Assessment of muscle strength

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


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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