Competencies
- AN17.1: Describe and demonstrate the type, articular surfaces,capsule, synovial membrane, relations, movements and muscles involved, blood and nerve supply, and bursae around the hip joint.
- AN17.2: Describe anatomical basis of complications of fracture neck of femur.
- AN17.3: Describe dislocation of hip joint and surgical hip replacement.
Introduction
The hip joint is a ball-and-socket synovial joint formed between the head of the femur and the acetabulum of the hip bone. It transfers the weight of the upper body to the neck of the femur and supports the body’s weight while standing. It is the largest ball-and-socket joint in the human body.
Type
The hip joint is a ball-and-socket type of synovial joint. It allows movement in multiple directions and around several axes. Therefore, it is a multiaxial joint.
Articular Surfaces
The hip joint is formed by the following two articular surfaces:
Proximal articular surface (acetabulum)
- The acetabulum is a cup-shaped cavity of the hip bone. It consists of the lunate (horseshoe-shaped) articular surface, acetabular notch, and acetabular fossa. The lunate surface is covered with hyaline cartilage, which provides a smooth surface for movement. The outer rim of the acetabulum gives attachment to the acetabular labrum, a fibrocartilaginous ring that deepens the socket and improves the stability of the hip joint.
Distal articular surface (head of the femur)
- The head of the femur is smooth, rounded, and forms more than half of a sphere. Its articular surface is covered with hyaline cartilage, except at the fovea capitis, a small pit where the ligament of the head of the femur attaches.
Note: The articular surfaces of the acetabulum and the femoral head are curved to fit each other, but they do not completely match in size.
Ligaments of Hip Joint
The hip joint is strengthened and stabilized by the following ligaments:
- Capsular ligament
- Iliofemoral ligament
- Pubofemoral ligament
- Ischiofemoral ligament
- Ligament of the head of the femur (Ligamentum teres femoris)
- Transverse acetabular ligament
- Acetabular labrum
Capsular Ligament
The capsular ligament is a strong fibrous capsule that surrounds and protects the hip joint.
Attachments
Proximal attachment
- Attached to the margin of the acetabulum, about 5–6 mm beyond its rim.
- It is also attached to the transverse acetabular ligament and the acetabular labrum.
Distal attachment
- Attached to the intertrochanteric line on the anterior aspect of the femur.
Synovial Membrane
The inner surface of the capsule is lined by a synovial membrane. It also covers:
- The intracapsular part of the neck of the femur
- Both surfaces of the acetabular labrum
- The transverse acetabular ligament
- The fat pad in the acetabular fossa
Structure
- The capsule is thickest on its anterosuperior side.
- It becomes most tense when standing.
- It contains two groups of fibres:
- Inner circular fibres (Zona orbicularis): These fibres form a collar around the neck of the femur and help hold the femoral head in the socket.
- Outer longitudinal fibres: These fibres attach the capsule to the bone. Many continue along the neck of the femur as retinacular fibres, which carry blood vessels to the head of the femur.
Iliofemoral Ligament (Ligament of Bigelow)
The iliofemoral ligament is the strongest ligament of the hip joint. It is shaped like an inverted Y and prevents excessive extension of the hip.
Attachments
Proximal attachment
- Anterior inferior iliac spine (AIIS)
- Rim of the acetabulum
Distal attachment
- Intertrochanteric line of the femur
Structure
- It has:
- An upper oblique band
- A lower vertical band
- A thinner middle part
- This arrangement gives it its characteristic inverted Y shape.
Pubofemoral Ligament
The pubofemoral ligament is a triangular ligament that strengthens the lower and medial part of the joint capsule.
Attachments
Proximal attachment
- Iliopubic eminence
- Superior ramus of the pubis
- Obturator crest
Distal attachment
- Blends with the joint capsule and the iliofemoral ligament.
Ischiofemoral Ligament
The ischiofemoral ligament strengthens the posterior part of the hip joint capsule.
Attachments
Proximal attachment
- Ischium
- Margin of the acetabulum
Distal attachment
- Greater trochanter of the femur
Feature
- Its fibres follow a spiral course, which helps stabilize the joint during movement.
Ligament of the Head of the Femur (Ligamentum Teres Femoris)
The ligament of the head of the femur is a flat, triangular ligament covered by the synovial membrane.
Functions
- Carries a small artery to the head of the femur, especially important during childhood.
- Provides a small amount of stability to the hip joint.
Attachments
Proximal attachment
- Margins of the acetabular notch
- Base of the transverse acetabular ligament
Distal attachment
- Fovea capitis on the head of the femur
Transverse Acetabular Ligament
The transverse acetabular ligament is a continuation of the acetabular labrum that bridges the acetabular notch.
Function
- Converts the acetabular notch into a foramen.
- Allows blood vessels and nerves to pass into the hip joint.
Acetabular Labrum
The acetabular labrum is a ring of fibrocartilage attached to the rim of the acetabulum.
Features
- Triangular in cross-section.
- Deepens the acetabular socket.
- Improves the stability of the hip joint by firmly holding the head of the femur.
