Effect of birth season on detection rate of Graf type IIa hip joint

Objective To analyze the effect of birth season on detection rate of Graf type Ⅱa hip joint. Methods Infants borned in May 2016 to May 2017 were selected as a total sample, by using the static Graf technique, all those infants were examed by ultrasound.Winter(W) group (1 563 infants)and summer (S) group (1 712 infants) were selected as the studying subjects.The detection rates in the corresponding season and gender of infants with type Ⅱa hip were calculated respectively, which were analyzed by chi-square test. Results Type Ⅱa hip was detected in 5.00%(164/3 275) infants.The detection rates of infants with type Ⅱa hip corresponding to two groups were 6.33%(99/1 563) and 3.80%(65/1 712) respectively.The difference was statistically significant (χ2=11.06, P=0.001). The rates of male and female infants with type Ⅱa hip detected in W group were 5.04%(42/832), 7.79%(57/731)respectively.The difference was statistically significant (χ2=4.96, P=0.026). The rates of male and female infants with type Ⅱa hip detected in S group were 3.01%(25/830), 4.54%(40/882)respectively.The difference was not statistically significant (χ2=2.72, P=0.099). Conclusions The birth season has a significant effect on the detection rate of Graf Ⅱ a hip, and winter-born baby girl should be paid more attention. Key words: Graf type Ⅱa; Hip; Season