Objective To analyse the reasons of failure of metal- backed patellar component and observe the clinical outcome of the revision procedure. Methods Thirty isolated patellar revision for failed metal- backed patellar components following total knee arthroplasty in 22 patients were reviewed. All had similar total condylar knee prosthesis inserted with retention of the posterior cruciate ligament and resurfacing of the patella. There were 4 males and 18 females. Knee Society Score rating system was used for the final evaluation. Results In average the failure occurred in 62.3 months (ranged from 26 to 96 months). The majority of patients presented with metallic crepitus(80％ ) and pain of the knee(70％ ). At surgery, full thickness polyethylene wear exposing the metal- backing was present in 76.7％ with surface damage of the femoral components in 36.7％ . There was tilting of patella in 9 knees and dislocation of patella in 2 knees. All 30 knees underwent successful isolated patellar component revision with cemented polyethylene patellar buttons. Final follow- up averaged 42.5 months, all manifestations were reported significant improvement in 22 patients. The average knee score improved from 73 points(ranged from 27 to 88) pre- revision to 87 points(ranged from 60 to 100) at the final follow- up. Conclusion Resurfacing of the patella in total knee arthroplasty with metal- backed patellar components carries a significant risk of early failure. Malalignment and maltracking of patella may be a predisposing factor to early failure in metal- backed patellar components.

Objective To understand the prevalence of HIV infection and its influencing factors in the premarital physical examination population in Dehong Prefecture, Yunnan Province, 2017. Methods The data of people receiving premarital medical examination was collected, the demographic characteristics was described and the related factors was analyzed by Logistic regression. Results There were 21 875 participants receiving premarital medical examination in Dehong. 98(0.45%) participants were confirmed positive for HIV and male infection rate was 0.47% (52/10 955) and female was 0.42% (46/10 920). Among the 98 patients, 20 patients were infected in the first time, and main route was sexual transmission accounting for 81.63% (80/98). Logistic multivariate regression analysis showed that age, ethnicity and drug use were the influencing factors for premarital couples infecting HIV. The risk of HIV infection in 31-40 and 41-50 years old group was higher than the people under 25 years old group(OR=3.78, 95% CI：1.81-7.89, P<0.001；OR=3.95, 95% CI：1.72-9.08, P=0.001). The infection risk of Dai and Jingpo ethnic group was higher than that of the Han ethnic(OR=1.86, 95% CI：1.06-3.29, P=0.031；OR=3.25, 95% CI：1.81-5.84, P<0.001). The risk of infection among drug users was much higher than non-drug users (OR=926.76, 95% CI：271.65-3 161.71, P<0.001). Conclusion Age, ethnicity, and drug use are influencing factors of HIV infection among premarital couples. Targeted measures need to be taken against risk factors. HIV infection is mainly transmitted by sexual transmission. It can be effectively detected and controlled through premarital medical examination.