The knee is a joint that manages the complex tasks of weight-bearing and mobility, allowing for movements like bending, straightening, and slight rotation. The knee is anatomically divided into three distinct compartments to organize its structure and function. This division helps physicians isolate the source of specific pain or mechanical issues. These compartments are the medial, the lateral, and the patellofemoral areas, each handling different aspects of the joint’s overall load and movement.
Defining the Medial Compartment
The medial compartment is the space on the inner side of the knee, positioned closest to the body’s midline. This area is defined by the meeting surfaces of the femur (thigh bone) and the tibia (shin bone). Specifically, the compartment is bounded by the medial femoral condyle, which is the rounded end of the femur, and the medial tibial plateau, which is the flattened, weight-bearing surface of the tibia. This inner section of the knee is subjected to significant forces, as it naturally bears a large proportion of the body’s weight during activities like standing and walking.
Key Structures Within the Compartment
Several structures within this space work together to facilitate smooth and stable movement. The ends of the bony surfaces—the medial femoral condyle and the medial tibial plateau—are covered in articular cartilage. This smooth, slick tissue provides a low-friction surface, enabling the bones to glide against one another during knee movement.
The medial meniscus, a C-shaped piece of fibrocartilage, sits between the femur and the tibia. It acts as a shock absorber and helps distribute compressive loads across the joint surface. The meniscus also stabilizes the knee by improving the fit between the rounded femur and the flatter tibial plateau. The medial collateral ligament (MCL) runs along the inner side of the knee, providing stability by resisting forces that push the knee inward.
Common Conditions Affecting the Medial Knee
The most frequent condition affecting this joint is medial compartment osteoarthritis (MCOA). This type of arthritis occurs when the load-bearing articular cartilage lining the bones begins to wear away. Because the medial compartment typically carries a greater share of the body’s weight, it is the most common site for knee osteoarthritis, often accounting for 60% to 70% of all knee OA cases. The loss of cartilage eventually leads to bone-on-bone friction, causing pain, stiffness, and a grating sensation known as crepitus.
Another prevalent issue is a tear of the medial meniscus, which can occur traumatically from a sudden twisting injury or degeneratively as the tissue weakens with age. Degenerative tears are frequently seen alongside MCOA, as the unstable joint environment places more stress on the meniscal tissue. A torn meniscus can cause mechanical symptoms, such as the knee locking or catching, and localized pain along the inner joint line. Both MCOA and medial meniscus tears are often exacerbated by activities involving repetitive loading, such as running or climbing stairs.
Initial Management and Treatment Options
Initial treatment for conditions of the medial compartment focuses on non-surgical methods aimed at reducing pain and improving function. Physical therapy is a primary approach, utilizing specific exercises to strengthen the quadriceps and hamstring muscles, which improves knee stability and load mechanics. Weight management is also effective, as reducing body mass directly lowers the compressive forces placed on the medial compartment surfaces.
Non-steroidal anti-inflammatory drugs (NSAIDs) can be used to manage pain and reduce localized swelling within the joint. Bracing may be recommended, particularly the use of an unloader brace, which is designed to shift pressure away from the damaged medial compartment to the lateral side. In cases of persistent symptoms, a physician may suggest an injection of a corticosteroid for temporary pain relief or a hyaluronic acid injection to improve joint lubrication.