A principle of physics as applicable to shoulder delivery

      This paper is only available as a PDF. To read, Please Download here.


      • 1.
        1. A wooden manikin, with shoulders too large to be delivered by pulling, is easily delivered according to a law of physics applicable to the screw.
      • 2.
        2. If the shoulders of a wooden manikin are so large that they can be delivered in only one way, it would seem that this way would be the easiest, and therefore the least dangerous, way to deliver a live baby.
      • 3.
        3. After the head has been born the shoulders of the baby resemble a longitudinal section of a screw engaged in three threads, the “pubic thread,” the “promontory thread,” and the “coccyx thread.”
      • 4.
        4. Any pulling on the baby's neck or axilla is mechanically incorrect because it violates a simple, well-known law of physics applicable to the screw.
      • 5.
        5. There is no stretching of the trapezius muscle, and consequently no danger of injuring the cervical nerves.
      • 6.
        6. The pressure is away from the perineum.
      • 7.
        7. This maneuver cannot be performed unless the posterior shoulder has passed the spines.
      • 8.
        8. Pressure from above, on the buttocks, must be applied by the operator (not an assistant) in order to synchronize the pressure of the two hands.
      • 9.
        9. The passage of a baby through the birth canal is, in the vast majority of cases, an engineering problem. By applying a law of physics applicable to the screw, we find that most of our difficulty is due to a “crossed thread” or improper inclination of some part of our screwlike object. For example, extension of the arms, or nuchal arms, in a breech delivery may prevent the shoulders from adopting the proper inclination or screwlike attitude necessary for delivery. In the vertex presentation extension of the arms along the baby's body may interfere with the proper inclination of the shoulders. A Bandl's ring does the same thing.
      To read this article in full you will need to make a payment

      Purchase one-time access:

      Academic & Personal: 24 hour online accessCorporate R&D Professionals: 24 hour online access
      One-time access price info
      • For academic or personal research use, select 'Academic and Personal'
      • For corporate R&D use, select 'Corporate R&D Professionals'


      Subscribe to American Journal of Obstetrics & Gynecology
      Already a print subscriber? Claim online access
      Already an online subscriber? Sign in
      Institutional Access: Sign in to ScienceDirect