P014 | THE INFLUENCE OF SUBCHONDRAL BONE CYSTS ON TISSUE PRESSURES IN THE TIBIOTALAR JOINT

Introduction: Subchondral bone cysts are an indicator of late stagehaemophilic joint disease (HJD); however, the implication of thesecysts on joint health is little understood. The aim of this study wasto assess, computationally, the influence of subchondral bone cystson tissue pressures through their inclusion in patient-specific finiteelement (FE) models.Methods: Chronologically sequential (minimum of 3 sequences over2 years), non-weightbearing Magnetic Resonance Imaging (MRI) sequences were acquired for three people with severe Haemophilia A. The main inclusion criteria for the study was the imaging presenceof subchondral bone cysts (n = 15). Segmentations of subchondralbone cysts, bones, and cartilage were generated, and segmentation specific FE meshes were created using Simpleware-ScanIP 2017.6 (Synopsis). FE models were developed to simulate the forces associated with neutral still standing—keeping the bone positions of the MR images—for each patient under two cyst conditions: with the cyst defined as intact bone, and as de-facto cystic tissue (Abaqus 2017, Dassault Systèmes). The tissue pressures were extracted from both the cartilage and bones, to investigate the influence of the cyst presence throughout the ankle.Results: For each patient, the volume and location of the subchondral bone cysts varied over time, and the maximum pressures in thecontact areas reflected this. 7 cases had cysts located in the tibiaalone, in these the maximum pressure increased on average by 77%(st. dev. 48%) in the tibia, 16% (31%) in the talus, and 32% (35%) inthe cartilage contact area upon the addition of cysts. 4 cases hadcysts in the talus alone—the pressure increased on average by 3%(26%) in the tibia, 66% (107%) in the talus, and 14% (24%) in the cartilage. The greatest variations were seen in the 4 cases where cysts were present in both bones, with an average increase of 137% (37%) in the tibia, 97% (51%) in the talus, and 120% (145%) in the cartilage.Discussion/Conclusion: This computational work showed that cystsof all sizes appear to increase the pressures across all components of the joint, although there is no clear correlation between the volume of subchondral bone cysts and the change in maximum pressure value. The presence of any cystic tissue within the joint is therefore likely detrimental to joint health, as larger tissue pressures may be linked to an increased rate of HJD progression