Background: This study compares the functional evolution between the first- and second-generation patient-specific instrumentation and conventional instrumentation pre-surgery and the third month post-surgery after TKA. We analyzed the functional outcomes achieved and the absolute gains of each study variable. In addition, we aimed to elucidate the results of the three surgical techniques regarding the surgery length of time, length of hospital stay, percentage drop in hemoglobin (Hg) at 24 h, and hip-knee-ankle angle post-surgery. Methods: We reported our experience in TKA using PSI Visionaire System® and CI technique in 688 procedures. The patients were divided into first (N=272) and second-generation (N=151) PSI designs. The control group (N=265) underwent TKA with the CI. The instruments for assessing the functioning were: visual analog scale, goniometry, 6-minute walk test (6MWT), and domains of the WOMAC Index. Results: The functioning achieved three months after surgery was lower in the CI than the first-generation PSI. The respective differences at absolute gains were found in the 6MWT and pain and function WOMAC scores (p=0.023, p=0.049, and p=0.018, respectively). The mean surgical time was higher in the CI compared to PSI designs (both p<0.001), and the mean hospital length of stay was higher in the CI compared to second-generation PSI (p=0.002). The percentual drop in Hg was higher in the first-generation PSI than with the CI (p=0.006). Conclusions: Three months after TKA, the functioning achieved with the first-generation PSI was greater than the CI. However, the functional results between second-generation PSI and CI were similar.

<p class="abstract"><strong>Background:</strong> The aim of the study was to analyze and compare the accuracy, efficiency and functional evolution between the first- and second-generation Patient-specific instrumentation (PSI).</p><p class="abstract"><strong>Methods:</strong> We report our experience in TKA using PSI Visionaire System^® (Smith and Nephew^®) in 456 procedures. The patients were divided into first- (N=272) and second-generation PSI design (N=184). For the accuracy was analyzed the mechanical results, namely Hip-knee-ankle (HKA) alignment post-TKA and outliers’ frequency; for the efficiency was analyzed the length time surgery, the length of stay and satisfaction, for the functional outcomes was compared the evolution at pain, range of motion, gait perimeter and the domains of the Western ontario and mcmaster osteoarthritis index (WOMAC). The t-test for independent samples was applied in the continuous numeric variables and Qui square tests in the dichotomic nominal variables. Statistical significance was p value&lt;0.05.<strong></strong></p><p class="abstract"><strong>Results:</strong> The alignment of the femur worsened significantly in the second-generation (p=0.002), but the alignment of the tibia was improved (p=0.010). However, not enough to improve significantly the HKA. No significant differences were observed in the frequency of outliers. The length of stay decreased in the second-generation (&lt;0.001). The functioning achieved at first and third months after surgery was lower in second-generation PSI; at first month in the pain and stiffness WOMAC (p=0.030; p&gt;0.001) and in the third in WOMAC stiffness (p&lt;0.001).</p><p class="abstract"><strong>Conclusions:</strong> The second-generation PSI of Visionaire system® improved the alignment of the tibia, but not the alignment of the femur. This change did not produce any improvements in functioning.</p>