Knee Mechanics: General Podiatry Concerns

2. Podiatrists mainly deal with foot and ankle problems, but the knee is not far behind. This is because the knee is so influenced by changes in foot position from the changes in shoe gear to the design of orthotic devices to the activities they participate in doing. You really can not treat the foot in isolation since “the foot bone is connected to the ankle bone, the ankle bone connected to the leg bone, etc etc”. The knee is influenced by the foot/ankle complex biomechanics, but also by its own independent joint motions, and also influenced from the hip and spine above. Some patients have a one to one relationship between their foot and knee mechanics, and some have a reverse relationship where the foot moves in one direction and the knee another direction. It is crucial to watch your patients walk and run and see what the influence of changes in biomechanics of the foot mean to how the knee moves (you can place the patient in different shoes, different wedges, even different speeds of running). The knee is like the big toe joint in that it is actually two joints in one (“double the pleasure, double the fun”). There is the joint between the femur (above) and the tibia (below), and the joint between the femur and knee cap (aka patella). Problems can occur from one or both joints at the same time. There are so many issues on how the knee cap moves that I can not keep up with all the names for the same problem (patello-femoral dysfunction, runner’s knee, dancer’s knee, biker’s knee, chondromalacia patella, quadriceps insufficiency, etc).

    In general, the knee moves with the foot. As someone walks and runs, you want internal rotation at the knee following heel contact (as the foot pronates). This motion is crucial for shock absorption at the foot, ankle, and knee. Then, you want external rotation at the knee from midstance to push off as the foot supinates. These motions, when in sync, produce little or no stress on the knee. But, when the motions are excessive or limited in one area or in opposite directions, trouble occurs. Orthopedists have been studying knee motion for years, along with physical therapists, so they can sense when the motions (or lack of) are problematic. I believe it is really having someone take the time to assess these simple issues to suggest if changing the abnormal stress can help the symptoms. I find gait evaluation to be crucial in this area, not only in the discovery phase, but then in changing the motion to reverse the abnormal stress. I think here lies the problem with knee pain. The physicians and PTs see the abnormal motion, but do not know how to reverse it (sometimes impossible), so surgery is too often gone to. Or, they never really watch the walking and running motions, so they assume it can not be caused by abnormal mechanics.

What are these abnormal stresses that are easily observable in gait?

    When we watch someone with knee pain walk and/or run, you look at various aspects of that motion that can produce problems and has cures. Unfortunately, since we are always looking for clues on what we know, sometimes we miss the real problem because we simply do not understand it. All of the following observations can cause problems and can be broken down to various treatment modalities.  These gait observations include:  

What is the foot doing?

What is the knee doing?

Is there abnormal pronation that is effecting knee motion that can be treated? Is there abnormal supination effecting knee motion that can be treated?

Is the foot pronation linked with internal femoral rotation, or does the knee externally rotate at that time? (indicating opposite motions)

Is there varus thrust at the knee with excessive foot supination, or with excessive foot pronation? (causing wear of the medial knee compartment)

Does the foot pronate while the knee remains straight? (where torque stress can build up in the knee joint)

Is there limb dominance to the side of the worse knee pain? (Possible sign of short leg syndrome) Is there excessive internal femoral rotation more than foot pronation? (Possible sign of weak external hip rotators)

Is the knee functioning too flexed, instead of straightening during midstance? (Possible sign of tight hamstrings) Is the knee functioning too straight, instead of flexing during the heel contact phase? (Possible sign of weak quadriceps)