Congruent Weber-B Ankle Fractures Do Not Alter Tibiotalar Contact Mechanics

Key Points:

• Weight Bearing CT (WBCT) provides critical data otherwise missed in weight bearing radiographs when trying to understand the true impact of a fracture on joint stability.
• Computational biomechanics, when paired with bilateral WBCT imaging, provides a better understanding of the complex anatomical and mechanical nature of the ankle joint following a Weber B fracture.
• The findings of this study support a consideration for non-operative management of cases with bilateral congruency given their presumably low risk for post-traumatic arthritic development in the long term.

Weber B ankle fracture treatment methods are currently dictated by mortise congruency, malleolar alignment, deltoid ligament competence and fracture stability. Current clinical practices have shifted the focus to evaluating ankle stability using weight bearing radiographs, which has shown promise in reducing surgical interventions while yielding favorable clinical outcomes up to two years. Though, a strong biomechanical rationale for observations such as these has yet to be firmly established.

WBCT, a cone beam CT technology, has overcome these drawbacks by providing surgeons with bilateral ankle scans, allowing for 3-dimensional (3D) bilateral analysis of the ankle congruency under physiologic load. When combined with recent advancements in computational biomechanics, these two technologies provide a better understanding of the complex interplay between the anatomical and mechanical environment of the ankle joint following Weber B ankle fractures.

Dr. Matthias Peiffer et. al out of the Foot & Ankle Research and Innovation Lab (FARIL), in the Department of Orthopaedic Surgery, at the Massachusetts General Hospital, Harvard Medical School in Boston aimed to utilize WBCT and computational biomechanics to analyze 3D mortise displacement and contact mechanics in Weber B ankle fractures and compare them with the uninjured contralateral side. The researchers hypothesized that congruent Weber B fractures on WBCT would not have significant alterations in ankle joint contact stresses in comparison to the normal uninjured side.

Methods

32 patients who sustained a Weber B ankle fracture and underwent bilateral WBCT imaging at injury were included in the study. Segmentation into 3D models of bone was performed semi-automatically, and individualized cartilage layers were modeled based on a previously validated methodology. The 3D mortise congruency was then evaluated using the following parameters: alpha angle, fibular length, talocrural angle, medial gutter and tibiofibular clear space distance mapping. Then contact mechanics were evaluated by the mean and maximum contact stress of the tibiotalar articulation.

Results

Statistical analysis revealed that there were no significant differences for all anatomical parameters, as well as between the mean contact stress of the injured and uninjured side respectively. Contact mechanics were unaffected in congruent Weber B fractures.

Researchers noted that the findings support consideration of non-operative management of such cases given their presumably low risk for post-traumatic arthritic development in the long term. It was also expressed that a major strength of the study was the use of automated measurements to determine mortise congruency on WBCT by reducing the variability of measurements. By using WBCT, the mortise was evaluated in its functional position, which researchers said was critical for understanding the true impact of a fracture on joint stability.

To read the full study click here.