Knee pain

Last updated: June 27, 2025

Quick guide

Diagnostic approach

Targeted clinical evaluation
X-ray: initial imaging for most patients (See also “Ottawa knee rules.”)
CT: to evaluate complex fracture or dislocation
MRI: suspected ligamentous or meniscal injury
Ultrasound: effusion or bursitis
Cultures and PCR testing: of synovial, blood, and exposed mucosa for suspected gonococcal arthritis
Arthrocentesis with synovial fluid analysis: to help differentiate between subtypes of arthritis
See “Diagnosis of septic arthritis” for labs for infection and inflammation.

Ottawa knee rules

Management checklist

Uncomplicated musculoskeletal pain: POLICE principle, pain management, WBAT
Acute soft tissue injuries: Stabilize with a functional brace.
Consult orthopedic surgery for patients with acute traumatic injuries, severe mechanical issues, or end-stage osteoarthritis.
See also “Acute internal knee derangement,” “Acute gout management,” and “Treatment of septic arthritis.”

Red flag features

Inability to bear weight
Reduced range of motion
Severe pain or swelling
Fever or signs of infection
Deformity or instability
Decreased or absent pulses
Signs of peroneal or tibial nerve injury (sensory loss, weakness)
Knee dislocation or fracture
Extensor mechanism disruption (patellar or quadriceps tendon rupture)

Life-threatening causes

Septic arthritis
Tibiofemoral dislocation with neurovascular injury (e.g., popliteal artery injury)
Acute compartment syndrome

Summary

Knee pain can arise from acute traumatic causes (e.g., knee ligament injuries, meniscus tears, or fractures) and nontraumatic conditions (e.g., knee osteoarthritis). Clinical assessment includes pain characteristics (e.g., onset, duration, and exacerbating symptoms) and a focused examination of the knee. Imaging and/or laboratory studies (e.g., synovial fluid analysis) are based on the suspected underlying cause. Knee radiographs are typically the first-line imaging modality. Management is determined by the underlying cause.

Lower extremity osteopathy is discussed separately.

Etiology

Traumatic ^[1]

See ”Acute internal knee derangement” for details.

Knee ligament injuries
Traumatic meniscus tears
Fractures (e.g., tibial plateau fractures)
Dislocations (e.g., tibiofemoral joint dislocation, patellar dislocation)

Nontraumatic ^[1]^[2]^[3]

Degenerative or overuse
- Knee osteoarthritis
- Degenerative meniscus tears
- Chondromalacia patellae
- Patellofemoral pain syndrome
- Tendinopathies (e.g., patellar tendinopathy, iliotibial band syndrome)
- Bursitis (e.g., prepatellar bursitis)
- Pes anserinus pain syndrome
- Osgood-Schlatter disease
Infectious: septic arthritis
Inflammatory
- Crystalline arthropathies (e.g., CPPD, gout)
- Rheumatoid arthritis
- Popliteal cyst
Referred pain (e.g., from hip or spine pathology)

Clinical evaluation

Focused history ^[1]

Inciting factor or injury
Onset, location, alleviating or aggravating factors
Other localizing pain (e.g., hip, spine)
Constitutional symptoms
Past medical history
- Systemic illnesses (e.g., gout, autoimmune conditions)
- Prior knee injury or surgery

Focused examination ^[1]

Examination of the knee (e.g., joint effusion, Lachman test, McMurray test)
Skin and neurovascular examination
Examination of the spine
Examination of gait

In an undifferentiated acute traumatic knee injury, acute pain management and initial investigations (e.g., imaging) are advised before clinical evaluation, which may be limited due to pain and swelling. ^[4]

Physiological knee joint motion in three dimensions Ventral view of the knee joint incl. quadriceps femoris muscle Ligaments and menisci of the knee

Diagnostics

Choice of diagnostic study is guided by the suspected diagnosis and whether the presentation is acute or chronic.

