Pelvic incidence significance relative to spinopelvic risk factors for total hip arthroplasty instability

Abstract

Aims Pelvic incidence (PI) is a position-independent spinopelvic parameter traditionally used by spinal surgeons to determine spinal alignment. Its relevance to the arthroplasty surgeon in assessing patient risk for total hip arthroplasty (THA) instability preoperatively is unclear. This study was undertaken to investigate the significance of PI relative to other spinopelvic parameter risk factors for instability to help guide its clinical application. Methods Retrospective analysis was performed of a multicentre THA database of 9,414 patients with preoperative imaging (dynamic spinopelvic radiographs and pelvic CT scans). Several spinopelvic parameter measurements were made by engineers using advanced software including sacral slope (SS), standing anterior pelvic plane tilt (APPT), spinopelvic tilt (SPT), lumbar lordosis (LL), and PI. Lumbar flexion (LF) was determined by change in LL between standing and flexed-seated lateral radiographs. Abnormal pelvic mobility was defined as ∆SPT ≥ 20° between standing and flexed-forward positions. Sagittal spinal deformity (SSD) was defined as PI-LL mismatch > 10°. Results PI showed a positive correlation with parameters of SS, SPT, and LL (r-value range 0.468 to 0.661). Patients with a higher PI value showed higher degrees of standing LL, likely as a compensatory measure to maintain sagittal spine balance. There was a positive correlation between LL and LF such that patients with less standing LL had decreased LF ( r = 0.49). Similarly, there was a positive correlation between increased SSD and decreased LF ( r = 0.54). PI in isolation did not show any significant correlation with lumbar ( r = 0.04) or pelvic mobility ( r = 0.02). The majority of patients (range 89.4% to 94.2%) had normal lumbar and pelvic mobility regardless of the PI value. Conclusion The PI value alone is not indicative of either spinal or pelvic mobility, and thus in isolation may not be a risk factor for THA instability. Patients with SSD had higher rates of spinopelvic stiffness, which may be the mechanism by which PI relates to THA instability risk, but further clinical studies are required. Cite this article: Bone Joint J 2022;104-B(3):352–358.

Low pelvic incidence with low lordosis and distal apex of lumbar lordosis associated with higher rates of abnormal spinopelvic mobility in patients undergoing THA

“…In this study, we found that the variables that were statistically associated with the risk of abnormal spinopelvic mobility before THA were a standing SPT≤-10°, IP-LL ≥ 20°, and LF ≥ 20°, which matched the actual literature; 5 , 7 , 19 however, if the univariate analysis showed that a stiff spine with an LF ≤ 20° was associated, it was not in the multivariate analysis. This result is probably due to the close relationship between SSD and spine stiffness.…”

“…The outcome of interest was abnormal spinopelvic mobility, defined as ΔSPT ≥ 20° between the standing and relaxed-sitting positions. 7 We analyzed SPT≤-10°, LF ≤ 20°, PI-LL ≥ 20, PI ≤ 41°, SS < 35°, and the different groups of lordosis as risk factors in the overall population.…”

“…However, all patients who present with abnormal mobility of the pelvis do not have these risk factors, 7 and some authors attribute a higher risk of anterior impingement in patients with a low lordosis without degenerative spine, 8 - 10 explained by a stiffer lumbo-pelvic complex, describing them as “hip users”. 4 The PI being directly related to lumbar lordosis (lower in patients with low lordosis and higher in patients with high lordosis), 11 some authors consider a relation between the PI and abnormal pelvic mobility.…”

“… 4 The PI being directly related to lumbar lordosis (lower in patients with low lordosis and higher in patients with high lordosis), 11 some authors consider a relation between the PI and abnormal pelvic mobility. 9 , 10 However, recent studies have shown that the risk of having an abnormal spinopelvic mobility in patients with a PI < 41° is not increased by analyzing more than 9,000 consecutive patients, 7 and that the risk of dislocation following THA with the same boundary is not increased, 6 thereby concluding that the PI value alone may not be a risk factor for THA instability.…”

A leap towards personalized orthopaedic surgery and the prediction of spinopelvic mechanics in total hip arthroplasty

“…Instead, tailoring the functional orientation of the component to the distinct phenotype of the patient is now fundamental when undertaking THA, in particular to avoid instability. 4-6…”