What is the meniscus?
Each knee has two menisci, one on the inner portion and the other on the outer portion of the knee. They are small C-shaped pieces of cartilage between the tibia (shin bone) and femur (thigh bone) that function as shock absorbers. They also help distribute weight equally for balance and stability, and facilitate smooth and controlled movements of the knee.
How common are meniscus tears?
Meniscus tears can be acute, meaning that happen sudden from a single injury, or degenerative, meaning they happen gradually over time with general wear and tear. These tears tend to be more common in different age groups. Acute meniscus tears are very common knee injuries that frequently affect active individuals. In contrast, degenerative meniscus tears are more common in older individuals, affecting 6 out of 10 patients over age 65.
How do meniscus tears occur?
Meniscus tears are frequently the result of traumatic injuries and can occur during high-risk sports, including soccer, tennis and basketball. Typically, injuries mechanisms involve aggressive movements in which the knee twists or rotates during pivoting, kneeling, or squatting.
Degenerative tears occur from chronic wear and tear of the meniscus cartilage that accumulates with age. As patients age, the cartilage can become stiff and brittle. Tears can result from twisting motions or over hyper flexing the knee (excessive bending). Everyday activities including getting in and out of a car, squatting, and heavy lifting, can also cause tears.
Types of meniscus tears
There are many different types of meniscal tears. Broadly, tears can be described as partial thickness, meaning they only affect one side, or full thickness, meaning the tear goes all the way through the meniscus. Tears can be further described based on their appearance. Common types of traumatic tears include bucket handle tears, flap tears, and radial tears.
- Bucket handle tears are large, painful tears that cause significant swelling. They are called bucket handle tears because the long strip of torn tissue is separated from the rest of the meniscus and resembles the handle of a bucket. They are most commonly seen in young athletes, under age 35.
- Radial tears are the most common type of tear. These tears occur in an area of the meniscus where there is no blood supply, which limits the capacity for healing. For that reason, surgery is usually required.
- Horizontal tears can frequently be surgically repaired if they occur in an area of the meniscus that has good blood supply to facilitate healing after the repair.
- Flap tears are less common. When they cause symptoms, surgery can be performed to remove the flap.
- Tears are described as “complex tears” when they have more than one tear pattern. Typically, these involve both a radial and horizonal tear.
- Root tears – Approximately 10-20% of meniscus tears are root tears. These can be radial tears that occur within 1 cm of the meniscus attachment or bony avulsion of the root attachment. Root tears are can accelerate cartilage damage and can lead to early osteoarthritis.
- Ramp lesions are a specific type of meniscus injury that can be associated with ACL injuries. These are difficult to diagnose and require surgical examination with arthroscopy. Ramp lesions can cause pain, dysfunction, and potentially lead to instability.
The location of the tear
The location of the tear has a significant impact on the ability of the tear to heal and the corresponding treatment.
The meniscus has three zones of vascularity. The Red zone is the outer perimeter of the meniscus and has an adequate blood supply to facilitate healing. The Red-White zone is the transitional area in the middle of the meniscus with an intermediate blood supply and capacity for healing. Finally, the White zone is the innermost part of the meniscus with no blood supply and no ability to heal.
- Tears in the white zone are generally treated by removal of the meniscus, also called a meniscectomy.
- Tears in the red zone have a good blood supply which provides the necessary biological substances for healing following surgical repair.
- Tears in the red-white zone need to be assessed to determine whether surgical repair is required for healing.
What are the symptoms of a torn meniscus?
Common symptoms include: a popping sensation, localized pain and swelling on the inside or outside of the knee depending on the location of the tear. Other symptoms include stiffness, clicking, catching, or locking. Patients can also report instability, reduced range of motion, and difficulty walking.
Sometimes after 4-6 weeks, the knee will settle down. However, pain may return during daily activities including walking, running, and climbing stairs, with symptoms of intermittent swelling, instability, and locking of the knee. Over time, a torn meniscus can predispose the affected knee to the development of osteoarthritis.
How is a meniscus tear diagnosed?
The combination of a detailed history, comprehensive physical examination, x-rays, and an MRI is the key to successful diagnosis of a meniscus tear. Frequently, a torn meniscus can be diagnosed with a physical exam and special tests. X-rays cannot detect a tear, but will identify fractures, arthritis, and other conditions. An MRI can be ordered to confirm a diagnosis and provide an assessment of the extent of the damage, and any associated arthritic conditions.
The type of tear, size, and location will determine the course of treatment. Conservative management of small and partial tears may include rest, ice, compression, elevation, anti-inflammatory medications, and physical therapy. If pain and swelling do not resolve within 6 weeks, surgery may be indicated.
Other types of meniscal injuries such as ramp lesions require surgical repair. When the meniscus tear also involves an ACL injury, ACL reconstruction should be combined with ramp lesion repair. A standard rehabilitation protocol for ACL reconstruction will be recommended.
After surgery, the patient will be in a brace for six weeks. Range of motion exercises will begin quickly with the goal of achieving full extension, increasing range of motion, decreasing swelling, and regaining muscle strength and control. Return to sports will depend on the sport; however, generally takes 4-6 months.