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Osteoarthritis of knee
Other Resources UpToDate PubMed

Osteoarthritis of knee

Contributors: Shannon M. Kaupp MD, Sandeep Mannava MD, PhD
Other Resources UpToDate PubMed


Causes / typical injury mechanism: Osteoarthritis of the knee can be divided into primary and secondary types. Primary osteoarthritis implies that the articular cartilage degeneration occurs without a specific underlying cause. Secondary osteoarthritis is due to structurally abnormal cartilage, such as that in rheumatoid arthritis, or due to abnormal force distribution across the joint, as seen in patients with a prior injury or trauma. Osteoarthritis is a slow, progressive joint degradation process that typically occurs over 10-15 years, if not longer.

Classic history and presentation: Patients often present due to long-standing pain and stiffness in one or more joints. Further examination can reveal crepitus, bony enlargement or osteophyte formation, joint effusion, and point tenderness. Classically, the patient will have joint pain that worsens with activity, as opposed to an inflammatory arthritis that will improve with activity. Imaging is often used to diagnose the extent of joint arthritis and follow the joint's degenerative progression.

Prevalence: About one-third of people older than 65 years have knee osteoarthritis, so this disease has a very high prevalence among the general population. Recent estimates have shown that the prevalence will only increase, due to more people becoming overweight and obese.

Risk factors: There are many risk factors for knee osteoarthritis, including female sex (45% increased risk for women compared to men), older age, genetics, overweight or obese body mass index (BMI), previous joint injury / trauma (eg, intra-articular fracture, ligamentous injury, meniscal injury), joint malalignment, and repetitive joint damage.


M17.9 – Osteoarthritis of knee, unspecified

239873007 – Osteoarthritis of knee

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Diagnostic Pearls

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Differential Diagnosis & Pitfalls

  • Septic arthritis – Suspect if the joint is erythematous and/or warm with overlying erythema, painful motion, and systemic signs of illness. Medical comorbidities increase the risk of joint infection (eg, history of intravenous drug use, uncontrolled diabetes mellitus type 2).
  • Inflammatory arthritis (Rheumatoid arthritis, Psoriatic arthritis) – Suspect with multijoint involvement and when x-ray imaging shows bony erosions.
  • Meniscal injury – MRI imaging is used to rule this out.
  • Ligamentous injury – Anterior cruciate ligament injury (ACL), Posterior cruciate ligament injury (PCL), Medial collateral ligament knee injury (MCL), and Lateral collateral ligament knee injury (LCL). MRI imaging is used to rule this out.
  • Bone contusion
  • Osteochondritis dissecans of the knee
  • Pes anserine pain syndrome
  • Patellofemoral pain syndrome
  • Crystal arthropathy – See Gout and Calcium pyrophosphate deposition disease.
  • Lyme disease
  • Diffuse tenosynovial giant cell tumor (PVNS)
  • Cancer – Metastatic lesion versus primary sarcoma.

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Last Reviewed:12/09/2020
Last Updated:01/26/2021
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Osteoarthritis of knee
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