KNEE PHENOTYPING PRIOR TO TOTAL KNEE ARTHROPLASTY: CAN WE ELIMINATE THE NEED FOR LONG LEG RADIOGRAPHS WITH AN IMAGELESS ROBOTIC SYSTEM?

Introduction To study the correlation between Hip-Knee-Ankle angle(HKA), medial proximal tibial angle(MPTA) and lateral distal femoral angle(LDFA) measured by a)preoperative long leg radiographs with b)Intraoperative surgeon assessment of difference in cartilage thickness and c)postoperative processing using exact measured cartilage thickness on Robotic system. Methods We prospectively enrolled all patients undergoing primary total knee arthroplasty(TKA) by a single surgeon at a single center. All surgeries were performed with the help of an imageless robotic system (Velys, DePuy, USA). All patients underwent preoperative long limb radiographs at the same center using the same standardized protocol. Two observers measured the HKA, MPTA and LDFA on preoperative radiographs. Intraoperatively, based on surgeon estimation of cartilage loss in 1 mm increments, the MPTA and LDFA were estimated. Then, the surgeon measured the exact depth of cartilage using robotic data on the screen for femoral condyles (0.2mm increments) and tibial condyles (0.5mm increments). Using these the MPTA and LDFA were again estimated. Thus we had three values of MPTA and LDFA; from preoperative radiographs (MPTAp, LDFAp), intraoperative rough estimation of cartilage difference (MPTAi, LDFAi) and calculation based on exact cartilage depth (MPTAc, LDFAc). We used Spearman's correlation coefficient to calculate correlation between the three measurements. Results We recruited 40 patients(48 knees). The mean age was 69.6 years(range 51–84), BMI was 31.2(21.1–44.3) with 85.4% being women. There was a strong positive correlation between MPTAp and MPTAi(r=0.72, p<0.001), which increased with MPTAc(r=0.81, p<0.001). There was a strong positive correlation between LDFAp and LDFAi(r=0.79, p<0.001), and LDFAc(r=0.85, p<0.001). Conclusion HKA, MPTA and LDFA assessment using an imageless robotic system showed a strong correlation with radiographic measurements. The strong correlation with estimation of cartilage thickness by the surgeon, became stronger utilizing exact measurement of cartilage thickness. When using an imageless robotic system, surgeons can accurately calculate preoperative MPTA and LDFA, eliminating the need for preoperative long leg radiographs.