Contact stress exposure is thought to play a significant role in many aspects of joint degradation and pathology. Effective and accurate contact stress computation in native or pathological subject specific joints is an important tool in determining the role of contact stress in OA onset and worsening as well as eventually developing and monitoring interventions to prevent joint degradation. In the past FEA modeling has allowed for studies to be completed which relate contact stress exposure human ankle joint to the presence of radiographic OA. While promising, contact FEA for subject specific models is significantly limited by the number of cases that can be computed due to the difficulty of FEA modeling, as well as numerical convergence issues present in contact FEA. To obtain truly statistically powerful conclusions about the causes of joint degradation and OA onset large numbers of subject specific models will need to be created, run and analyzed. Rigid body spring modeling or RBSM has proven to be an effective method of contact stress measurement for both expedited evaluation of PTOA risk following tibial plafond fractures as well as for evaluation of BMLs worsening in a cohort of 38 at risk patients. RBSM treats cartilage as a bed of springs attached to an underlying rigid bone surface. It is a significant simplification from FEA in that it does not allow computation of internal stresses of an object, elaborate material treatments, or true deformation of an object. This simplification comes with the benefit of reduced computational and investigator burden due to the lack of numerical convergence issues as well as no FEA meshing step. A custom written RBSM algorithm was created in MATLAB which works in conjunction with a load balancing algorithm to iteratively solve contact solutions in both load and displacement control. This algorithm was first validated against a previously done physical validation study using two human cadaver ankles in a custom built fixture. The RBSM method was then used to replicate previously obtained FEA results in a study of 22 human ankle joints following tibial plafond fracture. FEA models and loadings were adapted for the RBSM method and run. The RBSM offered a significant speed increase while maintaining comparable results to the FEA. The ability of RBSM to predict PTOA development using a contact stress-time-area exposure metric was virtually unchanged (95% KL grade concordance and 100% OA concordance vs. 94% KL grade concordance and 100% OA concordance, for RBSM and FEA, respectively). The RBSM method was then combined with a feature based 3D-2D alignment routine custom written in MATLAB. This alignment routine uses a ray casting method to recreate a virtual x-ray silhouette edge for a 3D model. This model is then aligned to a 2D edge tracing based off an input radiograph depicting a functional pose of the bone. A global optimizer (simulated annealing) is used to determine the best Euler transform to place the bone in an accurate position in the recreated virtual scene. 38 subject specific knee models segmented from the MOST cohort were aligned to functional appositions bases off of fixed flexion standing radiographs. Contact stresses were then obtained from these aligned joints using RBSM to evaluate the relationship between contact stress level and bone marrow lesion worsening. It was found that as contact stress level increases so does the risk of BMLs worsening. As the worsening of BMLs is associated with joint pain, degradation, and pathology an expedited contact stress method which can accurately predict BML worsening is especially valuable.

<p>Osteoarthritis (OA) is one of the most prevalent diseases in the United States and also in the world. Cartilage plays a vital role in articular joints and its structural integrity and mechanical properties are diminished by OA. Post traumatic osteoarthritis (PTOA) is a prevalent type of OA and occurs after a significant joint injury. Currently, no treatments are available to prevent or delay the progression of any form of OA.</p><p>Collagen crosslinking improves the material properties of cartilage and has been proposed as a potential treatment for OA. The wear resistance of cartilage that had been crosslinked with CASPc, a light activated crosslinking agent, was tested. Results suggested that photo-initiated crosslinking improves the wear characteristics of cartilage.</p><p>Another treatment for PTOA is through biological intervention. Preliminary data from our lab showed that metformin rescues the chondrocyte response to injurious impact overloading in the initial 24 hours following impact. However, whether this treatment maintained cartilage integrity for an extended duration had not been investigated. Material properties of cartilage were analyzed with an indentation test at different time points post-impact to determine the functional effect of cartilage injury and metformin treatment. Changes in the composition of the cartilage were investigated through biochemical techniques.</p><p>Having an in vivo model for PTOA is key for testing any new therapeutic intervention. In this study a model was developed to deliver a consistent impact load to the posterior aspect of medial condyle of a rabbit knee. A drop tower was designed for impacting the rabbit knee, and load and acceleration were measured during the impact. A k-wire was passed through the condyles in the medial-lateral direction under the impact site to secure the condyle during the impact. Whether the impact parameters were affected by the location of the k-wire was evaluated. The location of the k-wire was varied in the anterior/posterior and proximal/distal directions in a knee joint of cadaveric rabbits and impact parameters were recorded. Multiple linear regression showed a correlation between the location of the k-wire and peak stress, loading rate, impact duration and work. Moreover a correlation was found between the damage induced to the cartilage and loading rate, impact duration and peak stress. This study indicated that k-wire location is critical to prevent fracture of the subchondral bone.</p><p>A pilot study was designed to investigate the in-vivo effect of the metformin treatment on PTOA. Impacted knee joints in rabbits were treated with intraarticular metformin or were untreated controls. At 12 weeks post-injury, the progression of OA in the rabbit knees was quantified by histology, and OA severity was assessed using OA Research Society International (OARSI) scoring. Although the number of animals in the study were limited, intraarticular metformin appeared to prevent the development of PTOA in the impacted rabbit knees.</p>