This study focuses on patients who are undergoing an arthroscopy due to subchondral insufficiency fractures of the knee (a type of stress fracture) and for whom arthroscopy using the OSSIOfiber Trimmable Fixation Nails (a type of implant) is the preferred treatment option. The purpose of the study is to determine whether the use of the OSSIOfiber Trimmable Fixation Nails for treating subchondral insufficiency fractures of the knee will result in improvement of patient-reported outcomes and imaging findings. Study procedures include medical record review, demographics collection, post-surgery imaging, and questionnaires. The OSSIOfiber Trimmable Fixation Nails is approved by the U.S. Food and Drug Administration (FDA) and is being used as approved; surgery using the Nails is not a research procedure.