Poster Presentation 29th Australian and New Zealand Bone and Mineral Society Annual Scientific Meeting 2019

Tibia cartilage thickness, cortical thickness and subchondral bone microarchitecture: varus- and valgus-aligned osteoarthritic knees vs. controls  (#186)

Egon Perilli 1 , Sophie Rapagna 1 , Bryant C Roberts 1 , Lucian B Solomon 2 , Dominic Thewlis 3 , Karen J Reynolds 1
  1. The Medical Device Research Institute, College of Science & Engineering, Flinders University, Adelaide, SA, Australia
  2. Department of Orthopaedics and Trauma, Royal Adelaide Hospital, Adelaide, SA, Australia
  3. Centre for Orthopaedic and Trauma Research, The University of Adelaide, Adelaide, SA, Australia

Introduction: In knee osteoarthritis (OA), regional changes in proximal tibia subchondral trabecular bone (STB) microarchitecture, cortical bone and cartilage thickness may reflect joint loading. However, reports are conflicting and the effect of joint alignment remains unexplored. This ongoing study quantifies tibia cartilage, subchondral cortical and STB of end-stage knee-OA patients with varus- or valgus-aligned joints, compared to control (non-OA) knees.

Methods: Tibial plateaus from 25 knee-OA patients (68±7years; varus-aligned (n=18), valgus-aligned (n=7); knee arthroplasty) and 15 cadavers (62±13years; controls) were micro-CT scanned (17µm/pixel). Cartilage thickness (Cg.Th), cortical plate thickness (Pl.Th), STB bone volume fraction (BV/TV) and corresponding medial-to-lateral (M:L) ratios were explored in four subregions (anteromedial (AM), anterolateral (AL), posteromedial (PM) and posterolateral (PL) condyles). Varus-OA and valgus-OA groups were compared to controls (Bonferroni-adjusted Mann-Whitney U-tests).

Results: Varus-OA exhibited lower Cg.Th in AM ROI (-59%, p<0.05) but higher laterally (up to +63%) compared to controls, whereas valgus-OA higher medially. In controls the Cg.Th M:L ratios were close to unity (range: 0.8-1.1), in varus-OA they were all below unity (0.2-0.6, p<0.05) whereas in valgus-OA they were similar to or higher than in controls. Pl.Th was higher medially in varus-OA compared to controls (up to +117%) and higher laterally in valgus-OA (up to +110%). Similarly, BV/TV was higher medially in varus-OA (up to +49%) and laterally in valgus-OA (up to +76%) compared to controls. In varus-OA, the M:L Pl.Th ratios and M:L BV/TV ratios were all above unity (range 1.4-2.0, 1.6-2.4, respectively) and higher than in controls (0.8-1.8, 0.9-2.1); in valgus-OA they were closer to unity (0.8-1.0, 0.8-1.1) and lower than controls.

Conclusions: OA and non-OA tibias differ significantly in Cg.Th, Pl.Th and STB microarchitecture depending on joint alignment, suggesting that joint structural changes in OA reflect differences in medial-to-lateral load distribution upon the tibial plateau, improving our understanding of the disease.