Measurement Analysis and Clinical Research of Lumbar Ligamentum Flavum and Lamina
Authors: Ming Ding , Chao Li 
Published: March 2024

Objective: To measure and analyze adult lumbar ligamentum flavum and lamina on imaging and cadaver specimens and study their clinical significance. Methods: Through lumbar spine MRI, CT imaging research and analysis and anatomical study of cadaveric upper lumbar spine, it was found that the lumbar lamina in the sagittal position is not a flat plate, but consists of a straight upper half and a backward curved lower half. Therefore, we proposed the concept of dividing the lamina into two parts: the "lamina body" which is straight above and the "lamina wing" which is curved below. There is a certain angle between the two parts, and the acute angle between them is called It is the "body wing angle". Therefore, we selected 30 elderly patients who underwent lumbar spine MRI and CT examinations in our hospital from March 2020 to December 2022 during the same period to conduct a measurement study of the ligamentum flavum and lamina on imaging, including 13 males and 17 females. Age 60 to 78 years old (67.2±5.5 years old), height 149 to 175cm (162±6.7cm), a total of 137 valid vertebral bodies were obtained for measurement. Because the lamina is displayed more clearly on CT, the lamina was measured. CT images were used for measurement, and the course and distribution of the ligamentum flavum were evaluated using MRI. Divide one side of the lamina into 3 equal parts, measure the length of the lamina body and lamina wings at the inner and outer 1/3 respectively, and take the average value; During the same period, anatomical measurements of the solid ligamentum flavum and lamina were performed on the lumbar vertebrae of 5 elderly cadavers (the specific age and height were unknown), with a total of 25 vertebral bodies. The lamina on one side was divided into 3 equal parts using the same method, and the inner and outer 1 were measured respectively. /3 The length of the lamina body, lamina wing, and body wing angle are averaged; the origin, end, and course of the ligamentum flavum of the lumbar vertebra are dissected to clarify its distribution characteristics. In order to analyze the clinical causes of secondary hypertrophy and wrinkles of the adjacent ligamentum flavum, determine the scope of laminectomy during posterior lumbar decompression and the protective measures for the adjacent ligamentum flavum. Results: The autopsy results showed that the ligamentum flavum was discontinuous, the ventral surface of the body of the lamina was straight and smooth, and there was no distribution of ligamentum flavum. The medial surface of the wings of the lamina was rough, and the ligamentum flavum was fan-shaped and widely started from the entire lamina. The ventral surface of the wings gradually thins downwards and ends above the lower lamina, with limited distribution of insertion points. The average length of the lamina body, the inner and outer 1/3 of the lamina wings and the body wing angle on the L1-L5 CT sagittal view: L1 lamina body 9.45±2.84 mm, lamina wing 9.92 ±2.65mm, body wing angle 26.2±4.3°; L2 lamina body 9.01±2.45 mm, lamina wing 10.63±2.87 mm, body wing angle 28.3±5.6°; L3 lamina body 8.56±2.62mm, lamina wing 12.32 ±3.25mm, body wing angle 30.4±6.8°; L4 lamina body 8.02±2.33mm, lamina wing 14.67±3.62mm, body wing angle 33.6±5.2°; L5 lamina body 7.06±2.62 mm, lamina wing 15.32±3.24 mm, body wing angle 32.4±6.9°. Autopsy lamina measurement results (average of inner and outer 1/3): L1 lamina body 13.08±1.58mm, lamina wings 18.86±1.72mm, body wing angle 21.05±2.96°; L2 lamina body 12.84±1.74mm, lamina wing 21.93±2.06mm, body wing angle 19.25±2.86°; L3 lamina body 12.29±1.47mm, lamina wing 20.44±1.6mm, body wing angle 27.25±3.74°; L4 lamina body 11.55±1.47mm, the lamina wing is 23.28±1.7mm, the body wing angle is 29.4±2.11°; the L5 lamina body is 12.75±1.76mm, the lamina wing is 20.91±2.01mm, and the body wing angle is 30±3.03°. The length of the lamina wing is greater than the length of the lamina body, and there is an acute angle between them. Although there are differences in data between the two sets of imaging and autopsy results, the length on imaging is smaller than the measurement results on autopsy, which is considered to be related to the fact that some tissues are not visualized on imaging. Conclusion: The lamina is divided into a straight lamina body and a posteriorly curved lamina wing; the lumbar ligamentum flavum is intermittent, starting from the ventral side of the lamina wing, starting from a wide, fan-shaped distribution, and ending at the upper part of the lamina body, the insertion point is limited; the integrity of the start and end points of the ligamentum flavum can effectively maintain the tension of the ligamentum flavum. During posterior lumbar laminectomy and decompression, the upper laminectomy range is too large to destroy the insertion point of the upper ligamentum flavum, causing the ligamentum flavum to return upward. Shrinkage, wrinkles, and hypertrophy are hidden on the ventral side of the lamina wing. The rear lamina wing is bonyly restricted, causing the ligamentum flavum to protrude forward into the spinal canal, causing spinal canal stenosis in adjacent segments, which is the main cause of recurrence of spinal canal stenosis after surgery. Standardizing the scope of laminectomy during surgery and retaining the insertion point of the ligamentum flavum in the upper half of the lamina, that is, the body of the lamina, is the main strategy to reduce postoperative secondary spinal stenosis.