Correction Of Coronal Tibiofemoral Subluxation After Opening Wedge High Tibial Osteotomy And Its Correlations With Other Lower Limb Force Line Parameters Such As Patellar Height

Coronal tibiofemoral subluxation is a common finding in radiographs of patients with knee osteoarthritis and has been associated with unexplained knee pain.However,there are controversies in different studies on the efficacy of surgical treatment for patients with coronal tibiofemoral subluxation and the relationships between the degree of subluxation and other parameters of lower limb force line such as patellar height also remain controversial among different researchers.The normal position of patella plays an important role in maintaining the stability of knee joint and normal activities.Accurate measurement of patellar height is of great significance for evaluating the stability of patella and making plan before operation around the knee joint.Various methods for measuring patellar height have been reported in previous literature,but these methods have their own advantages and disadvantages,and can not be applied for all patients in clinical.Recently,a novel patellar height measurement method using a linear equation of knee flexion angle was reported.Although its reliability has been verified in the original literature,the effectiveness in patients older than 49 years has not been verified by the proposer or other researchers.Therefore,the purpose of this retrospective study with imaging data of patients with knee osteoarthritis were to definite the relationship between coronal tibiofemoral subluxation and other parameters of lower limb force line such as patellar height,and to verify the effectiveness of the linear equation method,subsequently,provide guidance for correction of coronal tibiofemoral subluxation by opening wedge high tibial osteotomy and patellar height evaluation.Part One Change of coronal tibiofemoral subluxation after opening wedge high tibial osteotomy and its correlations with other lower limb force line parametersObjective:Coronal tibiofemoral subluxation（CTFS）is a common finding in radiographic examination of patients with knee osteoarthritis.However,previous studies have not extensively explored whether CTFS could be corrected by surgery and the degree of correction.Patellar height（PH）is also a common measurement index reflecting the stability of knee joint,especially in patellofemoral joint.But no study has confirmed the relationship between CTFS and PH.Thus,the purpose of this study was to determine whether CTFS could be corrected in the treatment of knee osteoarthritis by opening wedge high tibial osteotomy（OWHTO）;whether different degrees of preoperative CTFS would get different correction results after OWHTO;and to explore the relationship between CTFS and other parameters of lower limb force line parameters such as patellar height and their changes after OWHTO.Methods:This was a retrospective study of patients’radiographs.The clinical data of patients who had undergone medial OWHTO surgery in our hospital from September 2016 to January 2020 were retrospectively analyzed.To verify whether CTFS could be corrected by OWHTO surgery and define force line parameters related to CTFS,all patients were firstly evaluated as a whole.Parameters of lower limb,such as CTFS,mechanical axis angle（MAA）,anatomical axis angle（AAA）,joint line convergence angle（JLCA）,medial proximal tibia angle（MPTA）,tibial plateau slope angle（TPSA）,width of tibial plateau（WTP）,PH measured by ISI（Insall-Salvati Index）,were compared before and after surgery.Their postoperative change values（expressed asΔ₁:postoperative minus preoperative value）,correction loss at the last follow-up（expressed asΔ₂:last-value minus postoperative value）,were also calculated.Then,patients were divided into three groups according to preoperative CTFS value:minor CTFS group（MIN）:CTFS≤5 mm;mild CTFS group（MID）:5-10 mm;large CTFS group（Large）:CTFS>10 mm.CTFS values,MAA,AAA,JLCA,MPTA,TPSA,WTP,ISI,their postoperative changes and correction loss at the last follow-up were compared among three groups.SPSS 22.0 Statistics software was used to analyze the correlations between CTFS and lower limb force line parameters and their changes before and after OWHTO surgery and at the last follow-up.A P value less than 0.05 was considered as a representation of significant difference.Results:In 109 patients（118 knees）,the male/female ratio was 48/61;left knee/right knee:59/59;the range of age was 33-73 years（mean 52.51±7.64 years）,mean follow-up time was 26±10.08（1-27）months.Overall analysis of all patients showed that the CTFS value significantly decreased from 6.29±3.38 mm before OWHTO to 4.84±3.21 mm after operation（P<0.05）and 5.12±3.26 mm at the last follow-up（P<0.05）.The correlation coefficients between CTFS and MAA,AAA,MPTA,JLCA,TPSA,WTP and ISI were 0.126,0.144,-0.229,0.133,-0.175,-0.010 and 