Select the option that correctly mentions the instrument shown in the following image.

DSSSB October 2024

Obstetrics & Gynaecology

Easy

Appeared in: DSSSB October 2024

Explanation

The instrument in the image is a pelvimeter, specifically an external pelvimeter like Martin's pelvimeter.
It is characterized by its caliper-like design with two long, curved arms and a graduated scale near the pivot point.
Its primary function is to perform pelvimetry, which involves measuring the external dimensions of the maternal pelvis to assess its adequacy for vaginal delivery.

Option A: A cephalotribe is a destructive instrument used for crushing the fetal head in cases of obstructed labor with fetal demise. It looks like a pair of heavy forceps and does not resemble the measuring caliper shown.
Option B: A decapitation hook is a sharp, hooked instrument used in embryotomy to sever the fetal neck. Its appearance is completely different from the caliper-like pelvimeter.
Option D: A cranioclast is another destructive instrument, used to grasp and extract the fetal head after perforation. It is a type of forceps and does not match the measuring device in the image.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Identification of obstetric instruments as background academic context rather than a clinical decision trigger.
Understanding the use of a pelvimeter is crucial for assessing cephalopelvic disproportion (CPD), a condition where the fetal head is too large for the maternal pelvis, which can lead to obstructed labor.
Although clinical pelvimetry (manual assessment) and imaging have largely replaced instrumental pelvimetry, knowledge of these instruments and the pelvic diameters they measure is fundamental in obstetrics.
What if? If the interspinous diameter, the narrowest part of the pelvis, is found to be less than 10 cm, it could indicate mid-pelvic contraction, increasing the risk of labor arrest and the need for a cesarean section.

How to Approach the Question

First, carefully examine the image provided. Note the key features of the instrument: its overall shape (caliper-like), its parts (two long curved arms, a pivot, a measuring scale), and its apparent function (measuring).
Next, read the question and all the options provided.
Systematically evaluate each option against your visual analysis. The instrument is for measuring, which immediately points towards 'Pelvimeter'.
Eliminate the other options by recalling their functions. 'Cephalotribe', 'Decapitation hook', and 'Cranioclast' are all destructive instruments used in embryotomy, which is inconsistent with the measuring function of the instrument shown.
Confirm your choice. A pelvimeter is used to measure the pelvis (pelvimetry), which matches the instrument's design.
Select the option that correctly identifies the instrument based on this logical deduction.

Concept Tested & Keywords

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E6 Obstetrics Williams pp. 16-32, 15-32