Clinical Anatomy
- The iliofemoral ligament is the strongest ligament of the hip joint and is often considered the strongest ligament in the human body.
- The ligament of the head of the femur is developmentally a part of the joint capsule that becomes enclosed within the joint cavity.
- Posterior dislocation is the most common type of hip dislocation because the posterior aspect of the joint is relatively less reinforced than the anterior side.
Factors Affecting Stability of Hip Joint
The hip joint is one of the most stable joints in the body. Its stability is maintained by the following factors:
- Deep acetabulum: The deep socket of the acetabulum firmly holds the head of the femur.
- Acetabular labrum: The fibrocartilaginous labrum deepens the acetabulum and narrows its opening, providing additional stability.
- Strong ligaments: The ligaments of the hip joint, especially the iliofemoral ligament, strengthen the joint and prevent excessive movements.
- Surrounding muscles: The muscles around the hip joint provide dynamic support and help keep the femoral head in the acetabulum.
- Neck-shaft angle of the femur: The normal angle between the neck and shaft of the femur helps distribute body weight efficiently and contributes to joint stability.
- Atmospheric pressure: The negative pressure inside the joint cavity helps hold the head of the femur firmly against the acetabulum, reducing the risk of dislocation.
Relations of Hip Joint
The structures related to the hip joint can be divided into anterior, posterior, superior, and inferior relations.
Anterior Relations
The following structures lie in front of the hip joint:
- Tendon of the iliopsoas muscle
- Iliopsoas bursa, which separates the tendon from the joint
- Femoral nerve
- Femoral artery
- Femoral vein
- Femoral sheath
Posterior Relations
The following structures are located behind the hip joint:
- Gluteus maximus
- Piriformis
- Sciatic nerve and nerve to quadratus femoris
- Obturator internus with the superior and inferior gemelli
- Quadratus femoris
Superior Relations
The structures above the hip joint include:
- Reflected head of rectus femoris
- Gluteus minimus
- Gluteus medius
- Part of gluteus maximus
Inferior Relations
The structures below the hip joint are:
- Pectineus
- Obturator externus
- Adductor muscles of the thigh
- Hamstring muscles
Bursae around the Hip Joint
Several bursae are present around the hip joint. They reduce friction between muscles, tendons, and bones during movement.
- Trochanteric bursa: Located between the gluteus maximus muscle and the greater trochanter of the femur.
- Ischial bursa: Found between the gluteus maximus and the ischial tuberosity.
- Gluteofemoral bursa: Lies between the tendon of gluteus maximus and the vastus lateralis muscle.
- Subpsoas bursa: Situated between the iliopubic eminence and the tendon of psoas major. It may communicate with the hip joint cavity through a gap in the capsule between the iliofemoral and pubofemoral ligaments.
- Gluteus medius bursa: Located between the gluteus medius muscle and the greater trochanter.
- Gluteus minimus bursa: Located between the gluteus minimus muscle and the greater trochanter.
Blood Supply and Nerve Supply
Blood supply
- The hip joint receives blood from branches of the following arteries:
- Obturator artery
- Medial circumflex femoral artery
- Lateral circumflex femoral artery
- Superior gluteal artery
- Inferior gluteal artery
- The medial and lateral circumflex femoral arteries form an extracapsular arterial ring around the neck of the femur.
- Retinacular arteries arise from this arterial ring and supply the neck and most of the head of the femur.
- A small part of the head of the femur receives blood from a branch of the obturator artery, which passes through the ligament of the head of the femur (ligamentum teres femoris).
Nerve supply
The hip joint is supplied by branches of the following nerves:
- Femoral nerve (through the nerve to the rectus femoris)
- Anterior division of the obturator nerve
- Nerve to quadratus femoris
- Superior gluteal nerve
Movements of Hip Joint
The hip joint is a multiaxial ball-and-socket synovial joint. It allows movement in several directions. The following movements occur at the hip joint:
- Flexion and extension occur around the transverse axis.
- Abduction and adduction occur around the anteroposterior axis.
- Medial and lateral rotation occur around the vertical axis.
- Circumduction is a circular movement produced by combining flexion, extension, abduction, adduction, and rotation.
Table 13.1: Main muscles responsible for the movements at the hip joint
| Movement | Axis | Chief Muscles |
|---|---|---|
| Flexion | Transverse | Psoas major and iliacus |
| Extension | Transverse | Gluteus maximus and hamstring muscles |
| Adduction | Anteroposterior | Adductor longus, adductor brevis, and adductor magnus |
| Abduction | Anteroposterior | Gluteus medius and gluteus minimus |
| Medial rotation | Vertical | Anterior fibres of gluteus medius, gluteus minimus, and tensor fasciae latae |
| Lateral rotation | Vertical | Obturator internus, superior and inferior gemelli, quadratus femoris, and obturator externus |
| Circumduction | Multiple axes | Combined action of the muscles surrounding the hip joint |
Range of Hip Movements
The range of movement at the hip joint is limited by the ligaments, surrounding muscles, and the depth of the acetabulum.
