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Sagittal Plane Fibular Motion More Accurate Than Coronal Plane Measurements for Detecting Syndesmotic Instability

Key findings

  • The goal of this biomechanical cadaveric study was to compare the accuracy of assessing distal tibiofibular motion in the sagittal versus coronal plane for arthroscopic diagnosis of syndesmotic instability
  • The area under the receiver operating curve was 0.65 for anterior third coronal plane measurements, 0.73 for posterior third coronal plane measurements, and 0.91 for sagittal plane measurements
  • The sagittal plane fibular translation was significantly more accurate than coronal plane diastasis for diagnosing syndesmotic instability (P<0.001 vs. both of the coronal plane measurements)

When suspected syndesmotic instability is evaluated arthroscopically, fibular motion is usually assessed in both the coronal and sagittal planes. Massachusetts General Hospital researchers previously demonstrated the value of combining measurements from the two planes in a mathematical formula in Knee Surgery, Sports Traumatology, Arthroscopy. For the operating room, however, they wanted a simpler approach.

At Mass General's Foot and Ankle Research and Innovation Laboratory in the Department of Orthopaedic Surgery, foot and ankle research fellow Rohan Bhimani, MD, MBA; foot and ankle surgeons Daniel Guss, MD, MBA, and Gregory Waryasz, MD; and Christopher DiGiovanni, MD, chief of the Foot and Ankle Service, conducted a biomechanical human cadaveric study to determine whether coronal or sagittal plane measurements are superior in this setting.

In Foot & Ankle International, they recommend focusing on distal tibiofibular motion in the sagittal plane when arthroscopically evaluating suspected syndesmotic instability.


The researchers arthroscopically assessed the syndesmosis in 21 unpaired above-knee amputated specimens (mean age, 54; range, 22–78). Evaluations were first made with all ligaments intact, then after sequential transection of the anterior inferior tibiofibular, interosseous, posterior inferior tibiofibular, and deltoid ligaments.

A lateral hook test, anterior-to-posterior (AP) translation test, and posterior-to-anterior (PA) translation test were performed under 100 N of applied force. Anterior and posterior third coronal plane diastasis and AP and PA sagittal plane fibular translations were measured relative to the static tibia.


Receiver operating curve analyses revealed that the area under the curve was:

  • 0.65 (95% CI, 0.54–0.75) for anterior third coronal plane measurements, indicating a poor diagnostic test
  • 0.73 (95% CI, 0.63–0.84) for posterior third coronal plane measurements, indicating an acceptable test (P=0.19 vs. anterior third measurements)
  • 0.91 (95% CI, 0.85–0.96) for sagittal plane measurements, indicating an outstanding test (P<0.001 vs. both of the coronal plane measurements)


When arthroscopically evaluating suspected syndesmotic instability, clinicians should concentrate on sagittal plane motion with AP and PA stress examination.

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Related topics


Based on a systematic review, researchers in Massachusetts General Hospital's Foot and Ankle Research and Innovation Lab believe the commonly used threshold of 2.0 mm for distal tibiofibular diastasis may lead to overdiagnosis of syndesmotic instability during arthroscopy, and they suggest more evidence-based cutoffs.


Orthopedic surgeons at Massachusetts General Hospital have developed a clinically applicable, three-dimensional method of assessing syndesmotic (high ankle) instability on weight-bearing CT (WBCT) scans that measures "percentage of change," which is easier than using a numeric scale with an absolute value.