hip biomechanics

1. Regional Biomechanics
Hip Joint
Kinematics
Kinetics
Pathomechanics

2. Kinematics
• Bone Structure
• Capsule
• Ligaments
• Muscles

3. 1-Bony Articulation
 Femoral Head
(Superiorly, Medially,
Anteriorly).
 Acetabulum (Inferiorly,
Laterally, Anteriorly).
Horseshoe-shaped
(Acetabular Notch).
The deepest portion
(Acetabular Fossa).
Labrum Acetabular:
Is a wedged fibrocartilaginous ring
inserted into the acetabular rim
to increase the acetabular
concavity.

4. Frontal section
through hip joint

5. Lateral view of
hip bone

6. Anterior &
Posterior view

7. Angles of Hip Joint
(1)Center edge angle
• Seen in frontal Plane.
• Between two lines: 1st line:
Vertical line & center of the
head. 2nd line: Lateral rim &
center of the head.
• Average value: 22-42 degree.
• Function:
Provide lateral stability of the
pelvis “Coverage". Prevent
superior dislocation.
• Increased with age: that is why
congenital hip dislocation is common in
children ( diminished CE angle)

8. (2)Angle of Inclination
• Seen in frontal Plane.
• Lies between anatomical axis of the
neck and femoral shaft.
• Average value:150 in infancy &
decreased to 120 degrees in adults.
Pathological increase is Coxa Valga while
Pathological decrease is Coxa Vara .
• Function: Allow high degree of freedom.
”by moving the longitudinal axis of the
femur away from the hip joint”.
- N.B:The mechanical axis is a line from the
femoral head center to the midpoint of
femoral condyles. It makes 5-7 degrees with
the anatomical axis.

9. (3) Acetabular Anteversion Angle
 Seen in horizontal Plane.
 1st line: Anteroposterior vertical
line to the posterior rim.
 2nd line: Line connect the anterior
and posterior rim.
 20 degrees.
 Reason: Femoral condyles align
themselves so the knee joint axis
lies in the frontal plane.
 Function:
Prevent anterior hip joint
dislocation.

10. (4)Angle of Torsion
• Transverse Plane.
• Lies between the axis of the femoral neck
and the axis of the femoral condyles
“Frontal plane”.
• Facing anteriorly.
• 10-15 degrees. decreased with age. 40
degree in Newborn.
• Reason: Femoral condyles align
themselves so the knee joint axis lies in
the frontal plane.
• Function:
1- play a role in the hip stability.
2- one of the possible causes of excessive
internal or external hip joint rotation.
3- prevent threatening of congruency
during torsion.

11. 2- Capsule of the hip joint
 Strong, Dense, Shaped like a
cylinder sleeve.
 Attachment: Periphery of
acetabulum and cover neck
femoral neck.
 Thick anterosuperiorly, relatively
thin and loosely poster
inferiorly.
 Capsule has 4 sets of fibers
1- Longitudinal
2- Oblique
3- Arcuate
4- Circular

12. 3- ligaments
(1) Iliofemoral ligament
• Position: Fan-shaped, inverted letter Y. The thickest
and strongest ligament. In front of Jt.
• Attachment: Apex ”ASIS” Base “trochanteric” line.
Superior band “stronger”. Inferior band.
• Orientation: Downward, Inferior, & Lateral.
• Function:
1-limits hyperextension. 2-tight during Adduction.
3- Check both lat. & med. Rotation.

13. Iliofemoral
ligament

14. (2) Pubofemoral Ligament
• Position: Narrow band, Lower antermedial aspect
• Attachment: Superior pubic ramus to just at the end of
anterior capsule.
• Orientation: Downward, Inferior,& Lateral.
• Function:
1- Resist abduction & Extension.
2- Tense in lat. rotation and relax in med. rotation

15. a) Superior band b) Inferior band B) & C) behavior of iliofemoral
& pubofemoral in hip adduction and
(C) adduction

16. (3)Ischiofemoral ligament
• Position: Wide band on the posterior aspect,
Triangular shape.
• Attachment: post. & Inf. Aspect of acetabulum. To
inner surface of greater trochanter.
• Orientation: Outward & Anterior
• Function:
1- Superior fibers tight during extension, add. &med.
Rotation.
2- Inferior Fibers tight during flexion.

