Each hip bone is composed of three major parts: The ilium is the more bladelike upright portion, the ischium is the more inferior and posterior region that we sit on, and the pubis is the more anterior region. These hip bones form multiple joints to enable movement. To better understand the hip joint and its ligaments, as well as the insertions of muscles that move the hip joint, we should consider the proximal aspect of the femur.
Structure of Femur
The femoral head is a rounded knob that faces medially and has a depression in its center called the fovea capitis—translated as the “pit on the head”. The femoral head constricts to a region called the neck of the femur.
Laterally, there is a large, bony prominence called the greater trochanter, and more distally, medially, and slightly more posterior is the lesser trochanter. Of all the bony prominences in the human skeleton, trochanters are found only on the femur.
Anteriorly, running between the greater and lesser trochanter, there’s an intertrochanteric line. Posteriorly, between the two trochanters is more of a raised ridge, called the intertrochanteric crest.
Ball and Socket Joint of Hip
Now, let’s focus more on the hip joint itself—which is different from the pubic symphysis and sacroiliac joints that help form the pelvis.
The hip is a diarthrotic ball-and-socket joint between the acetabulum of the pelvic bone and the head of the femur. The rim of the acetabulum is not uniform throughout. At the anterior aspect, there’s a deficiency known as the acetabular notch—it’s bridged by a connective tissue band known as the transverse acetabular ligament.
The socket is also deepened by a rim of cartilage known as the acetabular labrum that actually reaches around and clasps the head of the femur—unlike the glenoid labrum of the shoulder, which made the flat glenoid fossa broader, but not deeper.
The actual articular surface of the acetabulum is known as the lunate surface for its moon-like shape; it is covered with articular cartilage, as is the head of the femur.
This article comes directly from content in the video series How We Move: The Gross Anatomy of Motion. Watch it now, on Wondrium.
Comparing Hip with Shoulder
Unlike the shoulder, the hip has an intracapsular ligament—which means it’s within the joint capsule itself—known as the round ligament of the femur—or sometimes by the Latin name ligamentum teres femoris. It attaches the deep aspect of the acetabulum to the fovea capitis on the head of the femur.
The combination of this ligament within the capsule and the depth of the acetabulum—caused in part by the labrum—help make the hip quite stable. Remember, when compared to the shoulder, the hip has much less mobility, but has much greater stability. That’s a trade-off in some synovial joints.
As a ball-and-socket joint, the hip is multiaxial, meaning it moves in x, y, and z axes of three-dimensional space. Anterior motion at the hip, like kicking a ball with a straightened knee, is flexion at the hip—remember, forward is flexion at ball-and-socket joints. Returning the hip to standard anatomical position or moving the straight limb back—like winding up to kick—is extension at the hip.
What would we call lifting the lower limb out laterally, away from the midline? If you said abduction, that’s correct. Pulling the thigh back toward the midline is adduction. Turning the toes in with a straight lower limb is medial rotation at the hip—but pointing the foot out, directing the toes out away from the midline, is lateral rotation. And while in no way as great a range of motion as at the shoulder, swinging the lower limb in an arc is circumduction.
Three Ligaments of Hip
Remember that the joint capsule is the sleeve of connective tissue that connects the bones in a diarthrotic joint, but not on their articular surfaces. In the hip joint, the capsule is composed of three ligaments that stabilize various aspects of the joint—and what’s particularly helpful is that they’re named for the three parts of the pelvis.
There’s an iliofemoral ligament, a pubofemoral ligament, and an ischiofemoral ligament.
- The iliofemoral ligament has the shape of an upside-down Y—it is anteriorly placed and passes from the anterior inferior iliac spine to the intertrochanteric line on the proximal anterior femur. The iliofemoral ligament is taut when standing and resists hyperextension to support our trunk without much additional muscle action at the hip and is said to be the strongest ligament in the body.
- The pubofemoral ligament blends with the inferior aspect of the iliofemoral. It connects the pubic bone to the inferior aspect of the intertrochanteric line on the anterior femur and limits excessive abduction and extension.
- The final ligament, the ischiofemoral, is the posterior part of the capsule. It spirals around from the ischium and attaches to the neck of the femur as its superior aspect. The ischiofemoral ligament also helps stabilize our standing position.
In addition, all three ligaments help limit medial rotation of the hip, which would cause the femur to turn internally. Together, they make the hip joint extremely stable—not only when standing, but also during our bipedal locomotion.
Common Questions about the Anatomy of the Hip
The hip is a diarthrotic ball-and-socket joint between the acetabulum of the pelvic bone and the head of the femur. The rim of the acetabulum is not uniform throughout. At the anterior aspect, there’s a deficiency known as the acetabular notch—it’s bridged by a connective tissue band known as the transverse acetabular ligament
In the hip joint, the capsule is composed of three ligaments that stabilize various aspects of the joint. There’s an iliofemoral ligament, a pubofemoral ligament, and an ischiofemoral ligament.
All three ligaments of the hip—iliofemoral, pubofemoral, and ischiofemoral—help limit medial rotation of the hip, which would cause the femur to turn internally. Together, they make the hip joint extremely stable—not only when standing, but also during our bipedal locomotion.