This document summarizes the biomechanics of the hip joint. It describes the bony anatomy including the femoral head, acetabulum, and labrum. It also discusses the capsule, ligaments including the iliofemoral, pubofemoral, and ischiofemoral ligaments. Muscles that act on the hip joint and the ranges of motion are outlined. Factors affecting hip joint stability and weight transmission through the joint are summarized. Pathomechanics related to variations in the neck shaft angle and angle of torsion are covered.

1. Biomechanics of Hip

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

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. Kinematics
Hip motion takes place in all three planes:
sagittal (flexion-extension)
frontal (abduction-adduction)
transverse (internal-external rotation)
Muscle, ligament and configuration…
asymmetric

34. Kinematics
Rang of motion : sagittal, frontal, transverse
0~140 0~300~15 0~25
0~90 0~70

35. Kinematics
35 to 40°
One gait cycle
Frontal plane
Transverse plane
Toe-off

36. Kinematics
Murray and coworkers (1969) studied the
walking patterns of 67 normal men of similar
weight and height ranging in age from 20 to
87 years and compared the gait patterns of
older and younger men

37. Kinematics
Old man : shorter strides
Decrease:
Rang of hip flexion,
extension
Plantar flexion of ankle
Heel-floor angle
Old man Young man

38. Kinematics
hip flexion of at least
120°
Abduction and external
rotation of at least 20 °

39. Surface Joint Motion
Surface motion in the hip joint can be considered
as gliding of the femoral head on the acetabulum.
Center of rotation:
estimated at the center of the femur head

40. Kinetics
Forces acting on the hip joint : must be
understood
Prostheses design
Fixation devices
Osteotomy operation
Rehabilitation
STATICS and DYNAMICS

41. 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).

42. 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).

43. 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.

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

45. 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.

46. 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.

47. 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 .

49. 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.

50. Reduction of joint reaction force:

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

52. 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

53. 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.

54. 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.

55. 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.

56. 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.