The more we practise yoga and become intimately tuned into our own bodies, the more we begin to realize that not all posture alignment cues are appropriate and/or beneficial for our body (not to mention the habits, patterns and injuries that have accumulated over a lifetime inhabiting it).
It can get quite confusing in a multi-level yoga class with all the various instructions: Do I let my knee travel beyond the heel in certain standing postures or should I never allow it? Should my hips face the side of the mat in Warrior 2 or Triangle even if my front knee collapses inward? Should I force my foot around the calf in Eagle pose or up into the hip crease for Half or Full Lotus pose even though I feel pain in my knee? Should my buttocks be on the floor in Hero Pose and should I lie back even if my butt lifts and my knees hurt?
In this article we explore the anatomy and the biomechanics of the knee joint and how to safely navigate in certain strengthening and stretching yoga postures.
The knee joint
The knee joint is a condylar hinge joint made up of three bones (femur, tibia and patella). The femur bone is longest bone in the human body and is part of the hip joint as well as the knee joint. The tibia is the bigger of the two lower leg bones - the fibula being the more thinner, more lateral, and one of the four bones that compromise the ankle joint. The kneecap (patella) is embedded in the patella tendon (a continuation of the four quadriceps muscles: rectus femoris, vastus lateralis, vastus medalis and vastus intermedius). The patella tendon attaches to the anterior portion of the superior tibia and is considered to be part of the patellofemoral joint.
Injuries can arise here when too much femoral force is applied (as in a Warrior 1 or Warrior 2 with the knee travelling beyond ankle and heel). This is why it is very important to stack knee over heel in higher centre of gravity postures such as these. During lower center of gravity postures such as Anjaneyasana (low lunge with the back knee lowered) it is safer to allow the knee to travel beyond ankle joint as most of the weight is heading down to the back knee on the mat. Also, stacking knee over heel is important in Warrior 2 or Triangle even if your hips need to not be squared to the side of your mat (instead a more angled hip towards front corner of mat) - it is safer for the knee to stack than to collapse inward/outward.
6 degrees of freedom
The knee joint has six degrees of freedom: flexion/extension, varus/valgus, and internal/external rotation. Flexion and extension are two movements in the sagittal plane and the most common movements of the knee (a hinge joint). The three hamstring muscles and two calf muscles flex the knee and the four quadriceps muscles extend the knee.
When the knee joint is in extension there is very little to no varus (medial)/vagus (lateral) movement or internal/external rotation happening at the knee joint. It is only when the knee is flexed that these four degrees of freedom can be explored/accessed. This is why we are able to explore our possible knee varus/vagus/rotation in poses such as Garudasana (Eagle), Virasana (Hero), or Padmasana (Lotus)...because our knees are flexed.
Injuries can arise in our knee ligaments if we try to rotate a flexed knee beyond its capabilities - often to make up for a lack of internal or external rotation in either the knee or the hip needed for poses such as these. Some people may never get their foot around the ankle in Eagle pose (or sit their buttocks down on the as in Hero pose) - there is just not enough internal rotation for some to support that expression of the pose safely. The same applies to those of us without enough external rotation: Lotus pose may never be a pose executed safely.
Four ligaments for knee stability
Four deep knee ligaments (anterior & posterior cruciate ligaments and medial & lateral collateral ligaments) ensure that the femur and tibia do not aggressively (or gradually with repetitive motion) shift away from each other causing traumatic and debilitating injuries (mostly to ligaments). Remember, ligaments are not elastic and once overstretched will not go back to their original shape.
Anterior Cruciate Ligament (ACL) & Posterior Cruciate Ligament (PCL)
Hyperextension in standing/balancing poses can overstretch these ligaments. It's therefore always a good idea (especially if you are a knee hyper extender like myself) to micro bend the knee while exploring standing or one leg balancing postures.
Medial Collateral Ligament (MCL)
Because this ligament can already be weak due to the Q angle - angle of the femur from hip socket toward inner knee - it is imperative to engage inner legs (deep front line of fascia from arches of foot to pelvic floor) to resist load in postures such as Warrior 1, Warrior 2, Side Angle, Reverse Warrior, and Triangle. Make sure you seal down the little toe-side of the back foot in these postures to encourage the arch of the foot and inner knee lift for support. Also, this is the ligament that can stretch/tear in poses such as Eagle or Hero if there is not enough inherent internal rotation of hip or knee.
Lateral Collateral Ligament (LCL)
One of the reasons why yoga teachers always instruct placing your foot either above or below the knee joint in Tree pose is to help protect lateral pressure into this ligament. This is especially important if you are attempting a creative version of Side Plank that places top foot in a Tree Pose configuration (most important to not press foot laterally into knee joint). Also, this is the ligament that can stretch/ tear if the knee is forced into Lotus if there is not enough inherent external rotation in hip or knee.
Menisci for Stability and Shock Absorption
The knee joint absorbs, transmits and redistributes force. Your menisci are very important knee stabilizers that play a very important role in this shock absorption: they will deform in shape in order to conform to the shock absorbing needs of the knee. This is most important in walking, running and jumping, often activities we tend to not perform on the yoga mat. Following the motto “if you don't use it you lose it” it's nice to add some bouncing in your yoga practice in postures like Tadasana (Mountain pose). Bouncing, in addition as being great for strengthening your knee menisci, is also beneficial for moving your lymph and toning/hydrating your fascia.
A practical exploration with Jennilee
Keep your knees safe during yoga - 30 mins, Hatha / Therapeutic
Join Jennilee in this short tutorial exploring the knees in yoga. After her brief talk on the anatomy of the knee (demonstrating on the skeleton), Jennilee continues with an information-based movement exploration of how to safely align the knee in certain strengthening and stretching yoga postures.