Oral Presentation 50th International Society for the Study of the Lumbar Spine Annual Meeting 2024

INTRODUCTION: Approximately 90% of chronic low back pain (cLBP) is nonspecific, lacking clear anatomical pathology and exhibiting tremendous heterogeneity in movement impairment [1]. The relationship between movement and cLBP remains unclear, though biological sex may be a contributing factor due to differences in anatomical features (spinal alignment, pelvic structure) [2,3] and pain experience [4,5]. Existing clinical guidelines overlook patient-specific factors on biomechanical function and rely on qualitative assessments, leading to misdiagnosis in 40-80% of cases [6]. To address this, we developed a patient-specific Kinematic Composite Score (K-Score), which distills full-body, dynamic patterns into a quantitative and robust metric. In this study, K-Scores are used to evaluate the severity and variability of mechanical impairment during a repeated maneuver (i.e. sit to stand (STS)), and are compared with patient-reported outcomes (PROs) for pain, physical function, and fear avoidance. We hypothesized sex-based associations between K-Scores and self-reported health outcomes in relation to cLBP. Exploring sex-based differences between overall movement quality and cLBP health outcomes may help clarify the uncertain patient-specific mechanisms underlying non-specific cLBP. 

METHODS: Markerless motion capture tracked full-body skeletal motion during five repeated STS for controls (CTRL, n=20, 40% male, age=58±21) and cLBP patients (n=205, (52% male (LBP-M), age=56±16), (48% female (LBP-F), age=55±15); IRB approved). Principal Component (PC) Analysis and Generalized Procrustes Analysis were employed to reduce data dimensionality and improve spatial alignment. The Kinematic Profile (K-Profile) used PC scores to capture prominent patterns across body landmarks. K-Scores were computed as the absolute difference between the individual’s K-Profile and control subject average. Repeated test variability was quantified as the maximum change between K-Scores. The Kruskal-Wallis test with Dunn's post hoc analysis was performed for pairwise comparisons, while linear regression models examined relationships between variables.

RESULTS: Controls exhibited no sex differences and minimal variation in movement patterns (K-Profile), movement quality (K-Score), and repeated variation, and therefore, were grouped for comparison (p>0.3). The LBP K-Profile variance exceeded the CTRLs', indicating less consistent overall movement patterns among patients, particularly for males (Figure 1A shaded regions).  For all STS trials, LBP K-scores were significantly lower and more variable over time, suggesting higher severity of mechanical impairment (p<0.001, Figure 1B). LBP-M demonstrated significantly worse initial performance (K-Score: LBP-M=59.4±17, LBP-F=71.6±12, p<0.001) and higher variation over subsequent repetitions (Figure 1C). However, there was no relationship between PROs or age with K-Scores or their repeated variability (R²<0.05). Further, there was no significance between PROs and sex (p>0.33).

DISCUSSION: We observed worse movement quality and higher variability among LBP patients. Significant sex-based differences in movement quality were observed among individuals with LBP but not CTRLs. This suggests that sex-based biomechanical differences among LBP patients are primarily linked to pain rather than anatomy. Further, while LBP-F and LBP-M reported similar health outcomes, LBP-M demonstrated higher impairment and variability compared to LBP-F, indicating a sex difference in the association between pain and biomechanical function. The findings underscore the importance of continued exploration into the relationship between sex, pain, and movement quality, ultimately paving the way for effective patient-specific cLBP intervention.