Introduction: It has become well recognised that sagittal balance of the spine is the result of an interaction between the spine and the pelvis. Knee flexion is considered to be the last compensatory mechanism in case of sagittal imbalance, but only few studies have insisted on the relationship between spino-pelvic parameters and lower extremity parameters. Correlation between the lack of lumbar lordosis and knee flexion has not yet been established.
Materials and methods: A retrospective study was carried out on 28 patients with major spinal deformities. The EOS system was used to measure spinal and pelvic parameters and the knee flexion angle; the lack of lumbar lordosis was calculated after prediction of lumbar lordosis with two different formulas. Correlation analysis between the different measured parameters was performed.
Results: Lumbar lordosis correlated with sacral slope (r = -0.71) and moderately with knee flexion angle (r = 0.42). Pelvic tilt correlated moderately with knee flexion angle (r = 0.55). Lack of lumbar lordosis correlated best with knee flexion angle (r = 0.72 and r = 0.63 using the two formulas, respectively).
Conclusion: Knee flexion as a compensatory mechanism to sagittal imbalance was well correlated to the lack of lordosis and, depending on the importance of the former parameter, the best procedure to correct sagittal imbalance could be chosen.