Muscle tests (isometric examinations) are performed in the directions of movement for which symptoms of a lesion were present during the active movement examination. Alternatively, if a mild muscle/tendon lesion is suspected, it is the direction in which the muscle and tendon concerned are active.
During isometric muscle tests, the examiner asks the patient to resist the force that they are applying in a certain direction of movement. It is important to instruct the patient that the aim is not to exceed the strength of the examiner. No movement should occur in the joint under examination and in the neighbouring joints.
The following two conditions should be kept in mind:
- The examiner should adopt a position that allows them to provide sufficient resistance.
- The grip determines the direction in which the patient will push. Accurate positioning of the hand providing the resistance is vitally important for a correct performance of the muscle tests.
During this examination, the examiner should pay particular attention to the occurrence of pain, as this is often indicative of a muscle/tendon cause.
The isometric examination only tests groups of muscles that jointly realease a movement. If pain symptoms arise during testing of various muscle groups, the examiner (after comparing left and right) should also test the various muscles as selectively as possible. A detailed examination of muscle strength forms part of the neurological examination. Nonetheless, major changes or left/right differences, as well as coordination disorders should be noted during this examination.
The examiner should be aware that the reason for examining muscle(s) will influence the result obtained. An orthopaedic examination is an isometric test and may only be one-sided. However, a neurological examination focuses on the absolute strength and the left/right comparison. A muscle or muscle group that causes pain when tensed may subsequently be tensed less powerfully (a muscle test is considered positive if pain can be established).
For minimal lesions, extend the muscle/group of muscles to the maximum length before performing the muscle test. Besides the isometric contraction, this applies an additional force as a result of which a possible lesion may be more clearly established. It’s advisable to perform the test in a different posture and more specifically, in the functional posture in which symptoms occur in daily life. Be aware that a positive test can also arise as a consequence of referred pain, or mechanically as a consequence of an increase in pressure (bursitis, hernia, abscess). A basic functional examination can be used to determine the functional system in which the complaint is located.
Once the muscle tests have been performed, data obtained by the examiner is combined (a likely diagnosis or hypothesis is established) such that a further course of management can be determined.
Palpation, specialised tests and other additional examination techniques can be used to determine the location more accurately. The likely diagnosis can be rejected, confirmed or established with even greater specificity. To obtain a better insight into the interpretation of the data obtained, 6 regularly-occurring situations from everyday practice will now be described in the following paragraphs.
#1 – There is a limitation in one or more directions of movement (active and passive) and pain occurs in the same direction of movement(s). The muscle tests are negative.
We may conclude that this is:
- A lesion in a non-contractile structure.
- A painful shortening of a contractile structure.
Note 1. For both the active and passive movement examination, the non-contracting structures are tensed. A lesion should therefore exhibit the same pattern of symptoms in both examinations.
Note 2. If muscle shortening is present, these muscles will be painful if extended. The principle of the muscle length test is based on this phenomenon. The pain location therefore provides extra information.
Possible location of the lesion:
- Intracapsular:
- Internal derangement (trapped meniscus).
- Osteoarthritis.
- Ankylosis/arthrodesis (complete lack of mobility and in principle, no pain should occur during an effort to move).
- Capsular:
- Arthritis.
- Partial capsular and/or ligamentous adhesion.
- Extracapsular:
- Ligamentous adhesion.
- Cyst.
- Bursitis, especially acute forms.
- Haematoma.
- Muscle/tendon shortening/contracture/adhesions/calcification/stenosis.
- Skin or tendon contracture.
#2 – There are no limitations during active or passive movement, yet pain occurs in the same direction of movement. The muscle tests are negative.
If we combine these results, this points to a non-contractile structure with a capsular or extracapsular location. Pathological changes that are located within the capsule usually result in movement limitation and are therefore less likely to be considered.
- Capsular:
- Initial stage of arthritis and/or osteoarthritis.
- Extracapsular:
- Bursitis/periostitis.
- Skin or tendon lesions.
- Referred pain as a consequence of an acute lesion elsewhere.
#3 – There is no limitation during active or passive movement and no change occurs in the existing pain. The muscle tests are negative.
The entire basic function examination is negative, whereas the patient still clearly indicates pain symptoms. In this situation, we are confronted with referred pain on the basis of a non-acute lesion that is located elsewhere in the body. This is usually pain that develops in a visceral organ (heart, gallbladder), radiating to a more superficially situated area (dermatome or myotome).
#4 – The amplitude of the excursions (active and passive) in the same direction are increased, possibly in the presence of pain. The muscle tests are negative.
There is hypermobility which may be caused by:
- Capsular and/or ligamentous hypermobility, e.g. as a consequence of trauma or neuropathy; congenital weakness or laxity of connective tissue structures around the joints also both exhibit a similar clinical picture.
- Arthritic deformation.
- Pseudo-osteoarthritis or a fracture.
#5 – Active excursion is limited, but passive excursion in the same direction is not. In both cases pain may be present. The muscle tests are positive and/or abnormal.
This is a situation in which a contractile structure causes complaints. In particular, the findings from the isometric muscle test examination give us a clear indication for this. Possible causes of this pattern of complaint:
- A myogenic lesion, e.g. forms of myopathy.
- A muscle/tendon lesion, e.g. a severe inflammation (-itis) or a rupture (e.g. of the rotator cuff or Achilles tendon).
- A neurogenic lesion.
- A psychogenic cause.
#6 – Pain is felt upon active movement, possibly with a limitation in one direction, whereas upon passive movement pain and possibly limitation in the opposite direction are experienced. The muscle test in the direction that gave rise to pain in the active movement examination and possible limitation of movement, is also positive.
In this case, only one diagnosis is possible – a muscle/tendon lesion. Actively, the pain is elicited due to the contraction and passively due to bringing the injured structure to its full length.
This situation can occur without there being any limitations in the joint. This will concern a muscle/tendon lesion in an early stage.