A sprain is a soft tissue injury of the ligaments within a joint, often caused by a sudden movement abruptly forcing the joint to exceed its functional range of motion. Ligaments are tough, inelastic fibers made of collagen that connect two or more bones to form a joint and are important for joint stability and proprioception, which is the body's sense of limb position and movement. Sprains may be mild (first degree), moderate (second degree), or severe (third degree), with the latter two classes involving some degree of tearing of the ligament. Sprains can occur at any joint but most commonly occur in the ankle, knee, or wrist. An equivalent injury to a muscle or tendon is known as a strain. The majority of sprains are mild, causing minor swelling and bruising that can be resolved with conservative treatment, typically summarized as RICE: rest, ice, compression, elevation. However, severe sprains involve complete tears, ruptures, or avulsion fractures, often leading to joint instability, severe pain, and decreased functional ability. These sprains require surgical fixation, prolonged immobilization, and physical therapy.
Signs and symptoms Pain Swelling Bruising or hematoma caused by broken blood vessels within the injured ligament Joint instability Difficulty with bearing weight Decreased functional ability or range of motion of the injured joint Ligament rupture may cause a cracking or popping sound at the time of injury Knowing the signs and symptoms of a sprain can be helpful in differentiating the injury from a strain or simple fracture. Strains typically present with pain, cramping, muscle spasm, and muscle weakness, and fractures typically present with bone tenderness, especially when bearing weight.
Causes Acute sprains typically occur when the joint is abruptly forced beyond its functional range of motion, often in the setting of trauma or sports injuries. The most common cause of sprains in general is repetitive movements (overuse).
Mechanism Ligaments are collagen fibers that connect bones together, providing passive stabilization to a joint. These fibers can be found in various organizational patterns (parallel, oblique, spiral, etc.) depending on the function of the joint involved. Ligaments can be extra-capsular (located outside the joint capsule), capsular (continuation of the joint capsule), or intra-articular (located within a joint capsule). The location has important implications for healing as blood flow to intra-articular ligaments is diminished compared to extra-capsular or capsular ligaments. Collagen fibers have about a 4% elastic zone where fibers stretch out with increased load on the joint. However, exceeding this elastic limit causes a rupture of fibers, leading to a sprain. It is important to recognize that ligaments adapt to training by increasing the cross-sectional area of fibers. When a ligament is immobilized, the ligament has been shown to rapidly weaken. Normal daily activity is important for maintaining about 80–90% of the mechanical properties of a ligament.
Risk factors Fatigue and overuse High-intensity contact sports Environmental factors Poor conditioning or equipment Age and genetic predisposition to ligament injuries Lack of stretching or "warming up", which when performed properly increases blood flow and joint flexibility
Diagnosis Sprains can often be diagnosed clinically based on the patient's signs and symptoms, mechanism of injury, and physical examination. However, x-rays can be obtained to help identify fractures, especially in cases of tenderness or bone pain at the injured site. In some instances, particularly if the healing process is prolonged or a more serious injury is suspected, magnetic resonance imaging (MRI) is performed to look at the surrounding soft tissue and ligaments.
Classification First degree sprain (mild) – There is minor stretching and structural damage to the ligament, leading to mild swelling and bruising. Patients typically present without joint instability or decreased range of motion of the joint. Second degree sprain (moderate) – There is a partial tear of the affected ligament. Patients typically experience moderate swelling, tenderness, and some instability of the joint. There may be some difficulty bearing weight on the affected joint. Third degree sprain (severe) – There is a complete rupture or tear of the ligament, sometimes avulsing a piece of bone. Patients typically experience severe joint instability, pain, bruising, swelling, and inability to apply weight to the joint.
Joints involved Although any joint can experience a sprain, some of the more common injuries include the following:
Ankle – Sprains most commonly occur at the ankle and can take longer to heal than ankle bone fractures. Most sprained ankles usually occur in the lateral ligaments on the outside of the ankle. Common causes include walking on uneven surfaces or during contact sports. See sprained ankle or high ankle sprain for more details. Inversion Ankle Sprain – injury that occurs when ankle rolls inward Eversion Ankle Sprain – injury that occurs when ankle rolls outward Toes Turf toe (metatarsophalangeal joint sprain) – forced hyperextension of the big toe upwards, especially during sports (initiating a sprint on a hard surface)
Knee – Sprains commonly occur at the knee, especially following intense pivoting on a planted leg during contact sports (American football, football, basketball, pole vaulting, softball, baseball and some styles of martial arts). Anterior cruciate ligament (ACL) injury Posterior cruciate ligament (PCL) injury Medial collateral ligament (MCL) injury Lateral collateral ligament (LCL) injury Superior Tibiofibular Joint Sprain – typically caused by a twisting injury to the joint connecting the tibia (shinbone) and fibula Patellar dislocation
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