Diagnosing a Sprain
The diagnosis of a sprain should focus on a thorough history of injury mechanism, physical examination findings, and application of validated clinical decision rules like the Ottawa Ankle Rules to rule out fractures before confirming a ligament injury. 1
History Assessment
When evaluating a potential sprain, gather the following key information:
- Mechanism of injury (inversion, eversion, plantar flexion)
- Timing of the injury
- History of previous sprains (a significant risk factor)
- Immediate symptoms (pain, swelling, ability to bear weight)
- Presence of high-risk features requiring urgent evaluation:
- High level of pain
- Rapid onset of swelling
- Coldness or numbness in the injured area
- Inability to bear weight
- Complicating conditions (e.g., diabetes) 1
Physical Examination
The physical examination should include:
- Visual inspection for swelling and hematoma
- Palpation for point tenderness over specific ligaments
- Special tests:
- Anterior drawer test for anterior talofibular ligament injury
- Crossed-leg test for high ankle (syndesmotic) sprains 1
Key Physical Findings for Grade III Sprains
Four key physical examination findings strongly associated with lateral ligament rupture:
- Swelling
- Hematoma
- Pain on palpation
- Positive anterior drawer test
When all four findings are present, 96% of patients have a lateral ligament rupture; when all are absent, only 14% have a rupture. 1
Timing of Examination
- Initial examination may be limited by pain and swelling
- Reexamination 3-5 days after injury is critical for distinguishing partial tears from complete ligament ruptures 1
- The sensitivity (84%) and specificity (96%) of the anterior drawer test are optimized when assessment is delayed for 4-5 days post-injury 1
Ottawa Ankle Rules
The Ottawa Ankle Rules should be applied to determine the need for radiography:
- Pain on the dorsal side of one or both malleoli
- Palpation pain at the base of the fifth metatarsal
- Palpation pain of the navicular bone
- Inability to walk at least four steps 1
These rules have excellent sensitivity (86-99%) and negative predictive value (97-99%), allowing clinicians to safely rule out fractures without radiography in 299 out of 300 patients. 1
Grading System for Sprains
Sprains are typically classified into three grades:
- Grade I (Mild): Minimal stretching of ligament fibers with microscopic tearing
- Grade II (Moderate): Partial tearing of ligament with some joint laxity
- Grade III (Severe): Complete ligament tear with joint instability 1
Advanced Imaging
- Ultrasonography: High sensitivity (92%) but lower specificity (64%) compared to delayed examination; requires experienced technician 1
- MRI: Excellent sensitivity (93-96%) and specificity (100%) for visualizing ligament injuries, osteochondral defects, and occult fractures 1
- Reserve MRI for cases with:
- Suspicion of high-grade ligament injuries
- Possible osteochondral defects
- Syndesmotic injuries
- Occult fractures
- Persistent symptoms 1
Common Pitfalls to Avoid
- Premature diagnosis: Examining too early when pain and swelling limit assessment
- Unnecessary imaging: Failing to apply Ottawa Ankle Rules properly
- Missing associated injuries: Not considering syndesmotic injuries or osteochondral lesions
- Inadequate follow-up: Not reassessing after swelling subsides
- Overlooking previous injury history: Not recognizing recurrent sprains as risk factors for chronic instability 1
Diagnostic Algorithm
- Assess injury mechanism and immediate symptoms
- Apply Ottawa Ankle Rules to determine need for radiography
- If radiographs are negative or not indicated, perform physical examination
- If examination is limited by pain/swelling, schedule follow-up in 3-5 days
- At follow-up, perform anterior drawer test and other special tests
- Consider advanced imaging only for persistent symptoms or suspected complications 1
Following this systematic approach will help ensure accurate diagnosis of sprains and appropriate management to prevent chronic instability and long-term complications.