Abstract
Introduction
Computer-assisted orthopaedic surgery (CAOS) has been shown to help achieve accurate, reliable and reproducible prosthesis position and alignment during total knee arthroplasty (TKA) [1]. A typical procedure involves inputting target resection parameters at the beginning of the surgery and measuring the achieved resection after bone cuts. Across CAOS systems, software/hardware design, mechanical instrumentation, and system-dependent work flow may vary, potentially affecting the intraoperative measurement of the achieved resection. This study assessed the cumulative effect of system-dependent differences between two CAOS systems by comparing the alignment deviation between the measurement of the achieved resection and the targeted parameters.
Materials and Methods
TKA resections were performed on 10 neutral whole leg assemblies (MITA knee insert and trainer leg, Medial Models, Bristol, UK) by a board-certified orthopaedic surgeon (BH) using System I (5 legs, ExactechGPS®, Blue-Ortho, Grenoble, FR) and System II (5 legs, globally established manufacturer). The surgeon was deemed as “experienced” user (>30 surgeries) with both systems. The target parameters for the TKA resections, as well as major differences between the two systems are summarized in Table 1A. The deviations of the intraoperative alignment measurements on the achieved distal femoral and proximal tibial resection from the target were calculated and compared between the two systems with significance defined as p<0.05.
Results
The alignment deviations (signed and unsigned) are presented in Table 1B. On average, System II had significantly higher deviation towards varus (2.2°) than System I (0.83° valgus) for the tibia (p<0.01) [Table 1B]. System I tended to measure slightly more in flexion (∼1°) than System II (∼0.5° extension) (p=0.03). System I demonstrated lower variability of the signed deviation (SD) than System II in tibial varus/valgus alignment, femoral flexion/extension, and femoral varus/valgus alignment [Fig. 1]. No significant differences were found in between systems in the unsigned errors. Both systems had measurement within the perceived acceptable range (within 3°) [2,3].
Discussion
Intraoperative measurement of the achieved TKA resections is important as it allows for intraoperative adjustment if the resections are not deemed suitable. Assuming a consistent surgical variability exhibited by the same surgeon with equal experience on both systems, this study demonstrated that some systems (System II) may have higher variability than others (System I), and exhibit clinically meaningful bias (tibial varus/valgus) while achieving or quantifying the resections. The variability may be caused by the cumulated effect of the differences between the two systems [see Table 1A]. As clinical alignment accuracy has been found to be system-dependent in a previous study [4], and archived resection parameters in the surgical report has been used as key inputs in relevant studies [5], the results here emphasizes the importance of taking into account the specific CAOS system in both clinical application and CAOS research.
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