The articularis genus muscle is a small, often overlooked muscle located in the front of the thigh, just above the knee. It is a skeletal muscle that plays a role in the mechanics of the knee joint. While its precise function has been an area of ongoing research, its general association with the knee joint is recognized.
Location and Structure
The articularis genus muscle originates from the anterior surface of the lower femur (thigh bone). It is situated deep to the vastus intermedius muscle, one of the four quadriceps muscles. The muscle is typically small, flat, and triangular, though it can vary and sometimes consists of several separate bundles.
The fibers of the articularis genus extend downwards to insert into the suprapatellar bursa and the synovial membrane of the knee joint capsule. The suprapatellar bursa is a fluid-filled sac above the kneecap (patella). Innervation for the articularis genus comes from branches of the femoral nerve, specifically from spinal nerve roots L2-L4. This muscle generally measures 1.5 to 3 cm in width. It can be distinct from the vastus intermedius or occasionally blend with it.
Role in Knee Movement
The primary function attributed to the articularis genus muscle is its action during knee extension. As the knee straightens, this muscle pulls the suprapatellar bursa and attached knee joint capsule superiorly (upwards). This upward movement helps prevent the bursa and synovial membrane from being pinched or trapped between the patella and femur during articulation.
This retraction contributes to smooth patellar tracking, the proper gliding motion of the kneecap within its femoral groove. While some research suggests its architectural parameters may not allow it to act independently, it is believed to work with the vastus intermedius and vastus medialis muscles. This cooperative action ensures fluid knee joint movement and prevents soft tissue impingement during extension.
Clinical Relevance
The articularis genus muscle has implications in various knee conditions, particularly anterior knee pain. Dysfunction or weakness can contribute to patellar tracking issues, where the kneecap does not move smoothly in its femoral groove. This can be a factor in conditions such as patellofemoral pain syndrome.
The muscle’s role in retracting the suprapatellar bursa is significant in preventing impingement. If it fails to function properly, this can lead to painful inflammation of the bursa, known as suprapatellar bursitis. In post-surgical knee recovery, such as after total knee arthroplasty (TKA) or anterior cruciate ligament (ACL) reconstruction, restoring full knee extension is a goal. The articularis genus contributes to full extension by ensuring the bursa and capsule are not entrapped.
Persistent anterior knee pain is common after TKA, and patellofemoral problems frequently lead to reoperation. Similarly, patellofemoral pain is a common complication following ACL reconstruction, often linked to quadriceps weakness and flexion contracture. Rehabilitation exercises aimed at regaining complete knee extension often indirectly benefit the articularis genus. Because of its small size and deep location, the articularis genus is sometimes overlooked in diagnosis and treatment.