| PURPOSEUnicompartmental knee arthroplasty(UKA)is an effective surgery for knee osteoarthritis(KOA)and has developed rapidly in recent years.Proper indication selection is the key to successful UKA,and whether patellofemoral joint degeneration is a contraindication to UKA is controversial.This study explored the effect of varus deformity and UKA on the biomechanics of patellofemoral joint by computer modeling simulation,retrospectively analyzed clinical data to the influence of patellofemoral degeneration on the efficacy of UKA,and discussed the "Jingu imbalance" theory in traditional Chinese medicine(TCM)on biomechanical change and treatment of KOA.METHODSl.Dicom files of knee CT and MRI were collected from the Natural Knee Database(https://digitalcommons.du.edu/natural_knee_data/)of the Center for Orthopedic Biomechanics,School of Engineering and Computer Science,University of Denver.The sample was a male,with age of 44-year-old,height of 183 cm,weight of 70.31 kg,BMI of 21.02.He had no skeletal deformities,fractures,tumors,infections and other diseases,and no history of trauma and surgery.Mimics21.0 software was used to extract the data and reconstruct the normal knee STL model.In Geomagic Studio 2014 software,repair,noise reduction and surfaceization,and then reverse process the corresponding geometric models of normal knee,varus 5°,varus 10°,varus 15°,mobile bearing UKA,fixed bearing UKA,and complete 6 groups of geometric solid STP models.Import the STP files into Hypermeshl4.0 software for meshing,export the BDF format files,and perform finite element mesh property setting,material parameter definition,load application,boundary condition constraints,and various calculation condition analysis in MSC.Patran2019,the finite element pre-and post-processing software.Cortical bone and cancellous bone corresponding to femur,tibia,patella and fibula,cartilage of each joint,meniscus,UKA prosthesis and bone cement were isotropic,uniform and continuous linear elastic materials,ligament and tendon were tensile-only nonlinear material.To simulate the state of human weight-bearing knee bending,during knee flexion,a tensile force of 200 N was applied to the end of the quadriceps tendon and the load of 1000 N was applied at the upper end of the femur.All nodes of the distal tibia and fibula were fixed and restrained,the six-degree of freedom was limited,and the femur was pushed by the rigid body bone block on the femoral diaphysis to complete the knee flexion.Weight bearing knee flexion from 0-140° was simulated in the 6 groups of knee models(normal,varus 5°,varus 10°,varus 15°,mobile bearing UKA,fixed bearing UKA).The contact stress and Von Mises equivalent stress of patellofemoral joint during knee flexion were analyzed.2.A retrospective analysis was performed on 112 patients accepted medial mobile bearing UKA in the single group of the Department of Orthopedic Surgery of China-Japan Friendship Hospital from September 2020 to September 2021.According to grading method by Jones based on the patellar axial X-ray,grade 0 or 1 was defined as normal patellofemoral joint group,and grade 2 or 3 was defined as patellofemoral degeneration group.With 1-year follow-up,the preoperative and postoperative HKA angle,OKS,AKS function and activity score,and range of motion(ROM)of the two groups were compared.3.Explain "Jingu imbalance" in KOA,analyze the relationship between the biomechanics and treatment of KOA and the "Jingu imbalance",and explore the significance of the theory of"Jingu imbalance" to the understanding and treatment of KOA.RESULTS1.With the weight-bearing knee flexion from 0-140°,the contact stress on medial and lateral patellofemoral joint gradually increased in general.The contact stresses on medial and lateral patellofemoral joint in the varus 15° group changed most significantly.The peak contact stress on medial patellofemoral joint in each group at different flexion angles was 0.37-4.89 MPa,with 0.41-3.44 MPa in the normal group,0.55-3.74 MPa in the varus 5° group,0.37-4.40 MPa in the varus 10°group,0.61-4.89 MPa in the varus 15° group,0.57-3.65 MPa in the mobile bearing UKA group,and 0.51-2.57 MPa in the fixed bearing UKA group.The peak contact stress on lateral patellofemoral joint in each group at different flexion angles was 0.21-4.82 MPa,with 0.51-3.96 MPa in the normal group,0.44-3.08 MPa in the varus 5° group,0.28-2.92 MPa in the varus 10° group,0.21-2.63 MPa in the varus 15°group,0.55-4.02 MPa in the mobile bearing UKA group and 0.63-4.82 MPa in the fixed bearing UKA group.For the contact stress on medial patellofemoral joint,varus 15°>varus 10°>varus 5°>normal>fixed beraing UKA>mobile bearing UKA,the contact stress on medial patellofemoral joint in varus 15° group is the highest,the varus 5° group