There are certain parts of your body that need special attention when it comes to protection. Two things that come to my mind are tendons and ligaments. These attachments between our bones (ligaments) and muscle to bone (tendons) are not endlessly elastic and when overstretched, can have a hard time returning to their normal, resting state. And, of course, if too much force is exerted on either one, they can rip or tear. Some people have experienced this: I can share that in a water skiing accident many years ago, when I was in high school, I tore two ligaments in my knee. After surgery and rehabilitation, the knee is great but it begs the question: what kinds of things can we do in yoga practice to protect our joints?
To that end, here are some things we can do to protect the joints during yoga practice:
Be mindful about bringing joints to their fullest range of either the long or short end of the range. This means that in a joint that flexes and extends, like the knee, take special care when in poses that bring you to one extreme ( full flexion ) or the other (full extension). If you think of a joint’s range of motion (ROM) as a continuum, it’s important to be really connected to your body as poses take your into the far end (either side) of this range of motion. Teachers: make special note when you teach to avoid “teaching to the end point.” Students are very likely to push themselves to the position you suggest, even if their tendons, muscles and ligaments do not have the necessary flexibility to allow them to safely reach this point. One thought is to suggest moving into the pose in a more conservative way and then offer a progression, but cue them to watch for signs that they are locking their joints or rounding the spine, or whatever compensatory shape the body will take to indicate the joint does not have the flexibility needed to get safely into the pose.
Watch for signs that the body is sitting in a joint like a hammock. This can happen in poses where we hold them for longer than a few breaths. We can tend to check out or can try to push  ourselves outside the range we have available in the joint. The body will always look for a way out and there are many poses where we can end up sitting in the joint without any muscular support around the joint itself. A typical pose that can illustrate this is a low lunge, with the forearms down on the floor, inside the foot of the bent knee (think: Lizard Pose). It’s typical for people to sink very low in the shape and as that happens, they’ll collapse in their upper body, sink into their shoulders, allow their knee to flop out to the side ( extreme external rotation at the hip of the bent knee) and sink deep into their sacroiliac joint (low back). The lower they go, the less muscular support is around the joint. While this might feel good (or for some students, they’ll state they can’t “feel anything” unless they go this low) it’s not great for the joints involved. The idea here is to support the joints through muscular action and allow the muscles to stretch.
Protect joints that are built for a high level of mobility: Joints like the shoulder and the hip are ball and socket joints. These afford us great mobility but it comes with the responsibility of being sure our movements are done with care and awareness. The traditional movement we do a great deal in yoga practice that can put the shoulder joint at risk is moving from High to Low Push Up. While I won’t go into it here in great deal, the rotational forces on the shoulder joint as we move from “high” to “low” can be healthy or what they is called “shearing” due to the shape of the joint. There are quite a few movements like this in yoga practice and poses that leverage the shape and flexibility of the joint. The best advice is to move with caution and awareness to protect joints for the long term.
Once you loose your foundation, there’s greater potential for the joint to be at risk. We use leverage a great deal in yoga to create the stretch we need. Think of a pose like Bridge Pose. In order to stretch the hip flexors, we need to have the feet in the proper position so we can push up and off the floor in such a way to get a good stretch. If our heels are too far back and too close to our hips, our knees will extend out “beyond” our ankles putting both joints in an awkward position and decreasing our leverage. Also, in a pose like a Straddle Forward Fold, the deeper we go, the more we potentially loose the foundation of the outer edges of the feet on the mat. This starts to put our ankle joints and knees in an awkward position.
For those that have a double jointed quality, keep a slight bend to support the joint through muscular support. Some people come to yoga and they are double jointed. Sometimes people are not even aware of the mechanics behind it; they just know some of their joints can go “beyond straight.” Depending on the pose, this can be a rather tricky condition to have. I used to have a student who could get up into Upward Bow Pose (commonly called Wheel) and she literally could not get out on her own  because her elbows locked. I worked with her to learn how to keep a slight bend in her elbows as she came up and that allowed her to safely come down. Knees and elbows are the joints most commonly noted in yoga practice around this issue. A suggestion for safety is to keep the joint slightly bent so you can work the muscular support of the joint.
Yoga is great for joint health and the long term prevention of conditions like arthritis. It’s important to keep joints healthy for the long term by practicing with mindfulness and an awareness of the movements that potentially can put our joints at greater risk. Once these tendons and ligaments are damaged, it’s hard to repair them and get back on track. As with all poses, staying connected to the breath and out of a sense of pushing or competing will keep the practice pure and safe.