The knee joint connects the thigh bone (femur) to the shin bone (tibia) and includes the kneecap (patella). Numerous muscles contribute to its function and stability, allowing for a wide range of motions. Understanding the muscles around the knee, particularly those on the medial, or inner, side, is important for overall knee well-being and preventing discomfort.
Understanding the Medial Knee Muscles
The medial aspect of the knee involves several muscles, with a primary group forming a structure known as the pes anserinus. This term, translating to “goose’s foot” in Latin, describes the conjoined tendons of three distinct muscles that insert on the anteromedial surface of the proximal tibia. The three muscles that contribute to the pes anserinus are the sartorius, gracilis, and semitendinosus.
The sartorius muscle originates from the anterior superior iliac spine of the hip bone and travels obliquely across the front of the thigh. Its tendon curves around the medial condyle of the tibia to join the pes anserinus insertion. The gracilis muscle is a long, thin muscle located in the inner thigh, originating from the pubic bone and extending down to insert on the medial tibia as part of the pes anserinus.
The semitendinosus muscle is one of the three hamstring muscles found at the back of the thigh, positioned posteromedially. It originates from the ischial tuberosity in the pelvis and inserts onto the medial surface of the tibia, contributing to the pes anserinus. Within the pes anserinus, the sartorius tendon is most anterior, the semitendinosus is most posterior, and the gracilis lies between them. Additionally, the vastus medialis obliquus (VMO), a part of the quadriceps muscle group, is located on the inner side of the thigh and inserts onto the medial border of the patella and the knee joint capsule.
Roles of Medial Knee Muscles
The muscles forming the pes anserinus perform several actions that contribute to both hip and knee movement. The sartorius muscle flexes, weakly abducts, and laterally rotates the thigh at the hip. At the knee, it flexes the leg and can medially rotate the leg when the knee is flexed.
The gracilis muscle primarily adducts the thigh, pulling the leg inward toward the midline of the body. It also assists in knee flexion and medial rotation of the leg at the knee joint, helping to stabilize the inner hip and thigh.
The semitendinosus muscle, as part of the hamstring group, extends the hip and flexes the knee. It also medially rotates the tibia on the femur when the knee is flexed. All three muscles of the pes anserinus collectively aid in tibial internal rotation and provide resistance against rotational and valgus (knock-knee) stresses, thus contributing to knee stability. The vastus medialis obliquus (VMO) is a component of the quadriceps that contributes to knee extension. Its specific fiber orientation also allows it to pull the patella medially, which is important for maintaining the kneecap’s proper alignment within the trochlear groove during knee flexion and extension.
Maintaining Medial Knee Health
Issues affecting the muscles on the inside of the knee can lead to discomfort and limitations in movement. A common condition is pes anserine bursitis or tendinopathy, which involves inflammation of the bursa or tendons located beneath the pes anserinus insertion. This condition often presents as pain and tenderness on the inner aspect of the leg, just below the knee joint.
Repetitive knee movements, such as those in running or stair climbing, can irritate the bursa and surrounding tendons. Factors like tight hamstrings, obesity, knee osteoarthritis, and abnormal knee alignment can increase the likelihood of developing pes anserine bursitis.
Another concern can be issues with the vastus medialis obliquus (VMO) muscle. Weakness or altered activity of the VMO can contribute to patellar mal-tracking, leading to instability and pain around the kneecap. This can result in conditions such as patellofemoral pain syndrome. Such problems can make daily activities like walking or using stairs challenging.
Caring for these muscles involves a combination of practices aimed at promoting flexibility and balanced strength. Regular stretching, particularly for the hamstring muscles, can help reduce tension that might contribute to pes anserine issues. Strengthening exercises, focusing on both the quadriceps, including the VMO, and the hamstrings, can improve overall knee support and stability. Maintaining a healthy body weight can lessen the stress on the knee joint and its associated soft tissues. Using proper body mechanics during physical activity and avoiding sudden increases in training intensity can also help prevent overuse injuries.