Assessment Of Femoral Prosthesis Location In The Sagittal Plane After Unicompatmental Knee Arthroplasty With Extramedullary Technique:a Radiographic Analysis

Objective:The mobile Oxford unicompartmental knee arthroplasty(UKA)implant has been widely used with an intramedullary guide for femoral preparation.We modified the femoral guide technique based on the tibial cut first and spacer block technique and achieved good coronal alignment.This study was performed to evaluate the sagittal parameters of femoral prosthesis after extramedullary technique-guided UKA by comparing it with conventional MP technique-guided UKA.Methods:From January 2019 to December 2019,We retrospectively evaluated 68 consecutive knees(58 patients)which underwent UKA using the extramedullary technique.An equal number of knees which underwent UKA with the conventional technique were matched as the control group.Taken on postoperative day 3,standard femoral lateral radiographs of all 66 lower limbs were analyzed twice by one author between a month.Distance between anterior cortex of femur and anterior edge of femoral prosthesis(DAE),distance between distal femur and proximal edge of femoral prosthesis(DDP),angle between sAA and central column axis of femoral prosthesis(SAAFPA)were measured.Two-sided Pearson correlation coefficient were obtained to identify the correlations between DAE&DDP,DAE&SAAFPA,DDP&SAAFPA.The statistical analysis was done using SPSS Version 23.0.A p value less than 0.05 were considered to be significant.Results:In the extramedullary group,the mean DAE was(18.75±4.28)mm,the mean DDP was(26.74±2.91)mm，the mean SAAFPA was(9.96±5.62)°.In the MP group,the mean DAE was(20.16±5.38)mm,the mean DDP was(24.98±3.23)mm,the mean SAAFPA was(10.34±4.29)°.Among the extramedullary group,for the knee with prosthesis of size L(n=1),the DAE was 21.74mm,the DDP was 27.11mm,the SAAFPA was 6.74°.In group of size M prosthesis(n=16),the mean DAE was(21.54±4.20)mm,the mean DDP was(27.56±3.32)mm,the mean SAAFPA was(10.58±6.20)°.In group of size S prosthesis(n=44),the mean DAE was(17.73±4.36)mm，the mean DDP was(26.33±2.71)mm，the mean SAAFPA was(9.53±5.35)°.In group of size XS prosthesis(n=5),the mean DAE was(18.55±5.47)mm,the mean DDP was(24.10±1.17)mm，the mean SAAFPA was(12.62±6.01)°.DAE correlated positively with SAAFPA in group M and XS(r=0.511,p<0.05;r=0.615,p<0.05;respectively).DDP correlated positively with SAAFPA in group M and XS(r=0.957,p<0.05;r=0.983,p<0.05;respectively).Conclusions:No significant difference was found in the sagittal measurements of femoral prosthesis between the extramedullary group and the MP group.The discreteness of DAE and DDP in KOA patients were not high while the mean SAAFPA was similar in different subgroup,which indicate that the modified MP technique could guarantee a relatively constant sagittal location of femoral prosthesis of the same size.