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.
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Anatomy and Biomechanics of the Hip Joint
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.
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.
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.
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
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
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