[Ultrasound hip joint screening in newborn infants. Is twin pregnancy a risk factor for dysplasia?].

Purpose: This study aimed at investigating whether twin pregnancy is a risk factor for congenital dysplasia of the hip.
Method: From 1987 until 1994 the hips of 3739 (1902 male, 1837 female) newborn were examined by ultrasound (screening) according to Graf's technique. We compared the results of twins and the other newborn (non-twins). The examinations were performed by 19 physicians. 73 (2%) of the newborn were twins (29 male, 44 female).
Results: In the group of 3666 non-twins we found the types of hip IIa (alpha < 55 degrees) to IV (Graf's classification) in 237 (6.5%) newborn: 136 (3.7%) right side/183 (5.0%) left side. Only 2 (2.7%) of the 73 twins showed these types of hip. We found 4% (149/3739) breech presentations at birth in the entire group. 3.9% (141/3666) in the group of non-twins and 11% (8/73) cases in the twin group. 5.2% (190/3666) of the non-twins and 2.7% (2/73) of the twins required a treatment with abduction orthosis or Pavlik harness.
Conclusion: This report shows that the types of hip IIa (alpha < 55 degrees); IIc; D; IIa, IIb and IV according to Graf and a required treatment in twins was significantly not more frequent than in the other newborn (non-twins), although twins showed more often a breech presentation at birth. The different kind of breech position in twins (hips and knees in flexion, legs and feet parallel) and non-twins (hips in flexion, knees in extension) could be one reason for these results. Besides, non-twins assume their breech position earlier than twins with a consecutively longer period of time of mechanical stress on the hips.