Osteoarthritis (OA) affects more than four million people in the UK alone. Bone marrow lesions (BMLs) are a common feature of subchondral bone pathology in OA. Both bone volume fraction and mineral density within the BML are abnormal. The aim of this study was to investigate the effect of a potential treatment (bone augmentation) for BMLs on the knee joint mechanics in cases with healthy and fully degenerated cartilage, using finite element (FE) models of the joint to study the effect of BML size. FE models of a human tibiofemoral joint were created based on models from the Open Knee project (simtk.org). Following initial mesh convergence studies, each model was manipulated in ScanIP (Synopsys-Simpleware, UK) to incorporate a BML 2mm below the surface of the tibial contact region. Models representing extreme cases (healthy cartilage, no cartilage; BML region as an empty cavity or filled with bone substitution material (200GPa)) were generated, each with different sizes of BML. Models were tested under a representative physiological load of 2kN.Abstract
Introduction
Methods
Bone marrow lesions (BMLs) have been extensively linked to the osteoarthritis (OA) disease pathway in the knee. Semi-quantitative evaluation has been unable to effectively study the spatial and temporal distribution of BMLs and consequently little is understood about their natural history. This study used a novel statistical model to precisely locate the BMLs within the subchondral bone and compare BML distribution with the distribution of denuded cartilage. MR images from individuals (n=88) with radiographic evidence of OA were selected from the Osteoarthritis Initiative. Slice-by-slice, subvoxel delineation of the lesions was performed across the paired images using the criteria laid out by Roemer (2009). A statistical bone model was fitted to each image across the cohort, creating a dense set of anatomically corresponded points which allowed BML depth, position and volume to be calculated. The association between BML and denudation was also measured semi-quantitatively by visually scoring the lesions as either overlapping or adjacent to denuded AC, or not. At baseline 75 subjects had BMLs present in at least one compartment. Of the 188 compartments with BMLs 46% demonstrated change greater than 727mm cubed, the calculated smallest detectable difference. The majority of lesions were found in medial compartments compared to lateral compartments and the patella (Figure 1A). Furthermore, in the baseline images 76.9% of all BMLs either overlapped or were adjacent to denuded bone. The closeness of this relationship in four individuals is shown in Figure 1B. The distribution of lesions follows a clear trend with the majority found in the patellofemoral joint, medial femoro-tibial joint and medial tibial compartment. Moreover the novel method of measurement and display of BMLs demonstrates that there is a striking similarity between the spatial distribution of BMLs and denuded cartilage in subjects with OA. This co-location infers the lesions have a mechanical origin much like the lesions that occur in healthy patients as a direct result of trauma. It is therefore suggested that OA associated BMLs are in fact no different from the BMLs caused by mechanical damage, but occur as a result of localised disruption to the joint mechanics, a common feature of OA.
