The inner thigh is a descriptive term commonly used to identify the area between the legs, extending from the groin down to the knee. While this phrase is understandable in everyday conversation, human anatomy uses precise terminology to define and classify this region based on its structure and function. The formal anatomical name allows for an exact discussion of the muscles, nerves, and vessels housed within this area.
Defining the Medial Thigh Region
The formal anatomical designation for what is commonly called the inner thigh is the Medial Compartment of the Thigh. This compartment is one of three major fascial divisions of the upper leg, separated from the anterior and posterior compartments by connective tissue membranes. It extends from the pubic and ischial bones of the pelvis downward toward the femur and tibia. The medial compartment is also frequently referred to as the Adductor Compartment, reflecting the primary function of the muscle group contained within it: adduction, the movement of pulling the leg toward the midline of the body.
The Core Adductor Muscle Group
Adductor Muscles
The Adductor Compartment is defined by the adductor group, which controls the position of the leg. The five primary muscles in this group are the Adductor longus, Adductor brevis, Adductor magnus, Gracilis, and Pectineus. The Adductor magnus is the largest and most powerful muscle, uniquely described as having both an adductor portion and a hamstring portion due to its dual functions. The Adductor longus is the most superficial and is often involved in groin strains, while the Adductor brevis lies deeper beneath it.
Innervation and Location
The Obturator nerve, which arises from the lumbar plexus, provides the primary nervous supply for nearly all muscles in this compartment. The nervous supply is not entirely uniform, however. The Pectineus muscle is typically innervated by the femoral nerve, and the hamstring portion of the Adductor magnus receives its supply from the tibial nerve. The Gracilis is a long, slender muscle that extends down to the tibia below the knee joint.
Primary Role in Movement and Stability
The main mechanical job of the medial thigh muscles is hip adduction, pulling the leg toward the body’s midline. This action is fundamental to everyday movements, such as squeezing the legs together or stabilizing the lower body while standing on one leg.
Beyond adduction, these muscles contribute to several secondary actions at the hip joint. The Pectineus and the upper parts of the Adductor longus and brevis assist in hip flexion, the motion of bringing the knee toward the chest. The Adductor magnus, with its hamstring component, assists in hip extension, the motion of moving the leg backward.
The adductor group also plays a significant role in pelvic and hip stability during locomotion. They work in coordination with the gluteal muscles to maintain proper alignment while walking, running, or changing direction.