Cartilage Injuries in the Knee of an Athlete

What is a cartilage injury?

Cartilage injuries are common in athletes and can be seen in sports that require a lot of twisting and pivoting around the knee joint, such as football and basketball. There are two types of cartilage within the knee joint: articular cartilage and meniscus.

Articular cartilage coats the surface of the three bones that make up the knee joint: the femur, the tibia, and the patella (kneecap). The main purpose of articular cartilage is to provide a smooth surface for the bones to glide against one another and to act as a shock absorber. Injury to the articular cartilage can occur when there is a force applied to the cartilage that exceeds its capacity. Articular cartilage does not have a blood supply and must rely on the fluid in the knee joint (called synovial fluid) for its nutrients. Because of this, the articular cartilage has very little capacity to repair itself when injured. Ongoing damage to articular cartilage that results in exposure of the underlying bone surface is the fundamental defect in the common end stage condition known as osteoarthritis. 

The meniscus is the other type of cartilage within the knee joint; there is one on the inside (medial meniscus) and outside (lateral meniscus) of the knee. It is in a semilunar (crescent) shape that is attached to the outer portion of the tibial surface and conforms to the rounded portion of the end of the femur where articular cartilage resides. The meniscus has many functions but is primarily thought to act as a shock absorber, distributing or spreading the forces (incurred in standing, walking, running, etc.) between the femur and tibia, much like the friction-minimizing characteristics of an O-ring. Injury can occur when a person twists or rotates the upper leg while the foot remains planted on the ground. The very outer portion of the meniscus has a blood supply and has the capacity to heal when torn. The central one-third of the meniscus has a variable healing capacity, and the most inner portion of the meniscus is frequently not repairable.

What symptoms are present with an acutely torn cartilage?

In general there is sharp pain in the knee with either full extension or deep flexion, depending on the location of the tear. There can be some swelling of the knee that usually occurs over a 24 hour period but can occur rapidly within 1-2 hours. There can also be a description of catching, popping, or even locking where the knee is unable to fully extend. If a piece of the torn articular cartilage or meniscus is wedged between the femur and tibia, the knee can be very painful and have limited motion such as locking because of the mechanical block. Symptoms of the cartilage tear may disappear on their own, but they frequently persist and require surgical treatment.

How can a cartilage tear be diagnosed?

In addition to the described symptoms, a physical exam and x-rays can be used to help with the diagnosis. Physicians may use a test in which the doctor flexes (bends) the leg, then rotates the leg outward or inward while extending it. This can elicit or reproduce the pain in the knee joint and is suggestive of a meniscal tear. Articular cartilage tears may present as joint line pain but in general are much more difficult to diagnose based on the physical exam. An MRI, which uses powerful magnets to cause the tissue to produce signals detected by a computer, can be used to confirm or identify the cartilage injury. Finally, arthroscopy, which is placing a small camera (5 millimeters in diameter) in the knee joint and displaying the images on a television screen, can be used to identify meniscal tears and articular cartilage lesions.

What is the treatment for a cartilage injury?

The treatment really depends on the severity of the symptoms. If the symptoms from the initial tear were mild and resolve themselves, then a muscle strengthening program is frequently recommended that may include:

• Straight leg raises
• Stationary bicycle riding against low resistance
• Leg extension with small weights
• Exercises in a pool

If the tear is more extensive, resulting in persistent pain, recurrent swelling and possibly mechanical symptoms such as locking, popping or catching, then the knee may require arthroscopic or open surgery to either repair or remove the torn cartilage.


For more information, contact the HSS Sports Medicine and Shoulder Service.