Summary

The bisector of angle formed by two lines tangent to anterior and posterior fibula & tibia cortices was found strongly reliable providing patient- and level-specific direction for syndesmotic fixation.

Abstract

Anatomic syndesmosis reduction is necessary to restore ankle biomechanics and prevent poor clinical outcomes, but malreduction can be encountered frequently since the ideal fixation angle varies between patients and fixation levels. Recent studies have shown that any malalignment in syndesmotic fixation can lead to iatrogenic malreduction, and if the fixation is not placed perpendicular to the tibiofibular joint, the fibula may remain displaced. Ideal syndesmotic alignment is proposed to be the line connecting the centroids of fibula and tibia. We hypothesized that angle bisector of two lines tangent to anterior and posterior tibia & fibula provides accurate, patient-specific and level-specific angle for syndesmotic fixation. Lower extremity CT angiography of 50 consecutive patients (25 male, 25 female) without evident ankle pathology were evaluated. The average age was 52.8 (±18, range:18-75). Lines tangent to anterior and posterior cortices of tibia and fibula were drawn in the axial plane at both 2 cm and 3.5 cm distance to tibial plafond. Bisector of the angle formed between these lines was drawn and its relationship with the centroidal axis which is proposed to be the ideal syndesmotic axis was evaluated. The angle between bisector line & centroidal axis and the distance between their most lateral intersections with fibula were calculated. The measurements were made by three blinded observers. Interobserver and intraobserver consistencies were evaluated by ICC, in 2-way & mixed-effect model analyzing absolute agreement of exact measures. Independent samples, 2-tailed t-test was used to compare the values at 2 cm and 3.5 cm levels. The average centroidal axis-bisector angle was 2.1±2.1° at 2 cm and 0.6±1.3° at 3.5 cm level. The average distance to actual syndesmosis entry point was 1.0±0.9 mm at 2 cm and 0.4±0.4 mm at 3.5 cm level. The values didn’t show any significant difference according to gender. Intra- and inter-observer reliability analyses showed excellent correlation in all parameters (ICC>0.90). Angle bisector method was found reliable for determining accurate syndesmotic alignment and lateral entry point with a narrow range of variability between patients and also high consistency between observers. Angle bisector method can also be used intraoperatively with help of two K-wires and a sterile goniometer. Two K-wires tangent to anterior and posterior surfaces of tibia and fibula can be placed and the angle between these K-wires can be calculated with the help of a sterile goniometer. Then, the drill and preferred fixation implant can be applied in direction of the angle bisector. It can provide a patient- and level-specific angle for the application of syndesmotic implants without increasing the fluoroscopy exposure. It has the potential to be reproduced in a clinical setting thus can standardize the treatment of syndesmotic injuries compared to non-standardized conventional methods. Angle bisector method can pave the way for designing a new jig allowing accurate syndesmotic fixation. Its use can have a broad impact on functional outcomes of ankle injuries by decreasing the malreduction rates. However, cadaveric validation and safety studies should be conducted before possible clinical usage.