Posterior knee pain combined with stiffness can have many more causes than you could imagine - from a simple torn meniscus through baker's cyst to a serious thrombosis or even a tumor.
Fortunately most of the time even simple exercises can help well-being, and the usual combination of rest, ice, compression and elevation works very well too and drastic steps, such as amputation are rarely needed.
If you have Baker's Cyst, you will feel a swollen painful lump behind your knee. The lump will feel like a tiny water balloon. This is caused by the continuous rubbing of the cartilages behind the knee, which irritates the the soft tissue. This is particularly common with runners who repeat the same motion over and over again. The joint fluid gets pushed out of the joint, and it accumulates behind a knee and forms a cyst. The easiest way to get rid of this is to have it aspirated and draw out the fluid. If you have additional soft-tissue injuries, active release can help break up the scar tissue and make your knee feel less stiff. Baker's cyst can reoccur, but fortunately it rarely gets more serious. Mayo Clinic has a short but informative article on Baker's cyst.
Nerve or artery compression behind your knee can also result in pain and a feeling of stiffness. For example if you have popliteal artery entrapment syndrome, the popliteal artery gets compressed in the popliteal fossa. The cause is a malformation of the surrounding tissue. This restricts the blood flow to the leg, and can cause pain behind the knee, swelling, cramping, stiffness, and a tingling sensation much like being on pins and needles.
Over long time this can lead to the damage of the artery and your leg.
This injury is common only in athletic people, whose larger muscles can push on the popliteal artery thus trapping it. This issue is usually treated with a surgery.
Besides the popliteal artery getting trapped in the surrounding tissue, the peroneal nerve can get trapped too.
This usually happens during walking or running, and results in a shooting pain behind the knee. Surgery is rarely required, the treatment involves resting and range of motion (ROM) and strengthening exercises.
Besides a nerve getting compressed at your knee, a nerve compressed in your spine can result in similar pain.
This is because the spine hold the nerves which connect the brain and your body. If a nerve which connects to your knee is compressed inside your spine, it will feel just as if your knee had some problems.
So if you have knee pain and you can't seem to find the reason, it could be due to a nerve injury in your spine too.
If the nerve entrapment is serious, the treatment may require surgery, steroids and anti-inflammatory drugs to manage the inflammation and pain relievers to manage the pain. Braces are useful too as they get the load of the knee down.
Hamstring tendonitis can too cause pain and stiffness behind the knee. This kind of pain usually subsides a few minutes after you started your exercise.
Hamstring tendonitis usually happens to long distance runners whose hamstring gets overused as the hamstring muscles are used to slow down the forward-swing of the lower leg during running.
Just as any kind of muscle and tendon overuse this can result in tendonitis.
To fix this kind of issue it's the best to find a doctor who can do gait analysis, and find out which kind of muscles are overused and which one are not strong enough - often the buttocks muscles need a bit of strengthening.
For a quick exercise lie down on your back with your legs pulled up, and place a resistance band around your bent knees. Open your legs and let it work against the band. Three sets of 25 reps of this exercises will strengthen your buttock muscles. You will find even more exercises lower on this page. SportsInjuryClinic writes even more on hamstring tendonitis.
The menisci are two C shaped cartilages which sit in your knee between your thigh and shin bone. Simple wear-and-tear or a sudden twist can tear your meniscus. Afterwards your knee will feel stiff, swollen and it will be painful. As the meniscus reaches around inside of your knee, it can cause pain on any side.
Depending on the severity of the tear, the healing time can be between one to three weeks and it may come back easier afterwards.
If you have torn your meniscus, your knee will feel as if it would give way or it could lock up, if the torn tissue gets stuck inside of your knee.
Physical therapy and icing can help this type of injury, however if it reoccurs your best bet is to undergo surgery. The surgery usually consists of the doctor removing the torn part of the meniscus using a small incision on your knee.
The healing time after a surgery can be multiple months. Read more on this issue on Mayo Clinic.
Stabilizing braces can help with meniscus problems, as they take over some load from your knees.
Knee stiffness and pain in the back of the knee can also be a sign of a blood clot or a tumor. A tumor can cause knee pain even if your knee is unloaded, for example when your a lying on your bed.
A tumor is usually treated with a combination of radiation, chemotherapy, and surgery.
Deep vein thrombosis, or simply DVT can cause pain behind the knee too, and it's symptoms can be eerily similar to that of baker's cyst.
When a blood clot develops in the leg it will lead to swelling, stiffness, pain behind the knee when you try to walk or stand.
The skin can get discolored too, surface veins become visible. Your leg may feel warm, and it will tire easier than usual.
A deep vein thrombosis is a very serious issue, as the blood clot can break loose and may block a blood vessel somewhere else - in the heart, leading to a heart attack, in the lungs, leading to pulmonary embolism or in the brain leading to a stroke.
Smoking, being overweight, and sitting for a long time (think intercontinental flights) are the major risk factors for DVT.
