For 97-99% of joint replacement patients, surgery is tolerated and they remain free of infection. But for the remaining 1-3% of patients (approximately 30,000 Americans) whose joint becomes infected, researchers at the University of Texas Health Science Center at Houston and collaborators at Rice University and Shriners Hospital for Children-Houston are hard at work to prevent implant-associated bone infections, also known as osteomyelitis. Lead investigator Catherine Ambrose, Ph.D., from the Department of Orthopaedic Surgery at the UTHealth Medical School, published in The Journal of Bone and Joint Surgery the findings of the researchers’ studies dedicated to preventing joint infection with microspheres.
The research team developed bioresorbable polymer microspheres filled with tobramycin (an antibiotic), impregnanted metal cylinders with the microspheres, and coated the cylinders with Staphylococcus aureus before implanting them into surgically induced radial defects in rabbits. As a control, non-antibiotic-containing cylinders were implanted into the opposing limb of each rabbit. After evaluating the rabbits for two weeks for clinical signs of infection, all rabbits were sacrificed and the limbs were removed for analysis.
In all eleven rabbits, the limbs that received the antibiotic microsphere-containing cylinders were uninfected, despite being coated with the infection-causing bacteria. Only four limbs that received the non-impregnated cylinders were able to ward off infection, giving an infection rate of 64%. Moreover, integration of the cylinder with the body (which would be ideal to yield stability of the implant within the bone) was enhanced in the antibiotic microsphere group: 38.87% of the area of the implant contained tissue ingrowth, compared to 19.46% of the area in the infected limbs (p=0.01).
In addition to the stated benefits of the microspheres, healing was not impaired, and the antibiotics were released gradually to allow sufficient time for the treatment and prevention of infection. This work may culminate in future clinical studies, which would be encouraging because, according to Terry Clyburn, M.D., of Total Joint Services at the UTHealth Medical School, although osteomyelitis is rare during joint replacements, the results are devastating. He stated, “When these infections occur, it can be a huge setback for patients. Sometimes the implant has to be removed entirely to treat a painful infection and they require multiple surgeries. If these microspheres could prevent those infections from happening in the first place, this would be a significant advancement.” The advancement also has the potential to be used alongside fracture fixation devices used to treat open fractures in trauma patients.