mobile, it is deeper and the medial side is stabilised by the medial collateral ligaments, a structure which holds the medial side of the tib fem joint tightly together allowing only a small degree of valgus to occur. Furthermore, the medial meniscus is attached to the medial collateral ligament reducing its mobility further. The horns of the medial meniscus are attached further apart from one another resulting in a lot less mobility of the meniscus itself which in effect limits the mobility of the femoral condyle on the tibial plateau.
The stability of the knee joint is mainly contained on the medial aspect of the knee as mentioned above. The knee joint compared to the hip and to the shoulder has a complex latticework of ligaments which stabilize the knee in more than one direction and which support one another. In addition to the ligamentous support the muscles act as flexible elasticated ligaments with semitendinosis, gracilis and sartorius acting to support the medial collateral ligament and tensor fascia lata, biceps femoris and popliteus acting to support the weak lateral collateral ligament.
The bony structure of the lateral tibial side of the knee on the other hand is much smaller as is the femoral condyle. This smaller contact point does however have a greater range of movement than the medial femoral condyle. It not only flexes and extends but pivots and rocks around the tibial plateau under the guidance of the ligaments and meniscus.
So there we have it a medial condyle which is stable and a lateral one which is mobile. This allows the knee to perform its function of propelling the knee forward but at the same time supporting the body weight.
Before we move on to the menisci let us take a look at the centrally fixed cruciate ligaments which have the function of controlling the axis of movement of the knee. Most people are aware of the functions of the cruciate ligaments – preventing anterior and posterior shift but they are less aware of their function in limiting internal rotation of the tibia on the femur and guiding the femoral condyles smoothly into position on the tibial plateau during extension.
If we look at a graph of the tensility of the ligaments we tend to see that all the ligaments are at their most tensile during extension. Due to their origins and insertion around the femur and tibia all ligaments tend to become more taut the further into extension the knee goes. This results in a “tight-packing” of the knee which allows for no rotation of the tib-fem joint at all when locked in full extension. Therefore the knee is most stable, least mobile, during extension and least stable when the knee is flexed. The close packing is due to the increased tensility of ligaments and the squashing of the menisci whose job it is at this stage to increase the congruity of the knee joint.
The menisci have the primary task of providing increased congruity to the unstable tibial plateau. The differences between the 2 menisci related to the functions that we mentioned above, which is that the medial compartment maintains the stability whilst the lateral compartment creates mobility. The menisci are made of fibrocartilage which allows them to stretch and be squashed. The medial meniscus is less mobile than the lateral meniscus due to its shape, it is a C shape and less able to swing back and forth. It is tightly bound to the tibial plateau and reinforced by coronary ligaments and the medial collateral ligament. The lateral meniscus is O shaped, highly mobile, unrestrained due to loose coronary ligaments, unattached to the lateral collateral ligament and attached to the popliteus muscle which actively pulls it posteriorly out of danger when it contracts. This allows for a much more mobile surface on which the lateral femoral condyle can rest.
Finally we consider the patella femoral joint which is a sesamoid bone designed to improve the efficiency of the quadriceps. It slides between the femoral condyles creating a much stronger force during flexion and extension. It is reinforced by retinacula tissue from medial and lateral muscles, a lateral femoral buttress and finally a thick layer of cartilage posteriorly to protect it from friction on the femur.
As osteopaths we are trained to build up a detailed picture of the way the patient uses the knees. What stresses does the patient's environment put on the various structures listed above? As osteopaths we must not be hasty to rush into the examination and treatment. The more information an osteopath gets from the patient the more focused will be the osteopathic examination and the better the treatment. The patient's work may influence the knee structure. Prolonged standing with a strong need for the illio-tibial band to contract causing an imbalance of the quadriceps, a history of a congenital hip displacement or Perthes that may influence the position of the hip and thus the q-angle, prolonged kneeling, repetative strains caused by regular rotatory forces.
In short, since ligaments are designed to support, most ligamentous injuries occur when the they are at their least flexible, in extension and the result is normally a force that stretches them beyond their physiological norm resulting in a partial tear. Menisci on the other hand are designed for movement and most meniscal injuries occur during movement, slightly out of sync with the movement of the femoral condyles becoming caught in between the femoral condyle and the tibial plateau and tearing partially.
To conclude, the knee is a classic case of function governing structure and for an osteopath to treat the joint effectively a deep understanding of the biomechanics makes the life of an osteopath much easier and more enjoyable. The osteopath can develop a clearer osteopathic diagnosis, a clearer osteopathic treatment plan and a more effective treatment.
For more info on knee pain: http://www.osteopath.co.il/knee-pain.php
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