Hip Complex

Chapter 18: Structure and Function of the Hip Complex

Hip Complex

• Composed of:

  • Femur

  • Acetabulum of the pelvis

• Type of joint:

  • Ball-and-socket joint

  • Involves two movements:

  • Trunk moving on stable lower extremity

  • Lower extremity moving on stable trunk

• Plays a major role in functional activities such as walking, running, and various sports.

Bony Structures

• Pelvis Features:

  • Ilium:

  • Anterior superior iliac spine (ASIS)

  • Anterior inferior iliac spine (AIIS)

  • Posterior superior iliac spine (PSIS)

  • Posterior inferior iliac spine (PIIS)

  • Ischium

  • Pubis

  • Forms an osteoligamentous ring (Ala of sacrum)

Detailed Bony Structures

• Femur:

  • Longest and strongest bone in the body

  • Head projects medially and anteriorly

  • Features:

  • Greater trochanter

  • Lesser trochanter

  • Trochanteric fossa

  • Linea aspera

  • Medial and lateral condyles

Angle of Inclination

• Defined as the angle between the femoral shaft and neck

• Normal angle: approximately $125^ ext{o}$

• Coxa vara: (decreased angle)

  • Femur and knees move more inward, resulting in a knock-kneed appearance

• Coxa valga: (increased angle)

  • Femur moves laterally, resulting in an outward/bowlegged appearance.

Femoral Torsion

• Defined as the relationship between the femoral neck and shaft.

• Normal anteversion: Femoral neck is $15^ ext{o}$ anterior to the condylar axis.

• Excessive anteversion (>15°): Femur rotates inward, presenting a pigeon-toed posture.

• Retroversion (<15°): Femur rotates outward, resulting in toes pointing out.

• Femoral Head positioning: Patients with excessive retroversion tend to 'out-toe' to better position the femoral head.

Joint Structures

Femoral Head

• Covered by thick articular cartilage except for the fovea

• Oriented medially, superiorly, and anteriorly

• Stabilized in the acetabulum by the ligamentum teres

• Blood supply:

  • Medial and lateral circumflex arteries

Acetabulum

• Acts as a deep socket that interacts with the femoral head.

• **Acetabular labrum:

  • Functions:**

  • Cushions and increases stability

  • Secures the femoral head within the acetabulum

• Hip ligaments:

  • Iliofemoral ligament

  • Pubofemoral ligament

  • Ischiofemoral ligament

  • All play a role in holding the femoral head in place.

Center Edge Angle

• Measures the degree of femoral head coverage by the acetabulum, indicating joint stability.

• Determined via X-ray and aids in diagnosing dysplasia or impingement.

• Increased angles means greater coverage and stability of the hip joint.

Ligaments

General Information

• Ligaments provide stability to the hip joint in various positions and motions.

• Significant ligaments include:

  • Iliofemoral ligament:

  • Anteriorly positioned

  • Known as the inverted Y ligament

  • Stabilizes in hyperextension and restricts medial hip rotation when extended.

  • Pubofemoral ligament:

  • Positioned anteriorly

  • Taut during lateral hip rotation when extended.

  • Ischiofemoral ligament:

  • Positioned posteriorly

  • Reinforces the posterior capsule and resists medial rotation in both flexion and extension.

Kinematics: Femur on Pelvis

• Hip Flexion:

  • Range: $0^ ext{o}$ to $120^ ext{o}$, influenced by knee position.

• Extension:

  • Begins from neutral $0^ ext{o}$, with a maximum of $30^ ext{o}$ extension when knee extended.

• Osteokinematics movements:

  • Medial rotation: up to $45^ ext{o}$

  • Lateral rotation: up to $45^ ext{o}$

  • Abduction: $45^ ext{o}$

  • Adduction: $30^ ext{o}$

Osteokinematics: Pelvis on Femur

• In a weight-bearing position, the pelvis moves on the femur.

• Close relationship exists between the pelvis, sacroiliac joint, hip joint, and lumbar spine, affecting overall motion.

Sagittal Plane Movements

• Anterior pelvic tilt:

  • Decreases the angle between anterior pelvis and femoral shaft.

  • Causes hip flexion and increased lumbar lordosis.

  • Anterior muscles become shortened, while hamstrings and glutes stretch.

• Posterior pelvic tilt:

  • Increases the angle, leading to hip extension.

  • Decreased lumbar lordosis and increased spinal flexion.

