====== Spino-pelvic angulation ======


Spino-pelvic angulation refers to the relationship between the [[spine]] and [[pelvis]], which plays a crucial role in maintaining [[posture]], [[balance]], and load distribution across the spine. It is particularly important in [[spinal surgery]], especially for conditions such as [[spinal deformity]], [[degenerative disc disease]], and [[spinal fusion]] planning.
----
Spine biomechanics, particularly [[sagittal balance]] and spino-pelvic angulation are determinant factors in the understanding of [[lumbar degenerative disease]]. These concepts translated into objective measurements are progressively being integrated into clinical practice. 

===== Key Spino-Pelvic Parameters =====

Several radiographic angles and measurements describe the spino-pelvic alignment:

[[Pelvic Incidence]] (PI)

The most fundamental parameter, as it remains constant for an individual.

A higher PI is associated with a more lordotic lumbar spine, while a lower PI correlates with a flatter lumbar curvature.

[[Pelvic Tilt]] (PT)

Measures the rotation of the pelvis in relation to the femur.

Defined as the angle between the vertical axis and a line connecting the center of the femoral head to the midpoint of the sacral endplate.

Increased PT (>20°) is often seen in compensatory mechanisms for sagittal imbalance.

[[Sacral Slope]] (SS)

The angle between the sacral endplate and a horizontal line.

Directly related to PI, as PI = PT + SS.

A high sacral slope suggests a lordotic lumbar spine, whereas a low sacral slope is associated with a kyphotic or hypolordotic lumbar alignment.

[[Lumbar Lordosis]] (LL)

The curvature of the lumbar spine, measured as the Cobb angle from L1 to S1.
There is an ideal relationship between PI and LL: LL ≈ PI ± 9°. A mismatch (PI-LL mismatch) can contribute to spinal malalignment and pain.

[[Sagittal Vertical Axis]] (SVA)

Measures the global sagittal balance by assessing the horizontal distance between the C7 plumb line and the posterior superior corner of S1.
An SVA >5 cm is considered indicative of sagittal imbalance, often requiring surgical correction.

===== Clinical Implications =====

Low Back Pain & Degeneration: Poor spino-pelvic alignment contributes to chronic mechanical back pain and degenerative changes.

Spinal Fusion Planning: Understanding spino-pelvic parameters helps in determining the optimal alignment to reduce adjacent segment disease post-fusion.

Sagittal Imbalance: Severe cases of mismatch (e.g., high PI-LL mismatch) lead to compensatory mechanisms such as pelvic retroversion, knee flexion, and increased thoracic kyphosis, which can cause disability.

Surgical Correction Strategies: Osteotomies (e.g., Smith-Petersen, pedicle subtraction) may be required to restore sagittal alignment in severe deformities.