Manual Therapy - Understanding the Knee Joint
Talking about "Unexplained" Pain in the Back of the Knee
- Dr. Jonathan Kuttner M.D.
The knee joint negotiates the forces between the two longest levers of the body – the tibia and the femur. At first sight, it seems poorly designed and ill-equipped to cope with such varied and dynamic forces
The knee has been described as an "elbow designed by committee". The knee sits between the two longest levers of the body – the tibia and the femur – with most of the weight of the body coming down on it (and from various angles in a sporting context).
Right leg, Posterior View
At first sight the knee seems ill-designed to deal with such titanic and dynamic forces. For starters, the bones do not fit tightly with each other.
The femur ends in two rounded condyles, while the top of the tibia is described as a ‘plateau’; a fairly flat surface for the femur to land on.
This means that there is a certain amount of slide, glide and rotation available at the knee.
This makes for a necessary adjustability, but is not so great for stability.
Knee ligaments go a long way toward limiting the compromise.
The medial and lateral collateral ligaments allow minimal sideways (medial or lateral) sliding of the two bones on each other.
The lateral collateral ligament (LCL)
The LCL is under the iliotibial tract, running from the femur to the head of the fibula, which peeks out from under the tibial plateau.
This ligament is not part of the knee capsule, and is very strong and hard to break.
Mid-Sagittal View
The Medial Collateral Ligament (MCL)
The MCL is part of the knee capsule, making it therefore a bit arbitrary in terms of where we place the scalpel and say ... ‘This is part of the MCL and this bit right next to it is not.’
The MCL, though strong, is not as strong as the LCL, and is therefore more prone to injury.
This applies especially with young female athletes, where wider hip joints (on average) and athletic endeavor combine to direct more force into the medial knee.
Once weakened, the MCL can be a trouble spot for the rest of one’s life, so it is a frequent site for surgery.
The other ‘crucial’ ligaments of the knee are the cruciate ligaments, so named because they cross in the center of the knee joint.
In spite of appearing to be in the middle of the joint, both cruciate ligaments, like the MCL, are simply stronger parts – thick and strong sections – of the complex knee capsule.
Anterior and Posterior Cruciate Ligaments (ACL and PCL)
The ACL and PCL prevent forward and backward sliding of the femur on the tibia, as well as locking in extension to prevent hyperextension of the knee.
There is nothing in the shape of the knee bones or patella that would prevent the knee from flexing to the front – this is the job of the ACL and PCL, which can be made too loose and overstretched by a sustained hyperextended standing posture.
The four major ligaments of the knee – medial collateral, lateral collateral, anterior cruciate and posterior cruciate – severely limit the side-to-side shearing of the two bones, and limit the front-to-back shearing enough to keep the two bones from sliding off each other in either direction. The cruciates also function to lock the knee from going into hyperextension.
Tearing or parting of the cruciate ligaments, especially the anterior one, is a not-infrequent football injury – it is, in fact, one injury that sent Moshe Feldenkrais on his quest for healing – and we all feel a little sick when we see a knee bent in the ‘wrong’ direction.
It is to the ligaments and not the bones that we must look for knee stabilization.
One last point about the ACL and PCL: they are arranged such that they loosen when the tibia is turned laterally on the femur, and tighten when the tibia is rotated medially, or when the femur is turned laterally on the fixed tibia.
Many of these knee-compromising injuries take place when the foot and lower leg are fixed on the ground and the upper body is turning into that knee.
Examples might include falling downhill over a ski, or that winning twisting backhand shot right after the foot is planted.
Cartilage
Both surfaces on the knee are well covered with thick cartilage, and there are additionally two menisci, semi-lunar cartilages that sit between the tibia and femur, and go a long way toward allowing the two surfaces of these bones to fit snugly with each other.
These cartilages lie loosely in the joint (though they manage to have connections with the cruciate ligaments and the medial hamstring tendons).
These C-shaped ‘rings’ of cartilage open when the knee is extended and the flatter end of the femur lies on the tibia, and close when the knee is flexed and the more rounded posterior part of the femoral condyles rest on the tibia.
This arrangement is great when it works, but for all the reasons cited above, these cartilages are subject to being frayed through grinding, or torn or cracked through shock injury.
They can even be folded over within the joint as a result of severe twisting.
Knee Joint Capsule
There is one more unique element of the knee joint that bears mentioning, because it shows what a marvelous piece of design the human body is.
The knee joint capsule, in addition to enclosing the area of the joint cartilages and menisci, has two extra ‘coves’ (see above).
One runs up in the front, under the patella, while the other sticks out the back of the joint and down, under the heads of the gastrocnemius.
The capsule cannot go out to either side because of the tight restricting collateral ligaments we described earlier.
When you put your leg forward, you contract the quadriceps.
This presses down on the patella, and the synovial fluid beneath it in the ‘cove’ at first cushions the patella, but is then squeezed through the joint into the back cove.
When you push off the foot a second later, you contract the gastrocnemius.
This is cushioned against the fluid, but then pushes that fluid back through the joint to the area under the patella.
In this way, the joint is lubricated very efficiently at both ends, and the large amount of cartilage in this joint is flushed and refreshed with its ‘food’, the synovial fluid.
Don't Run Before You Can Walk :)
Please note that this mechanism works best in walking, and not so well in running.
The best way to naturally care and feed a knee joint is to walk on it – if walking is not contraindicated – as this renews and repairs the cartilage.
Walking has about four million years of on-the-job training as a way of healing.
This is a solid and concrete example of how it works to renew us.
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