The mediating role of sacral slope in the relationship between lumbar lordosis and knee alignment in knee osteoarthritis: an imaging study

Objective: This study aimed to investigate the association between lumbar lordosis (LL) and the sagittal hip-knee-ankle angle (sHKA) in patients with knee osteoarthritis (KOA) and to quantify the mediating effect of the sacral slope (SS). Methods: This study enrolled 507 participants (left-side 302, right-side 205). Lateral full-length X-ray films of the lower extremities in weight-bearing position were collected from the research participants to measure radiological parameters such as lumbar lordosis (LL), sacral slope (SS), and sagittal hip-knee-ankle angle (sHKA), and SF-12 (12-items Short Form Health Survey) and WOMAC (Western Ontario and McMaster Universities Osteoarthritis Index) scores were also collected. Correlation analysis and Bootstrap mediation effect analysis were performed. Results: Among the 507 KOA participants, LL was positively correlated with SS, HKA, sHKA, and SF-12 scores, and negatively correlated with JLCA and WOMAC scores. The mediation analysis revealed that SS accounted for 10.74% of the total association of LL on sHKA. Conclusion: In patients with KOA, LL is closely related to sHKA, and this statistical association may be partially mediated by SS. This highlights the importance of adopting a "spine-pelvis-knee" perspective when assessing and treating KOA.