Segmental torsion assessment is a reliable method for in-depth analysis of femoral alignment in Computer Tomography

Abstract

Purpose De-rotational osteotomies are indicated in patients with pathologic femoral torsion. However, there is disagreement whether an osteotomy should be performed proximally or distally. Conventionally only the total torsion is measured, which does not allow differentiation between a torsional deformity located in the proximal or distal metaphysis or the diaphysis. The aim of this study is to validate a new multilevel measurement protocol for evaluation of the magnitude of torsion of the respective femoral segments in CT. Patients and methods The torsional profile of 30 femora was evaluated in CT scans. For separate measurements of the torsion of the metaphysis and the diaphysis, four axes where determined: one through the femoral neck, a second determined by the midpoint of the femoral shaft and the lesser trochanter, a third determined by a tangent dorsal to the popliteal surface, and a fourth axis posterior to the condyles. The total femoral torsion was measured between the first and the fourth axis, proximal torsion between the first and the second, mid torsion between the second and the third, and distal torsion between the third and the fourth axis. Four investigators performed all measurements independently and intraclass correlation coefficients (ICC) were calculated to evaluate intra-and inter-rater reliability. Results Average total femoral torsion was 22.6 ± 8.7°, proximal torsion 47.7 ± 10.6°, mid torsion −33.4 ± 9.9°, and distal torsion 8.3 ± 3.2°. Intra-rater ICC ranged between 0.504 and 0.957 and inter-rater ICC between 0.643 and 0.992. The majority of the ICC were graded as Balmost perfect^and some as Bsubstantial^agreement. Conclusion Evaluation of the segmental torsion of the femur allows in-depth analysis of femoral alignment. High reliability was shown for this measuring method in computed tomography, which can be deployed when studying interdependencies between joint pathologies and torsional deformities or when planning the site for an osteotomy. Level of evidence Level III.

Distal femoral varus osteotomy: results of the lateral open-wedge technique without bone grafting

“…Considering the relationship of patella instability to patella height (recorded as increased Blackburne-Peel ratios) [22], this could be interpreted as a hint to the potential of LOWDFO to increase patella stability in cases of patella alta in valgus knees. Thus, this interpretation would support the findings of Swarup et al However, in case of patella instability as well as in case of clinical suspicion of malrotation of the lower limb, a detailed rotational analysis should be considered additionally [23].…”

Reflections on Rotational Osteotomies around the Patellofemoral Joint

“…The correct quantification of FT is essential for diagnosing femoral torsional abnormalities, especially for surgical decision-making and planning of corrective osteotomies [7]. CT-based, segmental multi-level CT assessment, MR-based, and three-dimensional reconstruction measurements are available to assess FT more precisely [8][9][10].…”

“…Values of more than 25-30 • of total femoral antetorsion are considered as increased, decreased FT is defined as <10 • [1,[11][12][13][14][15]. Differences between the neck (proximal), mid (diaphysal), and distal femoral torsion were established [8][9][10]. In normal controls, a negative correlation between the neck torsion and shaft torsion was found, suggesting that the internal torsion of the neck is accompanied by an external torsion of the shaft [9].…”

“…In subjects with a high-torsion, a significant increase in the neck internal torsion in combination with a high lack in the shaft external torsion was described [9]. An evaluation of the segmental torsion of the femur allows a more detailed analysis of femoral alignment [8]. All three levels contribute to the total FT [9].…”

“…According to our experience, if total femoral antetorsion exceeds the normal by 25 • and no additional pathologic morphology in the PFJ is documented, femoral external rotational osteotomy should be considered, if it exceeds 30 • it is recommended [1,8,11] (Table 1). This applies to all patients with long lasting symptoms around the knee joint, clear pathologic findings during a clinical evaluation, and an unsuccessful conservative treatment.…”