Ultrasound Has Potential to Diagnose Subtle Syndesmotic Instability

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Syndesmotic ("high") ankle sprains can be difficult to diagnose, especially when there is no fracture and no diastasis of the tibiofibular joint evident on radiography. Some experts argue that when syndesmosis is suspected, direct arthroscopic visualization is warranted.

In addition to being invasive and costly, arthroscopy precludes an important element of diagnosis: it doesn't allow simultaneous evaluation of the contralateral uninjured side—often invaluable given the natural anatomic variations in the distal tibiofibular joint between individuals.

Noortje Hagemeijer, MD, lead researcher in the Foot and Ankle Research and Innovation Laboratory in the Department of Orthopaedic Surgery at Massachusetts General Hospital, Christopher W. DiGiovanni, MD, chief of the Foot and Ankle Center at Mass General, Daniel Guss, MD, MBA, orthopaedic foot and ankle surgeon, Gregory Waryasz, MD, foot and ankle surgeon and sports medicine physician, and colleagues have become the first to demonstrate ultrasound's abilities to evaluate the tibiofibular joint under stressed conditions and show in each individual what normal syndesmotic motion should be. Their report appears in Injury.

Study Methods

Twenty-eight healthy adult volunteers at the Mass General Foot and Ankle Center (16 men and 12 women; average age: 34) participated in this study between December 2018 and August 2019. All had two uninjured ankles.

Each participant was scanned twice by different examiners. Sagittal fibular translation was generated by applying a manual force to the fibula from anterior to posterior (A–P) and from posterior to anterior (P–A). Fibular translation and tibiofibular clear space (TFCS) were measured with no force applied and again during maximum force.

The dynamic stress exam was captured in real-time video, and each scan was analyzed by two independent examiners.

Results

Average fibular sagittal translation:

• Mean [+/- standard deviation (SD)] A–P fibular translation: 0.89 +/- 0.6 mm (cadaver arthroscopic studies have shown 0.2–0.6 mm)
• Mean (+/- SD) fibular translation: 0.49 +/- 1/1 mm (cadaver arthroscopic studies have shown 0.4–0.5 mm)

Mean (+/- SD) anterior TFCS:

• No force: 4.1 (+/- 1.0) mm
• Maximum force: 4.6 (+/- 1.0) mm
• TFCS widening: 0.44 (+/- 0.5) mm

Mean (+/- SD) posterior TFCS:

• No force: 6.1 (+/- 1.4) mm
• Maximum force: 6.1 (+/- 1.4) mm
• Closing TFCS: −0.03 (+/- 0.5) mm

In this cohort, including 28 participants, no fibular translation or TFCS differences in laterality were found when applying A–P or P–A force. Additionally, we found no relationship between participant-specific characteristics (sex, age, body mass index or height) and fibular translation or TFCS measurements.

Reliability

The inter- and intra-observer agreement coefficients of the fibular translation measurements were excellent.

Looking Ahead

Besides arthroscopy and ultrasound, options for diagnosing syndesmotic instability are weight-bearing radiography, weight-bearing CT and MRI. Of these, only ultrasound is readily accessible in a primary care office, inexpensive and free of ionizing radiation.

To build the argument for ultrasound as the gold standard in evaluating distal syndesmosis, studies of injured patients are warranted.

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