I have a client with a knee that is not staying in place, and the only muscle that looks like it would cross the joint where the problem is located is the extensor digitorum longus. I know there are lots of things to reason out here, but I need some exercises to stabilize this area. Any help would be great.
Thank you for your question and client concern. To assist you in your application, I will start by defining instability as you properly noted in your question. An instability can be viewed as a motion-stability inefficiency. In other words, in order to have stability, one must have motion. To have motion, you must have stability (albeit it must be the right amount of motion at the right time, in the right plane, at the right sequence). We are often taught one over the other, but in human function, motion and stability function together at varying levels.
To help you with your client, I would first recommend not thinking about muscles of a joint, rather the exact function you’re trying to improve. For example, we may decide to create optimal motion-stability of the knee during WALKING. The key to your client’s success is in understanding this function. Another example may be squatting. The point is, once the function is selected, then we can position the body against forces (which is authentic resistance training) to improve stability in a joint that may exhibit too much mobility (as you mentioned). Our goal in the selected function is to three dimensionally stimulate all the tissues surrounding the knee to accomplish this. A practical example can be applied through a single leg balance reach with a two arm anterior reach to waist height. By driving (reaching) the trail leg posteriorly and driving (reaching) both hands anteriorly, the lower extremity that remains on the floor will experience a reaction of hip flexion due to the hands moving forward and the opposite leg moving backwards, which will in turn load or stretch the posterior hip musculature of the lower extremity that is positioned against the floor. If the knee of the “floor leg” doesn’t move much (try keeping a slight flexion while performing), the distal hamstrings will be stimulated via the hip flexion reaction and thus provide stability to the knee complex. Think of a big rubber band being pulled from one end that then will transmit tension to the opposite end. This is otherwise known as efficient function, and in fact it’s what the body does naturally when working correctly!
Obviously, there’s more involved here, but hopefully this stimulates a thought process enabling you to understand how authentic real life function works and how to create an environment for efficient motion-stability. It’s always important to realize the parts of the body grow and develop to meet the demands of the WHOLE.
If you want more info pertaining to the functional knee, please refer to Gary Gray’s DVD on the knee (click here for info).