Approach to knee pain: Clinical sciences
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Knee pain is a common musculoskeletal symptom that can be caused by damage to any of the ligamentous, muscular, or bony structures comprising the joint. Most often, knee pain is associated with trauma and conditions such as fractures and ligament or meniscus injuries.
On the other hand, non-traumatic causes can be classified based on the presence of joint effusion. No joint effusion is common in conditions, such as patellofemoral pain syndrome, prepatellar bursitis, and osteoarthritis; while joint effusion is typically seen in septic arthritis, crystal-induced arthropathy, and non-infectious inflammatory arthritis.
If a patient presents with knee pain, the first step is to perform a focused history and physical examination. Start by assessing the patient’s history of trauma preceding the onset of knee pain.
If the patient reports trauma to the knee, consider traumatic causes of knee pain and assess their risk for fracture using the Ottawa knee rules.
Ottawa knee rules include the age of 55 or older, point tenderness at the fibular head, isolated point tenderness of the patella, inability to flex the knee to 90 degrees, or inability to bear weight on the affected knee.
If the patient does not have any of these characteristics, your patient has a low risk for fracture, so no further evaluation is needed.
On the flip side, if the patient meets any of the criteria, then they have a high risk of fracture, so you should order x-rays. If an x-ray is performed, it may reveal a fracture, for example a fracture of the tibia, patella, or other surrounding bones.
Let’s take a look when x-ray findings are normal. If the x-ray findings show no fracture, consider ligamentous or meniscal injury. The mechanism of injury and physical exam can help distinguish between injuries of the anterior cruciate, posterior cruciate, and collateral ligaments.
First, let’s start with the anterior cruciate ligament injury or ACL injury for short. Let’s say the patient's knee pain developed after suddenly pivoting the knee with the foot firmly planted on the ground. Also, the patient may report an audible pop during the injury, followed by knee instability and a rapidly developing effusion.
Sources
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- "Management of Osteoarthritis of the Knee (Non-Arthroplasty) Evidence-Based Clinical Practice Guideline (3rd Edition)" American Academy of Orthopaedic Surgeons (2021)
- "ACR Appropriateness Criteria® Acute Trauma to the Knee" J Am Coll Radiol (2020)
- "Knee Pain in Adults and Adolescents: The Initial Evaluation" Am Fam Physician (2018)
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- "Septic Arthritis: An Evidence-Based Review of Diagnosis and Image-Guided Aspiration" AJR Am J Roentgenol (2020)
- "Rheumatology and bone disease" Davidson’s Principles and Practice of Medicine (2023)
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