Joints
Intervertebral disc (symphysis intervertebralis)
The connection between two vertebral bodies: an anulus fibrosus of layered rings around a water-rich nucleus pulposus. With the two facet joints it forms the motion segment. Together the discs account for roughly a quarter of the length of the spine.
- Joint type
- Symphysis (cartilaginous joint), no capsule and no joint cavity
- Body region
- Spine
- Latin name
- Symphysis intervertebralis
Movements, axes and normal values
| Movement | Plane | Axis | Normal range | End feel |
|---|---|---|---|---|
| Flexion | sagittal | varies per level | per segment 8-13 degrees lumbar, wider cervically, least thoracically | firm springy (ligament) |
| Lateral flexion | frontal | sagittal (anteroposterior) | 3-6 degrees per segment, always coupled with rotation | firm springy (ligament) |
| Rotation | transverse | longitudinal | only 1-2 degrees per lumbar segment, considerably more thoracically | firm springy (ligament) |
- Close-packed position
- Maximal extension
- Resting (loose-packed) position
- Neutral segment position
- Capsular pattern
- No capsule, so no capsular pattern; restriction follows the pattern of the motion segment as a whole.
- Arthrokinematics
- The nucleus behaves like a water cushion: in flexion it shifts posteriorly, in extension anteriorly, and the anulus fibres on the stretched side tighten. Under load the disc expresses fluid and loses height; at night it draws it back in, which explains the roughly two centimetres of height difference across a day.
- Stability
- The anulus itself, plus the anterior longitudinal ligament checking extension and the posterior longitudinal ligament checking flexion. The latter is narrow in the lumbar spine, and that is precisely where a disc bulges posterolaterally.
- Palpation
- Not palpable. Segment height is judged from the distance between two spinous processes; the line between the highest points of the iliac crests indicates roughly L4 and serves as the counting landmark.
- Clinical
- A disc herniation is nucleus material breaking through the anulus, usually posterolaterally and usually at L4-L5 or L5-S1, irritating the nerve root below. Imaging says little without symptoms: bulging discs are just as common in people without pain. Degeneration by itself is ageing, not disease.
- Source
- Speciële anatomie van het houdings- en bewegingsapparaat (HU, 2013); BOKS anatomie Levensfasen (HU, 2024)