Project Summary/Abstract The primary objective of this project is to obtain observational data necessary to design a future clinical trial comparing arthrodesis to motion sparing surgery in patients with hallux rigidus (HR). HR is a degenerative disease of the first metatarsophalangeal joint (MTPJ1). It is the most common form of arthritis in the foot, affecting 1 in 40 people over the age of 50 with a 2:1 ratio of females to males. The MTPJ1 plays a critical functional role in walking as it carries approximately 119% of an individual's body weight with each step; therefore, the joint pain and loss of motion lead to a significant reduction in activity and quality of life for patients. HR is typically treated by modifications to or within the shoe combined with modifications of activity and NSAIDs. When these treatments are not effective, surgery may be performed. Arthrodesis (fusion) is an effective measure for pain control but eliminates motion at the joint leading to limited footwear options which can have a major impact on women, in particular, who wear shoes of varying levels of heel elevation. These limitations have driven patients to seek alternatives that spare MTPJ1 motion. Early promising results have intensified the debate over fusion versus joint sparing, but their comparative safety and efficacy is not established. Multiple joint sparing procedures include (1) various arthroplasties, (2) cheilectomy with or without osteotomy, and (3) a synthetic cartilage implant. These more modern techniques have not been compared with arthrodesis with the exception of one non-inferiority trial comparing a synthetic cartilage implant to arthrodesis which reported similar results for pain and function and implant failures after 2 years. There are no comparative trials evaluating cheilectomy. Arthroplasties including synthetic implants increase treatment costs but preserve motion. Therefore, there is a strong demand to determine if motion sparing is equally or more effective compared to arthrodesis in outcomes important to patients. The proposed observational study (and subsequent U01 trial) is intended to overcome the specific gaps in the literature and obstacles to designing a future trial including: (1) using observational data from several centers that employ multiple motion sparing procedures and arthrodesis to determine if there are appreciable differences that will require a single arm or multiple motion sparing treatment arms compared to fusion in a future trial, (2) identifying correlates of HR disease severity using an expert panel with exploratory data analysis of the observational data to begin the important process of developing and validating a novel HR classification system, (3) performing qualitative interviews of existing pilot study patients at various time points in the follow-up process to ascertain what outcomes are most important to them so that we can ensure the outcomes we include in the future trial match these preferences (for...