DVT is usually treated with blood thinners. Depending on the risks you may need to take the blood thinner for the rest of your life. You can learn more on DVT on Wikipedia.
The final reason for stiff knee with pain behind the knee is the Gastrocnemius tendonitis.
The gastroc tendons are the ones which connect the calf muscles to the back of your thigh bone.
These tendons are pulled on when you force your toes to point upwards while your knees are extended. This is a typical injury for bikers with weak buttocks muscles - the calf and the gastrocnemius tendons get overused which lead to inflammation. Uphill riding is a typical activity which can lead to this injury.
Use the usual combination of rest, ice, compression and elevation to fix this issue. Wearing a calf sleeve which provides extra compression helps a lot too. A good sleeve will support the muscle during exercises and it will reduce the strain just as the tendons start to heal. Fixing your equipment, wearing proper running shoes or using a better bike seat can help a lot too. Read more on Sporty Injury Clinic.
While the best treatment for your issue depends on the exact cause, in general these treatments are used for joint issues:
If your knee stiffness just started, RICE comes to the rescue: rest, ice, compress and elevate. Resting your leg a bit but keeping a light activity will make sure that you do not overstrain your leg while still saving it from growing weaker. Icing the painful spot for up to 15 minutes at a time will help reduce the pain and the stiffness. Compression sleeves help the muscles and tendons regenerate, as the sleeve takes over some load from your joint. Elevating your leg will help drain the excess fluid that usually builds up after an injury.
For affordable compression you may want to check the SB SOX sleeve. For crossfit while you have knee pain a 5mm sleeve such as the Bear KompleX sleeve is ideal. For heavy squatting a 7mm neoprene sleeve, for example the Mava sleeve is good.
If your leg is prone to stiffness after not moving it for some time, for example when sitting in the office or car, use simple movements before standing up to lessen your symptoms. Just bending your knees back and forwards or standing up for a few minutes every quarter hours helps to keep the knee active and prevents stiffness.
If you have a stiff knee from arthritis, omega-3, glucosamine and chondroitin are very effective at reducing the symptoms. Experiment with these supplements to see which ones work the best for you.
Stretching, range of motion (ROM) and strengthening help get rid of your knee stiffness as fast as possible. Almost all kind of knee stiffness reacts well to these exercises. Still, for the best results get your doctor's advice and stop the exercises if you feel pain.
To warm up before the exercises, perform 10 to 15 minutes of walking. Always ask your doctor about the exercises while you are just planning them. If the stiff knee, pain in back of knee does not improve you may need a more aggressive treatment.
While you may think that squats destroy knees, they can help a lot if you have knee issues. This is simply so because squats help strengthen the muscles muscles around the knees.
Tighten your thigh muscles and slowly lift your injured leg off the floor up until it's at 45 degrees. Hold this position for two seconds, then gently let your leg back down again. Do three sets of 15 repetitions.
For quad stretch, hold onto the back of a chair or a table for better balance. Lift one of your feet, grab your ankle and pull your heel gently towards your buttocks. Hold this position for about thirty seconds while keeping your knees together. Let your leg back down, and repeat with your other leg. Do one repetition of this exercise for each leg.
For wall squats stand with your back against a wall, with your feet shoulder-width apart and a ball between your lower back and the wall. Squat down slowly, take care that your knees are always behind your heels. Stop once your thighs are at 45 degrees and hold the positions for two seconds, then raise your body back up slowly. Do three sets of 15 reps.
To stretch your hamstrings, sit on the floor with your back held straight. Straighten your legs and keep your feet relaxed. Place your hands on your legs palms-down, and slowly slide them towards your heels as long as it's comfortable. Do not arch your back or lock your knees. Hold this position for half minute.
This exercise works because your hamstrings get stretched as your upper body slowly leans forward.
Knee marching is a really old school exercise, which is great for strengthening your muscles without overloading your knees.
You can do the knee marching either while sitting, or standing up.
If you are sitting in a chair, plant your feet on the ground. Next raise your thighs up from the chair one at a time, while keeping your shin vertical.
If you are standing, simply raise your thigh up until it is horizontal, while keeping your shin vertical. The other leg stays on the ground. Then let your leg back down, and repeat with the other leg. Do this exercise for 5 minutes. For better stability you can lean with your back to a wall.
For short arcs sit down on the floor with your legs held straight, and place a rolled up towel under your injured knee. Pull your toes towards yourself and squeeze your thigh muscles. Your foot will slowly rise from the ground. Hold this position for two seconds, then let your leg slowly back down.
Do 3 sets of 15 reps.
Standing hamstring curls is a simple exercise which help strengthen your hamstring muscles.
For the curls stand up with your back held straight. Hold onto a table or back of a chair for better balance. Keep on leg planted on the ground, and bend the other's knee until your heel touches your buttocks. Then lower your heel again and repeat with the other leg. The usual three sets of 15 reps works really well for this exercise too.