1. Overuse and Tendonitis
When a tendon around the knee gets irritated and inflamed from constant, repetitive use, it'll start to hurt. The affected area will usually swell, or a lump will develop along the tendon. Another sign: The pain in the area will increase when you move or flex the knee.
Try this: You can reduce the inflammation and consequently relieve the pain by resting and applying ice to the knee. Dr. Weiss also recommends eccentric exercises, like hamstring drops. Kneel on the floor with your feet underneath the couch to keep them in place (you should be facing away from the couch), then lean your torso toward the ground slowly.
Bad form while performing any physical act can cause both acute and chronic injuries. From walking to resistance training, proper form and technique are key to preventing stress and strain on the joints. If you normally don't experience knee pain but begin to at some point during your workout, check your form. The knee should not cave in or go over the toe when you're doing lunges and squats.
Try this: Stretch the muscle involved and perform non-weight-bearing AROM (active range of motion) exercises. Example: Sit on a chair and raise your knee up to your chest, release, and repeat with the other knee. If pain persists, ice, rest, and revisit.
3. Cartilage Pain
When people talk about torn cartilage in the knee, they're usually referring to a torn meniscus. Meniscal injuries are among the most common causes of knee pain among active people and can occur during any activity in which you forcefully twist or rotate the knee. Symptoms include clicking, popping, or snapping deep inside the knee. This usually happens from starting, stopping, and changing position fast, or simply from a sharp change in direction. It can also happen if you squat too low or get up from a chair in a weird way, says Weiss.
Try this: After a suspected meniscus injury, ice it immediately. You may need to see your doctor to determine whether you need a MRI. The MRI will not only confirm a tear but will let you know if the injury needs to be treated conservatively or not. Once given the okay to exercise, strengthen and stabilize the knee with standing leg raises, hamstring curls, and heel raises. You'll want to avoid full-knee extension type moves following an injury as they can further stress the already damaged joints.
4. Stretched Ligament
After a ligament is stretched, attenuated, or sprained, it doesn't return to the normal shape and tightness. This makes the knee joint unstable. When you suffer a ligament injury, like that of the ACL, a huge amount of swelling can develop, causing further dysfunction.
Try this: RICE is in order: rest, ice , compression, and elevation. Bracing is best for this injury.
5. Muscle Pain
Straining or tearing a muscle around the knee joint will cause pain in that area and will usually call attention to a specific spot on the muscle belly or musculotendinous junction. If you pull or strain the hamstrings, groin, or quads, it will most likely cause pain around the knee.
Try this: The best treatment for acute muscle pain would be cryotherapy initially, then moving toward heat and gentle stretching.
Overtime, cartilage that covers the long bones (called hyaline cartilage—it's different from fibrocartilage/meniscus) gets worn away, causing pain deep in the knee. Normal wear and tear is to be expected, but when someone experiences weight fluctuations or obesity, arthritis can happen earlier and advance to a greater degree.
Try this: The treatment of choice for any joint arthritis is heat or contrast bath, aquatic therapy, and gentle range of motion exercises (exploring the full movement potential of a joint). Avoid full extension on those ROM exercises.