As complicated as it is, the knee joint does not have a lot of versatility in its scale of movement.
The knee joint is capable of flexion, extension, and medial and lateral rotation to a certain degree. It's basically a hinge.
Due to this lack of rotational and lateral movement, the knee is the most vulnerable and susceptible joint to injury. Common knee injuries are:
* Patella refers to the kneecap. Medial collateral ligament is on the inner side of the knee, while the ACL is inside the knee itself - see the chart below. Pes Anserinus tendons cross the knee joint on the inner side of the knee and help stabilize it, and refer to the attachments of Sartorius (hip flexor), Gracilis (adductor), and Semitendinosus (one of the Hamstrings) muscles.
Many sports that require rotation and lateral movements: tennis, golf, soccer, baseball, football, basketball - put the knee at risk.
In yoga, we say that "the health of the knees depends on the flexibility of the hips."
This means that it's the hip that needs to rotate or move laterally to compensate for the lack of movement in the knees.
For example, if you play tennis, you often lunge out sideways to get the ball. This lateral lunging movement must originate entirely in the hip. The hips have to be able to move - be flexible enough to rotate out and in, and move the legs far out to the sides.
Another example is a dancer who has a wide range of movement in her dance routine. If she does not rotate the legs, or side steps, from the hips, the knees will suffer. I have met several Zumba class participants who complain about developing knee pain after taking Zumba classes. The reason: they are not taught to turn from the hips.
Bottom line is: we need to treat the knee as a simple hinge and
1. minimize any rotation,
2. stretch your hips regularly to have a great range of motion, and
3. make sure to move from the hips.
What happens when the knee rotates or moves laterally in sports?
The above-mentioned ligaments and the knee cartilage (meniscus) must bear the pressure of that unnatural movement.
The job of these ligaments is to hold the knee stable - to minimize movement. Hopefully they hold up. But if the pressure, or impact, is too great, they tear.
Sometimes, the tear is small - we feel a little twinge for a couple of weeks, until it's "healed." Sometimes, the tear can be a complete rupture of the ligament which may require surgery. With small tears, it may be even more complicated: the scar tissue may build up in the ligaments or the meniscus and cause a lot of pain and discomfort.
What can we do to help our knee ligaments?
4. Strengthen the muscles around the knee. Strong muscles will support these ligaments in their job of stabilizing the joint. These are Quads, Hamstrings, Adductors (inner thighs), and Calves.
Finally, as two common sayings state: "Stress creates Strength" and "If you don't use it, you lose it."
This means, to have strong healthy knees, we must use them! In the way, that the knees are meant to be used - weight-bearing, flexing fully, and extending fully.
In contrast to the popular belief, studies have found that runners who put a lot of stress on the meniscus, have a thicker and stronger cartilage than non-runners. That is because running, like walking, is weight-bearing exercise and the body responds to the stress of it by building extra layers of tissue.
5. Make sure to use the knees - put your body weight on them, flex and extend them fully every day!