Graduation Date

Summer 8-14-2026

Document Type

Thesis

Degree Name

Master of Science (MS)

Programs

Medical Sciences Interdepartmental Area

First Advisor

Kevin Dibbern, PhD

Second Advisor

Sara Putnam, MD

Third Advisor

David Kingston, PhD

Fourth Advisor

Hani Haider, PhD

Abstract

Subtle injuries of the distal tibiofibular syndesmosis are routinely missed on radiography, yet millimetric fibular malposition drives chronic instability and post-traumatic arthritis. Diagnosis has relied on two-dimensional tibiofibular widening, which assumes single-plane fibular displacement. Weightbearing CT permits loaded three-dimensional assessment, but the methods to apply it, and evidence that widening reflects true displacement, are insufficient. This thesis develops and validates a bilateral, contralaterally referenced six-degree-of-freedom (6-DOF) framework in a cadaveric model, in which seventeen matched limb pairs were imaged intact and after complete syndesmotic ligament sectioning under identical 356 N axial load. A pipeline combining anatomical coordinate systems with iterative closest point refinement referenced each injured fibula against its contralateral control with bilateral asymmetry serving as the noise floor. Against this floor, sectioning produced displacement across four of six degrees of freedom (all P ≤ 0.011), dominated by external rotation, present in 97% of limbs at a median of 2.57°. Combining the six components separated injured from intact ankles with an area under the curve of 94.1% (95% CI 87.0–99.7%; 88.0% cross-validated). Three-dimensional distance mapping tested whether widening reflects this displacement. External rotation, though most prevalent, contributed under 2% to any widening measure once translation was accounted for (all P > 0.13), remaining invisible to the gap. Overall widening was explained by lateral translation (R² = 0.50, P < 0.001), but anterior widening was explained by posterior and inferior translation (R² = 0.37 and 0.16; P < 0.001 and P = 0.019), so widening tracked only translations that separate the tibiofibular surfaces, not the dominant rotation. Despite complete sectioning, 91% of limbs showed under 1 mm of overall widening, yet 61% of those carried external rotation beyond 2°. Apparent widening is a faithful measure of the tibiofibular gap but an unreliable indicator of total fibular displacement and instability. Minimal widening does not exclude rotational instability, and a gap reduced on imaging can leave rotation unrestored, explaining rotational malreduction despite reassuring radiographs. These findings support integrating multiplanar, particularly rotational, assessment into injury-severity determination and reduction verification.

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