Knee pain is frequent for adolescents, especially those engaged in sports or undergoing rapid physical growth. Focused discomfort in the knee can indicate specific conditions unique to this age group, which differ vastly from causes of knee pain in adults. The teenage years combine skeletal immaturity and high activity levels, creating vulnerability at the knee joint. Understanding the precise source of the pain—whether related to growth, overuse, or acute injury—is the first step toward effective management.
Pain Related to Growth and Skeletal Immaturity
The most distinctive causes of knee pain in teenagers are linked directly to the ongoing process of bone growth. These conditions fall under apophysitis, which is the inflammation of a growth plate where a tendon attaches to the bone. Repetitive stress can pull on the softer, developing cartilage because bone growth often outpaces the flexibility of surrounding muscles and tendons.
Osgood-Schlatter Disease (OSD) is a common manifestation, typically causing pain and swelling just below the kneecap at the bony bump on the shinbone, known as the tibial tubercle. The powerful quadriceps muscles exert a pulling force through the patellar tendon onto this growth plate, especially during running and jumping. This repeated traction leads to irritation and the body’s attempt to repair it by laying down new bone, sometimes resulting in a permanent, visible bump.
A similar condition, Sinding-Larsen-Johansson Syndrome (SLJ), often occurs between 10 and 14 years old. Instead of affecting the shinbone, SLJ causes localized pain at the inferior pole, or bottom tip, of the kneecap where the patellar tendon originates. Both OSD and SLJ are self-limiting conditions that resolve once skeletal maturity is reached and the growth plates close.
Overuse and Mechanical Instability
Beyond the growth plates, many chronic knee complaints stem from repetitive strain and underlying issues with movement mechanics. Patellofemoral Pain Syndrome (PFP), often called “Runner’s Knee,” is the most prevalent cause of pain around the front of the knee. This condition is characterized by a dull, aching sensation behind or around the kneecap. The pain worsens with activities like climbing stairs, squatting, or sitting for prolonged periods.
PFP is fundamentally a problem of patellar maltracking, where the kneecap does not glide smoothly in the groove of the thigh bone. This improper movement can be exacerbated by poor movement quality, muscle imbalances, or dynamic valgus, which is the tendency for the knee to collapse inward during activity. Biomechanical factors, such as decreased quadriceps and hamstring strength or hip muscle weakness, increase the contact pressure in the joint, leading to friction and pain.
Another distinct overuse injury is Patellar Tendinitis, or “Jumper’s Knee,” which primarily affects older adolescents and young adults. This involves the patellar tendon itself, causing sharp, localized pain directly over the tendon just below the kneecap. Repetitive, forceful loading from jumping sports like basketball or volleyball creates micro-tears and degeneration within the tendon tissue. Unlike growth-related conditions, this pain is centered in the body of the mature tendon, not the growth plate, and relates directly to the high-impact demands of sport.
Acute Injuries and Traumatic Events
Sudden, forceful events can cause acute structural damage that demands immediate attention. Ligament injuries are common in sports that involve sudden stops, changes in direction, or twisting movements. The Anterior Cruciate Ligament (ACL) is frequently torn in non-contact scenarios, often accompanied by a distinct “pop” sensation at the time of injury.
An ACL tear compromises the knee’s stability and is often followed by rapid swelling within hours. These severe ligament injuries frequently occur alongside damage to other structures, such as the menisci. The menisci are C-shaped cartilage pads that act as shock absorbers in the joint. Meniscus tears in teens are usually traumatic, resulting from the same twisting mechanisms that injure the ACL, unlike the degenerative tears seen in older adults.
Traumatic bone injuries, particularly those involving the growth plates (physes), are a risk in the skeletally immature athlete. Since growth plates are weaker than the surrounding ligaments and bone, a forceful impact or twist can cause a growth plate fracture instead of a typical sprain or break. These injuries can affect bone development and require specialized care to ensure proper healing and prevent long-term growth issues.
When to Seek Professional Medical Attention
While many adolescent knee pains respond well to rest and reduced activity, certain warning signs indicate the need for a prompt medical evaluation. Any instance of severe, sudden pain or the inability to bear full weight on the leg following an injury should be assessed immediately. Significant swelling that appears rapidly, within minutes to a few hours, can signal serious internal damage like a ligament rupture or fracture.
Mechanical symptoms, such as the knee locking, catching, or feeling unstable or giving way, suggest a structural issue requiring expert diagnosis. Pain severe enough to wake the teenager from sleep, or knee pain accompanied by systemic symptoms like an unexplained fever, must be investigated to rule out serious underlying conditions. If the knee pain persists for more than two weeks despite appropriate rest and activity modification, a professional evaluation is warranted.