Classification of the Normal Variation in the Sagittal Alignment of the Lumbar Spine and Pelvis in the Standing Position**

• a, d - Medtronic

The coronal alignment of the human spine is well understood. It is normal when straight, and pathologic when curved. The differences between normal and pathologic curvatures are less clear in the sagittal plane. Many techniques have been published for measuring sagittal alignment, but a comprehensive classification system of that includes a description of the orientation of the pelvis has not emerged. This is unfortunate, since the majority of degenerative disease occurs in spines that are well aligned in the coronal plane, but exhibit highly variable morphology in the sagittal plane.

The purpose of this study was to document and classify the variation in the sagittal alignment of the spine in standardized radiographs made in a controlled standing position. A cross-sectional radiographic analysis of a cohort of 160 healthy volunteers was completed. The average age of the cohort was 27 years, with a range from 18 to 48 years of age, and consisted of 86 females and 74 males. At the time of enrollment, patients were questioned about their medical history. Those patients who were free of current or historical symptoms suggestive of spinal or orthopedic disease were included in the study. Volunteers were excluded if they had a history of chronic back pain, deformity, significant orthopedic disease, or an obvious radiographic abnormality such as spondylolysis, spondylolisthesis, scoliosis, or Scheuermann’s kyphosis.

A custom computer application for analyzing spinal anatomy on digitized radiographs (Optimage, Lyon FR) was used to analyze the full length lateral radiographs of the spine. Variations in the sagittal morphology of the spine and the lumbosacral junction were classified using a four-part classification system developed by the senior author in order to describe common patterns of reciprocal relationships between the orientation of the sacrum and the characteristics of the lumbar lordosis.

Type 1 Lordosis: Sacral slope <35 °, with low pelvic incidence. Lordotic apex @ at L5.

Type 2 Lordosis: Sacral slope > 35°. Lordotic apex @ at L4.

Type 3 Lordosis: Sacral slope > 35° and <45 °. The spine is well-balanced.

Type 4 Lordosis: Sacral slope > 45°, with high pelvic incidence. Lordotic apex @ L3

These data from healthy, young volunteers demonstrates that the human spine and pelvis manifests variable alignment in different individuals. The least common category, type 2, contained 18 patients, whereas the most common category, type 3, contained 60 patients. We have made several preliminary observations that certain types of sagittal alignment are more frequently associated with symptomatic back pain or degenerative diseases. For example, we have noted that patients with symptomatic disk herniations are most commonly classified as Type 1 or 2, patients with spinal stenosis are most commonly classified as Type 4, and we rarely see patients with significant complaints who are classified as Type 3. We believe that the ongoing collection and analysis of similar data in normal volunteers and patients seeking consultation for spinal disease will help to explore the relationship between native sagittal alignment and the relative risk of developing degenerative changes and pain in the lumbar spine.

• If noted the author indicates something of value received. The codes are identified as: a-research or institutional support; b-miscellaneous funding; c-stock or stock options; d-royalties; e-other financial or material support including consulting.

**The FDA has not cleared a drug and/or medical device the use described in this presentation (i.e., the drug or medical device is being discussed in an “off-label use).