Bio Mechanics Of The Hip

Biomechanics of the Hip

Pelvic Girdle • The two hip bones plus the sacrum • Can be rotated forward, backward, and laterally to optimize positioning of the hip joint

Pelvic girdle ilium

sacrum

acetabulum ischium

pubis

Obturator foramen

Pelvic Bone

Pelvic Bone

Anterior Tilt • Forward tilting and downward movement of the pelvis • Occurs when the hip extends

Posterior Tilt • Tilting of the pelvis posteriorly • Occurs when the hip flexes

Lateral Tilt • Tilting of the pelvis from neutral position to the right or left • Lateral tilt tends to occur naturally when you support your weight on your leg • This allows you raise your opposite leg enough to swing through during gait

Pelvic Rotation • Rotation of the pelvis defined by the direction in which the anterior aspect of the pelvis moves • Occurs naturally during unilateral leg movements (walking) – As the right leg swings forward during gait the pelvis rotates left

Hip Joint • Consists of – Pelvic bone • Acetabulum – Femur

Acetabulum

Acetabulum

Femur

Femur

Femur

Structure of the Hip • A ball and socket joint in which the head of the femur articulates with the concave acetabulum • The hip is more stable than the shoulder – Bone structure – The number and strength of the muscles and ligaments crossing the joint

Acetabular Labrum • Acetabulum is not a complete circle, open inferiorly • This opening is closed by the transverse ligament

Head Ligament • Head of femur attached to inside of acetabulum by ligamentum teres

Capsule

Ligaments • Iliofemoral ligament or the “Y ligament of Bigelo” – Triangular in shape – Supports hip anteriorly, resists extension, internal rotation and some external rotation

• Pubofemoral – Runs from the superior pubic ramus and the acetabular rim, to just above lesser trochanter – Resists abduction with some resistance to external rotation

Ligaments • Ischiofemoral ligament – From the ischium to the posterior neck of the femur – is directed upwards and laterally – Resists adduction and internal rotation – All three loose during flexion

Ligaments

Anterior view

Posterior view

Vascular

Vascular

Lumbar Division

Hip Goniometry • Flexion/Extension – 125-140 (with knees flexed)/0/10-20 – 90 (with knees extended)/0/10-20 • Abduction/Adduction – 45/0/20-30 • Internal Rotation/External Rotation – 35-45/0/40-50

Hip Movements • Hip Flexion

Hip Movements • Flexion – Psoas major – Iliacus – Assisted by: • Pectineus • Rectus femoris • Sartorius • Tensor fascia latae

Psoas major

Iliacus

Pectineus

Rectus femoris

Tensor fascia latae Sartorious Iliotibial band

Hip Movements • Hip Extension

Hip Movements • Extension – Gluteus Maximus – Hamstrings • Biceps Femoris • Semimembranosus • Semitendinosus

Gluteus maximus

Hip Movements • Hip Abduction

Hip Movements • Abduction – Gluteus Medius – Assisted By: • Gulteus Minimus

Gluteus medius

Gluteus minimus

Hip Movements • Hip Adduction

Hip Movements • Adduction – Adductor Magnus – Adductor Longus – Adductor Brevis – Assisted By: • Gracilis

Gracilis

Hip Movements • Internal/Medial Rotation – Gulteus Minimus – Tensor fascia latae

Hip Movements • External/Lateral Rotation – Obturator Externus – Obturator Internus – Quadratus femoris – Piriformis

Obturator Externus

Obturator Internus Piriformis Quadratus femoris

Angle of Inclination

Coxa Vara • The angle of inclination is less than 125 degrees • This shortens the limb • Increases the effectiveness of the abductors • Reduces the load on the femoral head • Increases the load on the femoral neck

Coxa Valga • The angle of inclination is greater than 125 degrees • This lengthens the limb • Reduces the effectiveness of the abductors • Increases the load on the femoral head • Reduces the load on the femoral neck

Hip Angles • 14-15 degrees • Moves CM more directly over base of support

Anteversion • The angle of the femoral neck in the transverse plane • Normally the femoral neck is rotated anteriorly 12 to 14 degrees with respect to the femur

Excessive Anteversion • Excessive anteversion beyond 14 degrees causes the head of the femur become uncovered • In order to keep the head of the femur within the acetabulum a person must internally rotate the femur

Retroversion • The angle of anteversion is reversed so that it moves posteriorly • This condition causes the person to externally rotate the femur

Loads on the Hip • During swing phase of walking: – Compression on hip approx. same as body weight (due to muscle tension)

• Increases with hard-soled shoes • Increases with gait increases (both support and swing phase) • Body weight, impact forces translated upward thru skeleton from feet and muscle tension contribute to compressive load on hip

250 N

600 N

Using A Walking Stick

Using a walking stick how it reduces JRF

Using a walking stick how it reduces JRF • In equilibrium sum of moments = 0 • Without stick MxA=WxB M

= (W x B)/A

Using a walking stick how it reduces JRF

Using a walking stick how it reduces JRF • With sitck (M x A)+(Ws x C) = W x B M = [(W x B)-(Ws x C)]/A • So the force required by the abductors M is smaller if a stick is used • The bigger C is, the smaller M is therefore a walking stick in the hand furthest away from the hip is most effective

Using a walking stick how it reduces JRF • In equilibrium, the sum of the forces in the Y plane = 0 • Without stick JRF sin θ  = M + W • With stick JRF sin θ + Ws = M +W JRF sin θ = M + W - Ws

Using a walking stick how it reduces JRF • Therefore JRF is less when a walking stick is used. Not only is M force smaller, but the upward force exerted by the stick reduces the JRF further

opposite same

hurt leg

W

hurt leg

W