Knee Capsule Strains

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, 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. This secretes synovial fluid. The knee capsule also contains bursae. These are fluid-filled sacs, and a fat pad located behind the patella.

Image of the Anatomy of the knee.

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.

Causes of Knee Capsule Strain Injury

Injury to the knee capsule can be caused by a variety of mechanisms. However, most commonly, the causes are:

• Hyperextension of the knee (most likely to injure the posterior capsule).
• External rotation.

These two mechanisms can also increase the risk of injury if performed simultaneously. Other mechanisms of injury may include:

• Planting the foot and twisting the knee.
• Overuse.
• A direct blow to the knee.

Symptoms of a Knee Joint Capsule Strain

Symptoms of a knee joint capsule strain injury may include:

• Sharp or achy pain.
• Swelling.
• Stiffness.
• Locking.
• Decreased range of motion.
• Tenderness in the joint.

Image showing the anatomy of the knee capsule.

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. 

Treatment of Knee Capsule Strain

Possible home treatments for a knee capsule strain injury can include: 

• The RICE method:
  • Rest.
  • Ice.
  • Compression.
  • Elevation.
• NSAIDs: Nonsteroidal anti-inflammatory drugs (pain medication such as ibuprofen).

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:

• Strengthening and stretching exercises 24-48 hours after minor injuries.
• Range of motion exercises.
• Education of a home exercise program.
• Pain management.

There should be a gradual return to normal activities after injury. In severe cases, surgery may be necessary to repair the damage.

Prevention of Knee Joint Capsule Strain

The following tips may be used to help prevent knee capsule strain injury:

• Proper warm-up including stretching before and after activity.
• Avoid sudden changes in intensity in activities.
• Wear shoes that fit properly and provide good traction.
• Maintain a healthy weight to reduce excess stress on the knee.
• Use knee guards when contact may be involved.
• Maintain strong, healthy leg muscles including calves, quadriceps, and hamstrings.
• Maintain proper technique, especially with weight-bearing activities.

Practicing regular injury prevention techniques will help keep your joints healthy throughout the course of a lifespan. 

Related Articles: Knee Arthritis and Rheumatoid Arthritis

By: Jon Stiffler, PTA

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