A method of treating a synovial joint by injecting particles of collagen-based material into the joint. The particles may be dehydrated before implantation, and rehydrated after implantation, or they may be implanted in a "wet" state--such as a slurry or gel. Radiocontrast materials may be included to enhance imaging of the injected material. Other additives may include analgesics, antibiotics, proteoglycans, growth factors, and/or other cells effective to promote healing and/or proper joint function.