What should I do for sudden onset knee pain with inability to bend the knee that started this afternoon?

Immediate Management of Sudden Knee Pain with Inability to Bend

Apply the RICE protocol immediately (Rest, Ice 15-20 minutes every 2-3 hours, Compression with elastic bandage, Elevation above heart level) and take over-the-counter NSAIDs if not contraindicated, then seek medical evaluation within 24-48 hours if symptoms persist or worsen 1, 2.

What You Need to Do Right Now

Immediate Self-Care (First 24-48 Hours)

• Stop all activities that stress the knee - no sports, running, or prolonged standing
• Ice application: 15-20 minutes every 2-3 hours while awake for the first 48 hours
• Compression: Apply an elastic bandage (not too tight - you should be able to slip a finger underneath)
• Elevation: Keep the knee elevated above heart level when sitting or lying down
• Pain relief: Take ibuprofen 400-600mg every 6-8 hours or naproxen 220-440mg every 8-12 hours with food (if no contraindications like stomach ulcers or kidney disease)

When to Seek Immediate Medical Attention (Go to ER/Urgent Care Today)

You need immediate evaluation if you have ANY of the following 3, 1, 2:

• Inability to bear weight or take 4 steps
• Severe swelling that developed rapidly (within 2 hours suggests bleeding in joint)
• Visible deformity of the knee
• Fever (suggests possible infection)
• Knee feels hot and red (infection concern)
• Complete inability to straighten or bend the knee at all (suggests locked meniscus or loose body)
• Knee gives way or feels unstable when trying to stand

When to See Your Doctor Within 24-48 Hours

Schedule an appointment if 1, 4, 2:

• You're over 55 years old (higher fracture risk)
• You have tenderness at the kneecap or head of the fibula (the bony bump on outer lower leg just below knee)
• Cannot flex knee to 90 degrees (right angle)
• Pain persists beyond 48 hours despite RICE protocol
• Swelling develops or worsens after initial injury

What Your Doctor Will Evaluate

Key History Points They'll Ask 1, 4, 2

• Mechanism: Did you twist, fall, or have direct impact? (Twisting suggests meniscus tear; direct blow suggests contusion or fracture)
• Timing of swelling: Immediate (within 2 hours = bleeding/fracture), delayed 6-24 hours (meniscus tear), gradual over days (inflammation)
• Popping sensation: Heard or felt a "pop" at injury? (Suggests ligament tear, especially ACL)
• Locking or catching: Does knee get stuck? (Suggests meniscus tear with displaced fragment)
• Location of pain: Front (patellofemoral), sides (meniscus/ligament), back (Baker's cyst)

Physical Examination Findings 1, 5

Your doctor will check:

• Joint line tenderness: Pressing along the inner or outer knee joint line (83% sensitive, 83% specific for meniscus tear) 5
• McMurray test: Rotating and extending your knee (61% sensitive, 84% specific for meniscus tear) 5
• Effusion: Fluid in the joint (suggests internal injury)
• Range of motion: How far you can bend and straighten
• Stability tests: Checking ligaments (Lachman test for ACL is most accurate)

Imaging Decisions 3, 1

X-rays are indicated if you meet Ottawa Knee Rules 1:

• Age >55 years
• Isolated tenderness of patella (no other bone tenderness)
• Tenderness at head of fibula
• Inability to flex knee to 90 degrees
• Inability to bear weight (4 steps) both immediately after injury AND in the office

MRI is NOT needed initially 3, 2. It's reserved for:

• Persistent symptoms after 4-6 weeks of conservative treatment
• When surgery is being considered
• When diagnosis remains unclear after adequate conservative trial

Most Likely Diagnoses Based on Your Description

Given sudden onset with inability to bend that comes and goes:

1. Meniscus tear (most likely if twisting injury): Joint line tenderness, intermittent locking/catching, delayed swelling 6, 5

2. Patellofemoral pain: Front knee pain, worse with squatting or stairs, common if under 40 and active 5

3. Acute ligament sprain: Instability, immediate swelling if severe, specific mechanism of injury 2

4. Patellar subluxation/dislocation: Kneecap shifts out of place, anterior pain, feeling of instability 4

Treatment Approach

Conservative Management (First-Line for Most Causes) 5

For 4-6 weeks, you should 5:

• Continue RICE protocol for first week
• Exercise therapy: Quadriceps strengthening (straight leg raises, quad sets) and hip strengthening
• Weight loss if overweight (reduces knee loading)
• Activity modification: Avoid aggravating activities but maintain movement
• Physical therapy referral if not improving after 2 weeks

Common Pitfall to Avoid

Do NOT assume you need MRI or surgery immediately 5. Even confirmed meniscus tears respond to conservative treatment in most cases. Surgery is only indicated for:

• Severe traumatic tears with displaced tissue (bucket-handle tears) causing true mechanical locking 5
• Failure of 4-6 weeks of appropriate conservative treatment 6
• Young patients with acute traumatic tears who are high-level athletes

Degenerative meniscus tears (age >40) should NOT undergo surgery even with mechanical symptoms - exercise therapy is superior 5.

Red Flags Requiring Urgent Surgical Consultation 6, 2

• True locked knee (cannot extend at all, not just painful to extend)
• Suspected complete ligament rupture with gross instability
• Open wound or penetrating injury
• Neurovascular compromise (numbness, coldness, absent pulses)

Bottom Line Algorithm

If you can bear weight and bend knee somewhat → RICE protocol + NSAIDs + monitor for 48 hours

If you meet Ottawa criteria OR symptoms worsen → See doctor for X-rays within 24-48 hours

If severe instability, true locking, or signs of infection → Go to ER today

If symptoms persist beyond 4-6 weeks despite conservative care → Consider MRI and specialist referral

The intermittent nature ("comes and goes") suggests a mechanical issue like meniscus tear rather than fracture, but you still need clinical evaluation to rule out serious pathology, especially given your inability to bend the knee 1, 2.