GET TO KNOW OUR RESEARCH TEAM

Gregory S. DiFelice, MD Founder & Chairman

Dr. Gregory S. DiFelice is a board-certified Orthopaedic Surgeon at Hospital for Special Surgery in New York. He is a surgical innovator and has developed several cutting-edge surgical techniques that allow him to save a patients’ torn ligaments, rather than replacing them, which is the current standard of care. His minimally invasive approach can cut the recovery time by more than half. His work with underserved communities for 15 years compelled him to investigate these less invasive procedures for the treatment of ligament injuries of the knee, and has contributed to a worldwide resurgence of interest in a PRESERVATION FIRST® approach to such injuries. He and his research team have published over 50 peer-reviewed articles and book chapters in the past five years on the topic of ligament preservation. This has resulted in two team members, Dr. DiFelice and Dr. van der List, being included in the top 50 most published authors in the world on the topic of ACL Injuries over the past decade. This journey, and the difficulties that he experienced challenging the surgical status quo, led him to establishing this foundation with the goal of supporting innovative surgical research. When he is not in surgery or at his clinic, he enjoys spending time with his family, skiing, playing his guitar, cooking, and baking up some wonderful treats.

Sebastian Rilk, MD

HEAD OF RESEARCH

2022-2024 RESEARCH FELLOW

Sebastian Rilk is a MD from the Medical University of Vienna, Austria and joined the research team as a postdoctoral researcher in 2022. While an injury ended his ice hockey career and led him to pursue medicine, it was his medical school experience as an orthopedics fellow in Vienna that led him to HSS and Dr. DiFelice in early 2022. Sebastian is currently working on his PhD on the topic of bone and joint regeneration in addition to his work at HSS. Sebastian is passionate about ice hockey and environmentalism and enjoys skiing and tennis in his free time.

Robert J. O'Brien, DrPH, PA-C

HEAD OF OPERATIONS

Robert J. O'Brien, DrPH, MHS, PA-C, joined DiFelice Orthopaedics 2015. His clinical work includes managing perioperative care for patients and first assisting in the operating room. Additionally, he has been involved in several research efforts to further analyze the role of ligament preservation. His professional interests include sports injury prevention, surgical innovation, preventive medicine, evidence-based care, and the effective integration of public health concepts into clinical medicine. He holds a doctoral degree in public health, and continues to work both clinically and in academics.

Maximilian Müller, MD

2024- 2025 RESEARCH FELLOW

Dr. Maximilian M. Müller is a fourth-year orthopedic resident at BG Klinikum Hamburg. After being a competitive athlete (German National Sailing Team) while studying in medical school, Max developed a strong passion for orthopedic and sports medicine research. In his experimental doctoral thesis Max could improve our understanding for alloplastic bone substitute materials. During his work in Hamburg he worked on various research projects on reconstructive knee surgery and osteotomies. He is an active member of several European knee surgery societies and committees. Though Max has finished his competitive sports career, he still often found either on the water (sailing, kitesurfing) or on the mountains (hiking, climbing, skiing).

Fidelius von Rehlingen-Prinz, MD

2023-2024 RESEARCH FELLOW

Dr. med. Fidelius von Rehlingen-Prinz is a fifth-year resident at UKE University Hospital of Hamburg, who is joining our team as a Research Fellow. Fidelius has a strong passion for orthopedic and sports medicine research and is an active member of several European arthroscopic surgery societies.

Daan Vermeijden, MD, PhD

2019-2021 RESEARCH FELLOW

Daan Vermeijden is currently working as a resident not in training in Orthopaedic Surgery in Hilversum, the Netherlands, and was just officially accepted into the residency program. After obtaining his Medical Degree, he spent 18 months at the Hospital for Special Surgery (HSS) in New York City doing research with Dr. DiFelice on the subject of primary repair of the anterior cruciate ligament. During this period, they investigated the indications and outcomes of this procedure and published numerous manuscripts in peer-reviewed journals. After his amazing time in New York, he returned to Amsterdam to do his residency in Orthopaedic Surgery. He completing his PhD on the topic of primary ACL repair.

Jelle van der List, MD, PhD

2015-2017 RESEARCH FELLOW

Jelle van der List is an orthopaedic surgical fellow. Since 2016 he has been working with Dr. DiFelice on research on the topic of primary anterior cruciate ligament repair and obtained his PhD on this topic, which was mainly based on the research that they have worked on.