By Elizabeth A. Murray, Mount St. Joseph University
Moving on to the six muscles of the medial compartment of the thigh, they are the obturator externus, the pectineus, the gracilis, and the three members of the adductor group. Only one of the medial thigh muscles crosses the knee joint, but all cross the hip joint and since most of those adduct the hip, some refer to the medial compartment as the adductor compartment.
Obturator Externus
The obturator nerve dominates the supply of the muscles of the medial compartment of the thigh, but as with the anterior thigh, there are exceptions.
Obturator externus originates on the anterior surface of the obturator foramen, passes posteriorly between the pelvis and the neck of the femur, and inserts just inferior to the attachment of the inferior gemellus muscle.
There is a series of lateral rotators deep in the gluteal region: piriformis, superior gemellus, obturator internus, inferior gemellus, and quadratus femoris. While it’s not easily seen at the posterior aspect of the hip joint, the obturator externus also attaches among that group—just between the insertion of inferior gemellus and quadratus femoris.
So, not only do the obturator externus and obturator internus flank either side of the obturator foramen of the pelvis, both also pass posterior to the hip joint to insert along the deep aspect of the intertrochanteric crest.
Obturator externus also laterally rotates the thigh like the other members in that sequence. However, it is supplied by the obturator nerve off the lumbar plexus, while those other lateral rotators are supplied by nerves off the sacral plexus.
Pectineus Muscle
The pectineus muscle originates on the superior ramus of the pubis and attaches to the pectineal line on the posteromedial femur. Because of its anterior origin on the pelvis and insertion on the medial femur, it flexes and adducts the thigh at the hip joint. In terms of its innervation, pec-tineus is pec-uliar because it may be supplied by the obturator nerve, by the femoral nerve, or may have branches from both.
It must be kept in mind, though, that both the femoral and obturator nerves are composed of the L2, L3, and L4 ventral rami of the lumbar plexus, so differences in the innervation are likely of little consequence.
This article comes directly from content in the video series How We Move: The Gross Anatomy of Motion. Watch it now, on Wondrium.
Gracilis Muscle
The most medially placed muscle of the medial compartment is gracilis; gracile means “slender”. It is a long, narrow muscle that originates on the inferior ramus of the pubis, runs along the length of the medial thigh, and attaches to the pes anserine region near the medial condyle of the tibia.
Like most other medial compartment muscles, gracilis adducts the hip and is supplied by the obturator nerve. But unlike any other muscle in the medial compartment, gracilis crosses the knee, and due to the position of its insertion, gracilis acts to aid flexion of the knee.
Adductor Group Muscles
The three muscles of the adductor group are named for their relative sizes: adductor brevis, adductor longus, and adductor magnus—magnus means “great” in Latin.
Typical of longus and brevis pairs, the adductor longus is more superficial. It sits just medial to pectineus and takes origin off the anterior aspect of the body of the pubic bone and inserts on the middle third of the linea aspera.
Adductor brevis is deep to the longus; it originates off the inferior pubic ramus and inserts on the proximal third of the linea aspera. Both adduct the thigh, but can also assist in flexion, due to their more anterior origin and posterior insertion. Both adductor longus and adductor brevis are supplied by the obturator nerve.
It must be noted here that sartorius, adductor longus, and the inguinal ligament border a region known as the femoral triangle, which is of clinical relevance due to the femoral artery, vein, and nerve within it. The femoral artery can be used to draw arterial blood gases, as well as for insertion of an intravenous line or a catheter for certain cardiac procedures.
The adductor magnus is another interesting muscle—it is said to have two parts, based on its different origins, insertions, actions, and even innervations. The adductor portion originates on the ischiopubic ramus and inserts on the linea aspera.
Like its longus and brevis buddies, the adductor part of adductor magnus is also supplied by the obturator nerve and adducts and flexes the thigh. But the adductor magnus also has what’s called its hamstring portion, which takes origin off the ischial tuberosity and inserts on the adductor tubercle projecting off the medial epicondyle of the femur.
Like the hamstrings of the posterior thigh, the hamstring portion of the adductor magnus extends the thigh and is supplied by the sciatic nerve.
Naming the Muscles
It is easy to understand why early anatomists called psoas major and iliacus two different muscles, despite the single insertion that allows the combined name iliopsoas, while adductor magnus also has two very distinct origins, but really just one name. But this reinforces that all this naming—whether of muscles, nerves, or anything else—is a human construct, it is simply a part of anatomical history.
One other feature, related to adductor magnus and how things are named, is the adductor hiatus—that is a natural opening within adductor magnus near the insertion of its hamstring portion. The femoral artery and vein pass through this gap to travel from the anterior thigh to the popliteal region behind the knee.
That’s the point where the femoral vessels are renamed as popliteal vessels. The large femoral artery and vein don’t run across the anterior knee, where we might kneel and compress them, but rather pass posterior to it, by going through the hiatus in adductor magnus.
Common Questions about the Thigh’s Medial Compartment Muscles
There are six muscles of the medial compartment of the thigh, they are the obturator externus, the pectineus, the gracilis, and the three members of the adductor group.
The three muscles of the adductor group are named for their relative sizes: adductor brevis, adductor longus, and adductor magnus—magnus means “great” in Latin.
Like most other medial compartment muscles, gracilis adducts the hip and is supplied by the obturator nerve. But unlike any other muscle in the medial compartment, gracilis crosses the knee, and due to the position of its insertion, gracilis acts to aid flexion of the knee.
