The Design Of Patient-specific Distal Femoral Cutting Guide And Its Application In Minimally Invasive Total Knee Arthroplasty

Objective To design a patient-specific distal femoral cutting guide using rapid reversal prototyping and 3D printing technology to verify the accuracy of osteotomy and successfully apply it to minimally invasive knee arthroplasty(MIS-TKA).Methods 1.A prospective self-control study was performed in 32 patients who underwent bilateral total knee arthroplasty between March 2015 and November 2015 in our department.The bilateral knee joints were randomly divided into patient-specific guide group and traditional surgery group.The patient-specific guide group obtained CT data of the lower extremities preoperatively.Patient-specific distal femoral cutting guides were designed and manufactured using rapid reversal prototyping and 3D printing techniques.The traditional surgery group were performed using conventional instrumentation.The operation time of the two groups was recorded,and the amount of distal femoral osteotomy was measured.Postoperative alignments were measured including the angle of the lower limb mechanical axis angle(HKA),the mechanical lateral distal femoral angle(mLDFA),and the mechanical proximal tibial angle(mMPTA).During the 6 weeks,3 months and 1-year follow-up,HSS scores were recorded.2.A prospective controlled study of 68 patients who underwent unilateral total knee arthroplasty in our department from January to December 2016 was performed.All patients underwent minimally invasive knee replacement with a Mini-Subvastus approach.They were randomly divided into two groups:one group underwent TKA with patient-specific techniques,another group underwent TKA with conventional instrumentation.The tourniquet time and blood loss were recorded in the two groups;postoperative HKA angle,mLDFA,and mMPTA were measured;Follow-up at 6 weeks,3 months,and 1 year after surgery was performed to record the HSS score.Results 1.The coronal alignments of postoperative femoral prosthesis and lower limb was significantly improved in the patient-specific guide group compared with the conventional surgery group(p<0.05);and femoral prosthesis alignment had fewer outliers(6%vs 25%).In addition,the operation time of the patient-specific guide group was significantly shorter(P<0.05),but the two groups did not have significant functional differences in the early postoperative period.2.The tourniquet time in the patient-specific guide group was significantly shorter than that of the traditional surgical group(P=0.007);There was no significant difference in the amount of blood loss between the two groups(P>0.05);There was no significant difference in the HSS scores at 6 weeks,3 months or 1-year follow-up(P>0.05);For the coronal alignments,the mLDFA of the patient-specific guide group was(90.9±1.3°),and the traditional surgical group was(91.5±1.5°),so that difference between the two groups was statistically significant(P=0.046);however,there was no significant difference between HKA and mMPTA after operation(P>0.05).The outlier of the femoral prostheses alignment in the two groups was 2(6%)and 8(24%).Conclusions The 3D-printed patient-specific distal femoral cutting guide can significantly shorten the operation time of conventional and minimally invasive total knee arthroplasty,improve postoperative alignments,and is simple to operate.This technique shortens the learning curve and is particularly suitable for inexperienced surgeons.However,large sample sizes and long-term follow-up studies are still needed to verify their long-term effects.