In-vivo Biomechanical And Functional Evaluation Of Total Hip Arthroplasty

Background:Total hip arthroplasty(THA)is a standard operation for treating advanced hip osteoarthritis.THA can effectively relieve pain,restore hip function and improve the quality of life of patients.However,some patients suffered from postoperative complications,including asymmetric gait,pelvic ptosis,claudication,and prosthesis dislocation.Studies have shown that most revision surgeries have resulted from the imbalance of soft tissue and incorrect prosthesis positioning.Accurate assessment of the hip muscle function of THA patients during the gait,the influence of femoral offset(FO)change on hip muscles,and the change of acetabular cup functional angle in walking,static standing,and lying posture are helpful to prevent postoperative complications and optimize rehabilitation training program.Methods:We recruited 22 patients with unilateral THA who were examined by CT scanning and biplane fluoroscopy.Objectives:(1)To explore whether THA can restore the motion symmetry of the hip and pelvis in patients with unilateral THA;(2)To simulate the starting and ending points of hip muscles on the three-dimensional hip joint model to determine the dynamic tension line and moment arm.To measure the changes of hip muscle length and moment arms between replacement and non-replacement side in THA patients;(3)To calculate the correlation coefficient(R)between FO and hip muscle moment arm;when the abduction moment arm increases and the other hip muscles moment arm decreases less than 5%,FO reconstruction is satisfactory;(4)To define pelvic function coordinate system with gravity line and anterior pelvic plane and measure functional anteversion angle and abduction angle in different postures.Lewinnek safe zone is used to determine the abnormal acetabular position during functional activity.Results:(1)During the gait,the hip internal rotation of the replacement side was significantly higher than that of the non-replacement side.In the swing phase,the hip adduction of the replacement side increased.In the support phase,the hip flexion range of motion of the replacement side decreased significantly.The femoral head translation range of the replacement side was smaller than that of the non-replacement side.Significant asymmetry of pelvic anteroposterior tilt angle and axial rotation angle was observed.(2)In the support phase,the abductor length of the replacement side increased,the moment arm decreased,the adductor length decreased,and the moment arm increased.In the supporting phase,the length of the superior,inferior,obturator and piriformis muscles on the replacement side increased.In contrast,the moment arm of the superior muscle on the replacement side decreased.During the gait,the length of the external obturator muscle on the replacement side decreased.During most of the gait cycle,the moment arm of the external obturator muscle and quadratus femoris muscle increased.In the support phase,the length of the extensor muscle on the replacement side increased,and the moment arm decreased.At the same time,the length of flexor muscle decreased,and the moment arm increased.(3)The decrease of FO after THA was significantly correlated with the decrease of abductor and external rotator moment arm(R > 0.5)and extensor moment arm(R > 0.4)during the whole gait.The increase of FO was significantly correlated with the decrease of flexor moment arm(R <-0.5)during the gait and the decrease of adductor moment arm(R <-0.4)in the standing phase.When FO increased by 2.3 to 2.9mm,the abductor moment arm increased,and other muscle moment arm decreased by less than 5.0%.(4)During level walking,the functional acetabular anteversion of the replacement side is larger,and the inclination is smaller than the native side.The functional acetabular anteversion on the replacement side is 5.5° ± 1.6°,and the inclination angle is 5.6° ± 2.3°.In comparison,the range of the function acetabular anteversion on the replacement side is 6.4° ± 1.4°,and the range of inclination angle is 5.0° ± 2.0°.The functional acetabulum anteversion and inclination measured during level walking and static standing were higher than the anatomical acetabular anteversion and inclination.THA components in Lewinnek safe zone fell outside the safe zone during over half of the gait cycle and static standing.Conclusion:(1)Asymmetric hip and the pelvic motion was found between the replacement side and the non-replacement side.(2)THA has adverse effects on hip stability.It is necessary to make a specific rehabilitation plan for the impact of THA.The accurate surgical technique can reduce the effect of THA on peripheral muscles.(3)FO increase of 2.0-3.0 mm after THA can improve the function of abductor and external rotator muscles and has a less adverse effect on other muscle groups.An accurate operation plan and optimal FO reconstruction are essential to restore THA patients’ normal hip muscle function.(4)The acetabular cup with a good anatomical position cannot guarantee good functional positioning in daily activities.