Review Question - QID 219636

Lumbosacral slip angle is the most predictive factor of slip progression and the most influential parameter on overall outcomes of surgical management. The slip angle is the angle made by the intersection of a line drawn down the inferior endplate of L5 and the perpendicular of a line drawn along the posterior cortex of the sacrum shown in Figure D (answer choice 4).

Isthmic spondylolisthesis is a common spinal pathology featuring the forward slippage or subluxation of a vertebral body over the inferior body as a result of a defect in the pars interarticularis. More prevalent in sports involving hyperextension, patients may complain of axial back pain, leg pain, and L5 radiculopathy in high-grade slips. Diagnosis can be made on lumbar spine radiographs with the majority (86%) occurring at the L5-S1 level. The Meyerding classification (Illustration A) is often used to determine the grade of spondylolisthesis, measured as a percentage of the translation of the vertebral body on lateral radiographs with grades III-V considered high-grade slips. Other measurements, including the pelvic incidence, pelvic tilt, sacral slope, slip angle, and lumbar index can be calculated on the lateral radiographs. Pelvic incidence has been found to correlate with disease severity while slip angle correlates with disease progression. Low-grade, asymptomatic slips are often treated with nonoperative measures. High-grade slips or symptomatic patients are indicated for surgery by typically posterior fusion with or without decompression. The ideal surgical management of spondylolisthesis is a highly debated topic.

Bhalla et al. provide a comprehensive review of isthmic lumbar spondylolisthesis. The authors highlight the importance of lumbosacral slip angle when evaluating spondylolisthesis. The recommended method for measuring is the angle made by the intersection of a line drawn down the inferior endplate of L5 and the perpendicular of line drawn along the posterior cortex of the sacrum. Greater risk of slip progression, risk of postoperative pseudoarthrosis, and mechanical instability are all correlated with higher slip angles. The authors note the importance of slip angle correction during surgical treatment. In conclusion, the authors stress the importance of evaluating spine-pelvic parameters, including slip angle, to develop the most appropriate treatment plan in patients with HGS.

Labelle et al. published a review and proposed a classification for spinopelvic sagittal balance in relation to spondylolisthesis. The authors propose a classification system that categorizes spondylolisthesis into 6 different sagittal postures based on radiographic findings, including the slip grade, pelvic incidence, and spino-pelvic balance. Given the debate on surgical techniques for spondylolisthesis, the authors recommend reduction techniques be employed in the setting of abnormal spinopelvic posture.

Kunze et al. published a review on treatment strategies for high-grade spondylolisthesis (HGS) in adults. Except for rare cases of cauda equina, the authors recommend trialing nonoperative management on all patients primarily. In patients who have failed nonoperative management, a variety of surgical techniques exist including in situ fusion, fusion and reduction combinations, and vertebrectomy. The authors' indications for reduction and fusion include a slip angle > 45°, severe sagittal imbalance, or increased risk of pseudoarthrosis with in situ fusion. This review highlights the various techniques and the debated indications of the ideal management. In conclusion, the authors emphasize the importance of spino-pelvic parameters in determining treatment and recommend future, higher-quality studies be performed to determine optimal surgical indications and interventions.

Figure A is a lateral of the lumbar spine demonstrating the lumbar index, a ratio between the anterior and posterior height of the slipped vertebrae. The lumbar index measures the amount of wedging of the anterior L5 vertebral body. Figure B is a lateral of the lumbar spine with lumbar lordosis measured. Lumbar lordosis is the angle made between the superior endplate of S1 and the superior endplate of L1. Figure C demonstrates pelvic tilt. A line from the midpoint of the sacral end plate is drawn to the center of the femoral head. The angle from this line and a vertical reference line represents the pelvic tilt. Figure D demonstrates measuring lumbosacral slip angle. This angle is made by the intersection of a line drawn down the inferior endplate of L5 and the perpendicular of a line drawn along the posterior cortex of the sacrum.
Figure E demonstrates the measurement of the sacral slope. Sacral slope is represented by the angle between a line parallel to the S1 endplate and a second horizontal line.

Illustration A shows the commonly used Meyerding classification of spondylolisthesis.

Incorrect Answers:
Answer 1: Figure A demonstrates the measurement of the lumbar index, a ratio between the anterior and posterior height of the slipped vertebrae. The lumbar index measures the amount of weding of the anterior L5 vertebral body. This is not the most influential measurement of slip progression or overall outcome.
Answer 2: Figure B demonstrates the measurement of lumbar lordosis. Although this is a factor in determining the overall spinopelvic balance, it is not the most influential on slip progression or overall outcome.
Answer 3: Figure C demonstrates pelvic tilt. A line from the midpoint of the sacral end plate is drawn to the center of the femoral head. The angle from this line and a vertical reference line represents the pelvic tilt. This is another important parameter in spino-pelvic balance but is not the most influential on slip progression or outcomes.
Answer 5: Figure E demonstrates the measurement of the sacral slope. Sacral slope is represented by the angle between a line parallel to the S1 endplate and a second horizontal line. The sacral slope is not the most influential parameter on the overall outcome or progression of spondylolisthesis.