Patellar Component Fixation Strength with Varying Bone Defect Following Revision Total Knee Arthroplasty

Purpose: Total knee arthroplasty (TKA) is an effective surgical treatment with only an 8.2% revision rate. A revision TKA can be initiated for several reasons including prosthetic loosening, infection, and pain. During a revision TKA, the three pronged “patellar button” may need to be removed and replaced from the posterior aspect of the patella. After removal, the quality of the remaining patellar bone is evaluated to determine if another patellar component is a viable option. Anecdotally, orthopedic surgeons visually inspect the patella to evaluate the amount of bone defect present. They then have to decide whether to replace the patellar button or pursue another path of repair. Currently there is no scientific basis to assist them in deciding how to best proceed. This study aims to determine the maximum shear force prior to failure of a cemented patellar component with varying degrees of bone defect. Methods: 60 pairs of patellae were harvested from embalmed cadavers. Each patella pair was visually inspected by an orthopedic surgeon and separated based on bone quality into a control (better bone quality) and experimental group (worse bone quality). Those within the experimental group were further divided into three groups, of 20 each, consisting of either a single defect, double defect, or triple defect. The patellae were then prepared as if performing an intraoperative revision TKA. Before cementing the patellar component, defects were created in each patella according to their experimental group (single, double, or triple defect) using a Dremel tool and metal washer to ensure each defect was the same size. A patellar component was then cemented to each patella using the same surgical procedure used during a revision TKA. After allowing the cement to cure, the patellae were potted into a mold using fiber glass resin. Maximum shear force was then tested with a material testing system (MTS). Results: The 60 pairs of patella range in age from 56 years old to 99 years old with an average age of 80. Thirty-one patella pairs were male (51.67%) and 29 pairs were female (48.33%). Data is currently being collected and analyzed regarding the shear force of the patellar component with the 3 different varying bone defect sizes. Conclusions: The further evaluation of the data will serve to provide physicians with clarity when faced with the question of what to do with the patella in the case of a revision TKA.