Characterizing and Restoring Joint Motion in Patients with Hallux Rigidus: Human Subject Testing

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PROJECT SUMMARY/ABSTRACT The first metatarsophalangeal joint (MTPJ1) is one of the sites most often affected by osteoarthritis (OA), leading to a condition called hallux rigidus (HR). This is very common, estimated to affect 25% of the adult population and increasing in prevalence with age. The number of patients seen by the Veterans Health Administration (VHA) for HR has more than doubled over the last decade. In contrast to degenerative OA at the hip and knee, which is commonly treated with joint replacement arthroplasties, the most common surgical treatment for severe HR is arthrodesis, which eliminates joint function. This approach does not allow modification of footwear, interferes with some activities (e.g., yoga, Pilates) and may lead to secondary complications such as metatarsalgia and mobility restrictions. To date, various designs for MTPJ1 arthroplasties have been proposed, but none have been particularly successful, with high failure rates due to loosening and regular reports of implant migration. This may be in part because of the relatively small amount of cortical bone in the metatarsal head and proximal phalangeal regions, making it difficult to achieve adequate fixation of the prosthetic components. Development of new implants aimed at addressing these problems has been limited by the quantitative data regarding the mechanical environment of the MTPJ1. Similarly, due to technological limitations, there is no precise 3D kinematic data available to describe the envelope of normal MTPJ1 function required during activities of daily living. Our recent work has established the groundwork for a computational modeling workflow to optimize MTPJ1 implant design, and we have had initial success generating novel, evidence-based implant concepts that emphasize strong initial component fixation. In this project, we intend to advance this work, increasing our ability to improve MTPJ1 implant technology through computational modeling and robotic gait simulation of human cadavers. These better-performing implants will ultimately lead to improved patient outcomes. We intend to achieve these aims by: 1) characterizing pathological and healthy MTPJ1 function during different activities of daily living; 2) using a cadaveric robotic gait simulator to measure the effectiveness of existing implants and our novel implants at restoring MTPJ1 function; and 3) further refining our musculoskeletal and finite element computational models of the MTPJ1, improving their accuracy and validating their ability to generate clinically-informative results. It is our working hypothesis that a successful MTPJ1 implant will exhibit both strong initial component fixation and physiologically normative joint biomechanics; presently, our preliminary design work has emphasized the former, while [the literature on knee joint replacements supports] the latter. We believe this research has the potential to reinvigorate the advancement of MTPJ1 arthroplasty, which at present is primarily driven by ideas rather than data. The knowledge disseminated from this research will allow surgeons and patients to make better decisions regarding surgical treatments for HR. Specifically, these data will help clinicians better understand the disease process of HR and lead to more physiologic MTPJ1 replacements that will ultimately result in an improvement in mobility and quality of life of veterans with HR. Upon completion of the proposed study, our group will have obtained the expertise to undertake a large clinical trial investigating surgical treatment of HR with the goals of developing a more rigorous classification of HR, and better insight into the various causes of MTPJ1 pain (e.g., dorsal first metatarsal osteophytes, MTPJ1 cartilage damage, or sesamoid arthropathy).