Standardization of torsional CT measurements of the lower limbs with threshold values for corrective osteotomy
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Re-establishing anatomic rotational alignment of shaft fractures of the lower extremities remains challenging. Clinical evaluation in combination with radiological measurements is important in pre- and post-surgical assessment. Based on computed tomography (CT), a range of reference values for femoral torsion (FT) and tibial torsion (TT) have historically been reported, which require standardization to optimize the significant intra- and inter-observer variability. The aims of this study were (re-)evaluation of the reference FT and TT angles, determination of the normal intra-individual side-to-side torsional differences to aid the surgical decision-making process for reoperation, and development of a novel 3D measurement method for FT.
Materials and methods
In this retrospective study, we included 55 patients, without any known torsional deformities of the lower extremities. Two radiologists, independently, measured the rotational profile of the femora using the Hernandez and Weiner CT methods for FT, and the tibiae using the bimalleolar method for TT. The intra-individual side-to-side difference in paired femora and paired tibiae was determined. A 3D technique for FT assessment using InSpace® was designed.
FT and TT demographic values were lower than previously reported, with mean FT values of 5.1°–8.8° and mean TT values of 25.5°–27.7°. Maximal side-to-side differences were 12°–13° for FT and 12° for TT. The Weiner method for FT was less variable than the Hernandez method. The new 3D method was equivocal to the conventional CT measurements.
The results from this study showed that the maximal side-to-side tolerance in asymptomatic normal adult lower extremities is 12°–13° for FT and 12° for TT, which could be a useful threshold for surgeons as indication for revision surgery (e.g., derotational osteotomy). We developed a new 3D CT method for FT measurement which is similar to 2D and could be used in the future for virtual 3D planning.
KeywordsRotational malalignment Malunion Corrective osteotomy Femoral torsion Femoral anteversion Femoral neck axis Tibial torsion Computed tomography Three-dimensional
Femoral neck axis
The technical and intellectual guidance of Mr. Walter Coudyzer (University hospitals Leuven, Belgium) during the design of this novel three-dimensional measurement method of femoral torsion using Siemens (Erlangen, Germany) MMWP InSpace®, and the statistical processing of Mr. Frederik De Keyzer with Analyse-it® (Leeds, LS3 1HS, United Kingdom) was greatly appreciated. Figures 2 and 3 are courtesy of the Department of Osteo-articular Radiology of the University Hospitals Leuven, Belgium.
There is no funding source.
Compliance with ethical standards
Conflict of interest
Prof. Dr. Willem-Jan Metsemakers is a consultant for DepuySynthes. Dr. Austin Fragomen is a consultant for DepuySynthes, Smith Nephew, NuVasive, and Globus. Prof. Dr. Harm Hoekstra is a member of the lecture bureau of DepuySynthes. Furthermore, all authors hereby disclose any financial and personal relationships with other people or organisations that could inappropriately influence this work.
Ethical approval was obtained from the Education-Support Committee of the Catholic University Leuven (KULeuven), Belgium.
Informed consent of all patients was obtained as for standard radiologic examinations.
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