The biomechanical model is concerned with the capacity for functional motion. That is, the movement required to perform ones occupations. It is based on mechanistic philosophy whereby the dysfunctional part is analysed.
What is the doman of concern of the biomechanical model?
The model is based on the assumption that voluntary movement and control are the result of muscle strength and function, joint integrity and range, and physical endurance or tolerance (Reed, 1984, p278). The capacity for motion therefore, has three main components (Kielhofner 1997):
1. Joint range of motion
What is the ASSUMPTIONS of the model?
Each joint is potentially able to move in certain directions and to certain limits of motion due to its bony structure and the integrity of surrounding tissues (Trombly 1995, p73).
Muscle Strength has been defined "as the capacity of a muscle to produce the tension necessary for maintaining posture, initiating movement, or controlling movement during conditions of loading of the musculo-skeletal system" (Smidt & Rogers, 1982, in Trombly 1995, p107). Muscle fibres of repeatedly recruited motor units hypertrophy in response to increased resistance or load thereby increasing strength (Downey & Darling, 1971, in Trombly 1995, p413).
Endurance is the ability to sustain effort. Energy is needed for a person to produce the required intensity or rate of effort over a period of time necessary to complete a given exercise or activity (Trombly 1995, p153). Factors influencing endurance may relate to oxygen supply from the cardiopulmonary system or to impairment of a muscle or muscle group through localised trauma to the muscle itself or other structure or reduction of innervation to the muscle (Trombly, 1995, p153).
What exactly is meant by range of motion, strength and endurance in biomechanical terms?
The central concern of this model is a limitation of sustained stability or movement that produces an incapacity to perform occupations (Kielhofner, 2004). That is, inadequate range of motion, Strength, and/or endurance for the requirements of a person's occupational performance (or daily life tasks).
A further area often addressed within this model which may impact on the capacity for motion is Oedema . The prognosis for untreated this problem is devastating: permanent loss of ROM, loss of sensation, and compromised nutrition to distal body parts, which may lead to amputation (Dutton 1995). Few occupational therapists would actively assess and treat Oedema alone, but need to know about its assessment and treatment in combination with other deficits addressed
Dysfunction of the biomechanical model
Structural instability (re Joints )
Maintaining and improving ROM
Maintaining &/or increasing Strength
High level endurance
Dysfunction or problems requiring treatment may be around issues such as:
and occupational performance areas:
Activities of daily living
When working within the biomechanical model, we consider performance components:
Range of movement (active [AROM] and passive [PROM]):
Jebsen Hand Function Test
manual muscle testing, eg Oxford Scale
percent of maximal heart rate
Intensity eg Metabolic costs of activity- METs.
volumetric measurement (water displacement)
Other components include dexterity and co-ordination, often measured using a peg test of some sort. Also sensation, although not strictly coming under this framework, it is often considered alongside the above.
Occupational Performance Areas
Activities of Daily Living
Nottingham ADL/Extended ADL
Tessa - The Enabling System and Skills Assessment
Valpar - Component Work Sample Series
What are some examples of evaluation techniques or tools you would use in each of these areas?
Prevention and Maintenance - to prevent deformity and maintain existing capacity for motion
Restoration - to improve diminished capacities for motion, strength and endurance
Compensation - to adapt for limited motion
Goals for intervention
upper extremity orthotics
Intervention within this model can be considered in the following areas:
Substitute for lost motion
Consider the use of teaching adapted procedures over issuing equipment, and see what advantages and disadvantages you can come up with. Once you have a list, click below for some hints.
Require habit change
Lack external prompts
Require habit change
Lack external prompts
Adapted procedures are preferred over equipment. The main reasons to teach adapted procedures are:
Consider what you have read, and see what advantages and disadvantages of using equipment you can list. Click on the button below and compare your list with what is here.
Good face validity
Adaptive Devices or equipment is probably the most commonly used or applied intervention technique for occupational therapists working n this model. The main reason for the use of equipment is to compensate for loss of ROM or strength. Sometimes equipment is prescribed for the loss of or absence of limb function, and sometimes to prevent deformity (e.g. splints with arthritis). What are the advantages and disadvantages of using equipment.
Support of painful joints (eg arm slings, arm troughs, playboards) such as a painful shoulder, elbow, wrist or hand
Immobilization for healing or protection of tissues
Provide stability or restrict unwanted movement/motion
Prevention of contractures or normalising tone
Restore mobility to joints
Upper extremity orthotics has been defined by Desharies (in Trombly & Radomski 2002, p313) as any medical device added to a person's body to support, align, position, immobilize, prevent or correct deformities, assist weak muscles, or improve function; also known as a splint, brace, or support.
