Assessment of muscle strength
Symptoms arising from resisted contractions
The
Oxford scale is relatively quick and easy to use, and is used widely in
clinical practice. However, it is not very objective, functional or sensitive
to change as the movements resisted are concentric contractions and the spaces between
the grades are not linear. Nevertheless, it provides a guide to muscle strength
and is somewhat sensitive to
change.
Measurements using isokinetic machines
Objective measurements of strength throughout different joint
angles and at different velocities are made more accurately using isokinetic
machines, such as Cybex or Kin-Kom. These machines are particularly valuable in
rehabilitative regimens such as anterior cruciate rehabilitation programmes and
can determine the strength ratio of the quadriceps to the hamstrings, or the
ratios of the operated versus the non-operated leg. Objective markers such as
percentages of strength ratios or ratios of operated versus non-operated leg may
be used in setting discharge protocols. Isokinetic machines have been found to
be reliable and valid in measuring muscle torque, muscle velocity and the
angular position of joints (Mayhew et
al. 1994). However, they are limited in
their use, and Wojtys et al.
(1996) suggest that agility and
functional exercises may be more beneficial than isokinetic machines in the strengthening
of muscle. Differentiation tests of
muscles and tendons
These are contractile structures and are therefore tested by
performing a contraction against resistance. A pain response and/or apparent
weakness may indicate a strain of the muscle at any particular point of the range
of movement. Full range should be checked as the muscle may be weak only at a
particular point in the range. Muscle length may also be tested, particularly
those muscles that are prone to become tight and then lose their extensibility.
Muscles that pass over two joints and have mobiliser characteristics are
particularly prone to tightness. Examples of these are the hamstrings, rectus
femoris, gastrocnemius and psoas major. The length of the muscle is tested by passively
moving the appropriate joints. The stretch is compared with the other side to
determine reproduction of pain and/or restriction of movement.
Passive insufficiency of muscles
This occurs with muscles that act over two joints. The muscle
cannot stretch maximally across both joints at the same time. For
example, the hamstrings may limit the flexion of the hip when the knee joint is
in extension as they are maximally stretched in this position. However,
if the knee is flexed passively, then the hip will be able
to flex further as the stretch on the hamstrings has been
reduced.
Active
insufficiency of muscles
This, too, occurs with muscles that act over two joints. The
muscle cannot contract maximally across both joints at the same time. An
example is the
finger flexors. If you are to make a strong fist, you may notice
that the wrist is in a neutral or an extended position when you do this action.
Now, if you attempt to actively flex your wrist joint whilst keeping your
fingers flexed, you will find that the strength of the grip is greatly
diminished. This is because the wrist and finger flexors are unable to shorten
any further and so the fingers begin to extend or lose grip strength.
Differentiation tests of ligaments
Ligaments are non-contractile structures and are tested by putting
the structure on stretch. Examples are a valgus strain of the knee to stretch
the medial collateral ligament of the knee or passive inversion of the subtalar
joint to stretch the lateral ligament of the ankle. A positive test would be a
pain response or observation or feel of any excessive movement of the joint
when compared with the other side.
Differentiation tests of bursae
Bursae are sacs of synovial fluid. Inflammation of these (bursitis)
results in tenderness and/or heat on palpation. The tenderness is often very
localised to the site of the inflamed bursa.
Differentiation tests of menisci
The history and mechanism of injury combined with anterior joint
tenderness and the inability to passively hyperextend the knee are useful
diagnostic markers of meniscal injury. Rotation on a semi-flexed weight-bearing
knee is a common cause of injury. A history of locking, whereby the joint
momentarily locks and is unable to actively or passively release itself from
the position, is also common. Objectively, the knee joint is unable to fully
flex/hyperextend passively.
Characteristics of degenerative joint disease
Signs and symptoms may include:
• pain that increases on
weight-bearing activities (standing and walking, walking downstairs particularly);
• insidious onset of symptoms
followed by progressive periods of relapses and remissions;
• pain and stiffness in the
morning;
• stiffness following periods of
inactivity;
• pain and stiffness that arise
after unaccustomed periods of activity;
• bony deformity (e.g.
characteristic varus deformity may follow from collapse of the medial compartmental
joint space);
• reduction of the joint space
observed on X-ray, with bony outgrowths or osteophytes.
Writing up the assessment
It is imperative to record the assessment immediately following the
physical testing. Patient notes should be completed on the day of the
assessment for legal reasons. Ensure that your
assessment findings are clear and concise, and
that they highlight the main points (it may be
useful to include one subjective and one objective marker).
Formulate a problem list in agreement with the patient.
Agree and record SMART goals (specific, measurable, achievable,
realistic, timed) with the patient. Use the problem-orientated
medical records (POMR) system. Remember, if
you have insufficient time to conduct a full
and thorough assessment you can always continue with
this when the patient attends for his/her subsequent appointment.
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