The knee is the most commonly injured joint by adolescent athletes with an estimated 2.5 million sports-related injuries annually. The knee is comprised of numerous structures that make up and stabilize the joint. The main structures, and the most well known, are the femur, tibia, and the patella (or kneecap). These bones are surrounded by a variety of ligaments and tendons that stabilize the joint. In addition to the ligaments and tendons, a structure called the articular capsule surrounds the joint in layers to stabilize and support the knee.
The knee capsule consists of two main layers, an outer layer and an inner layer. The outer layer is made up of a tough, fibrous membrane that is made up of ligament tissue. The inner layer is made up of a synovial membrane, which secretes synovial fluid. The knee capsule also contains bursae, which are fluid-filled sacs, and a fat pad located behind the patella.
The primary function of the outer layer of the knee capsule is to provide stability to the joint by holding the bones of the knee in their correct positions. The synovial membrane of the inner layer secretes a viscous material called synovial fluid. This synovial fluid functions to lubricate the joint, helping to reduce friction and irritation of the bones, ligaments, and tendons when the knee joint moves. Overall, the knee capsule allows the full knee to have flexion, or bending motion, due to the folds within the capsule.
Injury to the knee capsule can be caused by a variety of mechanisms. However, most commonly, the causes are:
These two mechanisms can also increase the risk of injury if performed simultaneously. Other mechanisms of injury may include:
Symptoms of a knee capsule strain injury may include:
Most often, pain from an injury to the knee capsule will get worse with activity and will be relieved with rest. Additionally, pain can be worsened by bending the knee, weight-bearing, or walking. Pain can range from mild to severe depending on the severity of the injury.
Possible home treatments for a knee capsule strain injury can include:
All knee injuries should be evaluated by a doctor as soon as possible, especially if no improvement is seen with home treatment. A physician may be able to prescribe physical therapy which may consist of:
There should be a gradual return to normal activities after injury. In severe cases, surgery may be necessary to repair the damage.
The following tips may be used to help prevent knee capsule strain injury:
Practicing regular injury prevention techniques will help keep your joints healthy throughout the course of a lifespan.