Radiological assessment of lower limb torsional deformities: a narrative review

The evaluation of both femoral and tibial torsional profiles remains a challenge in the orthopedic practice since there is no agreement on the most precise and reliable measurement method and technique. The aim of this review is to collect and critically report the most relevant and up-to-date evidence on the radiological techniques available to determine lower limb torsional deformities and to discuss the advantages and limitations of each technique to better define their optimal field of application.

Literature research on PubMed, Embase, and Google Scholar databases was performed, utilizing the following search string: "torsion" AND ("lower limb" OR "femur" OR "tibia"). Relevant clinical and preclinical studies evaluating different radiological techniques to assess lower limb torsional deformities, and possibly comparing them, were collected and critically reviewed.

Computed tomography (CT) is still considered the best method to measure both femoral and tibial torsional angles. Its main limitation, the radiation exposure, has been recently addressed with ultra-low dose protocols that were proven to be as accurate as standard protocols. On the other hand, magnetic resonance imaging (MRI) offers a nonionizing, radiation-free option that is now considered almost equivalent to CT. However, MRI consists in a long and expensive procedure that can be hindered by issues linked to metal implants, patient's positioning and measurement variabilities. Lastly, three-dimensional (3D) reconstructions derived from low-dose biplanar radiographies (LD-BRs) have been proposed as a low-radiating, quick and reliable solution to overcome the limitations of both MRI and CT scans.

To date, CT has still to be considered the gold standard for the radiological assessment of lower limb torsional deformities. Nonetheless, MRI and LD-BR have been proven to be valid and reliable alternatives, especially in specific clinical settings.