This cross-sectional study of 149 healthy adults established normative values for pelvic incidence and derived a validated equation for predicting expected lumbar lordosis. It confirms that pelvic incidence — a fixed morphologic parameter — is the master regulator of the entire sagittal spinal-pelvic alignment chain. The predictive model allows clinicians to compare a patient's measured lordosis to their individualized expected value, identifying when posture falls outside biomechanical equilibrium.
Every patient's "normal" lumbar lordosis is individualized — it is set by their pelvic incidence. Before planning a spinal fusion or deformity correction, measure the patient's pelvic incidence. A patient with incidence of 40° needs far less lordosis than one with incidence of 70°. Restoring the population average without accounting for individual incidence is the wrong target.
The equation pelvic incidence = sacral slope + pelvic tilt has direct clinical consequences. When a patient compensates for flatback or adjacent-segment kyphosis by rotating the pelvis backward (increased pelvic tilt), sacral slope must decrease — lordosis flattens further. The pelvis is not a passive structure; it is an active compensator with a fixed budget determined by incidence.
This paper provides the normative reference (53° ± 9°) and the two boundary thresholds (44° and 62°) that spine surgeons use to categorize patients as low-, normal-, or high-incidence types — a framework that directly informs how much lordosis to restore and how much compensatory range remains.
Patients whose measured lordosis falls outside the predicted confidence limits are by definition outside biomechanical equilibrium, which the authors link to pathological patterns including spondylolisthesis, low back pain, and postural impairment.
This cross-sectional study of 149 healthy adults established normative values for pelvic incidence and derived a validated equation for predicting expected lumbar lordosis. It confirms that pelvic incidence — a fixed morphologic parameter — is the master regulator of the entire sagittal spinal-pelvic alignment chain. The predictive model allows clinicians to compare a patient's measured lordosis to their individualized expected value, identifying when posture falls outside biomechanical equilibrium.
Every patient's "normal" lumbar lordosis is individualized — it is set by their pelvic incidence. Before planning a spinal fusion or deformity correction, measure the patient's pelvic incidence. A patient with incidence of 40° needs far less lordosis than one with incidence of 70°. Restoring the population average without accounting for individual incidence is the wrong target.
The equation pelvic incidence = sacral slope + pelvic tilt has direct clinical consequences. When a patient compensates for flatback or adjacent-segment kyphosis by rotating the pelvis backward (increased pelvic tilt), sacral slope must decrease — lordosis flattens further. The pelvis is not a passive structure; it is an active compensator with a fixed budget determined by incidence.
This paper provides the normative reference (53° ± 9°) and the two boundary thresholds (44° and 62°) that spine surgeons use to categorize patients as low-, normal-, or high-incidence types — a framework that directly informs how much lordosis to restore and how much compensatory range remains.
Patients whose measured lordosis falls outside the predicted confidence limits are by definition outside biomechanical equilibrium, which the authors link to pathological patterns including spondylolisthesis, low back pain, and postural impairment.