17. Ischiofemoral
ligament

18. (4)Ligamentum Teres
• Position: Inside the Joint, flat, narrow
triangular. Three bundles: Post ischial , Ant
Pubic & Intermediate bundle
• Attachment: Apex at fovea capitis to
acetabular notch.
• Orientation: downward.
• Function: Minimal mechanical role. It
contributes to the vascular supply of the
femoral head.

19. Ligament
teres

20. Muscles of the hip joint
• Flexors: “Iliopsoas”, rectus femoris, sartorius, tensor
fascia lata, pectineus, Add Longus, magnus & gracilis.
• Extensors: “GL Maximus”, hamstring, GL Medius, Add
magnus, Piriformis.
• Adductors: Pectineus, Add. Brevis, Longus & magnus and
gracilis.
• Abductors: “GL Medius & Minimus” Maximus, sartorius,
tensor fascia lata.
• Lat Rotators: Obturator internus & externus. Gemellus
Sup&Inf. Quadratus femoris & Piriformis.
• Med Rotators: No ms with primary function. But Anterior
portion GL medius & tensor fascia lata.

21. Muscles around hip joint

22. Functions of the hip joint
1- Support (HAT)
2- Closed Kinematic Chain: both the proximal and
distal end is fixed.
3- Provide a pathway for the transmission of force
between the pelvis and lower extremities and the
thrusting propulsive movements of the legs are
transmitted to the body.

23. Stability of the hip joint
• Closed-packed position: “Max.
Stability” Full Extension, slight med.
Rotation & Abduction. ”Less
Congruency” because ligaments are
taut.
• Loose-packed position “Min.
Stability. Full Congruent” Position:
flexion 90, small abduction & small
lat. Rotation “Quadruped Position”
because ligaments are slack

24. Stability of the hip joint
• The position of
greatest risk for
dislocation occurs
when the hip is flexed
and adducted ( sitting
with thigh crossed).
Mild force along the
femoral axis can cause
posterior dislocation.

25. Factors affecting stability of the hip Jt
1- Atmospheric pressure: -ve pressure inside
the Jt.
2- Shape of the articulating surface.
3- Labrum acetabular.
4- Direction of the femoral neck.
5- Capsule encircle the femoral neck.
6- Ligaments & Periarticular ms.

26. Surface motion of the hip joint
• Definition: motion happen at the articular
surfaces and can not be observed by the
eyes.
• From neutral position: Flexion “posterior
Spin” & extension “anterior spin”. Opposit
direction.
• From other position: Flex & Ext, Abd & Add,
Med & Lat, rotation. Spinning & Gliding.

27. Open and Closed chains of the hip joint
Open kinematic chain: head and trunk follow the
motion of the pelvis. (Lumber-pelvic rhythm)
Closed Kinematic Chain: head remains upright.
The lumbar spine tends to be the first line of
defense in both open and closed kinematic chain
of the hip joint.

28. Lumber-pelvic rhythm
A) Lumber pelvic rhythm during trunk flexion ( at
hip , pelvis and lumbar spine) aims to
increase ROM than might be available to one
segment.
45 degrees lumber flexion with trunk
inclination) & 90 degrees hip flexion
Sequence: flexion of lumbar spine , ant. Pelvic tilt
then hip flexion.
B) Lumber pelvic rhythm during trunk extension.
the reverse.
C) “closed kinematic chain”
Lumber spine rotate in one direction while
the lumber spine rotate in opposite direction

29. Trunk flexion
A) normal rhythm B) limited hip flexion C) limited lumber flexion.

30. Trunk extension
A) Early phase by extension hip B) Middle phase occurs by extension of
lumbar spine C) In last phase the muscle activity reduced.

31. Weight transmission through the hip joint
• Major Trabecular systems
1-Medial trabecular system “compression”
2-Lateral trabecular system “shearing &
tensile”
• Minor Trabecular system
1-Medial accessory
2-Lateral accessory

32. Trabecular system

33. Kinetic
• Static:
1- Bilateral stance :
symmetrical & asymmetrical.
2- Unilateral stance
• Dynamic:
Two peak forces the 1st (4w)
just after heel strike, the 2nd
(7w) just before toe off
(Abductor ms).

