(This article is an adaptation from the book Your Body, Your Yoga by Bernie Clark.)
That “ouchy” feeling many yoga students get when their back leg is on the floor in low lunges or even pigeon pose (see figure 1 below) comes from pressure on the kneecap. Why is that? More importantly, what can we do about it?
Let’s first take a look at why this pain can sometimes happen.
FIGURE 1: The back knee in low lunges and pigeon pose can press against the floor and cause discomfort for some students.
The kneecap, or patella (Latin for “small plate”) is shaped like a teardrop (see figure 2). It is technically a sesamoid bone, which means that it grows inside a tendon—in this case the tendon of the quadriceps, acting like a pulley, and redirecting the force of contraction from the quadriceps to the shinbone (tibia). The underside (posterior) of the patella is covered in thick, slick, slippery cartilage that helps to distribute compressive force when the patella is pressed against the femur.
FIGURE 2: Front (anterior) and back (posterior) views of an average-looking kneecap.
As we bend and straighten the knee, the patella glides along the far end of the thighbone, aka the femur (see figure 3). It was interesting to me to discover that the patella never actually comes in contact with the shinbone! It only slides up and down over the end of the femur. Eventually it slides into a groove (which has a variety of names like patellar groove, intercondylar groove, or the trochlea) at the bottom of the femur. How far it moves is variable—depending upon the size of the person, the size of the groove, the length of the femur, and the tension in the tendon—but on average, the patella can move about two inches, from full flexion to full extension. Of course, everyone is different, and for some people the patella can move nearly six inches.
FIGURE 3: The kneecap slides and glides: (a) In hyperextension of –10°, the patella is pulled up high on the distal femur; (b) in full extension, it sits slightly above the femoral condyles (the rounded ends of the femur), but not as high as in hyperextension; (c) with 20° of flexion, the patella is now contacting the femoral condyles; (d) at 90° of flexion, the superior portion of the patella is in contact with the condylar groove; (e) at 135° of flexion, the patella is sitting well embedded in the groove.
Now, here is the really fun part: As shown in figure 3, the position of the patella changes dramatically at various stages of knee flexion and extension.
• In (a), we see that in hyperextension the patella is lifted high on the femur. (The common cue to avoid hyperextension of the knee by lifting the kneecaps actually serves to deepen the extension. The quadriceps, while lifting the kneecap, pull the tibia forward, which is hyperextension.)
• In (b) we see that in full extension, but not hyperextension, the tendon is more lax and the patella sits a bit lower than its highest point. Once we start flexing the knee, the quadriceps engage to guard against too much flexion occurring too quickly, and this action once again causes the patella to rise up slightly.
• By about 20° of flexion (c), the patella touches the top of the groove and starts to make initial contact with the inner edges of the grooves. With greater flexion, the patella moves deeper into the valley.
• By 90° of flexion (d), the top portion of the patella has reached the top of the groove. From here, the patella now starts to slide down deeply into the groove.
• At 135° of flexion (e), it is sitting fully embedded. Notice, from 90° and onward, the patella is no longer touching the front of the femur at all—it is contacting only the bottom portion.
Depending on where your back leg is in a lunge, the patella may or may not be touching the floor at all. A student with limited hip mobility may have their back knee bent 90°, but the kneecap is directly pressing into the floor because their hips are right above the knee. A student with more range of motion, such as in figure 1b, can lean further forward in the lunge and put more weight onto the femur of the back leg (rather than on the kneecap)—but even in her case, since the knee is not bent 90°, the kneecap may still be pressing into the floor. In order for the patella to not press into the floor, the hips must be forward of the back knee and the back knee must be bent 90°.
When we look at the full extension position (no flexion at the knee, as in figure 3b), we see that the kneecap is perched right at the front of the end of the femur, which happens to be where the patella is in the back leg of very flexible students (such as the student in figure 1b). With the weight of the back leg supported mostly on the kneecap, the pressure of the patella on the femur can be quite intense—and this is when the “ouch” occurs. But watch what happens if we bend the back leg, as shown in figure 4e: If we bend the knee to 90°, the pressure is shifted from being on the kneecap to being more distributed along the femur—and the “ouch” disappears!
FIGURE 4: Options for removing the “ouch” in the back knee: a) place support under the shin so that the knee is floating; b) press the foot down enough to lift the knee off the floor; c) tuck the toes under to bend the knee a little bit; d) bend the knee and support the shin with a block; or e) let the shin or foot rest against a wall.
There are variety of ways that we can reduce discomfort in the back knee when in a lunge or pigeon. We can a) prop up the shin so that the knee is floating—when we put a cushion under the shin, the kneecap is raised off the floor entirely; b) press down the top of the foot to lift the knee off the floor—but this requires continuous muscular effort; c) tuck the back toes under, which bends the knee a little and may change the position of the kneecap on the femur enough to reduce or remove the “ouch” factor; d) bend the knee a lot and support the shin with a block—to avoid engaging the hamstrings to keep the knee bent; or e) rest the shin against a wall, providing the full 90° flexion that moves the patella into the groove. Of course, the simplest remedy may be just the old-fashion padding under the knee, placing a folded blanket, towel, sock or even the folded edge of the yoga mat under the kneecap.
However, most of these options may not be available, or could be awkward to use when flowing between postures. So, if you have ouchy knees in a low lunge or pigeon pose, why not try the bent-knee option for your back leg, and see if it helps. If you are not using a block or wall to support the bent leg, you will have to engage your hamstrings, which may be good for you! You’ll strengthen your hamstrings while adding a bit more stress to the quads.
In my next article, we will continue to look at the kneecap and how it moves in its groove. And we’ll discuss what it means for your front knee in postures like a high lunge or the warriors.