The lateral retinaculum is a ligament that helps hold your patella, or kneecap, in place. When the knee moves slightly out of place or becomes tilted in the joint, it can cause tension and pain in the lateral retinaculum. Stretching this ligament keeps the patella in place and the ligament healthy. But because of the ligament's location, adequately stretching it can be difficult. However, you can stretch the lateral retinaculum by stretching the muscles, tendons and ligaments around the knee joint, causing a secondary stretching effect on this connective tissue.
Stretch the quadriceps muscle. Stand, or lie on your side, and grab the ankle of your leg. Pull it up and behind you, bringing the foot as close to your buttocks as possible. Arch your back to maximize the stretch, holding it for at least 10 seconds. Although you will feel the strain and stretching most notably in your quadriceps muscle, the stretch will affect your lateral retinaculum.
Sit on the ground and perform the hurdler's stretch, which will stretch your hamstring. Place your leg in front of you flat on the ground, with your toes pointing upward. Lean forward with your torso over the upper leg, reaching for your toes to stretch the hamstring. The stretching will extend into the knee and will benefit your lateral retinaculum.
Stretch the iliotibial band. These two connective structures work closely with one another and you can stretch them both through the same exercise. Stand up and cross one leg over the leg you want to stretch. Place the crossed leg on the ground and stick the corresponding hip in that direction. Lean away from the side where the lateral retinaculum is being stretched and push your body until you feel stress in the connective tissue on the outside of your knee -- this is the iliotibial band. Hold this stretch for at least 10 seconds.
Repeat your stretching exercises three or four times a day.