and the two UKA groups were closer to normal groups.For the contact stress on lateral patellofemoral joint,during 0-60°knee flexion,varus 10°>normal>fixed bearing UKA>mobile bearing UKA>varus 5°>varus 15°,during 60°-140° knee flexion,fixed bearing UKA>normal>mobile bearing UKA>varus 5°>varus 10°>varus 15°.The peak Von Mises equivalent stress on the patellofemoral joint gradually increased with knee flexion increased.The peak Von Mises equivalent stress in each group was 0.20-3.55 MPa in different flexion angles,with 0.22-2.69 MPa in the normal group,0.36-2.39 MPa in the varus 5° group,0.38-2.53 MPa in the varus 10°group,0.35-3.55 MPa in the varus 15°group,0.20-2.20 MPa in the mobile bearing UKA group,and 0.32-2.45MPa in the fixed bearing UKA group.From the perspective of the overall change,for the peak Von Mises equivalent stress during knee flexion,the varus 15°>normal>varus 10°>fixed bearing UKA>varus 5°>mobile bearing UKA.The patellofemoral Von Mises equieffect stress in the varus 15° group was the highest,the lowest belonged to the mobile bearing UKA.2.There were 60 cases in the normal patellofemoral joint group and 52 cases in the patellofemoral degeneration group.There were no significant differences in baseline data between the two groups,no significant differences in OKS,clinical and functional AKSS,and no significant differences in preoperative HKAA angle,fixed flexion deformity and maximum flexion degree.The preoperative and postoperative HKAAs were 170.89±2.93° and 176.97±2.10° in the normal patellofemoral joint group and 170.71±2.51° and 176.81±2.02°in the patellofemoral degeneration group,respectively,with significant differences(P<0.001).The OKS of the two groups were 17.63±3.84 and 18.25±3.66 at postoperative 1 year,respectively,with no significant difference(P=0.3 9),but decreased significantly compared to the preoperative 37.55±6.84 and 38.44±6.11(P<0.001).The clinical AKSS at postoperative 1 year were 91.48±6.02 and 91.11±5.90,respectively,with no significant difference(P=0.75),but improved significantly compared to the preoperative 54.58±8.30 and 55.79±8.35(P<0.001).The functional AKSS were 88.11±7.32 and 88.56±7.09 at postoperative 1 year,respectively,with no significant difference(P=0.75),but improved significantly compared to the preoperative 57.78±7.29 and 56.83±5.60(P<0.001).The ROM at postoperative 1 year were 123.98±13.94° and 123.87±10.66°,respectively,and there was no significant difference(P=0.96).However,compared with the preoperative 109.70±17.41° and 108.77±15.09°,it improved significantly(P<0.001).3."Jingu imbalance" is an important mechanism of KOA,which is a refined summary of the biomechanical mechanism of the onset and progression of KOA.The anatomical characteristics of the knee joint make it prone to occur Jingu imbalance.Trauma,strain and other factors will also induce jingu imbalance.Jingu imbalance imbalance can cause abnormal load on the knee joint,destruction of cartilage and subchondral bone structure,and quadriceps muscle loss,etc.These changes will also aggravate the jingu imbalance of the knee joint,resulting the progression of KOA.Conservative treatment methods of KOA,such as massage,acupotomy under the guidance of jingjin theory,functional rehabilitation exercises,orthopedic braces and insoles are all related to relieve and correct musculoskeletal imbalance.At the same time,the surgical treatment of KOA should also restore the jingu balance.The "Jingu imbalance" theory will also help to understand the postoperative complications.In UKA,the evaluation of indications and contraindications and the optimization on surgical techniques all reflect the consideration of the jingu balance.CONCLUSION1.Knee varus deformity led to an abnormal biomechanical environment in which stress was unevenly distributed in the medial and lateral patellofemoral joint characterized by increased stress on the medial.Compared with varus 10° and varus 15°,after UKA,the stress on the medial patellofemoral joint decreased and that on the lateral patellofemoral joint increased,and the medial-lateral stress of the patellofemoral joint were relatively balanced.Compared with the fixed bearing UKA,the medial-lateral stress on the patellofemoral joint in the mobile bearing UKA was more balanced.Therefore,the medial-lateral stress balance performance on the patellofemoral joint of mobile bearing UKA was a little better than that of fixed bearing UKA.2.Patellofemoral degeneration did not affect the clinical outcomes of medial mobile bearing UKA at postoperative 1 year.3."Jingu imbalance" is an important mechanism of KOA,a refined summary of the biomechanical mechanism of the pathogenesis and progression of KOA,which has important significance during the evaluation and treatment of KOA. |
