Abstract
Introduction
Robotic-guided arthroplasty procedures are becoming increasingly common, though to our knowledge there are no published studies on robotic cutting guides in TKA. We introduced a new computer-navigated TKA system with a robotic cutting-guide into a community-based hospital and characterized the accuracy and efficiency of the technique with respect to bone cutting, component alignment and final limb alignment, and tourniquet time.
Methods
The first 100 cases from a single-surgeon were retrospectively reviewed following IRB approval. Intra-operative bone-cut accuracy and overall limb alignment as measured by the computer were collected and divided into consecutive quartiles: Group I, cases 1–25; Group II, cases 26–50; Group III, cases 51–74; Group IV, cases 75–100. All resections were planned neutral to the mechanical axis. Postoperative component alignment and the overall mechanical axis limb alignment in the coronal plane were also measured on standing long-leg AP radiographs by two independent observers at a minimum six weeks post-op. This mechanical radiographic alignment was available for 62 cases. Tourniquet time (the time prior to incision until after cementation) and robotic cutting guide use time were also analyzed.
Results
Intra-operative Computer Data: Bone-cut accuracy was a mean 0.1° valgus, SD±0.8° for both the femur and tibia (range, femur: 2.0° valgus to 1.5° varus; range, tibia: 3.5° valgus to 1.5° varus). Final limb alignment was within 3° of neutral for 98% (96/98) of cases (range: 2.0° valgus to 3.5° varus).
Radiographic Alignment Data: Pre-operative mechanical alignment ranged from −14.5° valgus to 21.5° varus. Radiographic femoral and tibial component alignment was within 3° of neutral in 98.4% of cases (61/62). Final limb alignment was within 3° of neutral for 87.1% (54/62) of cases (range: 4.5° varus to 4.5° valgus).
Learning curve: Mean tourniquet time was 10 minutes longer for Group I (60 minutes ± 9.9SD, range 46–79) than for groups II, III, and IV (average mean 49.5min, range 35–68), p=0.0001. Within Group I, mean tourniquet time for the first ten and second ten procedures was 65 ± 10.6 min and 55 ± 8.3 min, respectively, p=0.034. Robotic-guide use time was also longer for the first quartile (7.8 ± 1.9 minutes, range 4–12), than for Groups II, III, and IV (average 5.2 minutes, range, 3–8), p<0.001. There were no significant differences in any of the accuracy measures among the different groups (p>0.05).
Conclusion
Imageless computer-navigated TKA with a robotic cutting guide allowed one surgeon to make bone resections within 3° of neutral in 98% of cases. Radiographic limb alignment was less precise, which is consistent with the known limitations inherent to this measurement technique. During the learning curve phase, surgeons can expect the procedure to take an average of 15 extra minutes during the first ten cases and 5 extra minutes during the second ten without compromising accuracy.
