Knee Cartilage Defects

Knee cartilage defects are areas where the smooth, protective articular cartilage that lines the surfaces of the knee joint has been damaged or lost. Cartilage is a specialized tissue that cushions the bones, absorbs shock, and allows the joint to move smoothly. Unlike many other tissues in the body, cartilage has no blood supply, so it has very limited ability to repair itself when injured. When cartilage is damaged, it does not regenerate in the same way muscle or skin does, and even small defects can disrupt normal joint function.

These defects vary in size and depth, ranging from minor thinning of the cartilage layer to full-thickness lesions that expose the underlying bone. The location of the defect—such as on the femur, tibia, or patella—can influence the severity of symptoms. Left unaddressed, cartilage defects may contribute to progressive wear within the joint and increase the risk of developing osteoarthritis over time.

What are the causes of knee cartilage defects?

There are several ways in which cartilage defects can occur, with both acute and gradual processes contributing:

• Traumatic injury: One of the most common causes is a sudden injury to the knee, such as a fall, collision, or twisting motion. These injuries are especially common among athletes who play contact or high-impact sports like football, basketball, or soccer. A direct blow to the knee or a sudden pivot can shear cartilage from the bone surface.
• Sports-related stress: Athletes who put repeated, heavy stress on their knees—such as through running, jumping, sprinting, cutting, and pivoting—are at higher risk of developing focal cartilage defects, especially if combined with other injuries like ligament tears or meniscus damage.

A “focal defect” is a specific, localized area of cartilage damage in the knee joint. Because cartilage acts as the smooth surface that allows bones to glide against one another, repeated high-impact loads can cause small areas of cartilage to crack, thin, or break away. Over time, this damage does not spread evenly across the knee; instead, it often concentrates in one spot, creating a “focal” (targeted) defect.

• Degenerative changes: Over time, the natural aging process and cumulative wear on the joint can cause cartilage to thin and break down. This type of degeneration is often gradual and may be accelerated in individuals with abnormal joint alignment, prior injuries, or genetic predisposition.
• Osteochondritis dissecans: In some cases, a piece of cartilage and the underlying bone lose their blood supply, leading to separation and defect formation. This condition is most often seen in adolescents and young adults who are active in sports.
• Other contributing factors: Mechanical issues such as joint instability, poor alignment, or muscle imbalance can also place uneven pressure on the cartilage, creating conditions where defects are more likely to form.

What are the symptoms of knee cartilage defects?

The symptoms associated with cartilage defects vary depending on the size, location, and severity of the injury. However, several common patterns are seen:

• Pain: Patients often experience sharp or aching pain within the knee. Pain may worsen with activity, particularly during weight-bearing movements such as running, jumping, or climbing stairs.
• Swelling: Recurrent or persistent swelling is common, caused by joint inflammation or the presence of loose cartilage fragments.
• Stiffness and loss of motion: Damage to cartilage can cause the joint to feel stiff, especially after periods of rest, and may limit the ability to fully bend or straighten the knee.
• Catching or locking: Loose cartilage or irregular joint surfaces can interfere with smooth movement, leading to sensations of catching, clicking, or locking during activity.
• Instability or giving way: While less common than pain or swelling, some individuals may feel that the knee is unstable or gives out during sports or daily activities.

For athletes, these symptoms often translate into difficulty performing at peak levels. Loss of speed, agility, or endurance can be the first signs that a cartilage defect is affecting joint performance.

How are knee cartilage defects diagnosed?

Because cartilage cannot be seen on plain X-rays, diagnosing cartilage defects requires a combination of history, physical examination, and advanced imaging.

• Clinical evaluation: A sports medicine specialist begins by discussing the patient’s symptoms, activity level, and history of injuries. Physical examination includes assessing for tenderness, swelling, joint alignment, and range of motion. Specific tests may be performed to evaluate joint stability and to identify pain with weight-bearing or certain movements.
• Imaging studies: Magnetic resonance imaging (MRI) is the most valuable non-invasive tool for evaluating cartilage. MRI can detect both small and large lesions, assess the depth of damage, and identify any associated injuries such as ligament or meniscus tears. In some cases, computed tomography (CT) scans may be used to provide additional detail on bone involvement.
• Arthroscopy: In certain situations, when symptoms persist and imaging is inconclusive or when surgical planning is required, arthroscopy may be performed. This minimally invasive procedure involves inserting a small camera into the knee to directly visualize the cartilage surfaces. Arthroscopy allows precise assessment of lesion size, location, and severity.

As a board-certified orthopedic surgeon specializing in sports medicine, cartilage restoration, and shoulder/elbow care, Dr. Brian Waterman brings extensive experience in treating athletes and nonathletes alike with knee cartilage defects. Whether managing injuries sustained during competition or addressing chronic cartilage issues, Dr. Waterman’s goal is to help patients maintain long-term joint health and active lifestyles. We invite you to contact Dr. Waterman to schedule a consultation when you have knee pain to receive a reliable diagnosis and all your treatment options. His office is located in Winston Salem, NC.