Smallest pelvic diameter in anteroposterior plane of inlet: March 2009
Ans. A: Obstetric Conjugate Antero -posterior diameters: Anatomical antero-posterior diameter (true conjugate) (11cm)-from the tip of the sacral promontory to the upper border of the symphysis pubis. Obstetric conjugate (10 cm)-from the tip of the sacral promontory to the most bulging point on the back of symphysis pubis which is about 1 cm below its upper border. It is the shoest antero-posterior diameter. Diagonal conjugate (12 cm)-1.5 cm longer than the true conjugate. From the tip of sacral promontory to the lower border of symphysis pubis. External conjugate (20 cm)-from the depression below the last lumbar spine to the upper anterior margin of the symphysis pubis measured from outside by the pelvimeter. It has not a true obstetric impoance. Transverse diameters: Anatomical transverse diameter (13cm) -between the fahest two points on the iliopectineal lines. It lies 4 cm anterior to the promontory and 7 cm behind the symphysis. It is the largest diameter in the pelvis. Obstetric transverse diameter: It bisects the true conjugate and is slightly shoer than the anatomical transverse diameter. Oblique diameters: Right oblique diameter (12 cm) -from the right sacroiliac joint to the left iliopectineal eminence. - Left oblique diameter (12 cm) -from the left sacroiliac joint to the right iliopectineal eminence. Sacro-cotyloid diameters (9-9.5 cm) -from the promontory of the sacrum to the right and left iliopectineal eminence, so the right diameter ends at the right eminence and vice versa.
Obstetric conjugate
Diagonal conjugate
True conjugate
transverse conjugate