Examination of power in the limbsThis screening examination will detect and discriminate between the common causes of limb weakness: radiculopathies, mononeuropathies, polyneuropathy, pyramidal tract lesions, and less common causes such as muscle and NMJ disorders.
Screening examination of power
The principles of power testing
- Instructions should be short, in plain every day simple words, supplemented by a visual demonstration of the required movement.
- Test power across just one joint so that just one muscle or functional group is being tested at a time
- Support and stabilise the limb proximal to the joint across which the movement is being tested, particularly if it is weak.
- In general the muscle is most powerful when fully contracted, and should be tested in this position provided the joint is not locked. When testing elbow and knee extension have the joint slightly flexed by 30 - 40 degrees to avoid this problem.
- In the tests illustrated the normal muscle is usually stronger than an examiner using reasonable force. This allows a definite decision to be made - normal or weak.
Shoulder abductionInstruction to person being examined ''Put your arm up like this - demonstrate - Keep your arm up, don't let me push it down''
Examiner's action Push downward on the elbow (to get maximum leverage). You should not be able to overcome the muscle with reasonable force.
Elbow flexionInstruction ''Bend your arm up like this. Pull your fist towards your nose. Don't let me straighten it.''
Examiner Allow the person to almost fully flex the arm. Support the elbow with one hand (this is important in weak patients) and attempt to straighten the flexed, supinated forearm, pulling on the lower forearm, not the hand, since if the patient has weakness at the wrist the test of elbow flexion will fail. Remember test across just one joint. The forearm should be supinated to decrease the effect of brachioradialis.
Elbow extensionInstruction ''Push your arm to me, and don't let me bend it''
Examiner Support the arm at the elbow and push toward them holding the forearm at the wrist.As an alternative technique to demonstrate subtle weakness have the person hold their elbows in to their sides with forearms flexed at 90 degrees . Holding both wrists pull upward. Weakness of one or both sides will be obvious.
Wrist extensionInstruction ''Keep your wrist back, don't let me pull it down/straight.''
Examiner Hold the lower forearm, and firmly attempt to straighten the dorsiflexed wrist
Wrist FlexionInstruction ''Keep your wrist down, don't let me pull it up/straight.''
Examiner Hold the lower forearm, and firmly attempt to straighten the flexed wristWrist flexion is not a critical part of screening arm strength. Disproportionate weakness of wrist and finger flexion is a striking feature of the chronic condition inclusion body myositis, often encountered in specialist clinical examinations.
Finger extensionInstruction ''Keep your fingers out straight, don't let me bend them''
Examiner This is a test of extension at the MCP joints. It is important to support the palm and apply pressure to the PIP joints, testing extension at only one set of joints, because extension at the PIP joints is performed by the small hand muscles.
Finger flexionInstruction ''Curl your fingers like this and don't let me straighten them''
Examiner Attempt to straighten the flexed fingers.Having the patient grip two of the examiners fingers is an inferior technique.Flexion occurs at the MCP, PIP and DIP joints performed by the intrinsic muscles of the hand, the flexor superficialis and the flexor digitorum profundus respectively.Testing flexion of the individual distal phalanges is particularly informative in ulnar neuropathy. If fingers 4 and 5 are involved the lesion is likely localised to the elbow.
Finger abductionInstruction ''Spread your fingers apart, push your index finger towards your other hand. Don't let me push it back''Examiner
Examiner Push on the finger at PIP joint level. Almost all people are able to resist reasonable force applied at this point, but will give way if further distal. Look at the muscle and palpate it with your other hand.It is usually only necessary to test the first dorsal interosseous muscle to establish whether the Ulnar nerve function is intact.
Thumb abductionInstruction ''Hold your hand out like this - hand out, palm up, push your thumb towards your nose, don't let me push it down on to your hand.''
Examiner Push down on the thumb over the IP joint. Look at and palpate the muscle. The thumb must be abducted in a plane perpendicular to the palm to eliminate the influence of Abductor Pollicis Longus as much as possible.
Hip flexionInstruction ''Bend your leg up like this, don't let me push it down.''
Examiner Push towards the foot. This movement is often poorly performed, particularly by older women.
Hip extensionInstruction ''Keep your leg on the bed. Don't let me lift it.''
Examiner Pull up under the heel. The patient's buttocks should be lifted off the bed if they are fully exerting themselves.
Knee extensionInstruction ''Bend your knee, now try to straighten it.''
Examiner Allow the knee to be slightly bent, at 135-150 degrees, and try to bend it more as the patient attempts to straighten it. If done with the leg straight the knee will lock preventing testing of Quadriceps power.Be careful of the skin around the ankle which may be fragile and the shin tender in older people. Very vigorous testing can cause fracture.
Knee flexionInstruction ''Bend your leg and don't let me straighten it''
Examiner Support the knee with one hand and attempt to straighten the flexed leg with the other hand holding the ankle.Often poorly performed.
Ankle inversionInstruction ''Twist your foot inwards, (like this) and don't let me straighten it'' Inversion and eversion are often a difficult movements to explain to the patient.
Examiner Attempt to overcome the inversion, and twist the foot from inverted to a dorsiflexed pasition
Ankle dorsiflexionInstruction ''Keep your leg on the bed, and pull your toes up towards your head''
Examiner Push very firmly along the line of the leg against the distal metatarsals in an effort to overcome the movement. This a strong muscle and the leverage should be the maximum possible favouring the examiner.
Ankle eversionInstruction ''Twist your foot outwards, don't let me straighten it.''
Examiner Attempt to overcome the eversion of the foot.
Ankle plantar flexionInstruction ''Push your foot down, don't let me push it up''
Examiner This is a powerful muscle and the examiner should exert enough force to move them bodily on the couch. The most effective test is to have the patient attempt to stand on tip toe of the leg under test taking the other foot off the ground. At the same time look for wasting of the posterior calf muscles.