Effect Of Cup Medialization On The Stress Distribution In Cementless Femoral Stem-bone Interface In Total Hip Arthroplasty

CbjectiveTo study the effect of cup medialisation on the stress distribution in cementless femoral stem-bone interface in Total Hip Arthroplasty by three-dimensional finite element mechanical analysis and bone density measurement and analysis.Methods1.Finite element analysisThe pelvis and femur of normal people were selected as experimental subjects.Spiral CT scan and computer simulation technology were used to establish the model and the total hip arthroplasty was simulated.The acetabular cup was moved inward by deepening the acetabular bed where the cup was placed.The degree of inward displacement based on the hip joint center as the starting point coordinate.Moved horizontally inward until the inner side of the rotation center to 10mm.An experimental group was set every 2mm interval with a total of six experimental groups.When appling a joint load,the Von Mises stress distribution of cementless femoral stem-bone interface was observed.Meanwhile,the abduction angle of the hip joint was observed and the angle of the acetabular rim-femur impact was measured.2.Bone density measurement and analysiswe selected 23 patients who underwent total hip arthroplasty and cup medialisation from August 2015 to July 2017 in Zhujiang Hospital.Bone mineral density was measured regularly in Zone 1 and Zone 7 of the proximal femur and the relationship between the degree of inward displacement and the change of bone mineral density was analyzed.Result1.The cup medialisation did not change the stress cloud distribution of the femur.The mean stress in cementless femoral stem-bone interface was statistically different in each group.The mean,extreme deviation and standard deviation of the stress were highly negatively correlated with statistical difference.The stress decreased as the degree of cup medialization increased.SO did the extreme deviation and standard deviation,which meaned cup medialization made the stress more evenly distributed.The stress changes in zone 1 and 7 were consistent with the stress changes in the whole stem-bone interface.2.The abduction angle of the hip joint ranged from 43.81° to 26.73° when the cup moved inward from 0 to 10 mm.3.The continuous monitoring results showed that bone mineral density decreased slowly in 1 month after operation and the decrease amplitude was greater in 3 and 6 months after operation.The bone mineral density decreased gradually and even increased in 12 months after operation.With the increase of inward displacement,the mean of bone mineral density decreases gradually and the decrease rate rised significantly when the inward displacement was more than 6 mm.ConclusionThe cup medialisation in Total Hip Arthroplasty can reduce the Von Mises stress in cementless femoral stem-bone interface and make it more evenly distributed,but it also reduces the abduction range of the hip joint.