1. It is a landmark used for pudendal nerve block analgesia.
2. Deep transverse arrest usually occurs at this plane.
3. It is at this plane that the internal rotation of the fetal head occurs during labour.
4. It marks the beginning of the backward curve of the pelvic axis.
Select the correct answer using the code given below.
Obstetric Significance of the Plane of Least Pelvic Dimensions
The plane of least pelvic dimensions (mid-pelvic plane) extends from the lower border of the symphysis pubis, through the ischial spines, to the sacrum (usually the junction of S4-S5). The ischial spines are its most important landmark and the narrowest part of the pelvic canal through which the fetal head must pass.
Analysis of Each Statement
- Statement 1 — Pudendal nerve block landmark (Correct): The ischial spine, which lies on the plane of least pelvic dimensions, is the standard anatomical landmark used to locate the pudendal nerve (as it crosses the spine near the sacrospinous ligament) for administering a pudendal nerve block for perineal/vaginal analgesia.
- Statement 2 — Deep transverse arrest (Correct): Deep transverse arrest is defined as arrest of the fetal head in the transverse diameter precisely at or below the level of the ischial spines, i.e., at the plane of least pelvic dimensions, when internal rotation fails to occur.
- Statement 3 — Internal rotation of the fetal head (Correct): Internal rotation of the fetal head classically occurs at the level of the ischial spines (the plane of least pelvic dimensions), where the head first meets resistance from the pelvic floor and levator ani sling, triggering rotation to the anteroposterior diameter.
- Statement 4 — Backward curve of the pelvic axis (Incorrect): The pelvic axis is curved (the "curve of Carus"). It runs vertically downward through the plane of the inlet, then curves backward starting at the level of the plane of greatest pelvic dimensions (not the plane of least dimensions), continuing forward again as it approaches the outlet. Attributing the start of the backward curve to the plane of least dimensions is anatomically incorrect.
Conclusion
Since statements 1, 2, and 3 are true descriptions of the obstetric significance of the plane of least pelvic dimensions, while statement 4 incorrectly describes an event that actually occurs at the plane of greatest pelvic dimensions, the correct combination is 1, 2 and 3.
Important Questions from Applied Anatomy
- Which one of the following is NOT a support of uterus, preventing its descent?
- Which one of the following statements regarding Bartholin's glands is NOT true?
- Consider the following statements regarding diameters of a normal female pelvis:
1. AP diameter is the shortest diameter at brim
2. Oblique diameter is the largest diameter of inlet
3. Diagonal conjugate cannot be directly measured
Which of the statements given above is/are correct? - The vaginal pH in childbearing age normally ranges between
Which of the following are correct regarding pelvic cellular tissue?
1. It supports the pelvic organs.
2. It forms protective sheath for blood vessels and terminal part of ureter.
3. It prevents infection to be spread out of pelvis.
4. Marked hypertrophy of pelvic cellular tissue occurs in pregnancy.
Select the answer using the code given below.
