Standing on single foot-binding test yields satisfactory results as a novel method

Key points

1. 01The SOSF-B test uses an elastic bandage to temporarily stabilise the ankle while the patient stands on one foot, mimicking syndesmotic support
2. 02Diagnostic accuracy was 87.06% (20 degrees) and 85.88% (0 degrees) versus 72.94% for MRI and 67.06% for palpation
3. 03A positive SOSF-B test raised the probability of DTSI from 28.7% to 72%; a negative result lowered it to 6.8%
4. 04The test is non-invasive, low-cost, and does not require imaging equipment
5. 05Arthroscopy confirmed DTSI in 32 of 85 participants (37.6% prevalence in this surgical cohort)

How it was conducted

Design

Prospective, cross-sectional, double-blind diagnostic accuracy study

Participants

85 adults with history of ankle trauma scheduled for ankle arthroscopy at a single centre (January 2021 to January 2022)

Index tests

20-degree SOSF-B test, 0-degree SOSF-B test, MRI, and syndesmosis ligament palpation

Reference standard

Ankle arthroscopy with probe measurement of distal tibiofibular joint space (gap greater than 1 mm = DTSI positive)

Primary outcome

Sensitivity, specificity, PPV, NPV, LR+, LR-, and diagnostic accuracy of each test versus arthroscopic findings

What they found

• 20-degree SOSF-B test: sensitivity 87.5% (95% CI 70.07-95.92), specificity 86.79% (95% CI 74.05-94.09), PPV 80% (95% CI 62.54-90.94), NPV 92% (95% CI 79.89-97.41), LR+ 6.625 (95% CI 3.28-13.37), LR- 0.14 (95% CI 0.06-0.36), diagnostic accuracy 87.06%
• 0-degree SOSF-B test: sensitivity 84.38% (95% CI 66.45-94.10), specificity 86.79% (95% CI 74.05-94.09), PPV 79.41% (95% CI 61.59-90.66), NPV 91.2% (95% CI 77.81-96.33), LR+ 6.39 (95% CI 3.15-12.94), LR- 0.18 (95% CI 0.08-0.41), diagnostic accuracy 85.88%
• MRI: sensitivity 78.13% (95% CI 59.56-90.06), specificity 69.81% (95% CI 55.49-81.26), PPV 60.98% (95% CI 44.54-75.38), NPV 84.09% (95% CI 69.33-92.84), LR+ 2.59 (95% CI 1.65-4.05), LR- 0.31 (95% CI 0.16-0.61), diagnostic accuracy 72.94%
• Palpation: sensitivity 71.88% (95% CI 53.02-85.60), specificity 64.15% (95% CI 49.75-76.51), PPV 54.76% (95% CI 38.83-69.83), NPV 79.07% (95% CI 63.52-89.42), LR+ 2.01 (95% CI 1.32-3.05), LR- 0.44 (95% CI 0.25-0.78), diagnostic accuracy 67.06%
• Post-test probability with positive SOSF-B (0 degrees): 72% (up from pre-test 28.7%); with negative result: 6.8%
• DTSI prevalence in the arthroscopic cohort: 32/85 (37.6%); associated complications included synovitis, osteochondral lesion of the talus, and chronic lateral ankle syndesmosis injury

Limitations

• Participants were drawn exclusively from patients already scheduled for surgery, so results may not generalise to community or primary-care ankle sprain populations
• Small sample size (n=85) limits the precision of diagnostic accuracy estimates
• Generalised ligament laxity, present in 9 cases, may confound the test result; its effect on DTSI stability requires further study
• EMG was not used to objectively quantify muscle contraction, and reliance on patient self-report of posterior muscle group effort introduces subjectivity

Why it matters

For patients

Patients with ongoing ankle pain or instability after a sprain may benefit from this simple bedside test to help determine whether further investigation or surgery for high ankle injury is needed, potentially avoiding costly MRI.

For clinicians

The SOSF-B test offers better sensitivity and specificity than MRI and palpation for DTSI in a surgical cohort, making it a practical first-line screening tool; a positive result should prompt confirmatory imaging, while a negative result substantially reduces disease probability.

For readers

This single-centre diagnostic study provides preliminary validation for a novel, low-cost physical test for a commonly missed ankle ligament injury, though independent replication in broader populations is needed before widespread adoption.