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Orthopaedic Biomechanics > Joint reconstruction > Flashcards

Joint reconstruction Flashcards

1
Q

What are the objectives of disc replacement

A

Relieve back pain from degenerating disc

Provides an alternative to joint fusion - that preserves movement

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2
Q

Design considerations for disc replacement

A

Range of motion

Stresses (compressive, shear, bending, axial)

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3
Q

What are the 4 categories of artificial disks

A

Composite: Metal and UHMWPE sandwich
Mechanical: Material articulating with another
Nucleus: hydraulic component
Elastic: Deformable core

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4
Q

What are the 4 categories describing level of constraint

A

Constrained
Semi-constrained
Unconstrained
Deformable

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5
Q

Describe a composite unconstrained model

A
  • UHMWPE sphere
  • CoCr alloy endplates
  • Increase in flexion-extension and axial rotation compared to intact – excessively large range of motion
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6
Q

What part of the spine are composite unconstrained model used in

A

Lumbar spine

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7
Q

Describe a composite constrained model

A
  • CoCr alloy endplates
  • UHMWPE ball
  • Implant design intentionally restricts range of motion (smaller range of motion than unconstrained)
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8
Q

What part of the spine are composite constrained model used in

A

Cervical & Lumbar

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9
Q

Describe a mechanical semi-constrained model

A
  • CoCr metal-on-metal

* An issue with metal on metal is Metallosis

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10
Q

What part of the spine are mechanical semi-constrained model used in

A

Lumbar

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11
Q

Describe a nucleus/elastic deformable model

A
  • Polyurethane nucleus
  • Titanium alloy shells
  • ‘Press fit’ into spine
  • Takes more of anatomical approach
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12
Q

What part of the spine are nucleus/elastic deformable model used in

A

Cervical

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13
Q

Possible complications of disc replacement (5)

A 
Loosening
Fracture
Heterotopic calcification
Adjacent segment pathology
Wear
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14
Q

What are the 2 functional divisions of the ACL

A 
Anteromedial bundle (AMB)
Posterolateral bundle (PLB)
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15
Q

What kinds of motion are AMB and PLB responsible

A

AMB –> Prevents excessive anterior translation

PLB –> Controls rotational movement

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16
Q

What causes strain (and thus tear) of ACL

A

Forces on anterior tibia by quadriceps

Knee valgus movements

17
Q

Activities that can lead to ACL rupture

A

Pivoting
Jumping backwards (skipping, gymnasts)
Non-contact deceleration

18
Q

Pros and Cons of Allograft for ligament replacement

A

PRO: Person will not have to donate their own ligament
CON: biomechanical properties may be altered due to sterilisation

19
Q

Pros and Cons of Autograft for ligament replacement

A

PRO: No sterilisation necessary
CON: Donor site instability, Injury during procedure

20
Q

Pros and Cons of Synthetic graft for ligament replacement

A

PRO: High ultimate tensile strength, no donation needed
CON: Endogenous properties difficult to replicate

21
Q

Sites of ligament autograft

A

Patella tendon
Quadriceps tendon
Hamstrings tendon

22
Q

What needs to be done when using tendons to replace ligaments

A

Ligamenterisation - process takes over a year

23
Q

Why do tendons need to be ligamentarised

A

Tendons can onlt take significant load in one direction

24
Q

What is the advantage of replacing both bundles of ACL and not just AMB

A

give a result closer to endogenous ACL

25
Q

Objective of osteotomy

A

to modify load transmission by changing the alignment of the bone. Some examples

26
Q

Describe pathophysiology of Perthes’ disease

A

Blood supply to femoral head is temporarily disrupted leading to ischaemia and eventual necrosis

Dead tissue is replaced with woven bone which is weaker so fails under the loads a normal femoral head is subjected to

After years, this heals (re-ossification) but femoral head has a different shape than it normally would

27
Q

What type of Osteotomy is done to treat Perthes’ disease

A

Aim is to increase femoral head coverage by acetabulum
Close wedge osteotomy on FEMUR
Open wedge osteotomy on PELVIS

28
Q

Effect of Perthes osteotomy on muscles

A

decreases the moment arm of the abductor muscles which means that a larger force will need to be generated to achieve the same torque/moment so the muscle will be tired

29
Q

What type of Osteotomy is done to treat UNICOMPARTMENTAL osteoarthritis

A

An OPEN wedge osteotomy to straighten the mechanical axis

30
Q

Which compartment of the knee joint is more likely to suffer from osteoarthritis and why?

A

Medial

The reaction force from the ground acts on the medial compartment

Orthopaedic Biomechanics (15 decks)

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