Imaging ^[5]^[6]

Knee x-rays
- For acute traumatic knee pain according to Ottawa knee rules: full knee x-ray series
- For chronic knee pain ≥ 6 weeks: frontal (e.g., anteroposterior), lateral, and tangential patella views ^[1]
Knee ultrasound: for effusions and/or evaluation of superficial structures (e.g., prepatellar bursa)
CT knee without contrast: for acute knee pain in patients with complex fractures (e.g., tibial plateau fractures) or suspected occult fractures
CT angiogram lower extremity with IV contrast: for significant trauma (e.g., suspected tibiofemoral dislocation)
MRI knee without contrast
- For acute knee pain with any of the following:
  - Occult fracture suspected
  - Acute internal knee derangement
  - Complex fractures
  - Meniscus tears or knee ligament injuries ^[2]
- For chronic knee pain with negative initial knee x-rays and/or any of the following:
  - Suspected osteomyelitis
  - Joint effusion
  - Osteochondritis dissecans
  - Loose bodies
  - History of cartilage or meniscal repair
  - Prior osseous injury

Laboratory studies ^[1]

CBC and ESR: assessment for infection or inflammation
Rheumatoid factor, anti-CCP: evaluation for rheumatoid arthritis
Serum uric acid: for suspected gout
Synovial fluid analysis: for suspected septic arthritis or crystalline arthropathy
Cultures and PCR testing: for suspected disseminated gonococcal arthritis

Common causes

Common causes of knee pain in adults
Condition	Characteristic clinical features	Diagnostic tests	Management
Knee osteoarthritis	Patients typically > 45 years of age ^[2] Chronic, activity-related pain and swelling Morning stiffness Mechanical instability, locking, and/or catching	Clinical diagnosis Knee x-ray ^[2] Joint space narrowing Osteophytes	Nonpharmacological (e.g., exercise, weight loss) Pharmacotherapy (e.g., NSAIDs, intra-articular steroids) Arthroplasty following failed conservative treatment See also “Management of osteoarthritis of the knee.”
Anterior cruciate ligament injury ^[7]	Posttraumatic pain and/or instability Hemarthrosis Popping sound before symptom onset Knee buckling and impaired mobility	Lachman test, anterior drawer test, and pivot shift test Knee x-ray: to exclude tibial avulsion fracture MRI knee: ligament injury	Acute pain management Orthopedic referral Arthroscopic surgery often required Conservative management for certain indications
Meniscus tear (traumatic or degenerative)	Exacerbated by activity or weight-bearing Intermittent joint effusion Joint line tenderness Restricted extension	Provocative tests for meniscus injury (e.g., McMurray test) MRI knee: meniscal injury, effusion Arthoscopy: if MRI contraindications or with athroscopic treatment	Conservative (e.g., POLICE principle, physical therapy, knee brace, NSAIDs) Arthroscopic treatment for severe traumatic tear (e.g., bucket handle tear, persistent symptoms) See also “Treatment of meniscus tear.”
Crystalline arthropathy (e.g., CPPD, gout)	Acute onset Erythema, swelling, and/or warmth Past similar episodes Triggers Gout: purine-rich foods or alcohol (See “Acute gouty arthritis.”) CPPD: joint trauma or surgery, acute illness	Joint aspiration ↑ WBC, ↑ neutrophils Gram stain and fluid culture: negative Gout: monosodium urate crystals CPPD: CPP crystals Gout: ↑ serum uric acid Acute phase reactants: typically ↑	Pharmacotherapy: NSAIDs, colchicine, and/or corticosteroids Avoidance of triggers See also: “Management of gout” “Management of CPPD disease.”
Septic arthritis	Acute onset Erythema and/or swelling Fever Inability to bear weight	Joint aspiration ↑ WBC, ↑ neutrophils ↓ Fluid glucose level Gram stain and fluid culture: typically positive ↑ Acute phase reactants Blood cultures: often positive NAAT and culture if suspected gonococcal arthritis	Urgent orthopedic consult IV antibiotics Surgical drainage See also “Treatment of septic arthritis.”
Patellofemoral pain syndrome	Patients typically < 40 years of age ^[2] Anterior pain exacerbated by flexion (e.g., squatting)	Clinical diagnosis Knee x-ray: normal	Acute phase POLICE principle NSAIDs Recovery phase: physical therapy (e.g., quadriceps strengthening)

Start your trial, and get 5 days of unlimited access to over 1,100 medical articles and 5,000 USMLE and NBME exam-style questions.

Start free trial

Evidence-based content, created and peer-reviewed by physicians. Read the disclaimer