Download Arthroplasty

BIOMECHANICS OF
ARTHOPLASTY
OBJECTIVES
What is Arthroplasty?
 Introduction to Total Hip Arthroplasty
 Introduction to Total Knee Arthroplasty.
 Biomechanical Influences in Arthroplasty
 Forces acting at Hip joint
 Measurement of Forces acting on a joint with
instrumental implants

ARTHROPLASTY
Arthroplasty is an operative procedure of orthopedic surgery
performed, in which the arthritic or dysfunctional joint surface is
replaced with something better or by remodeling or realigning the
joint by osteotomy or some other procedure.
Commonly Replaced joints
Hip joint
 Knee Joint
 Shoulder joint
Others

INDICATION OF ARTHOPLASTY
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Osteoarthiritis (oa)
Rheumatoid arthritis(ra)
Avascular necrosis(avn) or osteonecrosis (on)
Congenital dislocation of the hip joint
Acetabular dysplasia (shallow hip socket)
Frozen shoulder, loose shoulder
Traumatized and malaligned joint
Joint stiffness
Failure of other surgeries or Conservative treatment
IMPLANT MATERIALS
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The metal and plastic are the most commonly used
implants.
Surfaces joint are replaced with a metal prosthesis, and a
plastic spacer is placed in between.
The metals used include titanium, stainless steel, and
cobalt chrome.
The plastic is called polyethylene.
CEMENTED V/S NON CEMENTED
The implant is secured to the bone by one of two methods

Cemented
When an implant is cemented, a special bone cement is used to
secure the prosthesis in

Non-Cemented
In the press-fit method, the implant is fit snuggly into the bone,
and new bone forms around the implant to secure it in position.
When an implant is cemented, a special bone cement is used to
secure the prosthesis in
TOTAL HIP ARTHROPLASTY
INDICATIONS FOR SURGERY
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Severe hip pain with motion and weight bearing
Joint deterioration and loss of articular cartilage
Osteoarthritis
Rheumatoid or traumatic arthritis
Ankylosing spondylitis
Osteonecrosis (avascular necrosis)
Nonunion fracture
Bone tumors
Failure of conservative management or previous
joint reconstruction procedures
CONTRAINDICATIONS TO TOTAL
HIP ARTHROPLASTY
Absolute
1.
2.
3.
4.
5.
6.
Active joint infection
Systemic infection
Chronic osteomyelitis
Significant loss of bone
Naturopathic hip joint
Severe paralysis of the
muscle
Relative
1.
2.
3.
4.
Localized infection
Progressive neurological disorder
Insufficient function of the
gluteus medius muscle.
Highly compromised/insufficient
femoral or acetabular bone stock
5.
Patients requiring extensive
dental work.
6.
Young patients who must or are
most likely to participate in highdemand activities.
COMPONENTS OF THERAPY-RELATED
PREOPERATIVE MANAGEMENT: PREPARATION
FOR TOTAL HIP ARTHROPLASTY
1. Examination and evaluation
 pain,
 ROM
 muscle strength,
 balance,
 ambulatory status,
 leg lengths,
 Gait characteristics,
 use of assistive devices,
 general level of function,
 perceived level of disability
2.
3.
4.
5.
6.
Information for patients and their
families about joint disease and the
operative procedure in nonmedical
terms
Postoperative precautions and their
rationale including positioning and
weigh.
Functional training for early
postoperative days including bed
mobility, transfers, gait training
with assistive devices.
Early postoperative exercises
Criteria for discharge from the
hospital
METHODS OF FIXATION
Cemented.
 Cementless
 Hybrid

CEMENTED VERSUS CEMENTLESS FIXATION
Cemented Fixation
• Acrylic cement allow early postoperative weight
bearing
Disadvantage
• Aseptic (biomechanical) loosening
• of the prosthetic components at the
• bone–cement interface in younger,
• physically active patients

