Recent studies in spine surgery [1-2] categorize spinopelvic mismatch groups based on patients' preoperative PILL values. What is not clear to me is how negative PILL patients are categorized (pelvic incidence is lower than lumbar lordosis). I have the impression that absolute PILL values are used to differentiate mismatch groups, but my data from an ongoing investigation does not seem to support this approach. In clinical practice, higher values of PILL are associated with increased disability and pain with higher PT and TPA (t1-pelvic angle). Comparing positive and negative PILL groups I found that negative PILL groups are associated with much lower PT and TPA values which are below the clinical thresholds describing mild deformity (PT=20, TPA=14 degrees). Thus, in my opinion, negative PILL should be classified as non-pathologic and treated differently than any of the positive PILL groups. Could anyone share thoughts on this one? Also, please let me know if you know of a study that looked at the correlation between negative PILL values and pain and disability scores and/or compare it against positive PILL groups. I am attaching some literature data and my own data.
1. Schwab et al. 2010: Adult Spinal Deformity—Postoperative Standing Imbalance
2. Diebo et al. 2015: Recruitment of Compensatory Mechanisms in Sagittal Spinal Malalignment Is Age and Regional Deformity Dependent
This question is outside my area of work. I am an anaesthesiologist and this question will be best answered by some orthopedic surgeon
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