Medial cortical bone thickness of the tibial diaphysis in osteoarthritis is related to lower extremity alignment and tibial morphology

Abstract

Background: The purpose of this study was to clarify (1) the differences in cortical bone thickness (CBT) of the tibial diaphysis between healthy and osteoarthritic knees and (2) the influences of the femorotibial angle (FTA) and inclination of the medial compartment of the proximal tibia (MCT) on tibial CBT.

Methods: The study assessed 60 subjects with varus knee osteoarthritis (OA) (22 males and 38 females; mean age, 74 ± 7 years) and 53 healthy elderly subjects (28 males and 25 females; mean age, 70 ± 6 years). Three-dimensional estimated CBT of the tibial diaphysis was automatically calculated for 2752-11,296 points using high-resolution measurements from CT. The standardized CBT was assessed in 24 regions by combining six heights and four areas. Additionally, the association between the CBT, each FTA, and MCT inclination was investigated.

Results: The OA group showed a thicker CBT in the medial areas than in the lateral areas of the proximal tibia, while the healthy group had a thicker lateral CBT. The medial-to-lateral ratio of the proximal tibia was significantly higher in the OA group than in the healthy group. The proximal-medial CBT correlated with FTA and MCT inclinations in the OA group.

Conclusions: This study demonstrated that varus osteoarthritic knees showed a different trend of proximal-medial CBT with associations in FTA and MCT inclination from healthy knees, possibly due to medial load concentration.

Keywords: Alignment; Cortical bone thickness; Healthy; Inclination of the medial compartment of the proximal tibia; Knee osteoarthritis; Tibia.

Fig. 1

Inclusion and exclusion criteria of the subjects OA: knee osteoarthritis, BMI: body mass index

Fig. 2

Automatic calculation in a 3D space using the high-resolution cortical thickness measurement from clinical CT data This technique relies on a mathematical model of the anatomy and imaging system that is fitted to data at a large number of sites around the tibia. Given the prior segmentation of the tibial diaphysis, CT values were examined along short lines that straddled and were perpendicular to the cortex

Fig. 3

An anatomical coordinate system for the tibia and cortical thickness of the tibia (CBT) mapped using a cortical mapping technique

Fig. 4

Three-dimensional lower extremity alignment assessment system Thirty-four skin markers were attached to the subjects. For the ten shank markers and 12 thigh markers, the original marker included a steel ball to detect its 2D position on X-ray images. The 3D position of the femorotibial bones can be estimated by superimposing 3D skeletal models onto the bony outline of the lower extremity under weight-bearing conditions using a 3D-to-2D image registration technique

Fig. 5

Femorotibial angle (FTA) and best-fitting “approximation plane” in the medial compartment of the proximal tibia (MCT) definition The FTA was the angle between the femoral and tibial anatomical axes projected onto the coronal plane in the femoral coordinate system. Schematic diagram shows that the MCT, and coronal angle of the MCT. The minimum angle in 3D space between the x-axis of the tibial coordinate system and the crossing line consisted of the xz-plane of the tibial coordinate system and the approximation plane of the MCT, which is defined as the coronal angle of the MCT.