Basic And Clinical Research Of Femoral Offset Restoration In Total Hip Arthroplasty

PartⅠThe radiographic study of femoral offset in normal hip jointObjective: To investage the range of femoral offset in the healthy Chinese and explore its clinical significance.Methods 100 cases of normal anteroposterior hip joints radiographic image were measured. Parameters included femoral offset, abductor lever arm , femoral head diameter, neck-shaft angle, the width of bone medullary cavity at the plane of lesser trochanter,20mm above and below the lesser trochanter,diameter of the narrow cavity and canal flare index (CFI). The correlation between femoral offset and other anatomical parameters in femur were explored by simple correlation analysis.The proximal femoral parameters between Chinese and the Western were compared. Results The range of femoral offset was 36.64±5.31mm,and the 95% confidence interval (CI )overall mean was 35.59~37.69 mm in healthy Chinese. The range of femoral offset was 38.58±5.66mm and the 95% CI overall mean was 36.97~40.19 mm in Chinese man. The range of femoral offset was 34.71±4.18mm and the 95% CI overall mean was 33.52~35.90 mm in Chinese woman .Femoral offset and abductor lever arm was positively correlated(r=0.73, P<0.01).Femoral offset was negatively correlated neck-shaft angle(r=-0.46, P<0.01). Femoral offset was positively correlated with femoral head diameter(r=0.35, P<0.05).There were no significance correlation between femoral offset and other parameters of the femoral medullary canal. There was a significant difference in the diameter of the femoral head, neck-shaft angle, femoral offset, abductor lever arm between Chinese men and women (P <0.05). There was a significant difference in neck-shaft angle,femoral offset between Chinese and the Western (P <0.01).Conclusion The range of femoral offset was 36.64±5.31mm,and the 95% CI overall mean was 35.59~37.69 mm in healthy Chinese. There was a significant difference in neck-shaft angle, femoral offset between Chinese and the Western.Restoration of femoral offset can recovery the length of abductor lever arm and balance the soft tissue of the hip.Femur prosthesis with different neck stem angle or modular prosthesis are suitable to reconstruct normal hip joint biomechanics.PartⅡ3 D finite element analysis of stress changes of prosthesis and femur before and after total hip arthroplastyObjective: To establish a three-dimensional finite element model of intact normal femur and determine stress distribution of prosthesis and femur before and after total hip arthroplasty. Methods: A finite element models of an intact femur and a femoral prosthesis were established by normal hip joint in vivo CT scans and Mimics 10.0 software; then stress distribution analysis was carried out when both joint contact forces and muscle forces were included in the loading. Results: The peak stress of intact femur was presented at the middle and upper regions of femur with compressive stress in medial side and tensile stress in lateral side. The stress pattern of implanted femur was similar to the one of intact femur with the obvious stress shielding at proximal femur. The stress pattern of femoral prosthesis was similar to the one of intact femur with stress concentration in the site of the combination of head -neck.Conclusions: Implantation of femur prosthesis may cause significant stress shielding in the proximal femur and stress concentration at the end of stem. This may be related with periprosthetic bone loss and aseptic loosening of stem and can be used to explain the mechanism of postoperative thigh pain. PartⅢBiomechanics analysis of prosthesis and femur before and after total hip arthroplasty using two differerent methors of femoral offset restorationObjective: To explore the change of stress distribution of prosthesis and femur before and after total hip arthroplasty with a long neck stem or high offset stem. Methods: A finite element models of an intact femur and femoral prostheses were developed by computed simulation, then a simulation surgery of total hip arthroplasty were taken and femoral prosthesis with long neck stem or high offset stem were implanted respectively. The changes of biomechanics of prostheses and femur before and after total hip arthroplasty with a long neck stem or high offset stem were observed. Results: There was no significant change of the stress transfer and stress distribution with increased femoral offset. The interfacial shear stress and interfacial micromotion increased in the bone-prosthesis interaction.The stress increased with increased femoral offset in the neck of prosthesis becaused of large bend moment. It was the mechanical basis of the fatigue of prosthesis. High offset prosthesis more uniformed stress distribution and provided less concentrate stress. Conclusions: The interfacial stress and micromotion in the proximal femur would increase with an increased femoral offset prosthesis. There was no significient difference betweeen two different methods of femoral offset restoration on the effect on the stress distribution of femur.Construction Restoration of femoral offset should be taken individually. High offset prosthesis was a good choice to restore femoral offset in THA.PartⅣClinical research between femoral offset restoration and joint function after total hip arthroplastyObjective: To explore the correlation between femoral offset(FO)restoration and joint function after total hip arthroplasty(THA) and influence factors of femoral offset restoration in operation. Methods: 61 patients were performed THA from Mar 2002 to July 2007 and follow-up was finished. There were 30 women and 31 men and the average age was 57.4 years (37 to 84 yr).The right hip had been replaced in 34, the left in 27. The mean duration of clinical and roentgenographic follow-up was 21.3 months (10~72m). FO, abductor lever arm, residual length of femoral calcar, leg length discrepancy and location of hip rotation center were measured from each radiograph. Gait,range of motion of hip,hip abduction strength and hip harris score were recored. Statistical data was performed using SPSS 10.0 software. Results: FO of 44 hip( 71.9%)were restored in 61 THA. Simple correlation analysis showed that FO correlated with the length of the abductor lever arm (r=0.673,P<0.001);residual length of femoral calcar (r=0.319,P<0.05);leg length difference (r=0.47,P<0.05), hip harris score (r=0.47,P<0.05). The difference of FO on both sides was correlated with the difference of horizontal and vertical hip rotation location on both sides (r=-0.17,r=0.60). The harris score, range of motion of hip ,hip abduction strength in construction group were better than those of no construction group(P<0.01).The gluteus medius gait,Trendelenburg sign(+)and other complications were less than those of no construction group. Conclusions Restoration of FO significantly influenced the hip abductor strength,leg length discrepancy,gait,range of motion of hip and hip stability.The infulence factors of FO restoration include the location of the hip rotation center,neck length of prosthesis ,neck stem angle of prosthesis and residual length of femoral calcar. To restore femoral offset in THA,template the both side hip preoperatively,select femoral prosthesis with more anatomical neck-shaft angle,modular leg length and soft tissue tensile intraoperative were necessary.