0.033,respectively.The correlation coefficients betweenΔ₁CTFS andΔ₁AAA,Δ₁MPTA,Δ₁JLCA,Δ₁TPSA andΔ₁ISI were 0.124,-0.125,-0.035,-0.104 and-0.110,respectively.The correlation coefficients betweenΔ₂CTFS andΔ₂AAA,Δ₂MPTA,Δ₂JLCA,Δ₂TPSA andΔ₂ISI were-0.067,0.091,0.034,-0.004 and-0.158,respectively,indicating very weak correlations.The patients were then divided into three groups according to preoperative CTFS values for analyzing.The mean preoperative CTFS of three groups were 3.28±1.40（0-5.00）mm,7.14±1.26（5.02-9.87）mm and 12.28±1.34（10.58-15.30）mm,respectively.OnlyΔ₁CTFS andΔ₁MPTA were significantly different among three groups after surgery,while there were no significant differences in the postoperative values and their changes of other parameters,and no significant differences in correction loss among three groups at the last follow-up（P>0.05）.Conclusions:Preoperative CTFS could be corrected by OWHTO,even if it was larger than 10 mm.CTFS correction was unrelated to postoperative changes of other lower extremity parameters such as PH,because there were only very weak correlations between CTFS and other parameters,and between CTFS changes and the corresponding changes of other parameters after surgery and at the last follow-up.Part Two Validation of a patellar height measurement method using a linear equation of sagittal patella angleObjective:Normal position of patella plays an important role in maintaining the stability of knee joint,especially for patellofemoral joint.Currently,there are many methods used for patellar height evaluation,but which method is more advantageous is still controversial.Recently,a sagittal patellar angle（SPA）method was proposed,which could be used to measure the SPA on lateral knee X-ray films and then compared it with the expected value calculated by linear equation Y=1.94+0.74×knee flexion（KF）angle on sagittal plane to evaluate the patellar height.The advantages of this new method are those it is easy to be applied and the restriction of knee flexion angle when patient was taking radiographs is not as strictly as other methods.However,the original literature only verified its usefulness for measuring patellar height of patients aged from 16 to 49 years after HTO surgery,but whether it could be used in patients older than 49 years has not yet been verified by any study.So that the purpose of this study were to verify the effectiveness of the proposed method using this new linear equation to assess patellar height in patients older than 49 years,and to compare its consistency with other commonly used patellar height measurement methods.Methods:A total of 202 outpatients who had taken knee radiographs from September 2016 to September 2019 were included in this retrospective study.Patellar height was assessed using the linear equation Y=1.94+0.74×KF proposed in a recent literature.In this study,patients were divided into two groups:the younger group（YG,age:17-49 years）and older group（OG,age:>49 years）.Imaging related indicators,such as KF（°）,SPA（°）,patellar articular surface length（mm）,patellar tendon length（mm）,were measured twice by two observers with the Picture Archiving and Communication system（PACS）at an interval of one month.The intra-group and inter-group consistency were compared,and the correlations among parameters such as IS index（Insall-Salvati index）,CD index（Caton-Deschamps index）and Y value was calculated by SPSS 22.0 software,P<0.05 was considered as a representation of significant difference.Results:A total of 143 patients（165 knees）were included in the YG,age:17-49（mean 31.62±11.38）years,male to female ratio:70（48.95%）/73（51.05%）,left knee/right knee:83（50.30%）/82（49.70%）,the mean Y value calculated by the mentioned linear equation was 31.50°±10.07°,the mean SPA value measured on lateral knee radiographs was 34.38°±12.38°,the mean IS index was 1.06±0.17,and the mean CD index was 1.04±0.18.There were 59 patients（78 knees）in the OG,aged 50-60（average 54.61±2.99）years,including 32 male patients（54.24%）and 27 female patients（45.76%）,42 left knees（53.85%）and 36 right knees（46.15%）.The mean Y value calculated by linear equation was 25.90°±11.55°,the mean SPA value was 29.36°±14.22°,the mean IS index was 1.06±0.18,and the mean CD index was 1.00±0.16.Intra-observer and inter-observer reliability of Y values in two groups were 0.999,0.999,1.000 and 0.999,respectively,showing high reliability and repeatability.However,Pearson’s correlation coefficients between Y value and IS and CD index were-0.213 and-0.216 in the YG,and-0.113 and-0.316 in the OG,respectively.Conclusions:The method using linear equation Y=1.94+0.74×KF to calculate expected SPA and compare it with actually measured SPA to assess patellar height can be used in patients older than 17 years,regardless of age and knee flexion angle when patients were taking an X-ray radiograph,but there were only weak correlations between Y value and IS and CD index.