Ultrasound is Appropriate and Should Be the First-Line Imaging for Acute Calf Injury with Pop and Pain
For a patient who heard a pop in the calf during pickleball with subsequent pain, bedside or diagnostic ultrasound is highly appropriate and should be performed to diagnose muscle-tendon injury, particularly gastrocnemius or Achilles tendon rupture.
Why Ultrasound is the Right Choice
Primary Diagnostic Considerations
The clinical presentation—audible "pop" with acute calf pain during sports activity—strongly suggests:
- Gastrocnemius muscle tear (medial head most common, "tennis leg")
- Achilles tendon rupture (complete or partial)
- Plantaris tendon rupture
- Less likely: soleus or other posterior compartment injury
Ultrasound excels at detecting all of these injuries 1, 2, 3. It can identify loss of muscle fiber continuity, fluid collections (hematoma), tendon discontinuity, and the exact location and extent of injury 3.
Ultrasound Performance Characteristics
For muscle injuries in athletes, ultrasound has become the first-line diagnostic imaging modality due to 3:
- Real-time dynamic assessment
- Multi-planar evaluation capability
- Immediate availability at bedside
- Cost-effectiveness compared to MRI
- No radiation exposure
- Ability to examine symptomatic areas specifically
The modality provides detailed anatomical information of calf structures and can confirm abnormalities beyond just ruling out DVT 4.
Clinical Algorithm
Step 1: Perform Focused Physical Examination
Look specifically for:
- Palpable gap or defect in the calf
- Thompson test (calf squeeze test) - abnormal if no plantar flexion occurs
- Decreased ankle plantar flexion strength
- Increased passive ankle dorsiflexion 5
Step 2: Obtain Bedside or Diagnostic Ultrasound
Examination technique 1:
- Standard approach: Patient prone, examine gastrocnemius and Achilles in longitudinal and transverse planes
- If initially negative but clinical suspicion remains: Re-examine with patient supine, knee flexed at 90 degrees, transducer pointing upward—this position may reveal injuries missed in conventional positioning 1
- Assess for: loss of fiber continuity, anechoic fluid collections, hypoechoic areas, tendon discontinuity
Step 3: Rule Out DVT if Indicated
While the acute traumatic mechanism makes DVT unlikely, if there are risk factors (immobilization, prior DVT, cancer, recent surgery), a focused compression ultrasound of the common femoral and popliteal veins is appropriate 6. This takes minimal additional time during the same examination.
Important Caveats
Operator-Dependent Limitations
Ultrasound requires adequate training and experience 3. However, emergency physicians and critical care providers have demonstrated reliable accuracy for focused examinations 6, 7.
Position Matters
Critical pitfall: A single negative ultrasound in the standard prone position does not rule out muscle tear 1. If clinical suspicion persists with negative initial findings, repeat the examination with the knee flexed before abandoning the diagnosis.
When Ultrasound May Not Be Sufficient
Consider MRI if:
- Ultrasound findings are equivocal
- Complete surgical planning requires detailed mapping
- Concern for deep compartment or complex injuries
- Medico-legal documentation needed
However, ultrasound should still be performed first as it provides immediate diagnostic information and guides subsequent management 3, 8.
Why Not Just Clinical Examination?
While physical examination (Thompson test, palpable gap) can diagnose Achilles rupture 5, ultrasound adds critical value by:
- Defining exact injury location and extent
- Distinguishing partial from complete tears
- Identifying the specific muscle or tendon involved
- Detecting complications (hematoma, retraction)
- Guiding treatment decisions and return-to-play timelines 3
Bottom line: Ultrasound is not just appropriate—it should be considered essential for optimal management of acute calf injuries with an audible pop, providing immediate, accurate diagnosis that directly impacts treatment planning 9, 3, 8.