| BackgroundAs the most successful and effective procedures developed for treatment of pain associated with end-stage hip diseases, the survival rate of the total hip replacement greater than80%at20years after surgery. Although the material science and the design ideas of hip prosthesis had great progress, but the results still not perfect with long-term survivals. The main influence factor is osteolysis induced by implant weae particles and subsequent aseptic loosening of the implant. At present, most studies suggest that the pathogenesis of wear-associated osteolysis includes inflammatory and osteolytic processes. The sustained chronic inflammatory response initiated by particulate debris at the implant-bone interface is manifested by recruitment of a wide array of cell types. These cells include macrophages, fibroblasts, giant cells, neutrophils, lymphocytes, and most importantly osteoclasts, which are the principal bone resorbing cells. The" cellular response" entails secretion of osteoclastogenic and inflammatory cytokines that favor exacerbated osteoclast activity and enhanced osteolysis. With osteolysis is increasingly severe, the patients need to perform revision of total hip arthroplasty, and the difficulty of surgery will be greatly increased, and the clinical results will be bad than the patients with sufficient bone mass. It is important to explore mothods that can reduce the generation of polyethylene wear debris, and reduce the impact of polyethylene wear to hip functional activities.This program was condueted to review the cases who were treated with total hip replacement from1997to2006by a single surgeon using cementless Zweymuller hip systems with ceramics to polyethylene bearing in Nanfang hospital, we evaluated the clinical results and the radiographic parameters in order to explore the correlation between linear wear and prosthesis positions in total hip replacement.ObjectiveTo measure the linear wear of the ultra high molecular weight polyethylene liner of the acetabular cup component and its direction, and investigate the correlation between polyethylene wear and those implanted prosthesis parameters in total hip arthroplasty.Method1. Follow-up methodsIn our study, the fellow-up methods mainly through telephone and out-patient recheck as well as home visiting. Patients who were unable to return for a follow-up evaluation due to a long distant from our hospital completed a telephone interview and sent recent radiographs radiological examination included anteroposterior Pelvis X-ray, anteroposterior hip X-ray and lateral hip X-ray.2. Clinical evaluationThe indexes contain:Harris hip score and activity level.3. Radiological evalutionThe indexes contain:acetabular cup abduction angle, acetabular cup anteversion angle, femoral offset, linear wear rate and linear wear direction. The migration in the femoral head center ralative to the axis of acetabulum opening plane on digital consecutive radiographs were examined to determined direction and degree of polyethylene linear wear.4. Statistical analysisWith linear wear rate and linear wear direction as the dependent variable respectively, Multivariate regressive analysis was used to find out correlation of wear with femoral offset, acetabular cup abduction angle, acetabular cup anteversion angle and others factor. The linear wear rate and linear wear direction were compared respectively in different groups such as acetabular cup abduction angle (≤45°,>45°), acetabular cup anteversion angle(<15°,>15°) and femoral offset (reproduction of a reconstructed femoral offset to within or without5mm of the native) using covariation analysis. Statistical analysis was performed using SPSS18.0(SPSS Inc, Chicago, IL). The P value less than0.05suggested that the results have statistical differences.Results1. Fellow-up results48cases(58hips) were available for following up, including20male(26hips) and28female(32hips). All patients were evaluated both clinically and radiographically. The average fellow-up period was7.3years(range5.1to12.6years). Initiai diagnosis:aseptic necrosis of femoral head were44hips, anky losing spondylitis were7hips, congenital dysplasia of the hip were2hips, femoral neck fracture were5hips. All the cases were performed THAs using lateral surgical approach. After the drain was removed on the2th postoperative day, and began to excise non-restrict loading walk. The hip prosthesis included BICON-PLUS acetabular cup system, UHMWPE liner,28mm Ceramic femoral head and SL-PLUS femoral stem.2. Clinical resultThe average preoperative Harris score improved from45.7points before surgery to93.7points at the time of follow-up.3. Radiological resultThe average angle of acetabular cup abduction was(46.90±9.50)°, the average angle of acetabular cup anteversion was (12.66±5.91)°,the average femoral offset was (35.10±5.34) mm, the average difference of both sides femoral offset was (0.13±5.01)mm. If the diference less than5mm as reproduction of native femoral offset, the reproducted rate was67.2%.The average linear wear amount was (1.19±0.58) mm at the time of the latest follow-up, the average linear wear rate was (0.17±0.08) mm/y, The average direction of linear wear was (34.2±29.3)°.4. Statistical resultThe correlation analysis showed that there exist the positive relation between linear wear direction and acetabular cup abduction angle(r=0.409, P=0.001). As acetabular cup abduction angle became larger, linear wear direction tend to deviate from the axis of acetabular cup, and the linear regression equation was y=29.431+1.333x(t=4.091, P=0.000). There exist the negative relation between linear wear direction and Harris score at the time of final follow-up (r=-0.332, P=0.011). Linear wear direction were no correlated with age, activity level, BMI, fellow-up times, acetabular cup anteversion angle, femoral offset, the difference of both sides femoral offset and linear wear rate. The evidences also indicates that there were positive relation between linear wear rate and activity level (r=0.404, P=0.002),and there exist the negative relation between linear wear rate and Harris score at the time of final follow-up (r=0.287, P=0.029).There were no association between linear wear rate and age, BMI, fellow-up times, acetabular cup abduction angle, acetabular cup anteversion angle, femoral offset, the difference of both sides femoral offset, linear wear direction.Analysis of covariance shown that there had no significant difference of the averge wear rate between abduction angle less than45°group and abduction angle greater than45°group (F=0.262, P=0.611); there had significant difference of the averge wear direction between two groups (F=12.785, P=0.001), the abduction angle greater than45°group had larger wear direction. The average difference of both sides femoral offset within5mm group compared with the average difference without5mm group, had significant difference in wear rate (F=4.108, P=0.048), the former get less wear rate; there had no significant difference of the averge wear direction between two groups (F=1.650, P=0.204). There had no significant difference of the averge wear rate between anteversion angle less than15°group and anteversion angle greater than15°group (F=0.004, P=0.951), and the same result in wear direction (F=0.960, P=0.331)Conclusions1. There had the positive relation between linear wear direction and acetabular cup abduction angle. As acetabular cup abduction angle became larger, linear wear direction tend to deviate from the axis and pointed to superolateral of acetabular cup. The greater cup abduction angle might result in uneven stress distribution and greater stress concentration superolaterally, consequently increase of wear; meanwhile, if the cup is too vertieal, the risk of impingement and dislocation inereases. The study also found that wear direction negative correlation with Harris score at the time of final follow-up, the result shown that overlarge acetabular cup abuduction angle could lead to bad clinical outcomes.2. The study had not observed correlation between acetabular cup anteversion angle and linear wear of polythylene liner. The degree of acetabular cup anteversion angle did not affect wear rate or direction.3. Reproduction of the native femoral offset was very important to adjust soft-tissue balance in THAs. Rrsearch found that the cases of difference of both sides femoral offset within5mm had less linear wear rate. |
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