Are Instrumented Knee Forces Representative of a Larger Population of Cruciate-Retaining Total Knee Arthroplasties?

It is not known if the loads and motions reported for instrumented knees are generalizable to a larger population of total knee arthroplasty (TKA) patients. The purpose of this study is to (1) report axial implant force data for chair and stair activities for a population of cruciate-retaining TKA patients and (2) compare the population forces to those measured with instrumented TKAs. Twenty-three subjects with a cruciate-retaining TKA underwent motion analysis during stair ascending, stair descending, chair sitting, and chair rising activities after informed consent in this institutional review board approved study. Axial TKA forces were calculated using a previously validated computational model. Differences between the mean and variability of population instrumented TKA peak forces and force impulses were tested using t tests and Levene test. Peak axial forces were 3.06, 2.74, 2.65, and 2.60 kN for stair ascent, stair descent, chair rising, and chair sitting, respectively. Force impulses were 123.3, 123.4, 153.5, and 154.0 kN*% activity cycle for stair ascent, stair descent, chair sitting, and chair rising, respectively. Population TKA and instrumented TKA peak forces were different for stair ascent (P = .03) and stair descent (P = .03) in the second half of the activity cycles. The variability of the peak forces and impulses were not different (P = .106 to P = .99). The forces and motions presented in this study represent cruciate-retaining TKA patients and could be used for displacement-driven knee wear testing. The forces are similar to those in the literature from instrumented prostheses of an ultracongruent cruciate-sacrificing TKA.