Abstract
Introduction
Clinical outcomes of UKA procedures are sensitive to malalignment of the components, and thus show significant variability in the literature. A new robotic procedure addresses isolated medial compartment osteoarthritis with the classic indications of UKA. Using precision planning through patient specific 3D modeling and reconstruction, a robotic arm gives the surgeon control of resurfacing the knee joint, allowing for consistent precision according to the previously chosen plan. Through the precise preparation of bone surfaces and inter-component alignment, this procedure is designed to significantly increase accuracy and decrease mal-alignment, thus increasing post-operative physical and function outcomes. This paper evaluates four year clinical outcomes of this novel surgical procedure.
Methods
The first seventy-three (42 male, 31 female) patients (average age: 71 ±10yrs) to receive a robotically assisted UKA enrolled in an IRB approved outcomes registry. Eleven patients were four years post operative and sixty-two patients were three years post operative at the time of the study. The average follow ups were 45 months and 35 months, respectively (range: 30 to 47 months). The tibial component for all patients was an all-poly inlay design.
Results
At one, two, three and four year follow up, all patients showed significant improvements, compared to pre-operative values, in range of motion (p<0.05), Knee Society Knee (p<0.001) and Function (p<0.001) scores, sf-12 PCS scores (p<0.001). Two patients have been revised, for a four year clinical failure rate of 2.34% at an average follow-up of 37 months. Both revisions were due to loosening of the tibial component and occurred at 23.6 and 17.5 months, respectively, after the index procedure. The first was revised to a TKA. The second patient (age 50, BMI 27.2) was revised to a unicompartmental onlay tibial component at 17.5 months after presenting with weight bearing pain in the medial compartment. Upon explantation of the inlay component, the surgeon observed perfect cement-to-bone integration and noted that the failure was due to debonding of the undersurface of the poly to the cement. Optimal alignment of the femur to the tibia remained intact and the patient showed no signs of progressing OA disease. The bone preserving nature of the original inlay tibial component preparation allowed the surgeon to convert the patient to an onlay component with minimal bone resection instead of conversion to a TKA. A cement channel has been added to the inlay design to improve cement fixation effectiveness. In addition, the undersurface of the tibial component has since been removed and replaced with a dovetail channel to improve lift-off resistance of the tibial inlay. This new design has shown to be 10 times stronger in laboratory push out tests.
Conclusions
This initial series of robotically guided UKA implantations provided significant improvement in the post-operative function of patients in every functional measurement with only two revisions to date, likely for improper patient selection. The introduction of new procedures and technologies in medicine is routinely fraught with issues associated with learning curves and unanticipated pitfalls. Because the explicit objectives of this novel technology are to optimize surgical procedures to provide more safe and more reliable outcomes, these favorable results provide the potential for significant improvements in orthopedic surgery.