Frontal Plane Movements

• Pelvic Tilting Side to Side:

  • Upward rotation triggers a hip hike and abduction of the supporting leg.

  • Downward rotation corresponds to adduction of the supporting leg, often related to Trendelenburg sign.

Horizontal Plane Movements

• Internal rotation: up to $15^ ext{o}$

• External rotation: up to $15^ ext{o}$

• Important during leg swing in ambulation.

Muscles of the Hip Joint

Hip Flexors

• Primary Flexors:

  • Iliopsoas

  • Sartorius

  • Tensor fasciae latae

  • Rectus femoris (dual function as knee extensor)

  • Adductor longus (serves as both abductor and flexor)

  • Pectineus

Iliopsoas Muscle

• Composed of:

  • Psoas major:

  • Attaches to vertebral bodies T12 and L1-L4, and lesser trochanter; essential for spine stabilization and hip flexion.

  • Tightness correlates with increased lumbar lordosis.

  • Psoas minor:

  • Present in about 60% of the population, may contribute to posterior pelvic tilt.

  • Iliacus:

  • Attaches to iliac fossa, sacrum, and lesser trochanter.

Sartorius

• Longest muscle in the body, crosses two joints.

• Attaches to ASIS and proximal tibia, facilitating flexion, lateral rotation, and abduction (often referenced humorously as the "leprechaun dance").

• Assists in anterior pelvic tilt torque.

Tensor Fasciae Latae

• Attaches to the iliac crest and the iliotibial (IT) band.

• Functions as a hip flexor and abductor, and serves as a secondary medial rotator.

• Works in conjunction with gluteus maximus to maintain IT band tension.

Rectus Femoris

• Also a two-joint muscle, responsible for hip flexion and knee extension.

• Attaches to the AIIS and tibial tuberosity; uniquely crosses the knee.

Adductors

• Organized into layers:

  • Superficial Layer: Pectineus, Adductor longus, Gracilis

  • Middle Layer: Adductor brevis

  • Deep Layer: Adductor magnus

Femoral Triangle

• Bounded by:

  • Medially by Adductor longus & pectineus

  • Laterally by Sartorius

  • Superiorly by Inguinal ligament

• Contains the femoral nerve, artery, and vein.

Adductor Function

• In the Frontal Plane:

  • Adductors engage in movement of the femur on pelvis and pelvis on femur.

• In the Sagittal Plane:

  • Posterior fibers of the adductor magnus become powerful hip extensors, especially at end-range hip flexion.

• Eccentric contractions provide stabilization during movements.

Extensors

• Major extensors include:

  • Gluteus maximus

  • Hamstrings (consisting of biceps femoris, semitendinosus, and semimembranosus)

  • Posterior head of adductor magnus

• Secondary extensors:

  • Gluteus medius

  • Adductor magnus (also serves as an extensor)

Gluteus Maximus

• Extends the hip against resistance, prominent during stair climbing, running, and jumping.

• Exerts peak force when the hip is around $70^ ext{o}$ flexion.

• Functions as a lateral rotator and contributes to posterior pelvic tilt when contracted.

Hamstrings

• Conduct dual functions:

  • Extend the hip and flex the knee.

• Importance of ability to extend the hip depends on knee position.

Abductors

• Key abductors:

  • Gluteus medius:

  • Anterior fibers aid in flexion

  • Posterior fibers help in extension and lateral rotation

  • All fibers work together to abduct the hip.

Abductors during Single Leg Stance

• Maintain pelvic stability to prevent stance leg drop during gait.

Lateral Rotators

• Include:

  • Gluteus maximus

  • Piriformis (associated with sciatica)

  • Act as lateral rotators and abductors, functioning as deep rotators based on hip position.

Medial Rotators

• Utilize anterior fibers of:

  • Gluteus medius

  • Gluteus minimus

  • Tensor fasciae latae

  • Additional muscles like adductor longus and brevis, and pectineus.

Rotators during Leg Stance

• Lateral rotators: Move pelvis away from the stance leg.

• Medial rotators: Move pelvis towards the stance leg.

Common Hip Pathologies

• Congenital Hip Dislocation/Dysplasia

• Legg-Calve-Perthes Disease

• Slipped Capital Femoral Epiphysis (SCFE)

• Coxa valga or vara

• Osteoarthritis: Most prevalent pathology affecting hip function.

• Hip Fractures: Second most common pathology.

• IT Band Friction Syndrome (ITBFS)

• Trochanteric Bursitis

• Hamstring Strain

• Hip Pointer (contusion of iliac crest).