The knee joint manages immense forces, making it prone to various injuries. While muscles and bone can sustain a contusion, the crescent-shaped cartilage within the knee requires a precise understanding of injury mechanics. This article clarifies the distinction between a bruise and the primary injury sustained by this specialized tissue, addressing the fundamental question of whether the meniscus can be bruised or is only capable of tearing.
Anatomy and Function of the Meniscus
The knee contains two menisci, specialized pads of fibrocartilage situated between the thigh bone (femur) and the shin bone (tibia). The medial meniscus is C-shaped and on the inside of the knee, while the lateral meniscus is semi-circular and on the outside. Both are crucial for distributing the body’s weight across the joint surfaces.
The menisci act primarily as shock absorbers, cushioning the impact of movements like running and jumping. They increase the contact area between the bones, reducing stress on the articular cartilage. They also contribute to joint stability and facilitate the distribution of lubricating fluid.
This fibrocartilaginous tissue is characterized by a unique architecture that determines its injury patterns. The outer portion, known as the “red zone,” receives a limited blood supply from the joint capsule. The inner two-thirds, called the “white zone,” is largely avascular, meaning it lacks a direct blood supply.
Can the Meniscus Sustain a Bruise?
A traditional bruise, or contusion, is defined by the rupture of small blood vessels, leading to localized bleeding and discoloration. Given the meniscal anatomy, a true contusion is generally not possible across the majority of the structure. The large, inner white zone is avascular, lacking the blood vessels necessary to rupture and cause a bruise.
However, the outer red zone does possess a blood supply. In the setting of severe trauma, a localized injury without a full tear can occur, which radiologists sometimes call “meniscal contusion” or post-traumatic meniscal edema. This diagnosis is characterized by an amorphous signal change seen on a Magnetic Resonance Imaging (MRI) scan, representing fluid accumulation or localized tissue disruption.
This meniscal edema is frequently found alongside a subchondral bone contusion, or bone bruise, resulting from the knee bones forcefully compressing one another. The pain experienced is typically a result of this associated bone bruising or damage to the surrounding vascularized tissue, not the avascular cartilage itself. Unlike a tear, this localized edema often resolves over time with rest and conservative management.
Understanding Meniscus Tears: Types and Causes
Since true bruising is rare, the primary structural injury is a tear, which occurs through two distinct mechanisms. Acute, traumatic tears typically affect younger, active individuals and result from a forceful twisting or pivoting motion while the foot is planted. These injuries often happen during sports involving sudden changes in direction, such as soccer, basketball, or skiing.
The configuration of the tear is highly variable, including radial tears, horizontal cleavage tears, and the more severe bucket-handle tear. A bucket-handle tear is a large, displaced fragment that can cause the knee to mechanically lock or catch, preventing full extension. The specific tear pattern and its location within the red or white zone dictates the potential for healing and necessary treatment.
Degenerative tears are the second major category, common in individuals over the age of forty. These tears result from a slow breakdown of the tissue due to age-related wear and tear, rather than a single traumatic event. They can be caused by a seemingly innocuous action, such as an awkward twist when getting out of a chair or rising from a squatting position.
Diagnosis and Recovery Options
A healthcare provider begins the diagnostic process with a physical examination, including specific maneuvers designed to stress the menisci. The McMurray test, for example, involves bending and rotating the knee to elicit a painful click or clunk suggesting a tear. However, the definitive diagnosis and precise tear pattern relies on advanced imaging.
Magnetic Resonance Imaging (MRI) is the preferred method, providing detailed cross-sectional images of the soft tissues within the joint. MRI allows clinicians to differentiate a simple degenerative change from an unstable tear. It also assesses if the injury is in the vascular red zone, which has a higher capacity for natural healing.
Treatment is guided by the tear’s size, location, and the patient’s symptoms. Non-operative management, utilizing the RICE protocol (Rest, Ice, Compression, and Elevation) and physical therapy, is often recommended for small, stable tears or most degenerative tears. If the tear is large, unstable, or located in the vascular red zone, arthroscopic surgery may be performed to either repair the torn tissue or remove the unstable fragment in a procedure called a meniscectomy.