Knee clicking during activities like squatting is a common experience, medically referred to as crepitus. Hearing a pop or a crack can be unsettling, often leading to concerns about joint health. The sound is usually a benign phenomenon caused by normal joint mechanics, but it can sometimes signal an underlying issue. The key distinction is whether the noise is accompanied by pain, swelling, or a grinding sensation.
The Mechanical Reasons for Clicking
Most knee noises are harmless and result from one of two primary mechanical events. One common cause is cavitation, the same process that makes a knuckle crack. The knee joint is lubricated by synovial fluid, a thick fluid containing dissolved gases like nitrogen.
When the knee rapidly changes position, such as during a squat, the pressure within the joint capsule quickly drops. This rapid pressure change causes the dissolved nitrogen bubbles to form a larger bubble, which then collapses or bursts, creating the audible pop. Since the gases need time to redissolve, this noise usually cannot be immediately replicated.
The second cause for a non-painful click is the movement of soft tissues, such as tendons or ligaments, snapping over bony structures. As the knee flexes during a squat, a tight tendon may momentarily catch on a bone prominence before quickly slipping past it. This rapid movement generates a clicking sound, often felt as a quick sensation. Tendons like the popliteus or the iliotibial band (IT band) are frequent sources of this soft tissue crepitus.
When Knee Sounds Indicate a Problem
While most clicking sounds are benign, a noise accompanied by discomfort may indicate a pathological issue. The most concerning sound is a grinding, grating, or crunching noise, which suggests friction between joint surfaces. This sensation occurs when the smooth cartilage covering the ends of the bones has begun to wear down or become roughened.
The presence of pain, swelling, or a feeling of the knee locking or giving way alongside the noise is a significant indicator of a problem. One common condition is Patellofemoral Pain Syndrome (PFS), where the kneecap (patella) does not track smoothly in its groove on the thigh bone (femur). This poor tracking causes the underside of the kneecap to rub against the femur, leading to a grinding sensation and chronic irritation.
More serious causes involve direct damage to the cartilage or menisci, the C-shaped shock absorbers in the knee. A tear in the meniscus or the early stages of osteoarthritis, where joint cartilage is deteriorated, can cause painful clicking, catching, or locking of the joint. If the crepitus feels like a grinding under the kneecap or is consistently painful, consult a physician or physical therapist for an accurate diagnosis.
Actionable Steps to Reduce Knee Crepitus
Improving your squatting mechanics is a practical first step to reduce both benign and symptomatic knee crepitus. Focus on ensuring your knees track directly in line with your feet and avoid letting them collapse inward during the movement, a motion known as knee valgus. Initiate the squat by pushing your hips back as if sitting in a chair, which helps engage the gluteal muscles and reduces excessive forward travel of the knees.
Targeted strengthening of the muscles surrounding the knee can improve joint stability and tracking. Specific attention should be paid to the vastus medialis oblique (VMO), the muscle on the inner quad, and the gluteal muscles, particularly the gluteus medius. Exercises like split squats emphasizing the VMO or resistance band side steps to activate the gluteus medius help ensure the patella tracks correctly.
Mobility and flexibility exercises address muscle imbalances that place undue stress on the knee joint. Tightness in the hip flexors, hamstrings, or calves can alter the body’s movement pattern, forcing the knee to compensate. Gentle foam rolling of the quadriceps and hamstrings before activity helps release tension, allowing for smoother joint movement and potentially reducing soft tissue snapping.