# Frequency of lumbopelvic malalignment in symptomatic hip instability and impingement – a prospective, diagnostic cohort study

## TL;DR

This study shows that lumbopelvic malalignment is common in patients with hip issues and highlights differences between hip instability and impingement.

## Contribution

The study provides new insights into the frequency and types of lumbopelvic malalignment in pre-arthritic hip deformities.

## Key findings

- 44.9% of patients had static lumbopelvic malalignment, with 'Hyperlordotic' being the most common type.
- AR patients had significantly lower pelvic incidence and tilt compared to HD and BHD patients.
- Functional lumbopelvic alignment showed minimal differences between HD, BHD, and AR.

## Abstract

The dynamic lumbopelvic interaction has gained increasing importance in hip-preserving surgery, even though the coexistence of lumbopelvic malalignment with pre-arthritic hip deformities has been poorly studied. This study aimed to examine (I) the frequency of static and functional lumbopelvic malalignment (II) and to compare the lumbopelvic alignment between symptomatic mild to severe hip dysplasia (HD) and impingement-driven acetabular retroversion (AR).

Sagittal lumbopelvic radiographs were reviewed in standing, relaxed-seated and deep-seated position for pelvic incidence (PI), pelvic tilt (PT), lumbar lordosis (LL), and sacral slope (SS). Static lumbopelvic alignment was classified as “Flatback”, “Normal”, or “Hyperlordotic” and functional lumbopelvic alignment was categorized as “Stiff”, “Normal”, and “Hypermobile”. Static and functional (Δ between the above-mentioned positions) lumbopelvic parameters were compared among HD, borderline hip dysplasia (BHD), and AR.

Ninety-eight patients undergoing hip-preserving surgery for HD (n = 47), BHD (n = 36), and AR (n = 15) were prospectively enrolled. Static lumbopelvic malalignment occurred in 44.9% of patients (44/98), with “Hyperlordotic” alignment being the most frequent (36/44). Additionally, 28.6% of patients (28/98) exhibited functional lumbopelvic malalignment. Static lumbopelvic parameters showed differences between hip instability and impingement, with lower PI (42° vs. 57.3°, p = 0.001; 42° vs. 53.7°, p = 0.01) and PT (5.6° vs. 15.8°, p < 0.001; 5.6° vs. 12.4°, p = 0.01) in AR patients compared to HD and BHD in standing position. Moreover, SS was significantly lower in AR (40.9° vs. 50.1°, p = 0.02) and BHD (43.8° vs. 50.1°, p = 0.05) compared to HD in deep-seated position. Significant differences in functional lumbopelvic parameters were observed only between HD and BHD in PT (Δ standing – deep-seated position, 7.1° vs. -1.2°, p = 0.04).

Static and functional lumbopelvic malalignment is prevalent in patients with pre-arthritic hip deformities. While static lumbopelvic parameters vary between instability- and impingement-driven hip deformities, functional lumbopelvic alignment is quite similar among HD, BHD, and AR.