Risk Factors For Malalignment Of Regenerate Deformity In Treatment Of Femur Bone Transport Using Unilateral External Fixator

Objective:In clinical practice,we discovered patients received femur bone transport and lengthen procedure adapting LRS mono-lateral external fixator may undergo inversion deviation at bone traction stage,which result in femur deformity and may interfere with future pelvic function.Therefore,this retrospective study aims to investigate the cause and risk factor contributing to axial deviation in femur bone transport with an LRS mono-lateral external fixator.Method:We retrospectively evaluate 27 patients received bone femur bone transport and lengthen procedure using an LRS mono-lateral external fixator.Radiograph data that contained AP position of the femur pre and post-surgery are obtained through PACS and analyzed by three different technicians.General information includes sex,age,weight,height,smoking history,function exercise and external fixation index.Radiograph data contain aLDFA,mLDFA,MPFA,LPFA,MAD,neck-shaft angle,lengthening length,transport distance,segment position,fixator-anatomical axial angle,transport length,number and mode of pin at transport segment,half pin-proximal distance,half pin-distant distance,bone-pin axial angle,fixator-pin axial angle,half pin bending,bone segment-fixator angle,standard bone-pin axial angle,standard fixator-pin axial angle,standard anatomical axial-fixator angle.The collected data are grouped according to the occurrence of inversion deformity.The inversion deformity group are divided into three subgroup as proximal inversion deformity group,transport segment inversion deformity group and combined inversion deformity group.Statistical analysis was performed with the SPSS 22.0 software(SPSS Inc,Chicago,IL).Descriptive statistics were conducted for all aforementioned variables to evaluate their effect on axial deviation and severity.Results:This study comprises 27 patients(23male,4 female),aged 14-59 years old(mean age 33.19±13.36years old)with 13 left-sided and 14 right-sided.The angle formed between transport segment and proximal segment is 7.94±9.41°(0.00°-26.87°),which is of statistical significance in transport segment inversion deformity(P=0.000<0.05).Moreover,there is statistical significance in half pin bending and traction length between deformity and non-deformity group while the position of segment,direction of bone transport and mode of pin insertion show no statistical significance.Conclusion:During the process of bone transport and length adapting mono-lateral external fixator,the margin of the traction bone may suffer from different degree of inversion.The main cause is the bending of half pin.additional,the traction length also contributes to inversion deformity and serves as one risk factor.Although other factors such as segment position,fixator-anatomical axial angle,mode of half pin insertion,limb shorten re-lengthen display no statistical significance,their role in deserve farther discussion.