Interexaminer reliability and accuracy of posterior superior iliac spine and iliac crest palpation for spinal level estimations

Objective: The purpose of this study was to compare the posterior superior iliac spine (PSIS) and the iliac crest as accurate anatomical landmarks for identifying spinal level. Methods: This study was conducted in 2 stages. First, 4 examiners examined 60 patients and blindly identified iliac crest and PSIS levels, and the interexaminer reliability of PSIS and iliac crest palpation were then analyzed. Second, 4 examiners attached a radio opaque marker at presumed PSIS and iliac crest levels in 72 patients, and posteroanterior lumbar radiographs were then taken. Four examiners then confirmed PSIS and iliac crest levels after radiographically identifying the marker levels and checked the spinal level at which the spinous process or interspace was crossed by drawing a horizontal line drawn between radio opaque markers. Results: The interexaminer reliability of palpation was significantly greater for PSIS level than for the iliac crest (P <.05). Spinal levels of estimated PSISs identified by palpation ranged from the L5-S1 interspace to the S2 spinous process, and the spinal levels of estimated iliac crest ranged from the L2-3 interspace to the L5 spinous process. Conclusions: Although PSIS palpation showed statistically higher interexaminer reliability than iliac crest level, clinicians should be cautious when applying this method as a measurement tool because estimated spinal level by palpation can be influenced inadvertently by examiner skill and anatomical variations.