Structure and function in the body are correlated. But that correlation is not linear.
There can be large variations in structure with function only minimally affected. For example, many people have a bulging intervertebral disc in their spine, but only a fraction of those individuals develop back pain.
Conversely, function may be affected, but the body structure may not reflect that limitation of function adequately. Some people with chronic back pain may have a normal back, radiologically.
Yoga is about living healthy and long, and finding positive self-transformation. As yoga practitioners or teachers, or just as human beings, we are looking to enhance the function of the body and mind, regardless of the structure we are presented with.
The structure of the body is malleable only to a certain extent, and changes in structure, or the absence of such changes, can be misleading. For example, when we work with the knees in asana to improve their function, their resting alignment may not change substantially; a knee cap that is pointing somewhat outward or inward may continue to remain in that alignment at rest. The alignment in movement may not change noticeably either. But the client may experience substantial improvement in function—reduced pain, increased stability, and greater range of movement perhaps.
Structural changes are generally a vehicle for functional changes for the latter is more important for quality of life. This is a central thread in yoga practice.
In the locomotor system, there are broad functional goals that can and should be cultivated systematically. A simple rule of thumb is to emphasize the movement patterns that human beings have evolved to do in a natural environment. We will explore this in other posts.