Foot and Ankle International - 2026-08-26 - Journal Article
The Superior Fascicle of the Anterior Talofibular Ligament Functions as a Restraint Against Internal Rotation: A Cadaveric Biomechanical Study.
Koyama T, Teramoto A, Mori Y, Murahashi Y, Takahashi K, Ueda N, Watanabe K, Aizawa T
Topics
Key Takeaway
Complete detachment of the ATFL superior fascicle increases internal rotation displacement by 2.9° at 30° plantarflexion, while partial detachment produces no significant kinematic change.
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Summary
This cadaveric study used a robotic testing system to sequentially transect the ATFL superior fascicle in three cumulative injury patterns and measured anterior translation, internal rotation, and inversion under standardized loads at three ankle positions. Complete superior fascicle detachment (type 3) produced significantly greater internal rotation at 30° plantarflexion versus intact and partial injury states (mean difference 2.9°, 95% CI 0.6°–5.0°, P=.01), while partial detachment (types 1 and 2) did not reach significance. No significant differences were found in anterior translation or inversion displacement across any injury condition.
Key Limitation
The small sample size (n=9) limits statistical power and may have masked significant differences in partial injury states, and cadaveric testing eliminates the dynamic neuromuscular contributions that modulate rotational laxity in vivo.
Original Abstract
BACKGROUND
Lateral ankle sprains frequently result in anterior talofibular ligament (ATFL) dysfunction, leading to chronic lateral ankle instability. The ATFL consists of superior and inferior fascicles; however, the stabilizing role of the superior fascicle remains unclear. We biomechanically evaluated its function using cadaveric models.
METHODS
Nine frozen cadaveric ankles were tested using a robotic system (FRS2015). The superior fascicle was sequentially transected arthroscopically to simulate cumulative 3 injury types: type 1, partial detachment at the medial margin of the fibular attachment; type 2, proximal detachment; and type 3, complete detachment. Anterior talar translation, internal rotation, and inversion angles relative to the tibia were measured as displacements under the anterior drawer, internal rotation, and inversion loads, respectively, at 15° dorsiflexion and 15° and 30° plantarflexion. In situ forces and ankle kinematics were also measured.
RESULTS
Internal rotation displacement at 30° plantarflexion was significantly greater in type 3 than in the intact (mean difference, 2.9°; 95% CI, 0.6°-5.0°; P = .01), type 1 (mean difference, 2.6°; 95% CI, 0.5°-4.8°; P = .02), and type 2 (cumulative with type 1; mean difference, 2.5°; 95% CI, 0.4°-4.5°; P = .02). With the numbers available, no significant differences were found among intact, type 1, and type 2, nor in anterior or inversion displacement across any conditions. The in situ force was greater in type 3 than in type 1 during anterior drawer and internal rotation loading, and ankle kinematics did not differ.
CONCLUSION
Partial injury to the superior fascicle of the ATFL was not associated with a statistically significant difference in ankle instability under the tested conditions, whereas complete injury was associated with significantly greater internal rotational displacement.
CLINICAL RELEVANCE
Injury to the superior fascicle of the ATFL is associated with increased internal rotational laxity, supporting the use of internal rotation testing, such as the anterolateral drawer test, when evaluating suspected ATFL injury.