Joint reconstruction Flashcards
What are the objectives of disc replacement
Relieve back pain from degenerating disc
Provides an alternative to joint fusion - that preserves movement
Design considerations for disc replacement
Range of motion
Stresses (compressive, shear, bending, axial)
What are the 4 categories of artificial disks
Composite: Metal and UHMWPE sandwich
Mechanical: Material articulating with another
Nucleus: hydraulic component
Elastic: Deformable core
What are the 4 categories describing level of constraint
Constrained
Semi-constrained
Unconstrained
Deformable
Describe a composite unconstrained model
- UHMWPE sphere
- CoCr alloy endplates
- Increase in flexion-extension and axial rotation compared to intact – excessively large range of motion
What part of the spine are composite unconstrained model used in
Lumbar spine
Describe a composite constrained model
- CoCr alloy endplates
- UHMWPE ball
- Implant design intentionally restricts range of motion (smaller range of motion than unconstrained)
What part of the spine are composite constrained model used in
Cervical & Lumbar
Describe a mechanical semi-constrained model
- CoCr metal-on-metal
* An issue with metal on metal is Metallosis
What part of the spine are mechanical semi-constrained model used in
Lumbar
Describe a nucleus/elastic deformable model
- Polyurethane nucleus
- Titanium alloy shells
- ‘Press fit’ into spine
- Takes more of anatomical approach
What part of the spine are nucleus/elastic deformable model used in
Cervical
Possible complications of disc replacement (5)
Loosening Fracture Heterotopic calcification Adjacent segment pathology Wear
What are the 2 functional divisions of the ACL
Anteromedial bundle (AMB) Posterolateral bundle (PLB)
What kinds of motion are AMB and PLB responsible
AMB –> Prevents excessive anterior translation
PLB –> Controls rotational movement
What causes strain (and thus tear) of ACL
Forces on anterior tibia by quadriceps
Knee valgus movements
Activities that can lead to ACL rupture
Pivoting
Jumping backwards (skipping, gymnasts)
Non-contact deceleration
Pros and Cons of Allograft for ligament replacement
PRO: Person will not have to donate their own ligament
CON: biomechanical properties may be altered due to sterilisation
Pros and Cons of Autograft for ligament replacement
PRO: No sterilisation necessary
CON: Donor site instability, Injury during procedure
Pros and Cons of Synthetic graft for ligament replacement
PRO: High ultimate tensile strength, no donation needed
CON: Endogenous properties difficult to replicate
Sites of ligament autograft
Patella tendon
Quadriceps tendon
Hamstrings tendon
What needs to be done when using tendons to replace ligaments
Ligamenterisation - process takes over a year
Why do tendons need to be ligamentarised
Tendons can onlt take significant load in one direction
What is the advantage of replacing both bundles of ACL and not just AMB
give a result closer to endogenous ACL
Objective of osteotomy
to modify load transmission by changing the alignment of the bone. Some examples
Describe pathophysiology of Perthes’ disease
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
What type of Osteotomy is done to treat Perthes’ disease
Aim is to increase femoral head coverage by acetabulum
Close wedge osteotomy on FEMUR
Open wedge osteotomy on PELVIS
Effect of Perthes osteotomy on muscles
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
What type of Osteotomy is done to treat UNICOMPARTMENTAL osteoarthritis
An OPEN wedge osteotomy to straighten the mechanical axis
Which compartment of the knee joint is more likely to suffer from osteoarthritis and why?
Medial
The reaction force from the ground acts on the medial compartment
