The Assessment Of The Postoperative Prosthesis Position Of Unicompartmental Knee Arthroplasty By CT 3-D Images

ObjectiveTo evaluate the postoperative prosthesis position of the medial compartment osteo-arthritis patients who underwent the Oxford unicompartmental knee arthroplasty using X-ray and three-dimensional CT images.To explain the advantage and feasibility of the measurement of postoperative prosthesis position by three-dimensional CT images reconstruction techniques.To analyse the reasons of malaligment of the components and discussing the improvement measures.MethodsA retrospective analysis was conducted on 28 patients(32 knees)who underwent Oxford Phase 3 unicompartmental knee arthroplasty for the medial unicompartmental knee osteoarthritis,application of minimally invasive techniques during the period 2013/4 to2014/12.Ten were males and eighteen were felames,with body weight index of 26kg/m~2.There were 12 cases of left knee,and 14 cases of right knee.The mean age of the 28patients was 67 years(range 62-73)at the time of surgery and the mean follow-up was 3.8months(range 1-12)and none of the patients was lost follow-up.There was no postoperative infection and prosthesis loosening happening on any patient.After the operation,get the images of lower limb by X-ray and CT scanning.When taking the anteroposterior X-ray,we place the knee in flexion 20°,X-ray orientation to foot in projection 10°.When taking the lateral X-ray,we require the knee in flexion 45°,and the condyles in overlapping.When taking the anteroposterior lower limb,we place the limbs in extension.We adjusted scan orientation to perpendicular to the mechanical axis of tibia,to obtain two-dimensional image data of the hip to the ankle.After the establish-ment of the two-dimensional image data to obtain lower limb joints by CT scan,the obtained images were imported into a computer with a medicall image processing software Mimics14.11(Materialise company,Belgium),and digital three-dimensional model of the lower limbs was established.Use the Mimics14.11 software to calibrate the femur force spools,the tibia force spools,the surgical epicondylar line,the knee joint center,the external ankle cords,the femoral coronal plane,the tibial coronal plane,the axis line of femoral prosthesis,the central lateral plane of femoral prosthesis,the axis line of tibial prosthesis,the plane of tibial prosthesis in 3-D images reconstruction.Then import three-dimensional datas to measuring software UGNX10.0 to analyse.To measure the limb alignment angle,the femoral component valgus angel,the femoral component flexion angle,the tibial component valgus angle,the tibial component slope angle using two methods in twice.To measure the femoral component rotation angle from epicondylar axis,the tibial component rotation angle from epicondylar axis in 3-D images.To analyze the datas using spss 19.0software.Results1、X-ray results:C angle was a mean of 177.93°,the standard deviation was 1.55°,the variance percent is 3.13%.A angle was a mean of 1.49°,the standard deviation was1.24°,the variance percent is 0.B angle was was a mean of 1.12°,the standard deviation was 5.40°,the variance percent is 34.38%.E angle was a mean of 0.84°,the standard devia-tion was 3.90°,the variance percent is 18.75%.F angle was a mean of 6.25°,the standard deviateon was 0.76°,the variance percent is 3.13%.2、CT results:C angle was a mean of178.01°,the standard deviation was 1.42°,the variance percent is 0.A angle was a mean of1.22°,the standard deviation was 0.92°,the variance percent is 0.B angle was was a mean of 2.64°,the standard deviation was 1.04°,the variance percent is 31.25%.E angle was a mean of 2.85°,the standard deviation was 1.45°,the variance percent is 15.63%.F angle was a mean of 6.29°,the standard deviation was 0.58°,the variance percent is 3.13%.G angle was a mean of-1.23°,the standard deviation was 2.55°,H angle was a mean of-6.05°,the standard deviation was 3.76°.3、There were significant defferences in A angle、B angle and E angle in the two measurement by X-ray.There were no significant defferences in all angles in the two measurement by CT.ConclusionsThe percentage variations of the femoral flexion-extension angle and the tibial varus-valgus angle were big,which was similar to the results previous published reported without computer-assisted tomography.The 3-D resconstrcution technique can accurately calibrate anatomical position based on CT scaning,and it’s more accurately to select the reference line in 3-D images than do it in 2-D images,and wo also can measure the rotationl angle of prosthesis in 3-D images.We remain unsure of the implications of com-ponent rotation,but it may be the aetiology of instability and mechanical symptoms seen in some UKA.