The hip joint is a ball and socket synovial joint that allows flexion, extension, abduction, adduction, and medial/lateral rotation. It connects the femoral head to the acetabulum and is stabilized by ligaments and muscles. Biomechanically, the hip acts as a fulcrum with the body weight and abductor muscles balancing each other. Total hip replacement aims to reduce joint reaction forces by centralizing the femoral head and lengthening the abductor lever arm. Proper restoration of offsets and version are important for implant stability and function.

1. ANATOMY AND
BIOMECHANICS OF HIP
JOINT
MODERATOR- DR V. AGARWALA
ASSISTANT PROFESSOR, DEPT OF ORTHOPAEDICS,SMCH
PRESENTED BY- DR UJJAL RAJBANGSHI
PGT ORTHOPAEDICS,SMCH

2. ANATOMY
 It is the largest joint of the human body.
 2nd largest weight bearing joint of human body.
 Hip joint is a synovial articulation between head of femur and acetabulum
.
 Type: Multiaxial ball and socket type of synovial joint
 Hip joint is designed for stability over a wide range of movements
 Descriptive planes:
• Flexion/extension : sagittal plane
• abduction/adduction : frontal plane
• medial /lateral rotation : transverse plane (circumduction)

3. ANATOMY - ACETABULUM
 Acetabulum is the depression or fossa where the femoral head
articulates .
 It is positioned in downward and outward direction
 The rim of acetabulum is raised slightly by a fibro cartilaginous collar
known as acetabular labrum. Inferiorly the labrum bridges across the
acetabular notch as the transverse acetabular ligament and converts
the notch into foramen
 The lunate surface of the acetabulum is covered by hyaline cartilage
except for fovea
 Acetabular fossa is non articular . Formed mainly by ischium and
contains loose connective tissue.

4. ANATOMY -FEMUR
 Head of femur is globular and forms 2/3 of a sphere.
 Covered by hyaline cartilage (except fovea)
 The femur connects to the head via femoral neck
 The angle of inclination is approximately 135 degrees
 The angle of anteversion or torsion is forward relationship of head and
neck.
 The angle of torsion is normally in the 12-15 degrees

5. ANATOMY -CAPSULE
 Strong, thick
 MEDIALLY : attached to margin of acetabulum, transverse
acetabular ligament, and adjacent margin of obturator foramen
 LATERALLY : attached to intertrochanteric line of femur,
Just proximal to intertrochanteric crest on posterior surface.
 Femoral neck : intracapsular
 Greater and lesser trochanter: extracapsular

6. ANATOMY –SYNOVIAL MEMBRANE
 Lines the intracapsular portion of neck of femur and
both surfaces of acetabular labrum, transverse ligament
and fat in acetabular fossa.
 Forms a tubular covering around the ligament of head
of femur and lines the fibrous membrane of joint

7. ANATOMY –LIGAMENTS
 The ligaments of the hip joint can be divided into two groups –
Extracapsular and Intracapsular
 3 ligaments reinforce the external surface of fibrous membrane and stabilize
the joint they are
1) iliofemoral ligament
2) pubofemoral ligament
3) ischiofemoral ligament
 Fibers of all three ligaments are oriented in a spiral fashion around the hip
joint so that the become taught when joint is extended.
 This stabilizes the joint and reduces the amount of muscle energy required
to maintain a standing position.

8. ANATOMY –LIGAMENTS

9. ANATOMY –LIGAMENTS
 Intracapsular :
 Ligament of head of femur. It is a relatively small structure, which runs
from the acetabular fossa to the fovea of the femur. – It encloses a
branch of the obturator artery (artery to head of femur), a minor source
of arterial supply to the hip joint.
 Transverse acetabular ligament.
 Acetabular labrum.

10. ANATOMY –LIGAMENTS
 LIGAMENTUM TERES:
 Also known as Round Ligament or Ligament of Head of Femur or foveal
ligament
 Triangular and Flat
 Ensheathed by synovial membrane.
 Transmits arteries to head of femur from acetabular branches of
medial circumflex and femoral arteries.

