The knee is one of the largest and most complex joints in the body. It is a hinged synovial joint that is located where the tibia and femur meet.
There are 4 main bones that connect and make up the knee joint:
- Femur (Thighbone) - the femur head creates the ball-and-socket joint of the hip (at the acetabulum) and creates the top of the knee at the lower end. The femur is the main bone of the leg and supports the weight of the body on the leg.
- Tibia (Shinbone) - connects with the knee at the upper end and the ankle at the lower end. It bears and distributes weight across the knee and to the ankle
- Fibula (Calf Bone) a slender bone located at outer side of the leg parallel to and slightly behind the tibia. Ligaments connect it to the two ends of the tibia. It helps strengthen the tibia and provides support in the slight rotation of the knee.
- Patella (Kneecap) - a tendon at the top of the patella and a ligament at the bottom hold the nearly heart-shaped bone in place at the center of the knee. It protects your knee joint.
The ends of these bones are covered with articular cartilage, a smooth substance that acts as a shock absorber and helps bones move easily. Articular cartilage is found on the femur, the top of the tibia, and the back of the patella. All remaining surfaces of the knee are covered by a thin lining called the synovial membrane, which releases a fluid that lubricates the cartilage and reduces friction to nearly zero in a healthy knee.
Between the femur and tibia are two C-shaped wedges of cartilage called menisci. These act as shock absorbers that cushion and protect the joint.
Numerous bursae (fluid-filled sacs) help the knee move smoothly.
Large ligaments connect the femur, tibia and kneecap and provide stability. The four main ones are:
- Anterior Cruciate Ligament (ACL) - the ACL controls the tibia's rotation and forward movement.
- Posterior Cruciate Ligament (PCL) - located in the center of the knee, the PCL controls the tibia's backward movement.
- Medial Collateral Ligament (MCL) - provides stability to the inner knee.
- Lateral Collateral Ligament (LCL) - provides stability to the outer knee.
Tendons (tough bands of soft tissue that connect muscles to bones) connect the knee bones to the leg muscles that move the knee joint and provide stability. The largest tendon in the knee is the patellar tendon, which covers the kneecap, runs up the thigh, and attaches to the quadriceps.
Knee pain is one of the most common complaints among patients of all ages. It is also the most commonly injured joint. Fortunately, knee problems don't usually require surgery and can be resolved with physical therapy and physician or physical therapist prescribed self-treatment methods (e.g., the use of anti-inflammatory medication, rest, ice/heat, home exercise programs, etc.).
However, if you suffer from any of these symptoms, you'll need to see your doctor as soon as possible.
- Severe edema (swelling)
- Inability to fully extend or flex the knee
- Obvious deformity in the leg or knee
- The knee is feverish to the touch in addition to being swollen and red
Common Causes of Knee Pain
Common knee problem complaints include:
- Sprained Knee Ligaments - overstretched or torn ligaments within the knee joint that connect the thigh bone to the shin bone. Sprained knee symptoms differ depending on which ligament is injured. The following are typical symptoms for the main ligaments:
- Anterior Cruciate Ligament (ACL) - the knee may pop at the time of injury and may buckle or otherwise feel unstable.
- Posterior Cruciate Ligament (PCL) - the back of the knee may hurt and may get worse when kneeling on it.
- Lateral Collateral Ligament (LCL) or Medial Collateral Ligament (MCL) - is tender where it is injured and may buckle toward the opposite direction from the injured ligament.
- Strained Knee Muscles/Tendons - overstretched or torn muscles or tendons typically caused by overuse but can also be the result of an accident or sports injury.
- Torn Meniscus - the menisci are two C-shaped pads of cartilage found in each knee joint that act as shock absorbers between the thighbone and shinbone and provide some stability in the knee. A torn meniscus is usually caused by jarring or rotating movements. This injury is common among athletes but can also happen to anyone during heavy lifting, kneeling, or deep squatting. Symptoms include pain, swelling, and a popping sensation.
- Patellar Tendinitis - also known as jumper's knee, patellar tendinitis is an injury to the tendon connecting your kneecap (patella) to your shinbone. Typical symptoms include pain between the kneecap and where the tendon attaches to the shinbone (tibia).
- Bursitis - inflammation of the bursa located near the knee joint. The two areas of the knee that are most susceptible to bursitis are over the kneecap or on the inner side of the knee below the joint. Bursitis typically occurs as a result of over-stressing or repetitive use of the areas around the joints.
- Arthritis - osteoarthritis (OA) is the most common in the knee. Other forms of arthritis that can affect the knee include:
- Rheumatoid Arthritis (RA)
- Gout - uric acid crystal buildup
- Pseudogout - calcium-containing crystals in the joint fluid
- Septic Arthritis - arthritis that develops when the knee joint becomes arthritic
- Patellar Fracture - also known as a broken kneecap. Clean, stable kneecap fractures or more severe open breaks or communities fractures are typically caused by a direct and hard fall onto the knee or a sharp blow to the kneecap typically due to the knee hitting the dashboard in a traffic accident. Symptoms include:
- Inability to bend or straighten injured knee
- Inability to raise the leg
- Inability to bear weight on injured knee
- Inability to walk
It is important to seek treatment for knee injuries and conditions no matter how minor it may seem to you. Some knee conditions, such as arthritis, can lead to increasing pain, joint damage and disability if left untreated. The good news is that knee injuries and conditions respond well to physical therapy and may not need surgery. This is a great reason to try physical therapy first!