Abstract
Introduction
Evaluations of Computer-assisted orthopaedic surgery (CAOS) systems generally overlooked the intrinsic accuracy of the systems themselves, and have been largely focused on the final implant position and alignment in the reconstructed knee [1]. Although accuracy at the system-level has been assessed [2], the study method was system-specific, required a custom test bench, and the results were clinically irrelevant. As such, clinical interpolation/comparison of the results across CAOS systems or multiple studies is challenging. This study quantified and compared the system-level accuracy in the intraoperative measurements of resection alignment between two CAOS systems.
Materials and Methods
Computer-assisted TKAs were performed on 10 neutral leg assemblies (MITA knee insert and trainer leg, Medial Models, Bristol, UK) using System I (5 legs, ExactechGPS®, Blue-Ortho, Grenoble, FR) and System II (5 legs, globally established manufacturer). The surgeries referenced a set of pre-defined anatomical landmarks on the inserts (small dimples). Post bone cut, the alignment parameters were collected by the CAOS systems (CAOS measured alignment). The pre- and post- operative leg surfaces were scanned, digitized, and registered (Comet L3D, Steinbichler, Plymouth, MI, USA; Geomagic, Lakewood, CO, USA; and Unigraphics NX version 7.5, Siemens PLM Software, Plano, TX, USA). The alignment parameters were measured virtually, referencing the same pre-defined anatomical landmarks (baseline). The signed and unsigned measurement errors between the baseline and CAOS measured alignment were compared between the two CAOS systems (significance defined as p<0.05), representing the magnitude of measurement errors and bias of the measurement error generated by the CAOS systems, respectively.
Results
The measurement errors are presented [Table 1]. For unsigned measurement error, System II was higher in the tibial varus/valgus alignment and posterior slope (p≤0.01), and lower in the femoral varus/valgus alignment (p=0.03), compared to System I [Fig. 1]. System II exhibited higher error bias towards tibial varus alignment (up to 2.59°), more posterior slope (up to 1.41°), and more femoral hyper extension (up to 1.6°) than System I (p<0.01) [Fig. 1]. The mean signed and unsigned errors were generally less than 1°, except for System II in the measurement of tibial varus/valgus alignment (signed and unsigned mean errors=1.93°).
Discussion
This study reported system-dependent bias and variability associated with intraoperative measurements of alignment parameters during TKA. The results showed that System I generally had lower variability and less bias than System II. Although the majority of the significant differences found were clinically irrelevant (<1° in means), System II was notably shown to produce on average ∼2° measurement errors in tibial varus/valgus alignment biased towards varus.
Intra-operative measurement of surgical resection parameters during imageless computer-assisted TKA surgery is a critical step, in which a surgeon directly relies on the real-time data to prepare the bony resections and check the final realized cuts. Clinical-level accuracy in alignment outcomes has been shown to be system-dependent [2], this study further suggested there are differences in system-level accuracy between CAOS systems.
