Objective To investigate the effects of exercise on knee cartilage tissue structure using quantitative MR T2 mapping. Methods Sagittal T2 maps of the knee joints of 26 healthy volunteers were obtained by using 3.0T MR before,immediately after, and 1 5 min after running.The original images were classified into three terms of knee cartilage T2 map after postreconstruction.The T2 values of regions of interest (ROC)(T2 pre ,T2 post ,T2 delay )in the superficial,middle and deep cartilage of femoral and tibial joint were measured.Statistical differences of cartilage T2 values of three terms after running were analyzed.Results For the tibial joint cartilage,the T2 pre ,T2 post ,T2 delay were (49.71 ± 1.95)ms,(44.30 ± 2.56)ms,(49.41 ± 1.62)ms in the superficial layer,respectively.The three terms T2 were (42.43 ± 2.23)ms,(39.01 ± 2.37)ms,(41.90±2.28)ms in the middle layer,respectively.The differences were statistically significant(F=55.673,16.759 respectively.P<0.001).While the three terms T2 were (19.39±2.13)ms,(19.20±2.22)ms, (19.49±2.05)ms in the deep layers cartilage,respectively.The differences were not statistically significant(F =0.122,P =0.886).And the differences between T2 pre and T2 post ,T2 post and T2 delay were statistically significant (all P <0.001)in superficial and middle alyers,but there were no significant difference between the T2 pre and T2 delay (P =0.610,0.403,respectively).For the femoral joint cartilage,the T2 pre ,T2 post ,T2 delay were (50.22 ± 1.47)ms,(45.60 ± 2.82)ms,(49.84 ± 1.84)ms in superficial layers,respectively.The three terms T2 were (42.67±2.23)ms,(39.36 ± 1.98)ms,(42.40 ± 2.57)ms in the middle layer,respectively.The differences were statistically significant (F=37.976,16.987 respectively,P<0.001).While the three terms T2 were (20.30±2.73)ms,(20.60±2.44)ms,(20.51± 2.24)ms in the deep layer,the differences were not statistically significant (F =0.098,P =0.907).And the differences between T2 pre and T2 post ,T2 post and T2 delay were statistically significant (all P <0.001)in superficial and middle layers,but there were no significant difference between the T2 pre and T2 delay (P=0.520,0.679,respectively). Spatial distribution of T2 values of articular cartilage from deep to superficial layers showed a ascending trend.T2 maps showed the spatial distribution trend of T2 value change.Conclusion T2 mapping can monitor quantitatively the changes of articular cartilage molecular structure after running.The change of articular cartilage T2 value after exercise is uneven and the change of articular cartilage structure after exercise is reversible.

Objective To investigate the risk factors of proximal junctional kyphosis (PJK) after posterior long segmental lumbar fusion for degenerative lumbar disease. Methods From October, 2012 to July, 2014, 118 degenerative lumbar disease patients who accepted posteri-or long segmental fusion and followed up at least 1.5 years were reviewed. All the PJK were evaluated with X-ray. Results Sixty-six pa-tients completed the follow-up (mean of 3.2 years), in which 12 patients with PJK (PJK group), and the others without (non-PJK group, n=54). There was significant difference in body mass index, bone density and the last Oswestry Disability Index scores (t>2.194, P<0.05) be-tween both groups, as well as the rate of the upper instrumented vertebra (UIV) located in the thoracolumbar segment (T11-L1) (χ2=4.63, P<0.05). The PJK angle was more in PJK group than non-PJK group pre-surgery, post-surgery and finally (t>3.862, P<0.001). Binary Logistic regression showed that osteoporosis (OR=5.328, 95% CI: 1.110~25.581), UIV located in the thoracolumbar segment (T11-L1) (OR=6.239, 95%CI:1.157~33.648) and the pre-surgery PJK angle>10° (OR=5.789, 95%CI:1.075~31.183) were the independent risk factors of PJK. Conclusion Osteoporosis, UIV located in the thoracolumbar segment (T11-L1) and the pre-surgery PJK angle>10° are risk factors of PJK af-ter posterior long segmental lumbar fusion.

Objective To understand the characteristics of long-working hours exposure of medical staff,and analyze the impact of long-working hours exposure on mental health problems such as occupational stress,depression,fatigue accumulation,and insomnia.Methods The cluster random sampling method was used to select the medical staff of 12 tertiary general hospitals in Guangdong Province as the research subjects,and the"Core Scale of Occupational Stress Measurement"and other scales were used to evaluate their occupational mental health.Results The average working hours of medical staff per day were(8.99±2.18)h;2,094 people were exposed during long working hours,accounting for 78.96%.The results of binary logistics regression analysis showed that after excluding the influence of sociodemographic factors such as age,long working hours(weekly working hours greater than 40 h)were the risk factors for occupational stress,depressive symptoms and fatigue accumulation of medical staff(P<0.01),and the longer the working week,the higher the risk of occupational stress,depressive symptoms and fatigue accumulation.Weekly working hours greater than 48 hours are risk factors for insomnia(P<0.01).Conclusion Long working hours are common among delivery workers on food delivery platforms,and long working hours are a risk factor for occupational tension and fatigue.