The knee is a major synovial hinge joint in the leg. Located at the articulation between the femur and tibia in the lower leg and the femur in the upper leg, the knee is a crucial joint in human locomotion. The stability of the knee joint is crucial to avoiding acute injury related to weak ligaments or recovering from surgery. By focusing on the anatomy of this magnificent example of human biomechanics, you will understand the purpose of stabilizing exercises and understand their utility in strengthening the joint.
Knee Flexors
Several muscles in the leg contribute to knee flexion. The major flexors are the three hamstring muscles: the semimembranosus, semitendinosus, and biceps femoris muscles. The gracilis muscle, located on the back of your inner thigh, aids in flexion of the knee as well. Two other muscle groups that contribute to knee stabilization are the gastrocnemius and popliteus muscles. These two flexors are located in the lower leg, and extend their tendons up onto the femor, thus contributing to flexion of the lower leg.
Knee Extensors
The only muscle group responsible for knee extension is the quadriceps. The connective tissue on the outside of the knee joint, known as tensor fasciae latae, also contributes to knee extension.
Knee Ligaments
The knee is filled with strategically placed collections of connective tissue known as ligaments. By creating a stable connection between the bones of the knee, these ligaments contribute a great deal to joint stabilization. If you have had an injury to one or more of these ligaments, it is important to understand the function of the ligament so you can exercise the muscles that will most significantly compensate for the loss of stability.
Intracapsular Ligaments
Inside the knee joint, several ligaments function to control the position of the tibia relative to the femor. For example, the anterior cruciate ligament acts to prevent the tibia, or lower leg bone, from being displaced forward relative to the femor, or upper leg bone. Similarly, a separate ligament, known as the posterior cruciate ligament, exists to prevent excessive posterior, or backwards, displacement of the tibia relative to the femur. Weakness in these ligaments following surgery or acute injury would require strengthening of knee flexors and extensors in order to compensate for the loss of ligament stability
Stability Exercises
By focusing on any weaknesses in your knee joint, you can adjust your muscle strengthening routine to correct these sources of instability. Straight leg raises are a great way to start strengthening your quadriceps and improving extension without placing too much stress on the knee joint itself. As you continue to exercise your quads, you may want to move on to wall sits, which require some knee flexion and are helpful in building significant stability. Ultimately, as you feel stronger and more confident in your knee, single leg knee bends are helpful in refining all-around stability. This type of exercise should be worked up to; it is a great test of baseline stability and will serve to improve fine balance and coordination in your knee muscles.
References
- "Tintinall's Emergency Medicine"; Hip and Knee Pain; Kelly O'Keefe and Tracy Sanson; 2010
- UCSF Medical Center Sports Medicine: Home Exercise Program for Knee Pain
- "Atlas of Human Anatomy"; Frank Netter; 2010
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