Hip Joint

Introduction

The hip joint connects the pelvis to the lower limb. It is a synovial ball and socket joint made up of the head of the femur and the acetabulum of the pelvis. The hip is designed to be highly stable and allows sufficient weight-bearing, with limited mobility.

There are many movements at the hip including flexion, extension, adduction and abduction, internal and external rotation, and circumduction. The joint is stabilised by a series of muscles and ligaments.

Articular surfaces

The hip is a multiaxial ball and socket joint. The articulating surfaces are the acetabulum of the pelvis and the head of the femur. Both of these surfaces are covered by a layer of hyaline cartilage, which helps to reduce friction and aid movement of the joint.

The acetabulum lies on the inferolateral aspect of the bony pelvis and forms a ‘cup’ for articulation with the head of the femur. The non-articular portion of the acetabulum contains loose connective tissue.

Clinical relevance: fractured neck of femur

A fractured neck of femur is usually caused by a fall, especially in older people. However, it can be caused by other conditions such as cancer. Fractures can be intracapsular or extracapsular depending on the location of the break, and management is guided by this.

The leg is typically held in a shortened and externally rotated position and patients are unable to weight bear.

Intracapsular fractures may be associated with avascular necrosis. This is because the blood supply to the head of the femur runs retrospectively up the femoral neck into the joint capsule, and can be disrupted following a fracture.

Clinical relevance: osteoarthritis of the hip

Osteoarthritis is a degenerative disease that primarily occurs in synovial joints. It involves degeneration of the articular surfaces. Symptoms of severe osteoarthritis include joint stiffness, reduced range of joint movement and joint pain.

Typical X-ray findings of osteoarthritis include:

• Joint space narrowing
• Subchondral sclerosis: hardening of the bone beneath the joint surface
• Osteophyte formation: small bony growths around the edges of the joint
• Bony cyst formation

For more information, see the Geeky Medics guides to osteoarthritis and interpreting a hip X-ray.

Ligaments

There are several ligaments which act to stabilise the hip joint.

The inferior aspect of the acetabulum is formed by the transverse acetabular ligament and helps to stabilise the inferior part of the hip joint.

The fovea of the femoral head is connected to the acetabulum via the ligament of the head of the femur (ligamentum teres). This ligament contains a branch of the obturator artery, which supplies the head of the femur.

The iliofemoral, pubofemoral and ischiofemoral ligaments spiral around the outer surface of the joint and act together to stabilise the hip.

Table 1. Ligaments of the hip

Bursae

Bursae are sacs filled with synovial fluid that act to reduce friction within the joint. The two main bursae in the hip are the trochanteric and iliopsoas bursae.

Blood supply and innervation

Blood supply to the hip joint

Arterial supply to the hip is mainly from the obturator artery, as well as the medial and lateral circumflex arteries, branches of the femoral artery, and the superior and inferior gluteal arteries. Branches of these arteries form an anastomotic network around the joint.

Innervation of the hip joint

Nerves supplying the hip joint include branches of the femoral nerve, obturator nerve and the superior gluteal nerve.

Muscles

There are several groups of muscles that act to move the hip joint. Movements at the hip joint include flexion, extension, internal and external rotation, adduction and abduction.

Table 2. Muscles acting on the hip joint.

Editor

Dr Chris Jefferies

References

Reference texts

• Richard L. Drake, A. Wayne Vogl, Adam W. M. Mitchell. Gray’s Anatomy for Students (Third Edition). Elsevier 2015.
• OpenStax. Anatomy and Physiology. Available from: [LINK]
• NHS.uk. 2022. Bursitis. Available from: [LINK]

Image references

1. Openstax. Anatomy and Physiology. 8.4 Bones of the Lower Limb. Licence: [CC-BY-SA]
2. Gaillard, F., 2022. Neck of femur fracture | Radiology Reference Article | Radiopaedia.org. Licence: [CC BY-NC-SA 3.0].
3. Openstax. Anatomy and Physiology. 9.4 Synovial Joints. Licence: [CC-BY-SA]
4. Openstax. Anatomy and Physiology. 9.6 Anatomy of Selected Synovial Joints. Licence: [CC-BY-SA].
5. Openstax. Anatomy and Physiology. 11.6 Appendicular Muscles of the Pelvic Girdle and Lower Limbs. Licence: [CC-BY-SA].