Measurement And Analysis Of The Joint Line Change After Total Knee Arthroplasty With Different Reference Points

Background:The change of joint line(JL)after total knee arthroplasty(TKA)affects the range of motion(ROM),clinical function and prosthesis survival,while a unified and standard criteria for joint line evaluation is still absent.At present,some bony markers,including the fibular head,the adductor point of the femur and the tibial tubercle,are used as reference points to measure the joint line.However,there is no literature to compare the evaluations using these different reference points.At the same time,there is a lack of comparison between these measuring techniques in terms of clinical outcomes.Objectives:1.To analyze the joint line changes using techniques based on bony reference points including the fibular head,the adductor point of the femur and the tibial tubercle before and after TKA,and to study the correlation between different techniques;2.To compare and analyze these different measuring techniques in terms of clinical outcomes.Methods:1.The positions of the joint line of the same group of patients underwent TKA with CR prosthesis by the same surgeon were respectively measured before and after surgery.Joint line was measured according to the reference points of fibular head,the adductor point of the femur and the tibial tubercle.The correlation between different measurements were analyzed.2.The changes in joint line were calculated and analyzed respectively The clinical results between the group with the joint line change greater than 4mm and the group with less than 4mm were compared.The joint line elevation group and the joint line decline group were also compared.The clinical results with change of joint line with different reference points were compared.Results:1.In the same group of patients,the mean change of joint line with fibular head as the reference point was-0.46mm(SD=2.36mm,range:-5-5.9mm),with the adductor point of the femur as the reference point was-0.95mm(SD=2.16mm,range:-6-4.3mm),and with the tibial tubercle as the reference point was 2.02mm(SD=3.40mm,range:-6.3～7.6mm).The comparison of four measurement methods shows there is a certain linear relationship(Y=0.606*X-0.0456,R2=0.5621)between the methods with the fibular head and the adductor point of the femur as reference points.There is no linear relationship between the measurements with the fibular head and tibial tubercle,the adductor point of the femur and the tibial tubercle as reference points.2.The visual analog scale(VAS)score decreased from 6.72±2.33 preoperative to 0.65±1.29 postoperative,the range of motion(ROM)increased from 108.2±22.5° preoperative to 115.6±13.69°in the last follow-up,and HSS score increased from 57.9±11.6 preoperative to 89.65±8.12 in the last follow-up.All changes were statistically different(P<0.05).With the tibial tubercle as reference,the Feller score and HSS score was significantly better in group with the joint line changes less than 4mm than the group more than 4mm(p<0.05).The ROM in joint line decline group(118.7±13.04°)was significant superior to the joint line elevation group(108.9±12.97°)(p=0.0094),there was no significant difference in the other results such as VAS score,Feller score and HSS score.There was no statistical difference between the clinical results and the measured results with the other reference points.Conclusions:1.There is a positive linear relationship between the results of joint line change with the fibular head and the adductor point of the femur as reference point.The joint line with the tibial tubercle as a reference changes a lot compared with the other two techniques,and there is no correlation between the measurements with the fibular head and tibial tubercle,the adductor point of the femur and the tibial tubercle as reference points.2.The proportion of patients with joint line changing more than 4mm for CR prosthesis is low in anteroposterior X-ray,while in the lateral X-ray with the tibial tubercle as the reference point,the proportion was relatively high.The clinical results show that the Feller score and HSS score of the group that the joint line changes less than 4mm with the tibial tubercle as the reference point is superior than that changes more than 4mm,and the ROM of the joint line decline group is superior to the joint line elevation group.