Anatomy
Head and Neck
Regarding the intervertebral disc, which of the following statements is CORRECT:
Answer:
A posterolateral herniation of the disc at the L4 - L5 level would be most likely to damage the fifth lumbar nerve root, not the fourth lumbar nerve root, due to more oblique descending of the fifth lumbar nerve root within the subarachnoid space.Intervertebral Disc
Anatomy / Head and Neck / Vertebral Column
Last Updated: 11th April 2019
Each vertebral body is separated from adjacent vertebral bodies by fibrocartilaginous intervertebral discs.
Structure
The intervertebral disc consists of the outer annulus fibrosus, a complex series of fibrous rings enclosing the central gelatinous nucleus pulposus.
![By OpenStax College [CC BY 3.0], via Wikimedia Commons](https://primary-cdn.frcemsuccess.com/wp-content/uploads/2016/07/intervertebral-disc.jpg)
Intervertebral Disc. (Image by OpenStax College [CC BY 3.0], via Wikimedia Commons)
Function
The intervertebral discs allows movements between the vertebrae and act as a shock absorber.
Clinical Implications
Degenerative changes in the annulus fibrosus can lead to herniation of the nucleus pulposus. A tear can occur within the annulus fibrosus through which the nucleus pulposus can track into the intervertebral foramen or into the vertebral canal, compressing the spinal nerve root. It commonly occurs posterolaterally where the annulus fibrosus is not reinforced by the posterior longitudinal ligament, and frequently affects the lumbar region.
The spinal cord only occupies about 2/3s of the space available to it in the vertebral canal. The lower a nerve root, the more steeply it slopes down and the further it has to travel before gaining its intervertebral foramen. Therefore, a posterolateral herniation of the disc at the L4 - L5 level for example, would be most likely to damage the fifth lumbar nerve root, not the fourth lumbar nerve root, due to more oblique descending of the fifth lumbar nerve root within the subarachnoid space.
Intervertebral Disc Herniation. (Image by OpenStax College [CC BY 3.0 (https://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons)
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
