The hip joint is a marvel of biomechanical engineering that allows for a wide range of movements while supporting the weight of the upper body. It is a ball-and-socket joint formed by the articulation of the femoral head (the ball) and the acetabulum of the pelvis (the socket). This design provides the joint with three degrees of freedom, enabling flexion and extension, abduction and adduction, and medial and lateral rotation.
Articular Surfaces and Cartilage The femoral head and the acetabulum are lined with articular cartilage, which is thickest at areas of greatest pressure and thinnest at the periphery. This cartilage is viscoelastic, meaning it can change shape under load, providing shock absorption and reducing friction during movement.
Ligaments and Capsule The hip joint is reinforced by a series of strong ligaments that provide stability. The iliofemoral, pubofemoral, and ischiofemoral ligaments are part of the joint capsule and limit hyperextension and excessive rotation. The ligamentum teres, although not a major stabilizer, carries a small artery to the head of the femur.
Musculature The muscles surrounding the hip joint not only produce movement but also contribute to joint stability. The gluteal muscles, particularly the gluteus medius and minimus, are key in stabilizing the pelvis during gait. The iliopsoas, a primary hip flexor, is significant for lifting the thigh. The adductors, located medially, bring the thigh back towards the midline, while the abductors, laterally, move it away.
Biomechanics of Movement During walking, the hip joint experiences forces several times the body’s weight. The joint reaction force is the resultant force acting on the femoral head, influenced by body weight, muscle activity, and external forces like gravity. Proper alignment and muscle function are crucial to distribute these forces evenly and prevent excessive wear on the joint surfaces.
Pathologies and Abnormalities Deviations from normal biomechanics can lead to conditions such as osteoarthritis. Dysplasia, where the acetabulum does not fully cover the femoral head, can lead to instability and early joint degeneration. Similarly, variations in the angle of inclination and torsion of the femur can alter the biomechanics and lead to joint stress.
Treatment and Rehabilitation Understanding the biomechanics of the hip joint is essential for designing effective treatments and rehabilitation programs. For instance, in cases of hip arthritis, exercises that strengthen the surrounding musculature and improve range of motion can help maintain function and reduce pain.
Biomechanical Research Current research in hip joint biomechanics involves sophisticated models that simulate joint movement and predict the effects of surgical interventions. These models help in preoperative planning and in designing prosthetic components for hip replacement surgeries.
2. IN T R O D U C T IO N
Primary Function: Supports the weight of the head, arms, and trunk
during activities like walking, running, and stair climbing
Force Transmission: Essential for transmitting forces between the
torso and lower extremities, crucial for body function
Joint Configuration: The ball-and-socket structure provides stability
and allows for significant mobility
Common Issues: Injuries and diseases are frequent; hip
derangement can alter stress distribution, leading to joint damage
Consequences: Altered stress can cause degenerative arthritis and
functional limitations, affecting daily activities
Anatomical Study: The chapter discusses the hip joint’s functional
anatomy, its range of motion, and the forces acting on it
3. KEY POINTS ON THE
ACETABULUM
Acetabulum Structure:
Concave part of the hip joint,
horseshoe-shaped due to the
acetabular notch
Articular Cartilage: Covers
the acetabulum, thickening
around the edges, especially
in the superior-anterior dome
region
Hyaline Cartilage: Articulation
occurs on the horseshoe-
shaped hyaline cartilage on
the lunate surface’s periphery
Acetabular Labrum: A
fibrocartilaginous lip that
deepens the acetabulum and
connects with the transverse
acetabular ligament to
prevent dislocation
Orientation: Faces forward,
outward, and downward;
misalignment can lead to
dislocation and osteoarthritis
Center Edge Angle: Indicates
acetabular coverage over the
femoral head in the frontal
plane, averaging 35° to 40° in
adults
6. T H E F E M O R A L H E A D A N D I T S
B I O M E C H A N I C S
Femoral Head Shape: Forms two-thirds of a sphere as part of the hip’s ball-
and-socket joint
Articular Cartilage: Varies in thickness, being thickest medially around the
fovea and thinnest peripherally
Strength and Stiffness: Differences in cartilage thickness affect the femoral
head’s strength and stiffness
Viscoelastic Nature: The cartilage’s viscoelasticity influences how the
femoral head bears loads
Load-Bearing Area: Initially concentrated at the lunate surface’s periphery, it
shifts centrally with increased loads
Load Transmission: The anterior and medial lunate surfaces bear most of
the load during daily activities
Measurement Challenges: Direct measurement of load distribution is
difficult due to technical limitations
This Photo by Unknown author is licensed under CC BY-SA.
9. KINEMATICS OF HIP
Hip Motion: Occurs in sagittal , frontal , and transverse planes
Sagittal Plane Motion: Flexion ranges from 0° to ~140°, extension from 0° to 15°
Frontal Plane Motion: Abduction ranges from 0° to 30°, adduction from 0° to 25°
Transverse Plane Motion: External rotation ranges from 0° to 90°, internal rotation from 0° to 70°
Daily Activity Requirements: At least 120° of flexion and 20° of external rotation are necessary for normal activities
Cultural Sensitivity: Range of motion requirements can vary based on cultural practices, such as floor sitting or kneeling
Environmental Factors: Age, movement speed, and task constraints like chair and stair height can influence reported ranges
of motion
10.
11. KINETICS OF
HIP
Substantial Forces: Kinetic studies reveal significant forces on the hip during
basic activities like standing, walking, or running
Biomechanical Analysis Goals:
Understand the factors and magnitude of forces on the hip joint
Identify activities potentially harmful to the joint and soft tissues
Compare the functioning of healthy versus diseased joints
Develop treatment and evaluation plans for hip-related conditions
Gain insights into the hip joint’s structure for optimal performance
Dynamic Model Challenges: Creating a comprehensive model is complex
due to internal force dynamics and measurement difficulties
Model Components: Should include muscle action lines and axes of rotation
in all planes, considering dynamic motion changes
13. E XT E R N A L FA C TO R S
I N F L U E N C I N G H I P M O T I O N :
Cane Usage: A cane should be
used on the side opposite to the
affected hip to reduce joint
reaction force
Study Findings: Neumann’s
study showed a 42% reduction
in hip abductor muscle activity
when using a cane
contralaterally
Force Reduction: Muscle
activity reduction translates to a
decrease in joint reaction force
from 3.4 to 2.2 times body
weight
Clinical Implication: These
findings inform clinicians on
how to advise patients with hip
issues to manage hip loading
effectively
