Objective: The primary objective is to assess the fixation and migration patterns of the CapFlex PIP implant system (produced and developed by several companies of KLS Martin Group) in vivo, using mRSA, over 10 years. Secondary objectives are to analyse survival, clinical scores and radiographic aspects of the CapFlex PIP implant system. Study design: A prospective cohort study with 10 years follow-up, in which 36 patients will be enrolled. Patients will be evaluated preoperatively, at 6 weeks, 6 months, 1 year, 2 years 5 years and 10 years. Study population: Patients 18 years or older who require a proximal interphalangeal joint arthroplasty as a result of osteoarthritis of a proximal interphalangeal joint. Main study parameters/endpoints: The main study parameters are the migration of the CapFlex PIP implant system of the distal as well as the proximal component (presented in x-, y- and z-direction). Secondary study parameters are the survival of the CapFlex PIP implant system, clinical scores and radiographic aspects. Nature and extent of the burden and risks associated with participation, benefit and group relatedness: Patients participating in the study will have the same risks when not participating in the study. Patients are asked to spend time to fill in the questionnaires and to have 3 extra visits to the hospital, next to the standard visits. Patients will have more follow up visits and will be followed using RSA analysis, which has as advantage that possible complications might be noticed earlier compared to normal follow up.