sprain
Meaning of sprain: The injury of a joint pushed past its range, damaging the bands that hold one bone to the next.
Definition of sprain
A sprain is an injury to a ligament, one of the tough fibrous bands joining bone to bone across a joint. It happens when the joint is forced beyond its normal range and the ligament is stretched or torn. Swelling, bruising, tenderness directly over the ligament and a sense that the joint is unsteady are the usual features, and the ankle is much the commonest site.
How does a sprain differ from a strain?
By the tissue damaged. A sprain injures a ligament, which joins one bone to another and limits how far a joint can travel. A strain injures a muscle or the tendon tying that muscle to bone, and those tissues move the joint rather than restraining it. The mechanisms differ to match: a sprain follows a joint forced past its limit, usually a twist or an awkward landing, while a strain follows a muscle stretched under load. Ligaments are built mainly from collagen fibers packed in parallel bundles, which resist pulling along their length and tear when forced sideways.
How are sprains graded?
By how much of the ligament has failed and whether the joint still holds together when it is tested. The grades describe a continuum rather than three separate injuries, and the boundary between them is a matter of judgment.
| Grade | Damage to the ligament | Effect on the joint |
|---|---|---|
| Grade one | Fibers stretched, structure intact | The joint holds firm |
| Grade two | Part of the ligament torn through | Some abnormal movement appears |
| Grade three | The ligament torn completely | The joint gives way under testing |
Why can a sprain hurt as much as a broken bone?
Ligaments carry a dense supply of nerve endings, including the receptors reporting joint position, so tearing one produces pain out of proportion to the amount of tissue involved. The inflammation that follows adds swelling, heat and further tenderness within hours. Pain and swelling therefore say little about severity, and a completely torn ligament sometimes hurts less than a partial tear once the torn fibers stop signaling. That overlap is why imaging is used to separate the possibilities, with plain films showing bone and MRI showing the ligaments themselves.
Also known as
Used in a sentence
The ankle sprain involved the ligaments on the outer side of the joint.
Good to know
Pain and swelling after a twisted joint track poorly with severity, since a completely torn ligament can hurt less than a partial tear once the torn fibers stop signaling.