Clicking Sound at the Patellofemoral Joint (Patellar Crepitus)

What Produces the Sound?

"During active or passive movement, the palm of one hand placed over the patella, crepitus will be felt if osteoarthritis has involved the patellofemoral joint." — S. Das, Manual on Clinical Surgery

Main Causes

1. Chondromalacia Patellae (most common in young adults)

• Pathology: Softening, fissuring, and fibrillation of the articular cartilage on the posterior surface of the patella; a "kissing lesion" may form on the opposing femoral condyle.
• Who: Young adults, especially females.
• Symptoms: Anterior knee pain worsened by stair climbing, prolonged sitting ("theater sign"), kneeling; knee may give way. Occasional swelling.
• Exam: Tenderness at patellar margin; crepitus when the patella is pushed medially/laterally against the femoral condyles; patellar grind test positive (pain with anterior-posterior pressure on the patella while the patient contracts the quadriceps).
• Note: The term has largely been replaced by patellofemoral pain syndrome (PFPS) clinically, as the correlation between cartilage pathology and symptoms is imprecise. Definitive diagnosis requires arthroscopy (ragged cartilage appearance).

2. Patellofemoral Pain Syndrome (PFPS)

• Most common cause of knee pain overall, especially in 20s–30s, women > men.
• Mechanism: Altered patellofemoral tracking due to quadriceps weakness (especially vastus medialis), hip abductor weakness, patellar subluxation, or malalignment.
• Symptoms: Gradual-onset anterior knee pain; worse going up/down stairs, squatting, prolonged sitting; clicking or grinding is common.
• Risk factors: Gluteal weakness, quadriceps weakness, patellar subluxation, prepatellar bursitis, arthritis, meniscal tears, quadriceps/patellar tendinopathy.
• Diagnosis: Clinical; knee X-rays to assess patellofemoral joint space and rule out osteoarthritis.
• — Rosen's Emergency Medicine

3. Osteoarthritis of the Patellofemoral Joint

• Pathology: Progressive cartilage loss; the commonest intra-articular source of clicking in older adults.
• Exam: Crepitus palpable (and sometimes audible) with passive flexion/extension while the palm rests over the patella.
• X-ray: Narrowing of patellofemoral joint space; osteophytes.

4. Medial Plica Syndrome

• Plica are embryological remnant folds of synovial tissue inside the knee that normally disappear; when they persist and become thickened (often after repetitive activity or synovitis), they snap over the medial femoral condyle.
• Symptoms: Medial knee pain, a snapping sensation (sometimes a visible snap) with repeated flexion/extension; palpable band parallel to the medial border of the patella.
• Diagnosis: Confirmed by MRI or arthroscopy.
• Treatment: Conservative (strengthening, stretching); arthroscopic resection if refractory.
• — Tintinalli's Emergency Medicine

5. Extra-articular Causes (dull thud, not a sharp click)

• Tendons snapping over bony prominences: medial hamstring tendon over the medial condyle, biceps femoris tendon over the fibular head, or iliotibial band over the lateral condyle.
• Tendon snapping over an exostosis (bony outgrowth).
• These typically produce a dull thud rather than a sharp intra-articular click.

6. Normal / Benign Crepitus

• In children and adolescents, a painless click as the patella moves over the condyle can occur in a completely normal joint and requires no treatment.
• Gas cavitation within the joint (like knuckle-cracking) is also benign.

Outerbridge Classification of Articular Cartilage Damage

Clinical Assessment

Management Principles