Project Summary/Abstract: The thumb carpometacarpal (CMC) joint is the second most common site of osteoarthritis (OA) in humans and the most common site of surgical reconstruction for OA in the upper extremity. The current standard of care includes removal of the trapezium followed by soft tissue modifications to prevent loss of strength due to proximal migration of the thumb after surgery (subsidence). The evidence demonstrating that strength loss after trapeziectomy is related to thumb metacarpal subsidence is inconclusive, so the need for these additional procedures remains controversial. The primary objectives of this study are to clarify the relationship between thumb metacarpal subsidence and thumb strength, and to develop and validate a new imaging protocol that can accurately estimate dynamic 3D thumb metacarpal subsidence using 2D radiographs. Achieving these objectives will improve future biomedical research and clinical evaluation of patients after trapeziectomy and may lead to a more effective surgical procedure for restoring strength after trapeziectomy. This study will include 50 patients who received trapeziectomy followed by either LRTI or suspensionplasty within the past 6 to 12 months. We will use dynamic biplane radiography to measure 3D thumb metacarpal kinematics while simultaneously measuring thumb force during pinching, grasping and jar opening. Next, we will use 3D imaging data from the first 30 patients to develop a new imaging protocol to estimate dynamic thumb metacarpal subsidence using 2D radiographs. The new protocol will then be validated on the remaining 20 patients. The first Specific Aim is to determine the relationship between thumb metacarpal subsidence and thumb strength. Achieving this Aim will address the gap in our knowledge as to how thumb subsidence affects strength after trapeziectomy. This advance in understanding how kinematics are related to strength can be used to improve surgical procedures that involve trapeziectomy. The second Specific Aim is to develop and validate a new clinical imaging protocol to accurately estimate dynamic thumb metacarpal subsidence after trapeziectomy. In this Aim, we will generate simulated radiographs from patient-specific bones and their pose to identify the optimal imaging configuration for measuring thumb metacarpal subsidence. This will overcome the hurdle that exists for accurately evaluating thumb metacarpal subsidence using clinical radiographs and it will lead to improved biomedical and clinical research related to measuring thumb subsidence after trapeziectomy. The results of this study may be used to inform the design of a better surgical procedure for patients with CMC OA, to improve clinical evaluation of subsidence after trapeziectomy, and to enable large-scale clinical trials involving patients after trapeziectomy. This study will be the first to combine biplane radiography and force measurement to characterize dynamic thumb kinematics and loading in vivo du...