34. Statics: bilateral Standing
• A- In the sagittal plane: LOG falls just
posterior to the hip joint axis (extension
moment) checked by passive tension in the
ligaments & joint capsule.
• B- In the frontal plane: the weight of the
HAT equals 2/3 of BW (1/3 for each hip).

35. Statics: Transverse stability of the pelvis:
• A- Symmetrical bilateral standing :
no muscle activity is needed.
• B- Asymmetrical bilateral standing :
simultaneous contraction of the ipisilateral
and contralateral abductors and adductors to
restore balance.

36. Statics: unilateral Standing
• Stance hip carries 5/6 (4/6 w. of HAT + ¼ w. of
the other LE) of total BW (820 N.)

37. Reduction of joint reaction force:
Importance: If the hip joint undergoes osteoarthritic
changes leading to pain on weight bearing, the JRF must
be reduced to avoid pain.
Several strategies could be used:
1- Weight loss:
Reduce of 1N of body weight will reduce JRF 3N.
Example: if the patient lost 10kg, so the JRF will be
reduced by …….. N.

38. Reduction of joint reaction force:
2- Reduction of abductor muscle force:
This could be achieved by reducing the moment arm
of the gravitational force through lateral leaning of
trunk towards the side of pain or weakness.
• If the lateral trunk lean is due
to hip abductor weakness,
gait is called gluteus medius gait.
• If it is due to hip joint pain , gait
is called antalgic gait.

39. Reduction of joint reaction force:
• 3- using the cane ipsilaterally and
contralaterally:
• Ipisilateral: provide some benefits in
energy expenditure by reducing the BW
by the amount of downward thrust
• Yet, lateral trunk lean is more effective in
reducing JRF than using the cane
ipsilaterally .

41. Reduction of joint reaction force:
• Contralaterally: relieves the hip joint of 60%
of its load in stance.
• Equation of equilibrium will be as follow:
Abductor muscle torque + cane torque
(latissimus dorsi) = Gravitational torque.

42. Reduction of joint reaction force:

43. Dynamics
• Two peak forces
• The 1st (4w) just after heel strike,
• The 2nd (7w) just before toe off (Abductor
ms).

44. Pathomechanics
(1)- Bone abnormality:
A) Neck shaft angle:
- Coxa Valga
- Coxa Vara
B) Angle of torsion:
Excessive Anteversion Toe-in gait
Retroversion Toe-out gait

45. Neck Shaft Angle
Coxa Valga
• 1-Decrease bending moment arm.
2-Decrease shear across the
femoral neck.
3- decrease the hip abductor
moment arm.
4-Increase the demand on the hip
abductors.
• 5-Increasing JRF.
6-Increases the amount of
articular surface exposed
superiorly superior
dislocation.
7- decrease stability.

46. Coxa Vara
• 1-Increase bending moment arm.
2-Increase shear across the femoral neck( increased density
of lateral trabecular system due to increased tensile forces +
increased liability of femoral neck fracture in adults and
slipped capital femoral epiphysis.
3- Increase the hip abductor moment arm.
4-Decrease the demand on the hip abductors.
• 5-Decrease JRF.
6-Decrease the amount of articular surface exposed
superiorly with decreased liability of superior dislocation.
7- Increase stability.

47. Angle of torsion
• Excessive Anteversion:
• - Femoral head twisted anteriorly increasing the
amount of anterior articular surface exposure
predisposing to anterior dislocation.
• -Subject will walk with toe-in gait to restore stability.
• -Decrease abductor muscle moment arm.
• -Increase demand on hip abductors.
• -Increase JRF.

48. Retroversion
• - Femoral head twisted Posterior decreasing
the amount of anterior articular surface
exposure
• -Subject will walk with toe-out gait to restore
mobility.
• -Increase abductor muscle moment arm.
• -Decrease demand on hip abductors.
• -Decrease JRF.