Dynamics of Distal Tibiofibular Joint in Correlation with the Position of the Syndesmotic Screw in Maisonneuve Fractures of the Ankle - A Cadaver Study

Abstract

Introduction: Maisonneuve-fractures of the ankle joint are best treated by fixation of the ruptured tibiofibular syndesmosis with one or two syndesmotic screws. A rigid fixation of the syndesmosis however, would lead to pain, limitation of range of motion and to early arthrosis of the ankle joint. The purpose of this study was to investigate the optimal position of the syndesmotic screw, which allows physiological movements in the syndesmosis. The influence of application of the screw through 3 or 4 cortical shells on the distal tibiofibular joints stability was also studied.
Material and Methods: 14 pairs of fresh frozen cadaver lower legs with intact knee joints were divided into two groups. In all specimens the soft tissue was removed and the distal tibiofibular ligaments exposed. The specimens were then potted in Araldit-G-bone cement. The syndesmosis and the interosseus membrane were then sharply dissected, to simulate a Maisonneuve-fracture situation. In group I (n = 7) the syndesmotic screw was applied in each pair directly above the upper end of the syndesmosis through 3 cortical shells (lateral and medial fibular shell, lateral tibia shell) on the one side and through 4 cortical shells on the other side. In the group II (n = 7) the syndesmotic screw was applied in each pair through four cortical shells, directly above the syndesmosis and 50 mm above the upper end of the syndesmosis on the either side. In both groups one pair served as control. The specimens were tested with an Instron 2000®-material-testing machine. A medio-lateral translation force was applied to each specimen. All testing was conducted in the plastic range of specimens and were destructive. Single factor analysis of variance and Student's t-Test were used for statistical evaluation.
Results: In the control specimen of both groups the mean maximal translation force (mTmax) was 1 500 N. In the first group mTmax for the screw with 3 cortical shells was 300 N, and for the four cortical screw 312 N. In the second group the mTmax with the screw directly above the syndesmosis was 380 N and with the screw inserted 50 mm above the syndesmosis 160 N. The higher the screw-level, the lower was the power needed to break the fibula in the screw level.
Discussion and Conclusion: There is no significant difference between syndesmotic screws with 3 or 4 fixed cortical shells at a medio-lateral load-axis: The more proximal the position of the screw, the fewer is the force needed to widen the distal tibiofibular joint. In both groups the stiffness achieved with the screws was significantly less than the control ones. The ankle joint was however, most stable with the syndesmotic screw inserted directly above the syndesmosis.

Key words

Ruptured tibiofibular syndesmosis - ankle fracture - biomechanic - positioning screw - injury

References

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