11. ANATOMY –LIGAMENTS

12. ANATOMY –NERVE SUPPLY
 Femoral nerve(anteriorly)
Femoral nerve not only supplies hip joint via intermediate and
cutaneous nerve of thigh, also supplies skin of front and medial side of thigh
 Anterior division of Obturator nerve(inferiorly)
 Nerve to Rectus femoris
 Nerve to Quadratus femoris (posteriorly)
 Sciatic nerve
 Superior gluteal nerve (superiorly and posteriorly)
Posterior division of obturator nerve supplies both hip and knee joint.
Therefore sometimes there is referred pain to knee joint.

13. ANATOMY –NERVE SUPPLY

14. ANATOMY –BLOOD SUPPLY
 The hip joint is supplied with blood from:
 The medial circumflex femoral and lateral circumflex femoral arteries,
which are both branches of the deep artery of the thigh (profunda
femoris)
 There is also a small contribution from the foveal artery, a small vessel
in the ligament of the head of the femur which is a branch of the
posterior division of the obturator artery
 The hip has two anatomically important anastomoses, the cruciate and
the trochanteric anastomoses, the latter of which provides most of the
blood to the head of the femur. These anastomoses exist between the
femoral artery or profunda femoris and the gluteal vessel

15. ANATOMY –BLOOD SUPPLY

16. ANATOMY-MUSCLES OF HIP JOINT

17. ANATOMY-MUSCLES OF HIP JOINT

18. ANATOMY-MUSCLES OF HIP JOINT

19. ANATOMY –MOVEMENTS

20. BIOMECHANICS –HIP JOINT
 The hip joint, or coxofemoral joint, is the articulation of the
acetabulum of the pelvis and the head of the femur
 Diarthrodial ball-and-socket joint
 There are three degrees of freedom:
 1. flexion/extension in the sagittal plane .
 2. abduction/adduction in the frontal plane .
 3. medial/lateral rotation in the transverse plane.

21. BIOMECHANICS –HIP JOINT
 THE NECK OF FEMUR:
 Angulated in relation to the shaft in 2 planes :
 sagittal & coronal
 Neck Shaft angle
 140 deg at birth
 120-135 deg in adult
 Ante version
 Anteverted 40 deg at birth
 12-15 deg in adults

22. BIOMECHANICS –HIP JOINT
 ACETABULAR DIRECTION:
 long axis of acetabulum points
 forwards : 15-20 degree ante version
 45 degree inferior inclination ante version

23. BIOMECHANICS –HIP JOINT
 AXIS OF LOWER LIMB:
 Mechanical axis line passes between center of hip joint
and center of ankle joint.
 Anatomic axis line is between tip of greater trochanter
to center of knee joint.
 Angle formed between these two is around 6-7 degrees

24. BIOMECHANICS –HIP JOINT
 First order lever
 fulcrum (hip joint)
 forces on either side of fulcrum
 i.e, body weight & abductor tension

25. BIOMECHANICS –HIP JOINT
 To maintain stable hip, torques produced by the body weight is
countered by abductor muscles pull.
 Abductor force X lever arm1 = weight X leverarm2

26. BIOMECHANICS –HIP JOINT
 FORCES ACROSS THE HIP JOINT IN TWO LEG STANCE:
 Lower Limb constitute 2/6 (1/6 + 1/6), and Upper Limb & trunk
constitute 4/6 the total body weight
 Little or no muscular forces required to maintain equilibrium in 2 leg
stance
 Body weight is equally distributed across both hips
 Each hip carries 1/3rd body weight (4/6 = 2/3 = 1/3 + 1/3)

27. BIOMECHANICS –HIP JOINT
 Single leg stance - Right
 Right Lower Limb supports the body weight & also the Left Lower
Limbs i.e. 5/6th total body weight.
 Effective Centre of gravity shifts to the non-supportive leg (L) &
produces downward force to tilt pelvis
 Right abductors must exert a downward counter balancing force with
right hip joint acting as a fulcrum. 4/6 +1/6 =5/6
 i.e. Body weight acts eccentrically on the hip and tends to tilt the pelvis
in adduction ---- balanced by the abductors

