Given what we put our knees through every day, it’s not surprising that most people have had minor knee problems at one time or another. And knee problems can develop from normal wear and tear, doing chores around the house, recreational activities, or any activity that results in a twisting injury or fall.

The knee is the largest joint in the body. It’s a “hinge” type joint that can also swivel on its axis, and the upper and lower bones of the knee are separated by two disks (called menisci). The upper leg bone (femur) and the lower leg bones (tibia and fibula) are connected by ligaments, tendons, and muscles. The surface of the bones inside the knee joint is covered by cartilage, which absorbs shock and provides a smooth, gliding surface for joint movement.

Even seemingly minor injuries to the knee can take weeks or even months to heal. Recovery times depend on the severity of the injury, your age, physical health, and what constitutes a full recovery for you — whether you’re happy to garden again or you’re racing in marathons.

Here’s a look at four of the most common knee injuries diagnosed in the ER.

ACL Tear

Cause: One of four ligaments crucial to the stability of the knee, the ACL (anterior cruciate ligament) can tear because of common sports maneuvers, such as cutting, pivoting, and sudden turning. Falling off a ladder or stepping off a curb and landing the wrong way can also tear the ACL.
Diagnosis: Sometimes difficult to diagnose immediately after an injury because of the pain and swelling. Once that
subsides in a few days, a specialist can use specific maneuvers such as the Lachman test, which involves pulling the shinbone forward to feel if an ACL tear is present. But usually an MRI is necessary to thoroughly evaluate the extent of the injury.
Treatment: Medical care depends on the severity of the tear. The first step is RICE: Rest, Ice, Compression with an elastic bandage, and Elevation of the leg. Medications such as acetaminophen, ibuprofen, or naproxen can reduce pain and swelling. More serious injuries may require a splint or brace to immobilize the knee. A specialist might prescribe weeks or even months of physical therapy to help restore range of motion and strength. Most ACL tears require surgery for the knee to function properly.
Prevention: When you play sports, wear properly fitted protective equipment, such as knee braces if recommended by your doctor.

MCL Tear

Cause: The medial collateral ligament (MCL) connects the femur to the tibia along the inside of the knee. Injury normally occurs when force is exerted on the outside of the knee, which pushes the joint sideways. That places stress on the inside of the joint, resulting in ligament damage.
Diagnosis: Based on a physical exam and the patient’s description of how the injury occurred. As with an ACL injury, swelling might prevent a thorough examination in the early phases. A specialist may follow up with an MRI to assess the severity of the tear, which is graded on a scale from 1 to 3.
Treatment: The first step is RICE and pain-relieving, anti-inflammatory medication. More serious injuries might require a splint or brace. Most patients can return to sports within a few weeks after treatment with physical therapy. Surgery may be needed to repair grade 3 injuries in which the ligament is completely torn.
Prevention: Get into good shape before participating in sports, and do proper stretching exercises to warm up muscles before athletic activity. Skiers should make sure bindings are adjusted correctly to release if a twisting injury occurs.

Kneecap Dislocation

Cause: The triangular bone (patella) that covers the front of the knee slips out of place due to twisting or banging, or because of a genetic predisposition.
Diagnosis: Starts with a physical exam. An X-ray might be taken to see how the kneecap fits in its groove.
Treatment: Minor dislocations can be reduced back into place manually by a doctor or athletic trainer. If the problem recurs, as it does in up to half of all patients, Ellis says, surgery may be required.
Prevention: Rehab exercises, such as those that strengthen quadricep muscles, can prevent recurrences. A specialist might prescribe a brace specifically made to prevent dislocation. Use proper technique when exercising or playing sports. In some cases, dislocation may not be preventable, especially if you’re genetically predisposed.

Medial Meniscus Tear

Cause: There is damage to the C-shaped cartilage that curves around the inside of the knee and cushions the joint. This happens especially in sports when sudden changes in speed or side-to-side movements cause the cartilage to tear or from an impact on the outside of the knee. Degeneration due to aging or repetitive use can also be the culprit.
Diagnosis: A physical exam will include a McMurray test, which involves bending the knee to assess flexibility. An X-ray might reveal degenerative or arthritic changes to the bones, or an MRI may be necessary.
Treatment: Small tears can be healed with RICE, anti-inflammatory meds, electrotherapy (ultrasound or laser therapy), and/or rehab exercises. More serious damage may need to be repaired in surgery.
Prevention: Keep the muscles around the knee in top condition with stretching and strengthening exercises. Work on the strength and flexibility of all the muscle groups in the leg.