How does the knee function?
The knee is a complicated joint that is critical for our ability to walk and run. It is composed of 3 bones: the tibia (or shinbone), the femur (or thigh bone), and the patella (or kneecap). In order to ensure that these 3 bones have smooth interactions with each other, they are lined with cartilage. Cartilage is crucial for knee function. It lubricates the joint and creates a smooth surface so that the tibia, femur, and patella can all glide in a synchronized fashion with each other. Without proper cartilage, these three bones can rub directly against each other leading to “wear and tear.” This can affect function of the joint, can be debilitatingly pain, and lead to knee arthritis.
What is the meniscus?
The menisci are two C-shaped shock absorbers in each knee that are located between the tibia and femur within the knee joint. The menisci play a crucial role in protecting the knee joint. They are shock absorbers critical to the long term health and function of the knee. When viewed as a cross section, they are wedge shaped. Their wedge shape allows them to create a perfect fit between the round end of the femur and the flat edge of the tibia within the joint. This fit allows for an even distribution of forces and minimizes regions of high contact pressure. The menisci have many more important roles in the knee, but their ability to absorb forces between the thigh bone and shin bone is the most crucial.
How do the menisci work?
The menisci have a unique composition of protein fibers that allow them to absorb forces. They have parallel fibers that expand circumferentially. They also have fibers that intersect these circumferential fibers at a 90-degree angle. Together, this creates a mesh-like honeycomb network. When you walk the femur (thigh bone) presses down on the tibia (shin bone). The menisci are between the two and will get squeezed as well. When the menisci are being compressed, a portion of the force is pushed outwards away from the knee joint due to this unique protein fiber configuration. By reducing the amount of force that is transmitted from the femur to the tibia, the menisci will protect the cartilage in the knee. Over years and decades, this cumulative protective effect is crucial. It will delay or prevent the onset of severe symptomatic arthritis.
How common are meniscus tears?
Meniscus tears can be acute, meaning they happen suddenly from a single injury, or degenerative, meaning they happen gradually over time with general wear and tear. 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?
Acute 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, when the knee is flexed beyond its normal range of motion (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 horizontal 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 and has an adequate blood supply to facilitate healing. The Red-White zone is the transitional area in the middle with an intermediate blood supply and capacity for healing. Finally, the White zone is the innermost part 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, knee 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.
Dr. Jorge Chahla specializes in the treatment of complex knee, hip, and all sports related injuries. He is a pioneer in cartilage restorations and minimally invasive techniques. Dr. Chahla has orthopedic clinics in Chicago, Naperville, Oak Brook, and Munster Indiana. Contact Dr. Chahla to schedule a consultation today.
At a Glance
Dr. Jorge Chahla
- Triple fellowship-trained sports medicine surgeon
- Performs over 500 surgeries per year
- Assistant professor of orthopedic surgery at Rush University
- Learn more