A Study On The Application Of X-ray Examination To Prevent Leg Length Discrepancy After Total Hip Replacement

Objective: Since Charnley[1]produced the first ultra-high molecularmulti-polyethylene artificial hip prosthesis in1960, the skill of hiparthroplasty has undergone enormous changes all over the world. Well,although its technology has been quite mature, its related complications arestill worthy for us to explore. A recent inquiry reported, leg length discrepancyas the second most cited cause of medical malpract ice litigation amongAmerican Association of Hip and Knee Surgeons[2]. Some scholars call thiscomplication it as “a lawyer wait”[3]. We often use X-ray examinationintraoperative with C-arm to prevent limb length discrepancy after total hipreplacement, but this method can be easily affected by body position.Therefore, the purpose of this study is to explore whether the changes of thepelvis or the femur will affect the accuracy of the X-ray method when it wasused to evaluate leg length equality in lateral position, and to study how todetermine the changes of the position of the pelvis and femur by theradiography, so as to correct the patient’s innormal body position.Methods: Randomly selected30patients or their family member whowere in hospital in Hand Surgery of Hebei Medical University fromNovember2011to December2012, then divided these30volunteers intothree groups called A,B and C. Each volunteer must take the pelvicanteroposterior radiography when they were in supine position and in lateralposition. Besides, Group A volunteers needed to take the pelvicanteroposterior radiography in lateral position with their femur flexing in10degrees,20degrees and30degrees. Group B volunteers needed to take thepelvic anteroposterior radiography in lateral position with their femuradducting in10degrees,15degrees and20degrees. Group C volunteersneeded to take the pelvic anteroposterior radiography in lateral position when their pelvis tilted10degrees,20degrees and30degrees on coronal plane.Measuring the distance (d) between the tip of the lesser trochanter and theinterteardrop line by the Auto CAD drawing software, calculating themeasurement difference (Δd) in different posture, then making statisticalanalysis to study how postural factors can affect perspective when it was usedto evaluate the leg length discrepancy in lateral position, and then to study thelateral X-ray changes in different positions.Result:1.Group A volunteers——Using the lowest point of teardrop asreference, when their femur flexed in10degrees, the tip of the lessertrochanter moved2.02±0.09mm in vertical axis of the body and it moved3.04±0.11mm in vertical axis when their femur flexed in20degrees, then2.10±0.11mm in30degrees.Comparing the d values of10degrees femuralflexion and30degrees femural flexion through Independent SamplesTest,P>0.05,so there was no statistical significance.2. Group B volunteers——Using the lowest point of teardrop as reference, when their femuradducted in10degrees, the tip of the lesser trochanter moved1.51±0.07mmin vertical axis of the body and it moved1.70±0.08mm in vertical axis whentheir femur adducted in15degrees, then0.94±0.05mm in20degrees.Comparing the values of10degrees femural adduction and20degreesfemural adduction through Independent Samples Test,P>0.05,so there wasno statistical significance.3. Group C volunteers——Using the lowest pointof teardrop as reference, when their pelvis tilted in10degrees, the tip of thelesser trochanter moved1.47±0.08mm in vertical axis of the body and itmoved0.91±0.12mm in vertical axis when their pelvis tilted in20degrees,then0.04±0.03mm in30degrees.Comparing the d values of10degrees pelvistiltion and30degrees pelvis tiltion through Independent SamplesTest,P<0.05,so there was statistical significance.Conclusion:Using perspective to evaluate the leg length equality in thelateral position is a viable method. In lateral,when the femur flexed from0to30degrees, or the femur adducted from0to20degrees, or the pelvis tiltedfrom0to30degrees on coronal plane, the location of the tip of the lesser trochanter—using the lowest point of teardrop as reference—will change nomore than1cm. The changes of the pelvis or the femur will not distinctlyaffect the accuracy of the perspective when it was used to evaluate leg lengthequality in lateral position. The extent of the femur adduction can be roughlyevaluated through the angle between the body midline and femoral anatomicalaxis. The extent of the pelvis tilt can be roughly evaluated through the anglebetween the body midline and the horizontal line.