Abstract
Introduction
With the development of 3D printing technology, there are many different types of PSI in the world. The accuracy of patient specific instrumentation (PSI) in primary total knee arthroplasty (TKA) is dependent on appropriate placement of the cutting blocks. However, previous reports on one type of PSI measured the difference between postoperative prosthetic alignment and postoperative mechanical axis and thus these reports did not evaluate intraoperative comparison of PSIs between two different designs. The purpose of this study was to evaluate the intraoperative accuracy of two different designed PSIs (My knee, Medacta International, Castel San Pietro, Switzerland) with two examiners using CT free navigation system (Stryker, Mahwar, NJ, USA) in regards to sagittal and coronal alignment.
Methods
We enrolled 78knees (66 patients) with a primary cemented TKA using two different designed CT-based PSIs (My knee, Medacta International, Castel San Pietro, Switzerland). All operations were performed by two senior surgeons who have experience with greater than 500 TKAs and greater than 200 navigated TKAs. Two examiners were same two surgeons. The study period was between June 2015 and November 2016. The local ethics' committee approved the study prior to its initiation, and informed consent was obtained from all patients. After placement of the PSI on the femur and tibia, the position of the PSI was evaluated by s intraoperative navigation. Two examiners placed two different types (STD(standard) and MIS(minimum invasive surgery)) of PSI on same joint. As required by the PSI, only soft- tissue was removed and osteophytes were left in place. Femoral MIS PSI was required partial remove of lateral cartilage. For the femur, the coronal position in relation to the mechanical axis were documented. For the tibia, the coronal alignment and the tibial slope were documented. Of note, intraoperative modifications to the PSI were not made based upon the results of the navigation. Rather, the findings of the intraoperative navigation were simply documented.
Results
The mean age of the cohort was 72.9±7.5years (range, 55–85years). The study included 11men and 55women, with a mean height of 151±8.2cm (range, 135–175cm), mean weight of 59.4±4.3kg (range, 42–82kg), and a mean of Body Mass Index of 25.9±3.6 (range, 17.2–36.4). HKA angle (supine position) measured by CT was 170.8 ±4.4 degree(range, 162.5–182degree). Diagnosis was osteoarthritis in all patient. There was no statistically significant difference in PSI position alignment for femoral flexion, tibial coronal angle, tibial slope between the two groups with two examiners. However, the intraoperative coronal position using the femoral STD PSI significantly deviated from using femoral MIS PSI from both examiners. (PSI vs. MIS, examiner1 p = 0.02, examiner2 p=0.04)
