Knee Pain and Stiffness: Differential Diagnosis and When to Seek Care

Knee stiffness and pain with limited flexion suggest intra-articular or periarticular pathology. Common causes by category:

Degenerative/Mechanical

• Osteoarthritis: Joint space narrowing, osteophytes, crepitus. Morning stiffness <30 min.
• Meniscus tear: Mechanical symptoms (clicking, locking, giving way); joint line tenderness.
• Chondromalacia patellae / Patellofemoral pain: Anterior knee pain, worse stairs/squatting.

Inflammatory

• Rheumatoid arthritis: Symmetric, morning stiffness >1 hr, synovitis, systemic features.
• Gout / Pseudogout: Acute monoarticular flare (red, hot, excruciating); crystals in synovial fluid.
• Septic arthritis: Medical emergency—fever, severe pain, guarded motion. Aspirate urgently.

Soft Tissue / Overuse

• Bursitis (prepatellar, pes anserine): Localized swelling, tenderness.
• Tendinopathy (patellar, quad): Load-related pain, tenderness at insertion.
• IT band syndrome: Lateral knee pain, worse downhill running.

Ligamentous

• ACL/PCL/MCL/LCL tears: instability, effusion, positive Lachan/pivot shift/varus-valgus tests.

Other

• Baker's cyst (popliteal swelling), referred pain (hip/spine), tumor (rare).

When to See a Clinician

• Inability to bear weight
• Marked effusion, redness, warmth
• Locking/giving way
• Fever with joint pain
• No improvement after 1–2 weeks conservative care

Initial Workup

History, exam (effusion, ROM, special tests), weight-bearing X-rays (AP, lateral, Merchant), ± MRI if internal derangement suspected.