Unit 2: Lower Limb Orthotics Flashcards
Describe an orthosis/orthotic device
An externally applied device used to modify the structural and functional characteristics of the neuromuscular and skeletal systems
What does the external force system comprise of
3 orthogonal forces: axial, ML and AP
3 moments acting in planes perpendicular to the force components
What is the internal force system
The action of body tissues which act to balance external forces
NOTE: the ground/foot force system, the internal force systems and the external force systems are all dependent upon one another
What is the orthosis/body force system
The system of forces generated between an orthosis and the body. Acts to resist or prevent abnormal motion, in effect modifying the internal force system
What is the direct action of the orthosis
The mechanism of an orthosis brought about by encompassing an impaired joint or body segment
What is the indirect action of the orthosis
The beneficial changes in external force system brought about at joints/segments that are not encompassed by the orthosis
What 2 aspects of orthosis design will affect its ability to create a desired improvement in function
Choice of components
Position of attachments
What forces must an orthosis/body force system need to resist or control directly
External moment acting about a joint
Normal force acting across a joint
Axial force across joint/segment
Normal force and moment acting on a body segment
What system must be employed by an orthosis to resist/control external moments NOT across a joint
Three-point force systems: aim to position the middle force as close to the joint as possible, with the other end forces as far away as possible
What system must be employed by an orthosis to resist/control external moments crossing a joint
Four-point force systems: ensure middle forces are as close to the joint as possible, with the end forces as far away as possible
What pressure system is used to resist both external moments and the normal force acting on a limb
Circumferential pressure system
What 4 components do all modern orthoses have
Interface components
Joints
Structural components
Cosmetic components
Give extrinsic factors that affect the response of soft tissue to its environment
Pressure
Shear
Microenvironment of the interface
Give intrinsic factors that affect the response of soft tissue to its environment
Reduced sensation Diminished attention Paralysis Diminished tissue turgor Failed vasomotor reflexes PVD Malnutrition Systemic disease
Factors that improve load transfer at the interface component
Large area of support, soft interface material, larger radius of curvature, contour the interface to the body shape, ensure good fit between orthosis and body
Name the 4 types of joint control
Free motion
Limited range of motion
Locked
Assistance or resistance to motion
Key qualities of orthotic structural components
Ability to withstand loads/avoid deformation, good cosmesis, lightweight inexpensive
Give examples of cosmetic components
Fillers, covers, sleeves and shells
What are contemporary lower limb orthoses commonly made from
Moulded thermoplastic shell interface components and a moulded thermoplastic foot piece
What are the 3 main categories of AFO application
Conditions which result in muscle weakness
UMN lesions
Conditions which lead to pain/instability due to loss of structural integrity
What problems will result from weak and absent dorsiflexion muscle control
Foot slap and foot drop
What orthosis is used to compensate for weak/absent dorsiflexion
Ortholen Posterior Leafspring Orthosis: joint function is achieved by the posterior strut = bends under loading for controlled plantarflexion, returns to neutral when load is relieved
What motion are no existing orthosis designs capable of providing
Active dorsiflexion beyond plantargrade
How does weak/absent plantarflexion commonly present
Excessive dorsiflexion prior to heel off
What orthosis is commonly used for weak/absent plantarflexion
Floor Reaction Orthosis: very rigid construction of the ankle section helps to resist large external dorsiflexion at midstance
How has the Floor Reaction Orthosis design been improved
Including an articulation in the AFO to allow some plantarflexion at heel contact, cushion heel, rocker sole
Consequence of weak pronator muscles
Foot hangs in varus, danger of further supination at foot contact leading to ligamentous injury
Consequence of weak supinators
Foot valgus = creates abnormally high dangerous stresses in the medial longitudinal arch
What orthosis is used for subtalar insufficiency
