The rectus femoris is a prominent muscle located in the anterior compartment of the thigh. It forms a significant part of the larger quadriceps femoris group. This muscle is unique among the quadriceps because it crosses both the hip and knee joints. Its name, “rectus,” comes from the Latin word for “straight,” reflecting its nearly vertical orientation down the thigh.
Anatomical Starting Points
The rectus femoris muscle distinguishes itself from the other quadriceps muscles by originating from the pelvis rather than the femur. It has two distinct tendinous origins, often referred to as heads: the straight head and the reflected head.
The straight head of the rectus femoris originates from the anterior inferior iliac spine (AIIS). This bony projection is found on the lower front part of the ilium, which is the largest and uppermost bone of the pelvis. The upper half of the AIIS specifically serves as the attachment point for this straight head.
The reflected head of the rectus femoris originates from a groove or ridge located just superior to the acetabulum. The acetabulum is the cup-shaped socket on the outer surface of the pelvis that forms the hip joint with the head of the femur. These two separate tendinous origins converge a short distance below their starting points to form the main body of the rectus femoris muscle.
Role and Connections
The rectus femoris plays a significant role in lower limb movement. The quadriceps collectively form the main bulk of the thigh and are considered among the most powerful muscles in the body.
The primary functions of the rectus femoris include extending the leg at the knee joint and flexing the thigh at the hip joint. Its ability to extend the knee is shared with the other quadriceps muscles, which is important for actions like kicking, jumping, and walking. Due to its origin on the pelvis and its path across the hip joint, it also contributes to lifting the thigh towards the abdomen.
The rectus femoris, along with the vastus medialis, vastus lateralis, and vastus intermedius, joins to form a common quadriceps tendon. This robust tendon then inserts into the patella, or kneecap. From the patella, the connection continues via the patellar ligament to the tibial tuberosity, which is a bony prominence on the front of the tibia, or shin bone.