From the Guidelines
The normal diameter of the lumbar spinal canal typically ranges from 15-23 mm in adults, and lumbar spinal stenosis is generally considered severe when the anteroposterior diameter of the spinal canal measures less than 10 mm. Symptoms typically become apparent when the diameter narrows to 10-12 mm, with measurements below 10 mm almost always producing clinical manifestations. These symptoms include neurogenic claudication (leg pain with walking that improves with rest), lower extremity weakness, numbness, and in severe cases, bowel or bladder dysfunction. The development of symptoms relates to the compression of neural elements within the canal, particularly the cauda equina. It's essential to note that the correlation between imaging findings and symptoms isn't always straightforward - some patients with radiographic severe stenosis may be asymptomatic, while others with milder stenosis may experience significant symptoms. This variability occurs because symptoms depend not only on the static canal diameter but also on dynamic factors such as posture, activity level, and individual differences in neural tolerance to compression. Clinical evaluation should therefore always accompany imaging findings when assessing the significance of lumbar stenosis 1.
Some key points to consider:
- The normal diameter range is crucial for understanding what constitutes stenosis.
- Symptoms can vary widely among individuals, even with similar canal diameters.
- Clinical evaluation is essential in conjunction with imaging to assess symptom severity and significance.
- The guidelines provided by the American College of Physicians and the American Pain Society offer recommendations for the diagnosis and treatment of low back pain, including the use of MRI or CT for evaluating patients with persistent back and leg pain who are potential candidates for invasive interventions 1.
Given the information and the need to prioritize morbidity, mortality, and quality of life, it is crucial to evaluate patients with persistent low back pain and signs or symptoms of radiculopathy or spinal stenosis with MRI (preferred) or CT only if they are potential candidates for surgery or epidural steroid injection (for suspected radiculopathy) 1. This approach ensures that treatment decisions are based on the best available evidence and consider the individual patient's circumstances, including their preferences, surgical risks, and potential benefits.
From the Research
Normal Diameter of Disc Space in Lumbar Vertebral Levels
- The normal diameter of disc space in the lumbar vertebral levels can vary depending on the specific level and the individual's age and sex 2.
- A study found that the average lumbar disc height was 5.6 ± 1.1 mm for men and 4.8 ± 0.8 mm for women at T12/L1, 6.9 ± 1.3 mm for men and 5.8 ± 0.9 mm for women at L1/2,8.1 ± 1.4 mm for men and 6.9 ± 1.1 mm for women at L2/3,8.7 ± 1.5 mm for men and 7.6 ± 1.2 mm for women at L3/4,9.2 ± 1.6 mm for men and 8.5 ± 1.6 mm for women at L4/5, and 8.8 ± 1.6 mm for men and 8.6 ± 1.8 mm for women at L5/S1 2.
- Another study found that the average distance of intervertebral space from the 1st to the 2nd lumbar vertebrae was 24.83%, that from the 2nd to the 3rd was 26.92%, that from the 3rd to 4th was 28.88%, that from the 4th to 5th was 29.60%, and that from the 5th lumbar vertebra to the 1st sacrum was 27.52% 3.
Severe Stenosis and Symptomatic Values
- Severe stenosis is typically considered to occur when the spinal canal diameter is less than 10 mm 4.
- A study found that the cutoff values for the normal sagittal diameter of the spinal canal (SCD) ranged from 14.5-10.1 mm for males and 15.0-9.9 mm for females 4.
- Another study found that a decrease of 1mm of disc vertical diameter was associated with a 1.3-3.3mm reduction of foraminal vertical diameter, which can lead to nerve root compression and symptomatic stenosis 5.
- The exact value at which stenosis becomes symptomatic can vary depending on the individual and the specific level of the spine, but in general, a spinal canal diameter of less than 10 mm is considered severe stenosis 4.