Cementless (biological) fixation
 porous-coated prostheses
 cementless press-fit technique
 Smooth (nonporous) femoral components
with cementless arthroplasty
 Coating of a bioactive compound called
hydroxyapatite
 Under 60 year of age
Disadvantage
Late weight bearing
CEMENTED OR CEMENT LESS
OPERATIVE PROCUDURE
Total Knee Arthroplasty
TOTAL KNEE ARTHROPLASTY
Indications for Surgery
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Severe joint pain with weight
bearing or motion
Extensive destruction of
articular cartilage
Marked deformity of the knee
Gross instability or limitation
of motion
Failure of nonoperative
management.
TYPES OF KNEE ARTHROPLASTY
TOTAL KNEE ARTHROPLASTY—DESIGN
SURGICAL APPROACH, FIXATION
Number of Compartments
Replaced
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Unicompartmental
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Bicompartmental
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Tricompartmental
TOTAL KNEE ARTHROPLASTY—DESIGN
SURGICAL APPROACH, FIXATION
Implant Design
 Unconstrained
 Semiconstrained
 Fully constrained
 Fixed-bearing or mobilebearing design
 Cruciate-retaining
TOTAL KNEE ARTHROPLASTY—DESIGN
SURGICAL APPROACH, FIXATION
Surgical Approach
 Standard/traditional or
minimally invasive
 Quadriceps-splitting or
quadriceps-sparing
TOTAL KNEE ARTHROPLASTY—DESIGN
SURGICAL APPROACH, FIXATION
Implant Fixation
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Cemented

Uncemented

Hybrid
OPERATIVE OVERVIEW
STANDARD APPROACH
COMPLICATIONS
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Intercondylar fracture
Damage to a peripheral nerve
Malunion
Loosening of prosthesis.
FLASHBACK
What is Arthroplasty?
 Introduction to Total Hip Arthroplasty
 Introduction to Total Knee Arthroplasty.

TODAY’S LECTURE
Biomechanical Influences in Arthroplasty
 Forces acting at Hip joint
 Measurement of Forces acting on a joint with
instrumental implants

WHY TO ASK QUESTIONS?
Most People do not listen with the intent to
understand; they listen with the intent to reply.
(Stephen Covey)
BIOMECHANICS OF ARTHROPLASTY
Purpose
 How to reduce weight on implant.
 How to implant design that can bear max weight
Results in
 Normal joint function
 Implant failure Problems
 Decrease Wear and tear
 Reduces chances of mechanical failure
 Minimize losening of implant
GOAL OF REPLACEMENT
Pain relief
 Long term restoration of function

