Total shoulder replacement is a surgery typically conducted to alleviate symptoms of arthritis such as chronic pain, limited range-of-motion, and impaired daily functioning.
A common challenge in shoulder replacement is that the native glenoid bone is worn posteriorly. In such cases, the surgeon typically either implants a standard glenoid component malaligned relative to the scapula, or reams away healthy bone on the anterior side to achieve normal alignment, both of which can lead to complications. One of the most serious problems with shoulder replacement is loosening of the glenoid implant, which occurs in approximately 5 to 10 percent of cases. Such patients typically require revision surgery. Gregory Lewis, Ph.D., in collaboration with April Armstrong, M.D., shoulder surgeon, Penn State Hershey Bone and Joint Institute, is actively engaged in research to understand the internal micromechanics of replaced glenoids with the aim of decreasing the risk of glenoid loosening. New findings, presented at the 2012 Orthopaedics Research Society annual meeting, compare glenoid loosening and implant construct damage with a new type of posterior-augmented polyethylene implant to fill in the resulting gap from bone loss (versus a conventional implant). Lewis explains, “We used human cadaver specimens to test how well the two types of implants hold up under simulated, physiologic cyclic loading. At various cycle intervals, up to 100,000 cycles, [equivalent to twenty-five high-load shoulder movements per day for ten years], we measured external implant micromotions along with internal construct damage.