Author Contributions: Dr Weir had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Study concept and design: de Vos, Weir, van Schie, Verhaar, Weinans, Tol.
Acquisition of data: de Vos.
Analysis and interpretation of data: de Vos, Weir, Bierma-Zeinstra, Verhaar, Weinans, Tol.
Drafting of the manuscript: de Vos, Weir, Bierma-Zeinstra, Weinans, Tol.
Critical revision of the manuscript for important intellectual content: de Vos, Weir, van Schie, Bierma-Zeinstra, Verhaar, Weinans, Tol.
Statistical analysis: de Vos, Bierma-Zeinstra.
Obtained funding: van Schie, Weinans.
Administrative, technical, or material support: de Vos, Weinans, Tol.
Study supervision: Weir, Verhaar, Weinans, Tol.
Financial Disclosures: None reported.
Funding/Support: This work was funded by Biomet Biologics LLC, Warsaw, Indiana.
Role of the Sponsor: Biomet Biologics LLC had no role in the design and conduct of the study; in the collection, management, analysis, and interpretation of the data; or in the preparation, review, or approval of the manuscript.
Additional Contributions: We thank Max Reijman, PhD, and Jan H. Waarsing, PhD (Department of Orthopedics, Erasmus University Medical Center, Rotterdam, the Netherlands), for their help with the study design, statistical evaluation, and interpretation of the data; Sten P. Willemsen (Department of Biostatistics, Erasmus University Medical Center), for his additional statistical analysis; and Cora van der Heijden, Ank de Vries, and Pauline Verschoor (Department of Sports Medicine, The Hague Medical Center Antoniushove, Leidschendam, the Netherlands), for their logistic help. These individuals were not compensated for their efforts. We thank the patients for their participation and the health professionals for referring them to the study.