The main purpose for prescription of orthotics under this approach is to compensate for reduced muscular strengh by substituting for weak or absent muscles (eg wrist splints, mobile arm supports etc). Orthotics have the same advantages and disadvantages as adaptive devices (Dutton, 1995), but in addition, they can tend also to be bulky and uncosmetic.
As well as bing useful within the compensatory approach, upper extremity orthotics can have a role to play in the areas of prevention and maintenance. Can you think what that might be? Click below for some ideas.
Reduce weight-bearing on lower limbs - either on a temporoary or permanent basis
To provide a wider base of support eg the use of a quad walker or a zimmer frame can achieve this
Support of unstable joints eg leg braces
Wheelchair prescription and modifications involves five main rationales, according to Dutton, 1995:
Facilitate proper positioning
Overcome architectural barriers
Permit transportation of objects
Other than substitution for a lost limb, and facilitating the ability to transport needed objects, why else do you think ambulatory or mobility devices are required for some individuals?
fixed toilet frames
raised toilet seats
Environmental Modifications can be considered
.... 'any equipment that changes the environment for everyone who shares space with the patient'....
(Dutton, 1995, p178)
To provide access
To promote independence
To promote safety
To promote energy conservation, work simplification, and joint protection
What are some examples that you have learned about of seen in practice?
b. Approach - restorative although may require some aspects of compensatory in the interim.
c. Assessments - dynamometer; observation of functional tasks; interview
d. Intervention techs - Stress to muscle tissue can be graded by increasing the speed and/or resistance needed to complete the task and by increasing the number or repetitions of an isotonic contraction or the amount of time an isometric contraction is held (Trombly, 1995, p246). Adaptation of tasks or activities
1. Client referred to occupational therapy outpatient service following an injury to her non-dominant upper limb - mid-shaft fractures of the radius and ulna as a result of blunt trauma secondary to fire work explosion during party celebrations. This occurred six weeks ago.
a. Problem - has difficulty sustaining a functional grip due to muscle weakness
b. Approach - preventative in respect to the risk of injury to the carer around moving and handling.
c. Assessments - carer and client interview, observation of transfer, risk assessment
d. Intervention techs - predominately education to the carer around correct body mechanics and moving and handling techniques with the father
You are working in the community and have been referred a very tall gentleman who is having trouble getting in and out of bed, requiring the assistance of one person. His daughter has contacted you, following his discharge from a nursing home - she is now living with him and is his main carer.
a. Problem - is unable to transfer off the bed effectively due to risk of injury to carer
b. Approach - preventative in respect to prevention of further injury
c. Assessments - client interview, work-site assessment, risk assessment
d. Intervention techs - predominately education to the client around correct body mechanics and moving and handling techniques within his workplace (and perhaps at home too regarding moving and handling at home)
3. Client referred to your service, who suffers from low back pain. He is a self-employed plumber. He is mainly involved in tasks that involve stooping and twisting, especially under sinks and around toilets.
a. Problem - is at risk of injury due to unsafe practices at work
b. Approach - predominately compensation (perhaps also prevention/maintenance in respect to positioning of the stump)
c. Assessments - interview, functional assessment (showering)
d. Intervention techs - environmental modification, education
A middle aged woman who has been referred to you following a below knee amputation three weeks ago of her left leg.
a. Problem - difficulty showering due to environmental barriers
b. Approach - restorative - early surgery, room for improvement
c. Assessments - interview, functional assessment (AMPS); Borg Scale of excursion
d. Intervention techs - education, training/retraining principles
Client has recently been discharged home following a coronary artery bypass graft (CABG). She had her surgery two weeks ago. She is currently functioning at a 3.5 MET level. She has a tendancy to overdo things.
a. Problem - unable to return to work due to limited endurance
b. Approach - compensatory - condition is progressive - will not improve
c. Assessments - functional assessment, risk assessment
d. Intervention techs - environmental modification, education around manual handling.
An eleven-year old boy who has Duchennes Muscular Dystrophy. He is wheelchair dependent and his mother is having increasing difficulties managing him in respect to bathing
a. Problem - difficulties with bathing due to reduced muscle strength
Widely used and documented
Easily understood by other professionals
Makes good use of problem solving process
Can be used in many settings
Flexibility in application
Quick results / patient sees positive benefits / increased motivation
Used for a variety of needs - acute or chronic
Reduced patient choice -reduced opportunity to plan/participate in process/ passive role non-compliant behaviour
Programme may become sterotyped/recipe-like
Overtly physical bias wider social, environmental issues ignored (reduced holitic approach) also may become a quick-fix of the problem/ over prescribing of equipment
What are the strengths and limitations of the Biomechanical model