Intra- and inter-operator reliability assessment of a novel extramedullary accelerometer-based smart cutting guide for total knee arthroplasty: an in vivo study

PURPOSE: The purpose is to verify the intra- and inter-operator reliability of an extramedullary (EM) accelerometer-based smart cutting guide for distal femoral resection during primary total knee arthroplasty (TKA). The hypothesis of the present study was that the use of the device would result in a good correlation between different operators with a difference between repeated measurements of less than 1°. METHODS: Twenty-five not consecutive patients with knee osteoarthritis undergone to primary TKA using an EM inertial-based cutting guide to perform distal femoral resection. In order to assess the agreement in femoral axis definition of the device, two operators performed three time each the manoeuvres necessary to define axis. Inter-rater agreement was evaluated with Bland and Altman agreement test. Intra-rater repeatability was evaluated analysing average results distribution of repeated measurements. Accuracy of the device was evaluated comparing differences between intra-operative device data with final implant alignment measured on post-operative longstanding x-rays using Students’ t test. RESULTS: Agreement between the two operators was statistically significant (p < 0.05) with a bias of − 0.4° (95% CI − 0.6° to − 0.2°). Average difference between cut orientation measured with device and final implant position, measured on x-rays, was 0.2° (95% CI − 1.5° to 1.7°) with no statistical difference between the two measurements. Final implant alignment, measured on x-ray, was 90.2°, with 95% of cases distributed within range 88.0° to 92.0° for varus-valgus and 2.8° and with 95% of cases distributed within range 2.0° to 4.0° for flexion–extension. CONCLUSIONS: The EM accelerometer-based smart cutting guide used to perform distal femoral resection during primary TKA demonstrated a good intra- and inter-operator reliability in the present in vivo study.