Sagittal Plane Shear Index for Planning Lumbar Stenosis Surgery

The Sagittal Plane Shear Index (SPSI) for Planning Whether to Fuse After Decompressing a Stenotic Lumbar Level

The objective of the clinical investigation is to assess the proportion of lumbar spinal stenosis surgical treatment plans that change when an objective measurement of spinal stability is included and applied following a simple treatment algorithm. The objective spinal stability metric is calculated from flexion-extension radiographs using previously validated methods.

Patients with previously diagnosed lumbar spinal stenosis and spondylolisthesis, who have consented to surgical treatment consisting of either decompression alone or decompression plus fusion will be invited to participate in the study. The initial surgical plan will be recorded prior to reviewing the sagittal plane shear index (SPSI). The sagittal plane shear index will be calculated flexion-extension radiographs. The measurements required to calculate SPSI will be obtained using previously validated methods. SPSI greater than 2 indicates that the translation-per-degree of rotation (TPDR) is above the upper limit of the 95% confidence interval observed in several hundred asymptomatic and radiographically normal individuals. SPSI will be reported to the surgeon after recording the pre-SPSI surgical plan. The surgeon will then decide whether to change the surgical plan. For example, if the initial surgical plan was to only decompress a level, and SPSI is greater than 2, the surgeon may plan to add fusion to the decompression. Conversely, if the initial plan was decompression plus fusion, and the SPSI indicates that the level is objectively stable, the post-SPSI plan may be to only decompress the level. The proportion of surgical plans that change after reviewing the SPSI report will be determined. If the proportion of surgical plans that change is greater than 15%, further research will be undertaken to explore whether deciding, based on objective measurement of spinal stability, whether to add fusion to decompression of a stenotic lumbar level will have a significant effect on clinical outcomes.

Inclusion Criteria:

1. Symptoms consistent with single level lumbar spinal stenosis based on judgment and experience of the investigator
2. Central and or foraminal stenosis confirmed by MRI as per the investigators clinical standards
3. Grades 1 (10 to 25%) or 2 (26 to 50%) anterior or retro-spondylolisthesis using the Meyerding scale [43]
4. Absence of lateral spondylolisthesis
5. No prior lumbar spinal surgery
6. Absence of American Society of Anesthesiologists (ASA) class IV or higher disease
7. The single level surgical technique planned (prior to viewing the spinal motion report) to decompress the level is not expected to destabilize the spine (fusion is not deemed necessary due to probable iatrogenic instability)
8. Prior to viewing the spinal motion report, the surgical plan includes decompression or decompression and fusion of only one level
9. Based on the investigators subjective assessment, the patient is able to flex and extend sufficiently to facilitate acceptable flexion and extension radiographs
10. The fusion technique planned prior to viewing the spinal motion report is the following: Instrumented posterior (pedicle screws and rods) with / without postero-lateral interbody fusion cage
11. Subject is able to understand and sign the study Informed Consent Form
12. Subjects is at least 18 years of age.
13. Subject has willingness and ability to comply with study procedures and visit schedules and able to follow oral and written instructions

Exclusion Criteria:

1. Lumbar stenosis without spondylolisthesis
2. Severe lumbar stenosis that requires a wide decompression where the investigator believes (based on experience and available research studies) that the decompression will destabilize the spine and fusion surgery is required regardless of preoperative SPSI
3. Pregnant women
4. Scoliosis involving a lumbar curve greater than 10 degrees
5. Stenosis at the level of a transitional vertebra
6. Lateral spondylolisthesis (Coronal plane translational misalignment between vertebrae)
7. Prior lumbar spinal surgery
8. American Society of Anesthesiologists (ASA) class IV or higher disease