Leg pain is a common yet potentially dangerous presenting complaint. It ranges from benign muscle strains to life-threatening conditions such as deep vein thrombosis (DVT) or necrotizing fasciitis.
Accurate assessment requires understanding traumatic, infectious, vascular, and joint-related causes.
Your uploaded chart provides a structured emergency medicine approach, which this article expands into a high-quality educational resource.
Red Flags in Leg Pain
These features require immediate investigation:
Red Flags
- Recent trauma
- DVT risk factors (OCPs, immobilization, cancer, smoking, travel)
- Fever
- Erythema
- Sudden swelling
- Groin/scrotal involvement
- Pain out of proportion → suspect necrotizing fasciitis
- No ability to move the joint → consider septic joint
Leg Pain Diagnostic Pathway
The chart organizes the evaluation into three main branches:
A. Trauma → Think fractures, ligament tears, meniscal injuries
B. DVT Risk → Rule out DVT
C. Erythema → Distinguish cellulitis vs. septic joint vs. necrotizing fasciitis
Let’s break each down.
A. Trauma-Related Leg Pain
These injuries commonly affect the knee and ankle.
1. ACL Tear
Clues:
- Knee injury with twisting mechanism
- Lachman test > anterior drawer test
- Instability, swelling
Workup:
Outpatient MRITreatment:
- Knee immobilizer
- Orthopedic follow-up
2. Ankle Injury
Follow specific guidelines (mentioned in Ankle & Foot Injury, p. 28 of your chart).
Suspect fractures, sprains, or ligament tears.
3. Collateral Ligament Injury (MCL/LCL)
Clues:
Laxity at 30° flexion with valgus (MCL) or varus (LCL) stressWorkup:
MRITreatment:
- Knee immobilizer
- Orthopedic follow-up
4. Knee Fracture
Apply the Ottawa/Pittsburgh Knee Rules (below).
Workup:
X-rayTreatment:
- Immobilization
- Orthopedic consult
5. Meniscus Injury
Clues:
- Clicking
- Locking
- Pain with rotation
Workup:
Outpatient MRITreatment:
- Knee immobilizer
- Orthopedic follow-up
B. DVT Risk and Vascular Causes
1. Deep Vein Thrombosis (DVT)
Clues:
- Unilateral leg swelling
- Pain
- Warmth
- Wells criteria positive
Workup:
- D-dimer
- Doppler ultrasound
Treatment:
- Anticoagulation
- Admission or close follow-up
2. Necrotizing Fasciitis
Clues:
- Pain out of proportion
- Bullae
- Rapid progression
- Fever, toxicity
Workup:
Clinical diagnosis (CT may assist but do not delay treatment)Treatment:
- IV antibiotics
- Emergency surgery
This is a life-threatening surgical emergency.
C. Erythema: Infection vs. Joint Pathology
1. Abscess / Cellulitis
Clues:
- Erythema
- Warmth
- Fluctuance
- Fever
Workup:
- Wound culture
- Bedside ultrasound to check for abscess
Treatment:
- Abscess → Incision & Drainage
- Cellulitis → Antibiotics
- Large or circumferential infections → Admission
2. Arthritis (Non-Infectious)
Differential includes:
- Osteoarthritis
- Rheumatoid arthritis
- Sarcoidosis
- Reactive arthritis
Treatment:
- Pain control
- Rheumatology follow-up
3. Gout
Clues:
- Sudden onset red, hot joint
- Often big toe (1st MTP)
Workup:
- Clinical diagnosis
- Joint tap if uncertain
Treatment:
- NSAIDs
- Colchicine
- Steroids (if NSAIDs contraindicated)
4. Septic Joint
Clues:
- Severe pain
- Joint immobility
- Fever
- Red, swollen joint
Workup:
Arthrocentesis (gold standard)Treatment:
- IV antibiotics
- Orthopedic emergency → joint washout
Ottawa & Pittsburgh Knee Rules
These rules help determine when an X-ray is necessary.
Ottawa Knee Rule
Order an X-ray if ANY of the following are present:
- Age ≥55
- Inability to walk 4 steps in ED
- Isolated tenderness of patella
- Tenderness of fibular head
- Inability to flex to 90°
Pittsburgh Knee Rule
Order X-ray if:
- Blunt trauma or fall AND
- Age <12 or >50, OR
- Inability to walk 4 steps
Pearls & Pitfalls (from the chart)
✔ Check calcaneal and lumbar spine films for jump injuries
High axial loads → possible spine injuries.
✔ Always palpate above and below the injury
Some fractures refer pain distally.
✔ Be cautious of tibial plateau fractures
Often subtle but dangerous.
Documentation Essentials
Accurate documentation supports clinical quality and medicolegal safety.
General
- Mechanism of injury
- Weight-bearing ability
- DVT risks (OCPs, smoking, immobilization, cancer)
Neurovascular
- Sensation intact
- Full ROM
- Distal pulses present bilaterally
- Capillary refill < 2 seconds
Skin
- Erythema, warmth
- Induration
- Fluctuance
- Drainage
Musculoskeletal
- Flexion to 90°
- Drawer tests
- Valgus/varus stress
- Rotation/clicks
- Compartments soft
Joint
- Erythema
- Tenderness
- ROM limitations
High-Yield Summary Table
| Category | Condition | Key Clues | Workup | Treatment |
|---|---|---|---|---|
| Trauma | ACL tear | Lachman > ant drawer | MRI | Knee immobilizer |
| Meniscus | Click/rotation pain | MRI | Ortho F/U | |
| Collaterals | Valgus/varus laxity | MRI | Knee immob | |
| Knee Fx | Trauma + Ottawa/Pittsburgh rules | X-ray | Immobilize | |
| Infection | Abscess/Cellulitis | Erythema, fever | US, wound cx | I&D or ABx |
| Emergency Infection | Nec fasc | Pain out of proportion | Clinical | ABx + surgery |
| Joint | Gout | Red, swollen MTP | Tap | NSAIDs/colchicine |
| Arthritis | Chronic pain | Clinical | Pain control | |
| Septic joint | No movement + fever | Arthrocentesis | ABx + surgery | |
| Vascular | DVT | Unilateral swelling + Wells | US, D-dimer | Anticoag |
FAQs About Leg Pain
1. What’s the most dangerous cause of leg pain?
Necrotizing fasciitis or DVT—both are emergencies.
2. When should I worry about septic arthritis?
If a patient has a red joint, inability to move, and fever → emergency.
3. How do I differentiate cellulitis from gout?
- Cellulitis = infection of skin; more diffuse
- Gout = sudden, severe joint pain; localized
4. When is MRI required for knee injuries?
For evaluating ligament tears or meniscal injuries.
5. Does every swollen leg need a DVT ultrasound?
Not if Wells score is low + negative D-dimer.
