If you look at an anatomy diagram, you’ll find that the bony plane of the posterior superior iliac spine is larger than that of the anterior superior iliac spine. With a larger bony plane, the needle tip is more likely to land and "bed down" easily. With a smaller bony plane, the needle tip drops as if point to point, like needle tip to awn; it’s easy to slip off and hard to keep the needle perpendicular.
Perpendicular needle entry is very important. A bone marrow puncture by definition has to go into the bone, and bone is hard, which means it takes effort. Perpendicular entry is like hammering a nail straight: the vertical force lets the needle go in more easily, so you can use the minimum strength and cause the child’s bone the least possible damage.
In clinical work, some bones are notoriously hard to penetrate, and when clinical teachers are doing the puncture, if it’s like drilling into bone, you can see from their expression that they’re using force. This effort is not only tiring; they’re also afraid of using too much force. The first time Student Zhang Desheng did one he was scared to death, how would he dare suddenly start drilling hard. If you can’t achieve perpendicular entry and the needle won’t go in, the psychological frustration for a novice, while serious, is nothing compared to the way a veteran can instantly fall apart.
Secondly, in clinical practice, the rate of bone marrow dilution during aspiration is quite high. What is bone marrow dilution? It means you can’t draw marrow, or draw too little, and the specimen you get is mostly blood. A specimen like that, sent to the lab for a marrow exam, is definitely unacceptable and must be redone, which is equivalent to a failed bone marrow puncture.
The problem is that if you choose the posterior superior iliac spine, the child has to lie prone to sleep, which somewhat compromises breathing. Perhaps based on that consideration, Student Zhang Desheng didn’t really dare to choose the posterior superior iliac spine. Mainly, this child’s parents were too hard to deal with, so the doctors simply didn’t dare take any risks.
If you don’t put the patient in the prone position, another option is to have the child lie on their side with both knees hugged tight to expose the posterior superior iliac spine. This position isn’t very easy to stabilize. Because of this, Student Zhang Desheng was fairly respectful of Student Xie’s opinion.
Getting a good position might be a bit difficult, but it’s better than what Student Xie said could happen with the anterior superior iliac spine: you can’t get the needle in, the needle wobbles in the middle for half a day, and the consequences of that would be much more serious.
With classmates coming to help, there was really no need to be that afraid.
They reported to Teacher Tian that they chose the posterior superior iliac spine, and both Teacher Tian and Teacher Wang agreed.
A few classmates started helping the child adjust his position. The other two surgery-track classmates, seeing this, came up to help as well.
They carefully turned the child into a lateral position. When controlling the child, they controlled the joints at their range of motion, rather than just pressing down hard on the child’s body.
Although they said "posterior superior iliac spine" for localization, the actual puncture point was the protuberant area between the posterior superior iliac spine and the fifth lumbar vertebra.
After they finished changing the child’s position, Student Zhang Desheng felt something different. Through his gloved hand, he could feel a relatively flat bony surface, which meant this position exposed the bony area to be operated on very well. It wasn’t like when he first palpated the anterior superior iliac spine and could only feel a little bump that made it hard to insert the needle.
He connected this with the fact that the child’s current position had been arranged by Student Xie. In his heart, Student Zhang Desheng praised her highly: Student Xie is impressive.
Being able to feel a broad, easy-to-enter puncture point naturally gives the doctor far more confidence.
Riding this momentum, Zhang Desheng then injected the local anesthetic with much higher precision, right onto the periosteum, doing it almost effortlessly. He palpated the area after the local anesthesia; then, when inserting the needle again, because he felt secure, he drove the bone marrow needle straight down. With one pull of the syringe plunger he quickly felt something come up. The whole process was unbelievably smooth.
The faster the doctor’s movements, the more the child’s pain and discomfort are reduced. Children, like adults, are most afraid of prolonged pain.
Seeing the student draw the marrow in just a few moves, the two supervising teachers nodded vigorously: these classmates did a good job, handled it themselves without needing teacher guidance.
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