Summary

The multi-level torsion assessment described, allows a reliable differentiation between the torsion of the lower leg in the proximal metaphysis, the diaphysis and the distal metaphysis and can be used as a powerful measurement protocol when studying interdependencies between joint pathologies and malrotation or when planning the site of an osteotomy in patients with rotational malalignment.

Abstract

Introduction

Torsional deformities of the lower leg can change the biomechanics and forces acting in the knee and ankle joint, whereas pathologic rotation can be treated with a derotational osteotomy of the lower leg. However, there is no consensus whether such procedures should be performed at the proximal or the distal metaphasis or at the diaphysis of the tibia. This lack in consensus is also related to a lack of knowledge and diagnostics. Conventionally only the total torsion of the lower leg between its very proximal and distal aspects is measured, which gives no information about the precise location of the torsional deformity. Therefore we suggest a new multi-level measurement protocol allowing a separate evaluation of the total, proximal, diaphyseal and distal torsion of the lower leg.

Methods

In this retrospective study the torsional profile of the lower leg was evaluated in 66 CT scans. Four axes were determined in the lower leg to perform a multi-level evaluation of the rotation. A tangent to the posterior cortex of the proximal tibia determined the most proximal axis. The midpoints of the tibia and fibula determined the second and third axis, once at the level of the tibial tuberosity and once three centimeters proximal to the tibial plafond. The fourth axis was determined by the midpoints of the medial and lateral malleolus. Total torsion was measured between the first and the fourth axis of (LL-total), proximal metaphyseal torsion between first and second axis (LL-prox), diaphyseal torsion between the second and third axis (LL-diaphys) and distal torsion between the third and fourth axis (LL-dist). Three investigators performed all measurements independently and intraclass correlation coefficients (ICC) were calculated to evaluate the inter-rater reliability.

Results

The overall mean value of LL-total was 32.7° (observer 1: 33.2 ± 7.1; observer 2: 31.6 ± 7.6; observer 3: 33.3 ± 8.5), LL-prox 44.5° (obs. 1: 45.3 ± 5.9; obs. 2: 43.6 ± 6.6; obs. 3: 44.6 ± 5.4), LL-diaphys 0.5° (obs. 1: 0.06 ± 8.0; obs. 2: 1.3 ± 8.1; obs. 3: 0.1 ± 8.5) and LL-dist -12.3° (obs. 1: -12.1 ± 3.1; obs. 2: -13.3 ± 4.4; obs. 3: -11.4 ± 3.3) (positive values indicate external torsion).
We found good inter-rater reliability for all measurements. The ICCs were: LL-total: 0.87, LL-prox: 0.746, LL-diaphys: 0.861, LL-dist: 0.631.

Conclusions

The method described allows a more precise localization of torsional deformities with good interrater reliability. Ongoing research focuses on intra-rater reliability and standard values of the torsion segments in healthy individuals. In the future, the suggested protocol might be a useful tool when studying interdependencies between joint pathologies and maltorsion. Derotational osteotomies of the lower leg could then be performed at the site of the maltorsion in an individual ‘a la carte’ manner.