Abstract
Introduction
Computer-assisted orthopaedic surgery (CAOS) provides great value in ensuring accurate, reliable and reproducible total knee arthroplasty (TKA) outcomes [1,2]. Depending on surgeon preferences or patient factors (e.g. BMI, ligament condition, and individual joint anatomy), resection planning (guided adjustment of cutting blocks) is performed with different knee flexion, abduction/adduction (ABD/ADD) and internal/external (I/E) rotation angles, potentially leading to measurement errors in the planned resections due to a modified tracker/localizer spatial relationship. This study assessed the variation in the intraoperative measurement of the planned resection due to leg manipulation during TKA, and identified the leg position variables (flexion, ABD/ADD, and I/E rotation) contributing to the variability.
Materials and Methods
Computer-assisted TKA (ExactechGPS®, Blue-Ortho, Grenoble, FR) was performed on a neutral whole leg assembly (MITA knee insert and trainer leg, Medial Models, Bristol, UK) by a board-certified orthopaedic surgeon (BH) at his preferred leg flexion, ABD/ADD, and I/E rotation angles. A cutting block was adjusted and fixed to the tibia, targeting the resection parameters listed in Table 1A. An instrumented resection checker was then attached to the cutting block to measure the planned resection at the same leg position (baseline). Next, the surgeon moved the leg to 9 sampled positions, representing typical leg position/orientation associated with different steps during TKA [Table 1B]. The planned resection was tracked by the CAOS system at each leg position.
Tibial resection parameters at each sampled position were compared to the baseline. Regression was performed to identify the variables (flexion, ABD/ADD, I/E rotation) that significantly contribute to the measured variation (p<0.05).
Results
The resection parameters at the baseline leg position are presented (see Table 1A). Clinically negligible variations were found across the 9 positions [Table 1B], with mean errors ≤0.1mm in resection depths and ≤0.2° in alignment parameters. For this particular system analyzed, leg flexion strongly correlated with the measurement errors in medial resection depths (p≤0.01, R2=0.76), lateral resection depth (p=0.01, R2=0.61) and posterior slope (p<0.01, R2=0.92) [Fig. 1]. The system tended to measure less in resection depths and posterior slope with an increased leg flexion [Fig. 1]. No other statistical significance was found (N.S.).
Discussion
The results here showed that ExactechGPS can provide robust measurements of the planned resection parameters during TKA, independent of the ABD/ADD and I/E rotation of the knee. Although for the system studied, measurement errors strongly correlated with leg flexion, the magnitude of the errors was clinically negligible (within ±0.5 mm/° at a confidence level of 95%) [Table 1B].
Although CAOS systems have been evaluated for accuracy in the spatial distance measurement and clinical alignment outcomes [2,3], the measurement accuracy of planned resection parameters due to change of leg position remains unknown, even though it directly impacts the final resection. This study provided an improved understanding of clinical variability on the measurement of planned TKA resection when using a CAOS system.
