Neurological Examination of the Lower Limbs

The general principles of neurological examination will be common to all parts of the body and a knowledge of anatomy is required to interpret findings. If the pathology can be explained by a lesion of a single nerve or group of nerves, it would appear to be a peripheral nerve lesion. Otherwise, especially where motor and sensory signs appear to be independent, it is probably a lesion of the central nervous system. This includes the spinal cord.

There is more than one way of performing a neurological examination and a clinician should develop his own technique. Poor technique will fail to elicit signs or will produce false results. In examinations such as MRCP, much emphasis is placed on correct performance of examination technique. The article on neurological history and examination covers many of the basic principles of examination and technique.

Note if there appears to be any damage to the feet. Neuropathic ulcers and even neuropathic joints are allowed to develop because there is no pain. Pain is a protective mechanism.

Sensation

Light touch can be tested by using a light touch of the finger, a piece of cotton wool or a small brush. It is important to touch and not to stroke as moving sensation, such as rubbing and scratching are conducted along pain pathways.

Sharp sensation is often tested by using a disposable needle. An ordinary pin may be preferable as it is less likely to draw blood but a new pin must be used for each patient.

• A logical progression is required. A sensible progress would be to start testing over the groin and to move down the front of the leg and up the posterior side as this moves progressively from L1 to S3 dermatomes.
• Some people would test first with sharp and then with light touch. A better technique may be to use both and to touch the patient with one or the other, saying to the patient, "When I touch you say sharp or soft."
• Testing for temperature sensation is often overlooked but it can be important. Tubes of hot and cold water may be used but an easier and more practical approach is often to touch the patient with a tuning fork as the metal feels cold. First touch the patient where sensation is thought to be normal, such as the arm and say, "Does that feel cold?" Then, when testing the limb, check that the patient is feeling the fork as cold and not just as pressure.

Proprioception

• Proprioception is often tested just in the great toe but it can be tested in other joints too. Take the toe between your index finger and thumb. Grasp the side of the digit so that movement is not felt as pressure up or down. Ask the patient to close his eyes and to tell you if you move the toe up or down.
• Vibration sense is transmitted along the same dorsal pathways as proprioception. It can be tested by placing a vibrating low frequency tuning fork on the patient's medial malleolus and asking him to tell you when it stops vibrating. This distinguishes the vibration sense from just feeling pressure.
• Vibration sense in the lower limb is a often diminished or lost in elderly people with no apparent neurological lesion.
• Joint position sense is also required for balance, gait and coordination.

The segmental level of sensation is:

• Upper part of the upper leg is L2
• Lower-medial part of the upper leg is L3
• Medial lower leg is L4
• Lateral lower leg is L5
• The sole of the foot is S1

Some aspects of sensation may be deficient because of central lesions. Astereognosis is the inability to recognise common objects by touch and it is tested with the upper limb.

Another test of cortical function, more suited to the lower limb is called extinction. Touch the patient in one place and ask him to open his eyes and point to the spot where he was touched. Repeat but this time, touch the patient in two places on opposite sides of their body, simultaneously. Again, ask him to point to where he felt the touch. With extinction he will point to only one place. With lesions of the sensory cortex in the parietal lobe, the stimulus is not felt on the side opposite to the damaged cortex. The sensation is "extinguished".

As with most aspects of examination, this starts simply by looking at the patient.

Inspection

• Note the resting posture. Is there unusual rotation or posture of a joint? Is the patient symmetrical?
• An upper motor neurone (UMN) lesion will produce disuse atrophy in the affected muscles. A lower motor neurone (LMN) lesion or myopathy will produce much more marked atrophy.
• A LMN lesion or myopathy will produce fasciculation. This is spontaneous discharges of groups of muscle cells to produce twitches in little areas of muscle. Striking an area with a jerk hammer may stimulate such action.

Tone

Tone is raised in an UMN lesion and reduced in a LMN lesion but the latter can be more difficult to distinguish from normal.

Ask the patient to relax and place your hand under his knee. Gently raise and lower it by about 10 to 15cm a few time, then, quite rapidly, raise it up until the knee is at about 90° and let it flop down. Throughout all this the heel will normally just slide along the couch. If it rises up in the air, tone is increased. Detecting hypotonia is rather more difficult. The leg feels floppy.

Simply noting that a muscle or a group contract is not enough. A robust assessment of power is required. This almost involves grappling with the patient and for a small doctor assessing a powerful man, it can be quite demanding. Power is usually graded from 0 to 5 with 0 being no contraction and 5 being full and normal power for the patient's physique. The scale is skewed towards the weak end and some people enhance it with supplements such as 3+/5 or 2–/5. The last digit indicates a scale of 0 to 5 as sometimes a scale of 0 to 4 is used.

• First test the flexors of the hip. With the patient lying on his back on the couch, ask him to raise a straight leg with the heel about 30cm off the couch. Try to push it down whilst he resists. This should be very difficult or impossible to achieve.
• Then test the quadriceps, the extensors of the knee. Ask him to bend the knee to about 90° or a slightly more obtuse angle and then to kick out against your resistance.
• To test the hamstrings, the flexors of the knee, ask him to bend the knee to about 90° again but this time to try to pull up his heel to his buttock whilst you resist.
• At the ankle it is possible to test extension, flexion, inversion and eversion and if there are local problems these should all be tested.
• If negative results are found or anticipated in examination of the lower limb, testing movement of the ankle can be replaced by testing extension of the great toe. Ask him to cock back the toe and to resist your attempt to push it down. Again, this is a strong movement that should be very difficult to overcome. The segmental level of the movement is S1.
• The gluteal muscles can be tested by asking him to lie on his front and extend his leg. Again, oppose the movement.

