Joint Reaction Forces, Padmasana, and the Knees
Article courtesy of Ray and Chris – The Daily Bandha
Yoga poses such as Padmasana can take your knees to the limit of their natural mobility. The idea is to do this without injuring yourself. Knowledge of anatomy and biomechanics can help. While it’s true that an injury can teach you a lot, I’ve been through that and those are hard lessons. For the rest of this incarnation, I’m opting for the easier lessons (at least with my yoga). We can learn a lot about how to avoid injuries in yoga from the vast fund of information available from
Joint Congruency
There is a concept in orthopedics known as joint congruency. This refers to joint surfaces maintaining their natural curvature when in contact with one another. A related concept is the joint reaction force. In essence, this is a combination of all of the factors that can produce pressure within a given articulation, such as the hip or knee. These elements include body weight, the contractile force of the muscles that surround the joint, or even someone “assisting” you to get into a pose. When the articulations are taken to extreme positions, the joint reaction forces tend to be concentrated over a much smaller area, creating the possibility of injury. To understand this, imagine 1 pound spread over 10cm2 of surface area versus 1 pound spread over 1cm.2 The force spread over the smaller region is more likely to cause injury. When practicing yoga, it is best to spread the joint reaction forces over a greater area by maintaining maximum congruency of the joint surfaces.
Padmasana (Lotus Pose)
Let’s look at the form of the body in Padmasana: the hips flex, abduct, and externally rotate and the knees flex (and rotate a small amount). The hips are ball and socket joints, enabling them to move in all directions and, especially for this pose, rotate. The knee is a hinge joint with a limited capacity for rotation. Thus we want to protect the knees in Lotus by obtaining most of the rotation from the hips. If the hips are tight, there can be a temptation to force the knees to rotate more than they should, creating a torque at the joint that can injure the articular cartilage and/or ligaments. Maintaining joint congruency of the knee minimizes abnormally high joint reaction forces being concentrated over a small area within the joint and limits stress on the ligaments. You can see from this video that the hip only has to release a small amount to protect the knee.
Tight Internal Rotators
As discussed, Padmasana involves externally rotating the femurs. Look at today’s video to see what happens when the muscles that internally rotate the hip are tight(the tensor fascia lata, gluteus medius, and gluteus minimus). This limits external rotation of the hip, which can compromise congruency of the knee joint. As a result, there can be increased pressure on the cartilage of the medial surface of the knee and abnormal stress on the lateral collateral ligament. Observe how releasing the internal rotators of the hip allows you to maintain the knee as a hinge. This removes the pressure on the inside of the knee and closes the opening on the outside.
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