Patient-Specific Implants and Instruments Improved Outcomes of Total Knee Replacement

Introduction: Patient-specific cutting guides (PSCG) built from imaging of the extremity can improve the accuracy of bone cuts during total knee replacement (TKR). Some reports have suggested that PSCG offer only marginal improvement in the accuracy of alignment and component positioning in TKA. We compared outcomes between TKRs done with PSCG versus standard, intramedullary-based instrumentation. Methods: Blood loss, duration of surgery, alignment of the mechanical axis of the leg, and implant position on standing, long-leg, and standard lateral digital radiographs were compared between a CT-guided, custom-built TKA implant (n = 50; ConforMIS iTotal, Boston, MA) implanted with PSCG, versus an off-shelf posterior stabilized TKA implanted with standard instrumentation (n = 50; NKII total knee, Zimmer, Warsaw, IN). The fraction of outliers (>3 degrees) was calculated for the two groups. Results: The mean mechanical axis of iTotal was 181 degrees with a fraction of outliers of 0.2, versus 178 degrees for NKII with fraction of outliers of 0.7. For frontal plane positioning of femoral components, fraction of outliers for iTotal was 0.04, versus 0.6 for NKII. For tibial components, corresponding values were 0.1 and 0.6, respectively. Sagittal plane outliers were 0.2 and 0.9, respectively, for femoral components; and 0.2 and 0.6 for tibial components. Surgery duration was 5 minutes less and blood loss was 100 mL less for iTotal than for intramedullary-aligned NKII. Conclusion: Patient specific instrumentation and custom-built implants showed a trend toward improved accuracy of alignment, reduction in blood loss and operating time, when compared to standard, off-the-shelf TKA implants with intramedullary alignment, with fewer radiographic outliers. Larger, randomized trials are necessary to evaluate this technology further, but the initial outcomes appear favorable, with no cost disadvantage to the custom-built implant.