Your knees are supported by a number of important muscles and tendons; without them, you wouldn't be able to extend, rotate and flex your knee. Perhaps surprisingly, there are no muscles that actually cross the knee joint; most of the supporting muscles originate in your thighs and hips and attach to your kneecap via tendons. Your knees play an integral role in how you move, so it’s vitally important to keep the muscles and tendons that surround and support them in good working order.
The Muscles That Allow You to Bend and Extend
The main muscles that give shape to your thigh are the quadriceps femoris muscle group. These four muscles connect to the patellar tendon, which attaches to your patella -- your kneecap. No actual muscles specifically cross the knee joint; most support the knee from behind and above. Extending down the outer thigh and connecting either side of the knee is the iliotibial tract or IT band, dense tissue that runs from the hips down to the tibia, the large bone in your lower leg.
Knee Support From the Thighs and Hips
Making up the quadriceps group, which allows you to extend your knee, are the rectus femoris, the vastus lateralis, vastus medialis and vastus intermedius; these four muscles join at your patellar tendon. This is what attaches to your kneecap.
Bringing Up the Rear
The hamstring muscles help you to flex your knee. These muscles are made up of the biceps femoris, the semitendinosus and the semimembranosus, which are all located at the back of your thigh. This group connects to the back of your knee. Other muscles that offer support to the knee from the back of the thigh include the sartorius muscle, the adductor magnus and the large gastrocnemius muscle which helps shape your calf.
Keeping Your Knees Healthy and Free of Injury
The American College of Sports Medicine recommends strengthening the muscles surrounding your knees to avoid damaging them. Use resistance training to strengthen your hips and thighs with such exercises as the dumbbell stepup, body-weight squat, the forward lunge and the hamstrings curl. Stretching to improve flexibility in those areas will also help you to avoid potential injury. Stretches include the supine hip flexor stretch and the Thomas stretch. Consult your doctor before performing any strenuous resistance-training exercises.