Summary

The study evaluated the impact of syndesmosis and deltoid ligament injuries on the rotational stability of the ankle joint as well as the effectiveness of different surgical repair techniques to restore the stability again.

Abstract

Introduction

The deltoid ligament (DL) complex, located on the medial side of the ankle joint, consists of a superficial and deep layer. It plays a crucial role in stabilizing the medial ankle joint. Despite its involvement in nearly two-thirds of all ankle fractures, there is no consensus on a surgical treatment strategy for its repair. Therefore, this study aims to (1) evaluate the contribution of the syndesmosis and deltoid ligaments on external rotation stability compared to intact ankle function and (2) assess the ability of surgical intervention to restore native external rotation ankle stability.

Materials & Methods
24 lower extremities were assigned to three groups with sequential dissection and repair of the anterior inferior tibiofibular and interosseous ligaments (AiTFL+IOL), superficial (SDL), and deep deltoid ligaments (DDL) performed in varying orders to evaluate their specific contribution to rotational (in)stability. After each intact specimen was loaded up to 7.0 Nm to evaluate the ligament rotation at 2.5, 4.0, 5.5, and 7.0 Nm (α2.5, α4.0, α5.5, α7.0), rotation-controlled cyclic loading was performed with a total of 1000 cycles consecutively after each surgical intervention to determine peak torque and stiffness at the end of each rotation level. One-way ANOVA with post hoc Tukey tests were performed for a significant pairwise analysis of the primary outcome variables (p ≤ .05).

Results

Each dissection step decreased rotational stiffness, with intact ankle showing the highest values for peak torques and torsional stiffness. Injuries to the AiTFL+IOL or SDL+DDL had the most significant impact on the rotational instability of the ankle joints. Dissecting the DL bundles separately in a different order showed that SDL cutting contributed significantly more to joint instability than DDL (p = 0.031). In the unstable ankle injury model with all ligaments cut (AiTFL+IOL+SDL+DDL), the residual joint stability ranged from 46% (α2.5) to 38% (α7.0) for 2.5 Nm to 7.0 Nm, respectively showing the lowest resistance to rotational loading.
Restoring rotational stability during sequential ligament repair, either IOL or SDL+DDL repair had the greatest impact (up to 28%) but still showed the lowest resistance to external rotation. Only the final repair stage with all ligaments addressed (IOL+SDL+DDL+AiTFL) provided near native peak torque restoration. The contribution of SDL+DDL was higher than that of isolated SDL or DDL repair. Additional AiTFL augmentation stabilized the ankle by 7-14% across all rotation levels. IOL repair with different configurations of DL augmentation also achieved a level of ankle stability comparable to the intact ankle joints.

Conclusion

The present study utilized an ankle-specific, rotation-controlled cyclic loading protocol along the linear elastic loading range of native ligament function. This approach enabled the evaluation of syndesmotic and deltoid injuries, as well as their subsequent repairs compared to the native ankle function. Our findings reveal significant insights into the heterogeneity of the deltoid ligament complex when concomitant with syndesmotic ligament injuries, highlighting noteworthy differences in rotational ankle stability between partial and complete deltoid ligament injuries and their repairs. This knowledge is crucial for appropriate surgical intervention in treating unstable ankle joints.