28. BIOMECHANICS –HIP JOINT
 USE OF CANE / WALKING STICK
 It creates an additional force that keeps the pelvis level in the face of
gravity's tendency to adduct the hip during unilateral stance.
 Decreases the moment arm between the center of gravity and the
femoral head(R)
 The cane's force must substitute for the hip abductors.
 Long distance from the Centre of hip to contralateral hand offers
excellent mechanical advantage

29. BIOMECHANICS –HIP JOINT
Cane and Limp
Both decrease the force exerted by the body weight on
the loaded hip
Cane: transmits part of the body weight to the ground
thereby decreasing the muscular force required for
balancing
Limping shortens the body lever arm by shifting the
centre of gravity to the loaded hip

30. BIOMECHANICS –HIP JOINT
 TRENDELENBURG SIGN
 Stand on LEFT leg—if RIGHT hip drops,
then it's a + LEFT Trendelenburg
 The contralateral side drops because the
ipsilateral hip abductors do not stabilize the pelvis to prevent the drop.

31. BIOMECHANICS –HIP JOINT
 Biomechanics in neck deformities :
 Coxa valga :
 Increased neck shaft angle
 Greater Trochanter is at lower level
 Shortened abductor lever arm
 Body weight arm remains same
 Increased joint forces in hip during one leg stance
 Less muscle force required to keep pelvis horizontal

32. BIOMECHANICS –HIP JOINT
 Coxa Vara
 Decreased neck shaft angle
 Greater Trachanter is higher than normal
 Increased abductor lever arm
 Abductor muscle length is shortened
 Decreased joint forces across the hip during one leg stance
 Higher muscle force is required to keep pelvis horizontal

33. BIOMECHANICS –HIP JOINT
 Joint Reaction Force
 Forces generated within a joint in response to external forces (both
intrinsic and extrinsic).
 Can reach 3 to 6 times body weight & is primarily due to contraction of
muscles crossing the hip.
 Twice during SLRT
 3 times in single leg stance
 5 times in walking
 Upto 10 times while running
 Reduced to half upon using a cane

34. BIOMECHANICS –HIP JOINT

35. BIOMECHANICS –HIP JOINT
 Biomechanics of THR
 Principle – to decrease joint reaction force
 Centralization of femoral head by deepening of Acetabulum - decreases
body weight lever arm
 Increase in neck length and Lateral reattachment of trochanter -
lengthens abductor lever arm
 This decreases abductor force, hence joint reaction force, & so the wear
of the implants.

36. BIOMECHANICS –HIP JOINT
 Joint reaction forces are minimal if hip centre placed in anatomical
position
 Adjustment of neck length is important as it has effect on both medial
offset & vertical offset

37. BIOMECHANICS –HIP JOINT
 OFFSETS:
 Vertical Height (offset) Determined by the Base
length of the Prosthetic neck and length gained by the
head
 Horizontal Offset (Medial offset) center of the head to the
Axis of the stem
IF……
Medial offset is inadequate -- shortens the moment arm -- limp, increase
bony impingement
Excessive medial offset – dislocation, increases stress on stem & cement --
stress fracture or loosening

38. BIOMECHANICS –HIP JOINT
 In regular THR , the Femoral component must be inserted in the same
orientation as the femoral neck to achieve the rotational stability .
 Modular component in which stem is rotated independently of the
metaphyseal portion
 Anatomical stems have a few degrees of ante version built into the
neck

39. BIOMECHANICS –HIP JOINT
 Femoral components available with a fixed neck shaft angle 135º
 Restoration of the neck in ante version - 10-15º
Increased ante version -- anterior dislocation
Increased retroversion -- posterior dislocation
 Cup placed in 15 -20 degrees of ante version and 45 degrees of
inclination

40. BIOMECHANICS –HIP JOINT
 HEAD DIAMETER :
 Large diameter head compared to
Small head – Less prone for dislocation – Range of
motion is more

41. THANK YOU