Table 13.2: Range of Hip Movements
| Movement | Normal Range |
|---|---|
| Flexion | 110°–120° |
| Extension | 15° |
| Abduction | 50° |
| Medial rotation | 25° |
| Lateral rotation | 60° |
CLINICAL INTEGRATION
- Close-packed position: The greatest contact between the articular surfaces of the hip joint occurs when the hip is slightly flexed, abducted, and laterally rotated. The close-packed position of the hip joint is extension with slight abduction and medial rotation. In this position, the joint capsule is fully stretched, making the joint most stable.
- Congenital hip dislocation (developmental dysplasia of the hip): Congenital hip dislocation occurs when the acetabulum does not develop properly and fails to cover the head of the femur completely. As a result, the head of the femur may move upward and backward out of the socket. The condition is present at birth or develops during early infancy and occurs in about 1 in 1,000 births. Affected infants may have unequal buttock folds, limited hip movements, a clicking sensation during hip examination, or a difference in the length of the lower limbs. Tight swaddling of infants and improper use of baby carriers may increase the risk of this condition.
- Perthes Disease (Legg-Calvé-Perthes Disease): Perthes disease is a childhood disorder caused by a temporary loss of blood supply to the head of the femur, resulting in avascular necrosis. The reduced blood flow causes the femoral head to become flattened and damaged over time. Children usually present with hip pain, limping, and restricted hip movements. On an X-ray, the hip joint typically shows an increased joint space.
- Coxa vara and coxa valga: The normal neck-shaft angle of the femur is about 127°. Coxa valga is a condition in which this angle increases to more than 135°, making the femoral neck more vertical. Coxa vara is the opposite condition, where the angle decreases to less than 120°, making the femoral neck more horizontal. Both conditions can affect hip stability and gait.
- Osteoarthritis of the hip: Osteoarthritis is a degenerative joint disease that commonly affects older adults. It occurs due to gradual wear and tear of the articular cartilage covering the joint surfaces. As the disease progresses, new bone called osteophytes forms around the joint margins, leading to pain, stiffness, and reduced hip movements.
- Referred pain of the hip joint: Pain arising from the hip joint is often felt in the knee rather than the hip itself. This is known as referred pain and occurs because the hip and knee joints share a common nerve supply.
- Aspiration of the hip joint: Hip joint aspiration is performed to remove fluid from the joint for diagnosis or treatment. In the anterior approach, the needle is inserted at the point where a vertical line drawn below the anterior superior iliac spine (ASIS) meets a horizontal line drawn from the greater trochanter. The needle is directed upward and slightly medially. In the lateral approach, the needle is inserted just above and medial to the greater trochanter until it reaches the bone.
- Age pattern of hip joint diseases: Different hip disorders are commonly seen at different ages. Congenital hip dislocation usually presents in children below 5 years of age. Perthes disease commonly occurs between 5 and 10 years. Coxa vara is most often seen between 10 and 20 years, while osteoarthritis usually develops in adults over 40 years of age.
- Fracture of the neck of the femur: The neck of the femur is the weakest part of the femur and is the most common site of fracture. These fractures usually require considerable force in young adults but commonly occur after minor falls in elderly individuals, especially women with osteoporosis. Depending on the location, they are classified as subcapital (just below the femoral head), transcervical (through the middle of the neck), intertrochanteric (between the greater and lesser trochanters), and pertrochanteric (just below the trochanters).
- Shenton’s line is a smooth curved line seen on a pelvic x-ray. It is formed by the lower border of the neck of the femur and the upper border of the obturator foramen. Any interruption or break in this smooth curve suggests a fracture of the neck of the femur or a dislocation of the hip joint.
- Shoemaker’s line is an imaginary line drawn from the tip of the greater trochanter to the anterior superior iliac spine (asis). In a normal hip, this line passes through or above the umbilicus. In fractures of the neck of the femur, the greater trochanter moves upward, causing the line to pass below the umbilicus.
- Hip replacement surgery: Hip replacement, also called hip arthroplasty, is a surgical procedure in which a damaged or worn-out hip joint is replaced with an artificial joint (prosthesis). It is commonly performed in patients with severe osteoarthritis or advanced hip damage. Depending on the extent of the disease, either a partial or total hip replacement may be carried out.
- Dynamic hip screw is an orthopedic implant used to treat fractures of the neck of the femur, particularly intertrochanteric fractures. The implant provides stable fixation while allowing controlled compression at the fracture site, which promotes healing.
- Langenbeck triangle (trigonum iliofemorale): The langenbeck triangle, also known as the trigonum iliofemorale, is an important anatomical landmark used during surgical exploration of the hip joint. Its apex is formed by the anterior superior iliac spine (asis), while its base extends between the anatomical neck and the greater trochanter of the femur. The sides of the triangle are formed by lines joining the apex to each end of the base.
Important Questions
- Describe the hip joints under the following headings: articular surfaces, ligaments, movements and applied aspects.
- List the various movements of hip joint and the muscles producing these movements.
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