Summary

This preliminary study shows that load during long leg standing X-ray for planning osteotomy may have less influence on angle measurement and as a result on surgical planning than believed in the past.

Abstract

Introduction

Recently corrective osteotomies around the knee joint regain popularity. If the procedure is correctly planned and properly performed, it has a potential for prolonging knee joint survival time, it will also significantly decrease pain and reduce inflammation. At this stage adequate planning with understanding of lower limb biomechanics is crucial. Long-leg standing X-ray is considered to be a gold standard of planning osteotomies around the knee joint. Standarized approach toward long-leg standing X-ray have been proposed and accepted by orthopaedic society. However, exact influence of proper loading and positioning hasn’t been fully understood. The aim of this preliminary study was to evaluate the influence of load and rotation on MPTA, JLCA, LDFA, and HKA measurement.

Materials And Methods

Patients with limb malalignment, who underwent long-leg standing X-ray and CT for torsional evaluation of the lower limbs had been identified in our clinic. Data of 38 patients was extracted and 3 individual calculations of MPTA, LDFA, JLCA and HKA were conducted independently by medical student, orthopaedic resident and orthopaedic specialist with special interest in knee joint. The evaluation covered both limbs. When evaluating torsional deformities scout CT has been chosen as a reference image for comparison with long-leg standing X-ray. Scout CT image presented low resolution however it still covered all the necessary areas of the limbs in a prone position without any load applied to the limbs. Differences between X-ray and CT measurements and standard deviation were calculated for each limb separately. Moreover interobserver reliability were calculated with usage of Interclass Correlation Coefficient (ICC).

Results

Our study evaluated 76 limbs in total. Mean age of the patients in our study was 29.5 (SD 15,4). Interobserver reliability of X-ray calculations showed good to excellent results in regard to JLCA -0,79, HKA -0,91 and LDFA – 0,87. Lowest interobserver reliability was found for MPTA -0,66. Scout CT highest interobserver agreement was found for HKA -0,94 and lowest: for JLCA – 0,39. Mean difference between scout CT and long leg standing X-ray was 1,72 for MPTA, 1,16 -JLCA, 1,41 LDFA and 1,63 for HKA. Mean standard deviation of angle differences was calculated at 1,47.

Discussion

Our results show that load doesn’t influence the calculation results in a way that would interfere with surgical planning. What’s interesting JLCA showed lowest dependance of load on the calculations which can suggest independence of this angle from load. Higher differences in MPTA and LDFA calculations can be caused by lower resolution of the scout CT image, which impedes the correct placement of the measuring points. Also most of the patients in this study presented torsional deformities of lower limb, which could influence results. Nevertheless, our preliminary results suggest that load during long leg standing X-ray could not be as important as assumed in the past. However, to verify this thesis, large scale of targeted research has to be performed in the future.