by Dr. Cathy Fieseler
(First in a series)
Knee pain is one of the most common complaints for which runners seek medical evaluation. Running is blamed for many maladies; usually there is an underlying reason for the injury, whether intrinsic (anatomy) or extrinsic (factors outside the body, such as overtraining). Running has been blamed for the development of knee arthritis, though a 20 year study performed by researchers at Stanford University found a lower incident of knee arthritis in runners than non-runners.
Why do runners develop knee pain? A basic understanding of the anatomy is a necessary component in any discussion of knee injuries.
The knee is a combination of 3 different bony articulations. The largest of these is the junction of the femur (thigh bone) and tibia (large shin bone). The patella (kneecap) sits in the groove created by the two knobs at the end of the femur; this little bone tracks in the femoral groove with motion and plays a critical role in performing activities that require extension (straightening) of the knee. The fibula (small bone in the outer aspect of the lower leg) does not articulate with the femur but does so with the tibia; the fibula is connected to the femur by a ligament along the outer aspect of the knee. Flexion (bending) and extension (straightening) are the main motions of the knee; rotation and small amounts of side to side motion also occur in the joint.
Ligaments are fibrous structures that connect bones; a sprain is a ligament injury. This may range from a mild stretch to a complete tear. The capsule is a sleeve that surrounds the knee. Thickenings in the capsule form the capsular ligaments. There are a pair of ligaments along the sides of the knee (medial and lateral collateral) and another pair that cross inside the joint (anterior and posterior cruciate). Ligaments provide the joint with stability. Injuries are typically due to acute trauma (twisting, etc.).
Muscles are the structures that make the joint work. Muscles originate on a bone above the joint and attach to a bone below the joint. In the case of the knee, muscles originate on the pelvis or femur and attach to the tibia or fibula. Muscles, such as the hamstrings, which cross two joints (the hip and the knee), are more prone to injury.
Tendons are extensions of the muscles that attach to bones. An acute injury to a tendon is a strain; tendinitis is an overuse injury of the structure.
The quadriceps is a group of 4 large muscles that are located in the front of the thigh. One of the muscles (rectus femoris) originates on the pelvis while the other 3 originate on the femur. Just above the knee, the quadriceps tendon is formed; this attaches to the patella. The patellar tendon attaches the patella to the tibia. The main function of the quadriceps is extension (straightening) of the knee.
The hamstrings is a group of 3 muscles that originate on the pelvis (on the ischial tuberosity – the little bony protrusion on the bottom of the pelvis that you sit on) and attach to the tibia and fibula. The main function is flexion (bending) of the knee, in addition to bringing the leg backwards at the hip (extension).
Abductors and adductors are muscle groups that run from the pelvis and attach on the inside and outside aspects of the knee respectively. They provide some stability to the knee. The main function involves motion of the hip.
There are two types of cartilage in the knee. The end of each bone (including the back of the patella) is lined by articular cartilage. This well lubricated cartilage allows the joint to move freely. Breakdown of this cartilage leads to arthritis.
The menisci are two C-shaped fibrocartilage structures that sit between the femur and tibia. They provide some cushioning and stability to the knee. A meniscus may be acutely torn, commonly with a twisting injury of the knee. The blood supply to the meniscus is poor, so injuries often will not heal. Over time, the meniscus loses some of its fluid content, becoming more brittle. A degenerative meniscus tear may occur with minimal trauma as we age.
A bursa is a lubricating sac that prevents structures from rubbing directly against each other. There are several bursae in the knee that prevent friction between the patella and skin or tendons and bone. A bursa may be injured acutely by a direct blow or fall or due to repetitive activities (overuse injury).
Now that you have a basic understanding of the anatomy, the next several installments will address specific knee injuries.
Dr. Fieseler is the Director of Sports Medicine for the Trinity Mother Frances Health System in Tyler, TX. She is a regular contributor to Running Times and has served as the chairperson for the sports medicine committee of the Road Runners Club of America. For more information on Dr. Fieseler’s medical services, click on Dr. Cathy Fieseler.
Bennett Cohen (the Savvy Runner) and Gail Gould are the Founders and Presidents of the International Association of Women Runners (IAWR). To learn more about this global community of women who share a passion for running, visit www.iawr-connect.com.