Summary

A newly developed system revealed significant differences of 3D lower extremity alignment between static standing position and stance phase of gait.

Abstract

Introduction

In daily life, gait is the most common and clinically significant weight-bearing activity. To our knowledge, no studies have directly evaluated the three-dimensional (3D) bony alignment of the lower extremities during the stance phase of gait (Lower Extremity Alignment at the stance phase during gait: LEA-gait) using X-rays and compared them with the standing position (Lower Extremity Alignment in the standing position: LEA-standing). In this study, we developed

Method

to accurately evaluate the LEA-gait and LEA-standing using fluoroscopic images. We hypothesize that LEA-gait in healthy elderly individuals differs from LEA-standing.

Methods

The power analysis indicated that a sufficient sample size for this research was 34. The study analyzed the LEA-Standing and LEA-Gait of 34 knees from 17 healthy elderly individuals (9 females and 8 males; average age 73.2 years). LEA-standing was evaluated using the 3D lower extremity alignment assessment system (Knee CAS, LEXI). The evaluation of LEA-gait was conducted using fluoroscopic device while participants walked on a treadmill parallel to the X-ray direction at a comfortable speed. The 3D digital bone models were projected onto the obtained fluoroscopic images, and the 3D-to-2D image matching technique was used to calculate the 3D posture and alignment (ZedMotion, LEXI). In this study, LEA-gait was determined by averaging the alignment from the three most vertical sagittal Mikulicz line images obtained during 10 gait cycles. For both LEA-Standing and LEA-Gait evaluations, a world coordinate system (WCS) was defined. The X-ray irradiation direction (aligned with the gait direction in LEA-gait) was set as the anterior-posterior axis (y-axis), the gravity direction as the vertical axis (z-axis), and the x-axis as the cross product of the y and z axes. All parameters were assessed within the WCS : 1) Coronal and sagittal inclination of the femur and tibia, 2) Tibial joint line angle relative to the floor (TJLA), 3) Hip Knee Ankle angle (HKA), 4) Knee flexion angle, 5) Femoral and tibial rotation angle, 6) Coronal and sagittal Mikulicz line inclination.

RESULT: Compared to LEA-Standing, both the femur (3.5°), tibia (3.2°), the coronal Mikulicz line (2.9°) and TJLA (3.3°) exhibited increased lateral inclination inLEA-gait (p<0.01). In the transverse plane, LEA-Gait showed a significant increase in external rotation of the femur (5.0°, p<0.01) compared to LEA-Standing, with no significant difference observed in the rotation of the tibia.

Discussion

The key finding is that LEA-Standing and LEA-Gait differ significantly in 3D alignment, particularly in clinically relevant coronal plane parameters. Previously, there has been no study that has assessed the alignment during the stance phase of gait in such detailed and three-dimensional terms. This provides crucial insights for interpreting coronal plane alignment during the stance phase of gait. In LEA-Standing, the TJLA was nearly horizontal, but it tilted laterally by 2.2° during gait. This suggests that the TJLA is not always parallel to the ground during the stance phase of normal knee gait, challenging the prevailing notion in prior studies on lower limb realignment surgery that the tibial joint surface should be parallel to the ground under load postoperatively.