THE RELATIONSHIP BETWEEN KNEE JOINT ALIGNMENT, 3-D JOINT SPACE WIDTH AND SUBCHONDRAL BONE PARAMETERS IN INVIDUALS WITH RADIOGRAPHIC OSTEOARTHRITIS: A MOST INVESTIGATION

Abstract

Joint alignment is an important factor in OA affecting how forces pass through the knee. The increasing use of weight bearing computed tomography (WBCT) in OA research has made the weight bearing stance an important consideration in 3-D imaging analysis, but its influence through biomechanics on the joint and subchondral bone is not fully understood. To investigate the relationship between knee joint alignment and 3-D joint parameters derived from joint space mapping of WBCT imaging in individuals with radiographic OA. WBCT of both knees was acquired at the 144-month visit of the Multicenter Osteoarthritis Study (MOST). Knees with a KLG ≥2 were included in the analysis, taking the side with higher KLG or averaging subsequent results from both sides if equal. Joint space mapping was performed to obtain the 3-D JSW distribution along with femoral (f) and tibial (t) subchondral bone thickness (ST) and trabecular attenuation (TA). Everyone's knee parameter maps were then transferred to a canonical joint surface. Alignment of the knee joint was measured as the angle between the central axis of the distal femur and proximal tibia in a coronal multiplanar reformat slab of the WBCT data: neutral alignment was set as zero with varus signed positive (figure part (a)). Statistical parametric mapping (SPM) was performed using a general linear model to test the dependence of each 3-D parameter distribution on alignment controlling for age, sex, mass, height, and joint space shape modes. SPM results were plotted on the canonical joint surface with unmasked regions representing a significance level of P<0.05. 136 knees were included in the analysis, 84 of which were females. Mean ± SD age was 66.4 ± 9.8 yrs; mass 85.3 ± 17.8 kg; height 1.69 ± 0.1 m. The distribution of radiographic grading was KL2 = 103; KL3 = 32; KL4 = 1. Mean alignment was 0.38 ± 3.80°. For each degree from valgus to varus, JSW was significantly narrower in the medial compartment and wider in the lateral compartment by up to 0.1 mm (figure part (d)). While TA was significantly greater by up to 10 AU in the medial femur (figure part (b)) and medial tibia (figure part (f)), there was up to 0.05 mm significantly thinner ST in the lateral femur (figure part (c)) and lateral tibia (figure part (e)). The opposite effects can be inferred for each degree towards valgus. The same analysis on KLG 0 and 1 knees in the same cohort (mean ± SD alignment 0.66 ± 2.94°) revealed no significant relationships. Subchondral bone plate and trabecular bone appear to behave differently in the medial and lateral compartments when considering knee joint alignment in individuals with OA. Greater subchondral trabecular bone attenuation was seen in the medial compartment with varus alignment, while greater subchondral bone plate thickness was seen in the lateral compartment with valgus alignment. Whether alignment is the cause or effect of OA and any altered biomechanics that may influence bone and joint space behaviour requires further investigation, but this study does establish that the forces associated with alignment appear to have different effects on subchondral bone in different compartments. National Institutes of Health, University of Kansas (R01AR071648), University of Iowa (U01AG18832) and University of California-San Francisco (U01AG19069). NS is a consultant for Integra BioLife, Trice Medical and Pacira Biosciences. TT has been a consultant for Curvebeam AI. The authors would like to thank participants and staff of the MOST study. CORRESPONDENCE ADDRESS: [email protected]