The knee joint relies on specialized tissue to function smoothly, allowing movement and bearing the body’s weight. Within the joint, two crescent-shaped pieces of cartilage, known as the menisci, act as shock absorbers between the thigh bone and the shin bone. Meniscal tears are common injuries, often resulting from trauma or gradual wear. This article focuses on the radial tear, a specific and problematic form of this injury.
Understanding the Meniscus
The menisci are two wedge-shaped structures of fibrocartilage found in each knee, one medial (inside) and one lateral (outside). These structures increase the contact area between the leg bones, helping to distribute the load across the knee joint. They also absorb shock, contribute to joint stability, and protect the articular cartilage.
The meniscal tissue’s ability to heal is directly related to its non-uniform blood supply. The outer one-third, known as the “red zone,” receives blood from the joint capsule and has the highest potential for healing. The inner two-thirds, the “white zone,” is avascular, meaning it lacks a direct blood supply and has a poor capacity for self-repair.
Defining the Radial Tear
A radial tear is a specific meniscal injury characterized by a split that runs perpendicular to the length of the meniscus, similar to a wheel spoke. This tear typically starts at the inner, free edge and extends outward toward the peripheral attachment. The radial orientation directly severs the circumferential collagen fibers that form the bulk of the meniscal tissue.
This severance is damaging because it destroys the mechanism known as “hoop stress,” the meniscus’s primary function in load distribution. When the knee is loaded, intact circumferential fibers convert vertical pressure into outward tension, much like a hoop or belt. A complete radial tear disrupts this tension, causing the meniscus to lose its ability to function as a shock absorber. A complete radial tear can result in a loss of function similar to that of a total meniscectomy, leading to significantly increased contact pressures on the joint cartilage.
Recognizing Symptoms and Diagnosis
Symptoms of a radial meniscus tear include sharp pain, especially along the joint line, and often rapid swelling. Patients experience pain when twisting, squatting, or bearing weight on the injured leg. Mechanical sensations like clicking, popping, or the knee “catching” or “locking” suggest a fragment of torn cartilage is interfering with joint motion.
Diagnosis begins with a physical examination, where a physician checks for joint line tenderness and tests the knee’s range of motion. Specific maneuvers, such as the McMurray test, are performed to reproduce symptoms by flexing, extending, and rotating the knee. While the physical exam can strongly suggest a meniscal tear, Magnetic Resonance Imaging (MRI) is the definitive tool used to confirm the injury. The MRI provides detailed images that confirm the tear’s radial type, its exact location, and the extent of the damage, crucial for determining the appropriate treatment plan.
Treatment Options and Recovery
Management of a radial tear follows two paths: non-surgical care or surgical intervention. Non-surgical treatment, involving rest, ice, compression, and elevation (RICE), along with physical therapy and pain medication, may be considered for smaller, stable tears or those located in the well-vascularized “red zone.” Physical therapy focuses on strengthening the surrounding muscles to provide external support.
Surgical management is often necessary for unstable or complete radial tears, particularly those extending into the avascular area. The preferred approach is meniscal repair, which involves stitching the torn edges back together to restore the tissue’s hoop stress function. This procedure is generally favored in younger patients to preserve the meniscus and protect the joint cartilage from long-term damage.
If the tear is complex, irreparable, or located in the white zone, a partial meniscectomy may be performed. This involves trimming and removing only the damaged, unstable tissue. Recovery from a meniscectomy is typically faster, often allowing a return to light activity within a few weeks. In contrast, a meniscal repair requires a much longer rehabilitation period, sometimes three to six months, for the tissue to heal fully before bearing significant load.