The knee joint is the junction of three bones: the femur (thigh bone or upper leg bone), the tibia (shin bone or larger bone of the lower leg), and the patella (knee cap). The patella sits over the femur at the front of the knee joint and slides when the leg moves. It protects the knee and gives leverage to muscles.

The ends of the three bones in the knee joint are covered with articular cartilage, a tough, elastic material that helps absorb shock and allows the knee joint to move smoothly. There are two menisci between the shinbone (tibia) and thighbone (femur) in the knee joint. The C-shaped medial meniscus is on the inside part of the knee, closest to your other knee. The U-shaped lateral meniscus is on the outer half of the knee joint.

These two menisci act like shock absorbers in the knee and enhance stability. The menisci help spread out the forces that are transmitted across the joint. Walking puts up to four times your body weight on the joint. Running puts eight times your body weight on the knee. As the knee bends, the back part of the meniscus takes most of the pressure.

There are two groups of muscles at the knee. The quadriceps muscle comprises four muscles on the front of the thigh that work to straighten the leg from a bent position. The hamstring muscles, which bend the leg at the knee, run along the back of the thigh from the hip to just below the knee. Keeping these muscles strong with exercises helps support and protects the knee.

The quadriceps tendon connects the quadriceps muscle to the patella and provides the power to extend the leg. Four ligaments connect the femur and tibia and give the joint strength and stability:

The medial collateral ligament (MCL) provides stability to the inner (medial) part of the knee.

The lateral collateral ligament (LCL) provides stability to the outer (lateral) part of the knee.

The anterior cruciate ligament (ACL), in the center of the knee, limits rotation and the forward movement of the tibia.

The posterior cruciate ligament (PCL), also in the center of the knee, limits backward movement of the tibia.

Other ligaments are part of the knee capsule, which is a protective, fiber-like structure that wraps around the knee joint. Inside the capsule, the joint is lined with a thin, soft tissue called synovium.

Meniscus Injuries

Causes

The meniscus is easily injured by the force of rotating the knee while bearing weight. A partial or total tear may occur when a person quickly twists or rotates the upper leg while the foot stays still (for example, turning to hit a tennis ball). If the tear is tiny, the meniscus stays connected to the front and back of the knee; if the tear is large, the meniscus may be left hanging by a thread of cartilage. The seriousness of a tear depends on its location and extent.

           Symptoms

·        Initially, pain particularly when the knee is straightened

·        Swelling

·        The knee may click, lock, or feel weak, unstable

Treatment

If the tear is minor and the pain and other symptoms go away, the doctor may recommend a muscle-strengthening program, ant-inflammatories and ice.  Exercises for meniscal problems are best started with guidance from a doctor and physical therapist or exercise therapist. The therapist will make sure that the patient does the exercises properly and without risking new or repeat injury. The following exercises after injury to the meniscus are designed to build up the quadriceps and hamstring muscles and increase flexibility and strength.

If the tear is more extensive, the doctor may perform arthroscopic surgery to see the extent of injury and to repair or remove the torn piece. The doctor can sew the meniscus back in place if the injury is in an area with a good blood supply, and if the ligaments are intact.

If the tear is in an area with a poor blood supply, the doctor may cut off a small portion of the meniscus to even the surface, this is called a partial meniscectomy.

ACL Ligament Injuries

Causes

The ACL is most often partially or fully torn (or both) by a sudden twisting motion (for example, when the foot is planted one way and the knee is turned another, such as skiing, soccer or basketball).

The PCL is most often injured by a direct impact, such as in an automobile accident or stepping into a hole.

           Symptoms

·        Pain and immediate swelling

·         Difficulty straightening and bending the knee 

·         Loud popping sound when the injury happened

·         Instability or buckling of the knee, especially when pivoting

Treatment

For an incomplete tear, the doctor may recommend rest and immobilizing the knee until pain is controlled, then physical therapy to strengthen surrounding muscles. The doctor may also prescribe an ACL brace to protect the knee during activity.

For a completely torn ACL in an active athlete or motivated person, the doctor is likely to recommend surgery. This is to prevent further injury to the knee and allow the patient to return to sports that require pivoting. The surgeon will reconstruct the torn ligament by using a piece of healthy ligament from the patient (autograft) or from a cadaver (allograft).

One of the most important elements in a patient's successful recovery after cruciate ligament surgery is a 4- to 6-month exercise and rehabilitation program.

Medial and Lateral Collateral Ligament Injuries

Causes

Most often a blow to the side of the knee that stretches or tears the ligament on the side of the knee. Such blows frequently occur in contact sports like football or hockey.

Symptoms

·        A popping sensation and the knee may buckle sideways.

·        Pain and swelling are common.

Treatment

Most sprains of the collateral ligaments will heal if the patient follows a prescribed exercise program. In addition to exercise, the doctor may recommend ice packs to reduce pain and swelling and a small sleeve-type hinge brace to protect and stabilize the knee. A sprain may take 4 to 6 weeks to heal. A severely sprained or torn collateral ligament may be accompanied by a torn ACL, which usually requires surgical repair.

Arthritis

Causes

Arthritis of the knee is most often osteoarthritis. In this disease, the cartilage in the joint gradually wears away. This is caused from use overtime, previous trauma or injuries to the area and excess weight. If this is hard to understand, think of what would happen to a pair of pants if you wore them daily for 10 – 20 years.  Certain areas would wear out; this is similar to what happens with your joints as you get older.

Symptoms

·        Stiffness

·        Pain and swelling

·        Locking of the joint

·        Sensation of grinding or clicking

Treatment

Medications to reduce pain such as aspirin or acetaminophen (Tylenol*); nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen or Aleve. Exercise to restore joint movement and strengthen the knee. Losing excess weight. Cortisone injections when pain is severe or lubricant injections if unable to take NSAIDS.  Surgery to clean up the loose cartilage and remove loose bodies may be helpful in early arthritis. In a person with severe arthritis where bone is rubbing on bone and no cartilage is left, a joint replacement may be the best option.

Chondromalacia

Causes

(KON-dro-mah-LAY-she-ah), refers to softening of the articular cartilage of the kneecap. This disorder occurs most often in young adults and can be caused by injury, overuse, parts out of alignment, or muscle weakness. Instead of gliding smoothly across the lower end of the thighbone, the kneecap rubs against it, thereby roughening the cartilage underneath the kneecap. The damage may range from a slightly abnormal surface of the cartilage to a surface that has been worn away to the bone.

Symptoms

·        Stiffness after sitting or standing for long periods of time

·        Dull pain around or under the knee cap

·        Pain with climbing stairs

Treatment

Perform low-impact exercises that strengthen muscles, particularly the inner part of the quadriceps, without injuring joints. Swimming, riding a stationary bicycle, and using a cross-country ski machine are acceptable as long as the knee doesn't bend more than 90 degrees. A Physical Therapist is quite helpful on giving a good exercise program without irritating the knee further.  Electrical stimulation may also be used to strengthen the muscles. Orthotics may help align the lower leg better taking stress off of the kneecap. Avoid crossing legs; try to avoid activities that require repetitive squatting or kneeling.

If these treatments do not improve the condition, arthroscopic surgery may be recommended to smooth the surface of the cartilage and "wash out" the cartilage fragments that cause the joint to catch during bending and straightening. In more severe cases, surgery may be necessary to correct the angle of the kneecap and relieve friction with the cartilage or to reposition parts that are out of alignment.