Polypropylene AFO: only able to eliminate subtalar motion because no designs are able to mimic subtalar joint motion
How to patients with unilateral knee extensor weakness overcome their instability
Lean forwards over the affected leg = brings GRF in front of the knee joint to create a stabilising moment
Note: if unable to do so, may require a Floor Reaction Orthosis
What two patterns of deformity are commonly seen in UMN lesion patients
Equinus and equinovarus
What orthosis is used for UMN lesion patients with equinus foot deformity
Polypropylene AFO
What is a problem with using a polypropylene AFO for equinus, and how can this be overcome
Prevents dorsiflexion during late stance or when performing activities such as squatting
Use an orthotic articulation which permits passive dorsiflexion whilst resisting plantarflexion
How does an AFO control ankle plantarflexion (e.g. in cerebral palsy children)
Moves the GRF posteriorly during mid and late stance = reduces the external knee extension moment, creates an external hip extension moment
Give a common cause of equinovarus
CVA
What orthosis is used for equinovarus
Polypropylene AFO: specifically shaped to emphasise the ML sites of force application
Give the common causes of impaired structural integrity of the ankle joint
Trauma and arthritis
Describe the Patellar Tendon Bearing AFO
Moulded plastic design consisting of a posterior ankle-foot shell that extends to the level of the knee crease, to which a hinged anterior shell (extending from mid-patella to ankle level) is attached
How does the PTB help to treat severely impaired structural integrity of the ankle
Provides an alternative skeletal loading bearing area proximal to the ankle
How should abduction/adduction instability be corrected
3 force system that applies a medial (for valgus) or lateral (for varus) force plus a distal and proximal force on the opposite side of the affected limb. Should also include an orthotic knee joint
What is the most common cause of AP instability
Rupture of the ACL
When would a KAFO be used
When patient has functional disorder affecting both the knee and ankle
Where the severity of the knee disorder and magnitude of controlling forces precludes the use of a KO
Where a KO would be preferred but there are problems with suspension
What are the 3 categories of applications of KAFO
Conditions that result in muscle weakness
UMN lesions that result in hypertonicity or spasticity
Loss of structural integrity of the knee or hip joints
How can patients overcome unilateral knee extensor power weakness
Flexing their trunk anteriorly to create a stabilising external knee extension moment
Manually pushing their thigh posteriorly
What are the most common UMN lesions which lead to KAFO prescription
Cerebral palsy, head injury and adult hemiplegia (due to stroke)
What response does the hemiplegic patient commonly adopt to achieve stance phase stability
Mass extensor response: ankle plantarflexion, knee extension, anterior trunk flexion
Note: these can lead to the development of a painful hyperextended knee
Describe the 3-force KAFO used to address the mass extensor response
One posteriorly behind the knee, the other two anteriorly proximally and distally
Also incorporate an orthotic knee joint: limits knee extension to just short of 180 degrees and permits near normal range of flexion
Identify the 3 main causes of loss of structural knee integrity
Trauma Joint disease (inflammatory or degenerative) Failed joint replacement
Describe the KAFO design commonly used to compensate for loss of structural knee integrity
KAFO with a moulded plastic quadrilaterally shaped thigh section (which creates the weight-relieving surface)
What are HKAFO usually prescribed for
Congenital hip abnormalities and paraplegia
What are the 3 categories of ambulation that a HKAFO must facilitate
Stand and swing through
Swivel
Reciprocating gait
Describe the stand and swing through mechanism
Conventional orthosis that incorporates locking hip and knee joints. Enables patient to stand and use walking aids to achieve swing through
Describe a swivel mechanism
A standing frame to which swivel mechanisms are added under each foot.
Pivoting is achieved by lateral trunk movement
Describe a reciprocating gait mechanism e.g. the Parawalker
Specially designed low friction orthotic hip joint with an extremely rigid alloy orthotic structure. Rigid structure reduces the degree of lateral trunk sway needed, and the low friction hip allows the free leg to swing forwards under the action of gravity
What is unique about the Reciprocating Gait Orthosis
Has a cable mechanism that imposes reciprocal action upon the orthotic hip joints
