distance from the sacrococcygeal junction to the middle of an imaginary line running between the left and right ischial tuberosities.
pos·te·ri·or sag·it·tal di·am·e·ter
(pos-tēr'ē-ŏr saj'i-tăl dī-am'ĕ-tĕr) Distance from the sacrococcygeal junction to the middle of an imaginary line running between the left ischial and right ischial tuberosities.