These are often referred to as deep tendon reflexes. Basically they represent a spinal reflex to a sudden, short stretching of the muscle. The requirements of a good jerk hammer and how to use it are discussed in neurological history and examination. UMN lesions will produce an enhanced reflex. LMN lesions will produce a diminished or absent response. Sensory input is also required. Reflexes can be graded from 0 that is no response to 5 that is brisk and sustained clonus. The briskness of the jerk is probably less important than any difference between the two sides.¹

Techniques will vary between individuals and the following description is a suggestion rather than a dictum.

• With the patient lying on his back on the couch, ask him to relax and use you left arm to support both legs under the knees. Raise them by about 30cm. The angle of the knee should be around 135°. Let the hammer fall on the tendon between the bottom of the patella and the tibial tuberosity. There should be a brisk contraction of the quads to kick out the leg.
• Again with the patient on his back, bend the knee to about 135° and externally rotate the hip so that the foot is pointing out. Take the foot in your hand and adjust it so that the ankle is at about 90° and make sure that the patient is relaxed. Strike the Achilles tendon about 2 or 3 cm above its insertion.
• Clonus is most often demonstrated at the ankle but can be seen elsewhere. With the patient on his back, bend the knee to about 135° and externally rotate the hip so that the foot is pointing out. Take the foot in your hand with the ankle at about 90°. Give a sharp dorsiflexion of the ankle, stretching the calf, and there is a clonic response from that muscle. The intensity and duration will vary with severity.
• Correct technique is important for the plantar or Babinski test. Use a fairly sharp object such as the point of a tendon hammer or a key. Take the foot with one hand and firmly draw the object along the sole from just in front of the heel, on the lateral side, moving over to the medial side just before the metatarsal heads. This should be done firmly and surely and it should not need repetition. One reason is that it is very unpleasant if done properly and it is often best to apologize to the patient for having to have done such a test. The other reason is that repetition may produce an unreliable response.

An alternative technique to elicit the ankle reflex is to ask the patient to lie on his front with his feet over the end of the couch. Take the foot in your hand with the ankle at about 90° and let the hammer fall on the tendon as before. This techniques tends to be more difficult to perform adequately than the one described above but it can be easier to demonstrate slow relaxation of the ankle jerk as is typical of myxoedema.

There is some dispute about how often ankle jerks are absent in old people with no apparent neurological lesions,^2,3 but it is said that the commonest reason for absent ankle jerks is failure to elicit them properly.

The segmental innervation of the reflexes is:

• Knee L3,4
• Ankle S1
• Plantar S1

Reinforcement

If a reflex is negative it may be possible to enhance it by reinforcement. This involves getting the patient to contract muscles briefly whilst the test is performed. The muscles to be contracted isometrically are in the upper limb to reinforce jerks in the lower limb and vice versa. The usual technique is to ask the patient to clasp his fingers together, interlocking from each hand, and at the call he gives a hard isometric pull for about 2 or 3 seconds. Call, "Pull" and as he pulls, about 1 second later, strike with the hammer.

Coordination of the lower limb can be tested by asking the patient to run his heel down the opposite shin and then repeating on the other side.

The most important test of coordination of the lower limb is to watch the patient walk. No neurological examination, especially of the lower limb, is complete without observing gait. This is an enormous topic and abnormal gait and gait abnormalities in children both have their own articles. Also watch the patient as he rises from the chair and note any abnormality of movement.

Romberg test

Ask the patient to stand still with the heels together. Then ask him to close his eyes. If he loses his balance, the test is positive. Be ready to catch him if he stumbles.

Balance requires 2 of the following 3 inputs to the cortex:

• Visual confirmation of position
• Proprioceptive and vestibular input
• A normally functioning cerebellum

If the patient can stand still with balance with eyes open but stumbles with eyes shut, there is likely to be a lesion in the cerebellum. This is a positive Romberg sign.

Interpretation of findings requires knowledge of anatomy. A number of possible findings are discussed here:

• Peripheral nerves tend to be mixed motor and sensory and so peripheral nerve lesions should affect both components. If the lesion is at the segmental level they may not coincide in terms of the sensory loss being directly over the motor loss.
• A purely motor or purely sensory loss is likely to be central in origin. Charcot-Marie-Tooth disease gives muscular weakness and wasting so that the legs resemble a champagne glass. There is no sensory loss.
• Peripheral neuropathy will produce a stocking distribution that is usually symmetrical or nearly so.
• Proximal myopathy may produce its most impressive features when the patient tries to rise from the chair, especially if it is rather low. Causes include Cushing's syndrome and thyrotoxicosis.
• Lesions of the femoral nerve will cause loss of power in the quadriceps and sensation over the anterior aspect of the thigh.
• The lateral peroneal nerve curls round the head of fibula where it is vulnerable to damage, especially as it is at about the same height as a car bumper. Damage causes sensory loss over the lateral lower leg with loss of dorsiflexion of the foot. The most obvious sign may be foot drop on walking.
• As the diagram below shows, lesions of the sciatic nerve can have very extensive consequences although they rarely affect all the distribution of that nerve. Both hamstrings and gastrocnemius may be weak.
• Meralgia paraesthetica is caused by compression of the lateral cutaneous nerve of the thigh as it passes under the inguinal ligament and pierces the fascia lata. The diagram below shows its distribution over the anterior, lateral, and posterior areas of the thigh. Typically, the patient complains of a burning or stinging sensation in the distribution of the nerve and it is aggravated by walking or standing and relieved by lying down with the hip flexed. There is no motor loss.