A knee sprain occurs when one or more knee ligaments is stretched or torn—often from bending, twisting, a sudden jolt, or direct impact.
There are four main ligaments in the knee that can be sprained.
1. Medial collateral ligament (MCL)
The MCL is a supporting ligament found on the inside of the knee. The ligament itself runs from the lower inside of the thighbone to the upper inside of the shin. Injury occurs when stress or force is applied to the outside of the knee, when it is still bent or pivoting.
MCL injuries are particularly concerning for football and soccer players, as well as skiers. This added risk is due to the bending, twisting, and turning movements involved in these activities. A football tackle to the side may cause this injury. It can also happen when a skier speeds down a mountain and falls without changing positions.
Feeling a “pop” or shift in the knee, or noticing swelling soon after the injury, are indications of an MCL tear.
2. Anterior cruciate ligament (ACL)
ACL injuries are a prevalent sports injury, especially for female athletes. There are over 200,000 ACL injuries reported each year,1 occurring mostly from playing basketball, soccer, skiing, or football. Unlike PCL or LCL injuries, approximately 70% of ACL injuries are not contact related.1
ACL injuries tend to occur when an athlete is:
- Quickly stopping or decelerating
A popping sensation at the time of injury is typical, and immense swelling develops in the following hours.
Other ligaments are usually injured as well when an ACL injury occurs from direct contact to the side of the knee. The “unhappy triad,” for example, is an injury involving the ACL, MCL, and medial meniscus, or cartilage in the knee.
3. Posterior cruciate ligament (PCL)
The PCL ligament is located at the back of your knee, and helps connect the thighbone to the shinbone. PCL sprains are uncommon and often occur in conjunction with additional knee injuries, such as bone bruises or cartilage and ligament injuries.
Direct impact causes PCL sprains. In athletics, this means falling with a bent knee, or twisting or hyperextending the knee. While PCL sprains are uncommon, Reggie Bush and Felix Jones are among the professional football players who have experienced a PCL injury.
PCL tears occur more frequently in these sports:
The severity of a PCL sprain ranges; typical symptoms include knee pain, swelling, and instability in the knee.
4. Lateral collateral ligament (LCL)
The LCL runs alongside the outside of the knee: from the bottom of the thighbone to the top of the lower leg. While the LCL helps stabilize the knee, it is also prone to injury. This type of injury can happen as a result of:
- Direct contact to the inner knee
- Twisting the knee
- Repetitive actions over time
Symptoms can vary, but typically include:
- Instability in the knee
- Pain, swelling, and tenderness in or around the knee
- Locking sensation in the joint upon movement
LCL injuries often occur as a result of football, basketball, or downhill skiing, among other sports demanding quick directional changes.
Since 55% of sports injuries affect the knee,2 it is important to be aware of and know your risk factors for frequent knee injury sprains.