FORCES AT HIP AND KNEE
External forces
 Internal forces
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MODIFICATIO IN IMPLANTS
Increase Stability
 Restoration of Mobility
 Prevent Complication
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Stability V/s Mobility?
 Implant with greater medullary canal fill
 Complication stiffness
DETERMINATION FORCES
These forces are measured with implant transducers or
inverse dynamic and analytical methods.
Involves calculating
 External ground reaction forces
 Approximating the limb segmental inertial forces.
 Location three dimensional forces position of joint.
APPROACHES TO STUDY
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Reduction method
Groups the muscle in functional units
Individual muscles are considered
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Optimization method
Force is distributed among muscles according to physical
parameters
Maximum muscle stress or endurance is considered
FORCES AT HIP JOINT
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Femoral Neck Angle:
FORCES AT HIP JOINT
Bergmann et al(1993) conducted an in vivo study of forces
acting on hip joint during daily activities . it states
Peak force increases with walking speed.
Noble,Helmke &Paul (1993) conducted a study on stem
size and features and foind
Stem with similar features experience similar forces
ROTATIONAL MOVEMENT ABOUT IMPLANTS
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Excessive bone implant
motion prevents bone
ingrowths into porous
coating
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Initial implant motion
is sensitive to off axis
loading
ROTATIONAL MOVEMENT ABOUT IMPLANTS
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Walking with decrease
ROM decreases pain
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Decrease head to neck
angle improves stability
RECONSTRUCTED JOINT GEOMETRY
Acetabular position
 Anterversion angle
 Neck to shaft angle
 Length of neck
 Attachment of muscles
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RECONSTRUCTED JOINT GEOMETRY
Example:
A decrease in head and neck angle and increase
in length of neck
• Increases efficiency of abductors
• Reduces joint contact forces
• Moves HOF deep within the acetabulum
RECONSTRUCTED JOINT GEOMETRY
Example:
An increase in neck shaft angle and decrease in
length of neck
 Decreases bending forces on femur
 Decreases efficiency of abductor
RECONSTRUCTED JOINT GEOMETRY
Positioning of joint centre
Joint forces are minimized if centre of
Joint is placed
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Inferiorly
Medially
Anteriorly
What happen if centre is opposite to above position
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Increased ground reaction forces
Decrease efficiency of abductor, adductors &flexors
Increases chances of loosening
RECONSTRUCTED JOINT GEOMETRY
Stem position within the femoral canal
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Valgus V/s Varus Conflicts
Biomechanical analysis favors valgus position
Subject studies show varus position can hold better forces
Gait abnormalities persist in varus patients
RECONSTRUCTED JOINT GEOMETRY
Periprosthetic bone loss
•
Wear particles from polyethylene and other material are
seen in joint fluid
•
Foreign body reaction and start osteoclastic activity
•
Bone loss
•
Undersized or unstable components cause more bone loss
RECONSTRUCTED JOINT GEOMETRY
Periprosthetic bone loss
Other causes
 Stress shielding
 Disuse of limb can also effect proximal tibia
 Preoperative bone condition
SUMMARY
Arthroplasty is the replacement of joint
 Hip and Knee are most commonly replaced joints
 Implants design and materials used in
Arthroplasty determine the quality and life of
replacement
 Different forces acting on a joint can be
calculated
 Modification in implant design and material can
be done on the basis of these calculations
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STABILITY OF JOINT
Complex articulation
 Soft tissue
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REASONS OF FAILURE OF IMPLANT
Cyclic fatigue of interfaces
 Implant material
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Forces on Knee are proportional to contact forces
SHIFTING OF LOAD
Tractive rolling forces of femur on tibia during
flexion
MEDIAL LATERAL LOAD DISTRIBUTION
Tibial component loosening is main cause of
failure
 It is due to imbalance between force acting at
both sides of knee
 During walking about 70% weight is put on
medial compartment
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MEDIAL LATERAL LOAD DISTRIBUTION
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Knee with varus alignment are most likely to
have uneven weight distribution thus leading to
loosening of tibial component
PATEL FEMORAL JOINTS AND LOAD
PATEL FEMORAL JOINTS AND LOAD
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Maintaining normal femoral
trochlear anatomy is important to
produce normal movement
People who have small trochlear
radius for patellar flang showed
increased knee flexion during
stance phase
This produced abnormal gait
pattern
Maintaining normal femoral
trochlear anatomy require excessive
bone cutting
JOINT LINE HEIGHT
Shifting of position of joint line superiorly lowers
the point of contact between patella and femur
 This decrease the flexion movement.
 If contact point is put 15mm below, it will reduce
more than 50% flexion during stair climbing
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POSTERIOR CRUCIATE LIGAMENT
Retaining
 Substituting
 Removing
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POSTERIOR CRUCIATE LIGAMENT
Limited range of motion and posterior
polyethylene tear can be due to pcl that is is too
tight
 Normal gait pattern and knee mobility is possible
in retaining surgeries
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POSTERIOR CRUCIATE LIGAMENT
In the absence of pcl posterior directed forces are
controlled by contact surfaces
 Variety of constrained design is possible to
compensate pcl
 Mobility is always compromised in cost of
stability
 Gait pattern and stair climbing is disturbed
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POSTERIOR CRUCIATE LIGAMENT
REASONS OF LEANING
Normal Rolling mechanism is lost
 Soleus muscle has to work more while stair
climbing
 Radius of femoral component changes during
flexion and extension
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CONFIRMITY
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The degree of conformity of femoral and tibial
components depends upon ratio of their radai
POLYETHYLENE
Damage to polyethylene can be
due to
Thickness
 Material properties
 Third body particle
 Area of high contact stress
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A metal backing was later
introduce to compensate
damage
ANTERIOR CRUCIATE LIGAMENT
Retained
 Removed
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An altered walking pattern is seen in patients
with acl sacrificing surgery
 Loss of joint Proprioception and function of ACL
may be the cause of this altered patterns.
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Studies are being conducted to clear the role of
ligaments after TKR