A sprain happens when a ligament, the tough band of tissue connecting two bones at a joint, gets stretched or torn beyond its normal range. The most common cause is a sudden twist, fall, or impact that forces a joint into an unnatural position. Ankles, wrists, knees, and thumbs are the joints most frequently affected.
How a Ligament Gets Damaged
Ligaments are designed to stabilize joints while allowing a controlled range of motion. When a sudden force pushes a joint past that range, the collagen fibers inside the ligament begin to stretch and fray. If the force is strong enough, fibers tear partially or completely. This is different from a strain, which involves muscles or tendons rather than ligaments.
The severity depends on how far the ligament is pushed. A Grade 1 sprain means the ligament is stretched or slightly torn, with mild swelling and tenderness. You can usually still walk or use the joint. A Grade 2 sprain involves a partial tear, producing moderate pain, swelling, bruising, and noticeable instability. A Grade 3 sprain is a complete rupture. The joint feels unstable, swelling is severe, and putting weight on it or using it normally is typically impossible.
The Movements That Cause Sprains
Most sprains result from one of a few predictable movements. In the ankle, the overwhelming majority happen when the foot rolls inward (inversion), stressing the ligaments on the outside of the ankle. Stepping on an uneven surface, landing awkwardly from a jump, or pivoting quickly during a sport can all force this motion. The weakest of the outer ankle ligaments tears first, and if the force continues, the next ligament in line follows.
Wrist sprains almost always come from falling onto an outstretched hand. When you instinctively reach out to catch yourself, your body weight drives through the wrist at an angle it isn’t built to absorb. The specific ligaments that get damaged depend on the exact position of your hand and wrist at the moment of impact. Knee sprains often follow a sudden change of direction, a direct blow to the side of the knee, or a hard landing that forces the joint to twist or bend the wrong way. Thumb sprains frequently happen during skiing or ball sports when the thumb gets caught and pulled backward.
The common thread is a sudden, forceful movement that exceeds what the ligament can handle. Gradual overloading or repetitive stress tends to produce different types of injuries. Sprains are almost always acute events.
Risk Factors That Make Sprains More Likely
Some people are more vulnerable to sprains than others, and the reasons fall into two categories: things about your body and things about your environment.
Body-Related Factors
A previous sprain is the single strongest predictor of a future one. Once a ligament has been stretched or torn, the healed tissue is often less organized than the original, leaving the joint slightly less stable. Weak muscles around a joint also increase risk, since muscles act as a secondary stabilization system. Poor balance and slow reflexes mean your body is less able to correct a misstep before the ligament takes the full load.
Joint hypermobility, a heritable condition where joints move beyond the typical range, has a more nuanced relationship with sprains than you might expect. Research published in BMJ Open Sport and Exercise Medicine found that hypermobile individuals were actually less likely to sustain ligament sprains across all sports studied. However, they were significantly more prone to joint dislocations, which occurred exclusively in the hypermobile group. So extra flexibility may protect against the stretching mechanism of sprains while increasing the risk of joints popping entirely out of place.
Environmental Factors
The surface you move on matters. A systematic review of lower extremity injuries found that foot and ankle injury rates are consistently higher on artificial turf compared to natural grass, across both older and newer turf generations. The likely explanation is that turf grips footwear more firmly, preventing the small amount of slide that natural grass allows when you plant and pivot. For knee injuries the picture is more mixed: rates are generally similar between surfaces, though elite football players show higher knee injury rates on turf.
Footwear plays a related role. Shoes with high traction on the wrong surface, or shoes that don’t adequately support the ankle, change the forces acting on your ligaments during quick movements. Fatigue is another environmental factor in practice: tired muscles respond more slowly and absorb less force, leaving ligaments exposed during the final minutes of a game or a long hike on rough terrain.
What Happens Inside the Joint After a Sprain
Ligament healing follows three overlapping phases. The inflammatory phase begins immediately. Within the first day, the area floods with immune cells that clear damaged tissue and signal for repairs. Swelling, heat, redness, and pain are all part of this process, not a complication of it. This phase peaks around days one through five.
The proliferative phase follows, roughly from days three through eleven. New blood vessels form to supply the area, and specialized cells begin laying down fresh collagen to bridge the torn fibers. The tissue at this point is fragile and disorganized, which is why re-injury is so easy during this window.
The remodeling phase is the longest by far. The new collagen gradually reorganizes and strengthens, but this process continues for months. Studies tracking ligament repair have found scar-like tissue still present two years after the initial injury. This is why a sprained ankle can feel “mostly fine” within weeks but remain subtly weaker and stiffer for much longer.
Recovery and Early Management
For decades, the standard advice was RICE: rest, ice, compression, elevation. Current guidelines have shifted toward a broader framework called PEACE and LOVE, introduced in 2019, which covers both the immediate aftermath and longer-term rehabilitation. The key differences are an emphasis on avoiding anti-inflammatory medications in the first few days (since inflammation is a necessary part of healing), introducing gentle movement and loading earlier than traditional protocols recommended, and addressing psychological factors like fear of re-injury that can delay recovery.
Grade 1 sprains typically resolve within one to three weeks. Grade 2 sprains often take three to six weeks before you can return to normal activity, though full ligament remodeling continues behind the scenes. Grade 3 sprains, where the ligament is completely torn, can require several months of rehabilitation and sometimes surgical repair, depending on the joint and the specific ligament involved.
Controlled, progressive loading during recovery is critical. Complete immobilization for extended periods weakens the surrounding muscles, reduces joint awareness, and produces a stiffer, less functional scar. Structured rehabilitation that gradually increases demand on the healing ligament leads to better tissue quality and a lower chance of spraining the same joint again.