2. INTRODUCTION
• Hip is a classical ball-and-socket
joint.
• It meets the four characteristics of
a synovial or di-arthrodial joint:
1. It has a joint cavity
2. Joint surfaces are covered with
articular cartilage.
3. It has a synovial membrane
producing synovial fluid.
4. Surrounded by a ligamentous
capsule.
3. FEMUR
• Longest and strongest bone in the human body
• Femoral head is covered with articular cartilage beyond the reaches
of the acetabular brim to accommodate the full range of motion.
• Ante version 12 to 15 degrees.
Coxa vara(<120) NORMAL
(120-135)
COXA VALGA(>135)
8. HIP ABDUCTORS
Gluteus medius
Gluteus minimus
Tensor facia lata
EXTERNAL ROTATORS(SHORT)
Piriformis
Superior gemellus
Obturator internus
Inferior gemellus
Quadratus femoris
INTERNAL ROTATORS
Tensor fasciae lata
Gluteus medius
Gluteus minimus
9. BLOOD SUPPLY
Blood Supply to Head of Femur
• Child, obturator artery via ligamentum
teres supplies epiphysis
• Elderly, main supply via retinacular vessels from
trochanteric and cruciate anastamoses
• Medial and lateral circumflex femoral vessels
10. BLOOD SUPPLY
• Superior gluteal artery
• Inferior gluteal artery.
• Transverse and ascending
branches of lateral circumflex
femoral artery.
• Transverse and ascending
branch of medial circumflex
femoral
• Cruciate and trochanteric
anastomosis
12. BIOMECHANICS OF HIP.
Science that deals with the study
of forces (internal or external )
acting on the living body
Forces acting on the hip
The abductor musculature ,acting
on the lever arm extending from
the lateral aspect of the greater
trochanter to the center of
femoral head ,must exert an equal
moment to the body weight arm to
hold the pelvis level
13. FORCES ACTING ON THE HIP
• Fig A. Lever arms acting on hip joint.
• Moment produced by body weight applied at body's center
of gravity, X, acting on lever arm, B-X,
must be counterbalanced by moment produced by
abductors, A, acting on shorter lever arm, A-B.
• Fig B. Lever arm A-B may be shorter than normal in arthritic
hip.
• Medialization of acetabulum shortens lever arm B-X,
• and use of high offset neck lengthens lever arm A-B. ,
• Fig c. Lateral and distal reattachment of osteotomized greater
trochanter lengthens lever arm A-B further and tightens
abductor musculature.
14. BIOMECHANICS OF HIP
• 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
• Anteversion
– Anteverted 40 deg at birth
– 12-15 deg in adults
15. 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 degrees.
16. BIOMECHANICS OF HIP.
• To maintain stable hip, torques produced by the body weight is
countered by abductor muscles pull.
• Abductor force X lever arm1 = weight X leverarm2
17. TRENDELENBURG GAIT
The factors influencing both the magnitude and the direction
of the compressive forces acting on the femoral head are
1) the position of the center of gravity
2) the abductor lever arm, which is a function of the neck-
shaft angle
3) the magnitude of body weight
18. STRATEGIES for reducing joint reaction force….
• This can be accomplished by limping, however the lateral movements
required take a considerable amount of energy and is a much less efficient
means of ambulation.
• Another strategy to reduce joint reaction force involves using a cane or
walking stick in the opposite hand.
• The moment produced from both the cane and abductor muscles
together produce a moment equal and opposite to that produced by the
effective body weight.
• The two-dimensional static analysis indicates that the joint reaction force
can be reduced by 50%(from 3 times body weight to 1.5 times body
weight)
19. PRINCIPLES 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
20. OFFSETS…..
• Vertical Ht (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, it shortens
the moment arm ,produce limp, increase
bony impingement
• Excessive medial offset – dislocation,
increases stress on stem & cement stress
# or loosening
