Measurement of height and length of the ISS The red lines are AHISS, MHISS, and PHISS in order of anterior to the posterior, the white line is LISS, and 'p' indicates posterior.  Abbreviations: ISS=Interspinous space; AHISS=anterior height of the interspinous space; MHISS=middle height of the interspinous space; PHISS=posterior height of the interspinous space; LISS=Length of the interspinous space