The Research Of The Co-relationship Between The Variation Of Femoral Offset And The Variation Of Leg Lengthen Discrepancy

Background :It has been more than 60 years since John Charnley who is father of total hip arthroplasty carried out total hip arthroplasty.At the beginning the material of artificial joint prostheses are made of stainless steel 、 Cr-Co alloy and Cr-Ti alloy;now developing to Co-Cr-Mo alloy. At the beginning the material of interface between the femoral head and acetabulum were metal-metal 、metal-polyethylene;and now developing to ceramics-ceramics 、ceramics-polyethylene.In the 70 s invented third generation bone cement technology and proposed Full fit and Press fit according to press principle in order to firm fixation and extend life of prosthesis.Although there are many technique relevant with total hip arthroplasty to support and develop,when total hip arthroplasty relieve patient,improve function of hip and promote the quality of patient,there will some unwanted complications happen after surgery,such as :prosthetic loosing、prosthesis related infections、periprosthetic fractures 、 the limbs lengthen discrepancy and luxation.Among of the complications the limbs lengthen discrepancy(LLD) is one of the common factors that cause patient’s dissatisfaction.Hip is function fulcrum between body weight and abductor,and the power of them maintain horizontal position of pelvis and normal gait cycle.There are two factors to maintain hip :1.standing balance:femoral offset(FO)、force arm of abductor、position of hip joint center and the legs lengthen etc;2.dynamic balance that consist of soft tissue and bone structure maintains hip stable during movement.FO is link connection between standing balance and dynamic balance,and is one of the most important factors of parameters of hip to maintain hip and the legs lengthen and the stable of hip.The definition of femoral offset is vertical distance from the hip joint center to shaft of femur.The size of femoral offset is decided by lengthen of femoral neck and size of neck-shaft angle.To reconstruct a normal biomechanics of hip is very important in total hip arthroplasty.Femoral offset is a important factor that can influence the design of femoral prosthesis,so that is to the a well function of hip.We want to recover function of hip and prevent dislocation and reduce the leg lengthen discrepancy when performing a operation.Increasing femoral offset has two positive results to stable hip:increasing isometric contraction and the force arm of abductor.While the hip joint center can not change size of femoral offset,it’s position’s change can influence abductor,then results in weakening the stable of hip、femoroacetabular impingement and dislocation.Now most researches about femoral offset are relating to recover abductor、extending life of prosthesis and reducing wear rate of acetabular line,but the researches about quantitative relation between femoral offset and the leg lengthen are lack.Objective: through calculating variation of femoral offset after surgery and then figuring out complications resulted from variation of femoral offset.Exploring the rule of complications result from variation of femoral offset,and that conclusion can direct clinical work and reduce complications.Data: 40 hips(preoperative and postoperative anteroposterior view radiographs of pelvic) admitted in the orthopaedic department from 2013 to 2015.28 male cases and 12 female cases,with an average age 57 years old(40-65years).There are 25 cases are ONFH(Osteonecrosis of the Femoral Head),which of them are 15 cases Ⅲ period and 10 cases period as Ficat stage;there are 15 caⅢ ses are arthritis,which of them are 5 cases period and 10 cases Ⅲ Ⅲperiod as K-L stage,with an average follow-up time of 18 months(6-25months).Method: We use Centricity Enterprise Web3.0 version to Retrospective study preoperative and postoperative patient’s anteroposterior view radiographs of pelvic of 40 cases,the measured parameters include:the preoperative and postoperative lengthen of femoral offset、the leg lengthen discrepancy、neck-shaft angle、reserved lengthen of calcar femorale、the size of prosthesis head and the position of the Hip Joint Center.Recording postoperative complications such as:the leg lengthen discrepancy and dislocation.The letter “n” is postoperative femoral offset minus preoperative femoral offset,and the letter “k” is the postoperative leg lengthen minus the postoperative leg lengthen.Then draw dot in the “n-k” quadrant.We can divide 40 cases into three groups :A group(within yellow ellipse x2+y2/4=1)、B group(between yellow ellipse x2+y2/4=1 and red ellipse x2/1.52+y2/9=1)、C group(outer red ellipse x2/1.52+y2/9=1).Statistical analysis using SSPS19.0 version software,and the results are compared to domestic’s and overseas’.We use Harris system to value the follow-up cases.Result: The difference of femoral offset(n=H1-H2) in three groups have a significance value according to variance analysis,A group is least(P=0.038 < 0.05).The difference of leg lengthen discrepancy(k=m-d) have a significance value according to variance analysis,A group is least(P=0.007<0.05).Conclusion: 1.Femoral offset must be strictly reconstructed and within the yellow ellipse(safe area) can reduce the leg lengthen within 20 cm and effective reduce incidence rate of postoperative complications;Differences of preoperative and postoperative leg lengthen discrepancy are between yellow ellipse and red ellipse(high risk area) can reduce the leg lengthen within 30 cm and postoperative complications has a high incidence rate; Differences of preoperative and postoperative leg lengthen discrepancy are out of red ellipse,and these cases has a highest incidence of complications,such as the leg lengthen discrepancy and dislocation.2.The cases that postoperative femoral offset reduced more than 10 cm while it’s sick side’s femoral offset shorter than contralateral side have a highly incidence rate of dislocation after surgery.3.Reserving a appropriate lengthen of calcar femorale and neck-shaft angle can reduce to least of the leg lengthen discrepancy;Controlling a appropriate position of hip joint center and strengthening soft tissue around hip can reduce postoperative dislocation.