Examination of Lower Extremity Muscle Strength

By admin On Jun 7, 2023

Ovid: Field Guide to the Neurologic Examination

Authors: Lewis, Steven L.

Title: Field Guide to the Neurologic Examination, 1st Edition

> Table of Contents > Section 2
– Neurologic Examination > Motor Examination > Chapter 26 –
Examination of Lower Extremity Muscle Strength

Chapter 26

Examination of Lower Extremity Muscle Strength

PURPOSE

The purpose of the examination of lower extremity muscle
strength is to localize neurologic pathology by looking for
characteristic distributions of muscle weakness.

WHEN TO EXAMINE THE MUSCLE STRENGTH OF THE LOWER EXTREMITIES

A screen of lower extremity strength (see Chapter 40,
Performing a Complete Neurologic Examination) should be performed on
all patients as part of the routine neurologic examination. If weakness
is suspected or found, a more detailed evaluation of lower (and upper)
extremity muscles is indicated to try to localize the patient’s
pathology.

NEUROANATOMY OF THE LOWER EXTREMITY MOTOR EXAMINATION

The upper motor neuron pathways that control the muscles
of the lower extremities end primarily within the lumbar spinal cord,
proceeding no further caudally than the first sacral level. The lower
motor neurons that innervate the muscles of the legs leave the spinal
cord primarily from the L1 through S1 levels. Table 26-1
summarizes the major innervation (root and nerve) of some of the most
clinically relevant muscles of the lower extremities, as well as the
functions of these muscles.

EQUIPMENT NEEDED TO TEST LOWER EXTREMITY MUSCLE STRENGTH

None.

HOW TO EXAMINE THE MUSCLES OF THE LOWER EXTREMITIES

Test and grade the muscles of the lower extremities according to the method described in Chapter 24, Approach to the Motor Examination. Figures 26-1, 26-2, 26-3, 26-4, 26-5, 26-6, 26-7, 26-8 and 26-9 illustrate and describe how to examine some of the major muscle groups of the lower extremities.

NORMAL FINDINGS

Normally, there should be no atrophy or fasciculations
of the muscles, and strength should be full (5/5) and symmetric in all
muscles tested of the lower extremities.

ABNORMAL FINDINGS

Strength

Any muscle strength in the legs that is less than 5/5 is abnormal.

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TABLE 26-1 Major Innervation of the Muscles of the Lower Extremities

Muscle	Function	Major Root Innervation^a	Nerve Innervation
Iliopsoas	Hip flexion	L1, L2, L3	Femoral
Quadriceps	Knee extension	L2, L3, L4	Femoral
Adductors	Hip adduction	L2, L3, L4	Obturator
Hamstrings	Knee flexion	L5, S1	Sciatic
Tibialis anterior	Foot dorsiflexion	L4, L5	Peroneal
Tibialis posterior	Foot inversion	L4, L5	Tibial
Extensor hallucis longus	Large toe dorsiflexion	L5	Peroneal
Peroneus longus	Foot eversion	L5, S1	Peroneal
Gastrocnemius	Foot plantar flexion	S1, S2	Tibial
^a This table names the roots with the most important, clinically relevant innervation to the given muscle.

Any focal muscle atrophy or
fasciculations in the muscles of the legs is abnormal and suggests
dysfunction of the lower motor neuron supplying those muscles.
Look for patterns of muscle weakness (in
the legs as well as the arms) to support or refute your suspicion of
the localization of the cause of weakness to the brain, spinal cord,
root, plexus, or nerve (see Table 24-3).

Figure 26-1
Examination of hip flexor (iliopsoas) strength. Ask the patient to lift
his or her thigh off of the bed or examining table, and then ask the
patient to resist you as you try to push the thigh down. What you might
say as you test the strength: “Don’t let me push your thigh down.”

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Figure 26-2
Examination of knee extensor (quadriceps) strength. Starting with the
patient’s leg bent (flexed) at the knee, ask him or her to attempt to
extend the leg at the knee against your resistance. What you might say
as you test the strength: “Push your leg against me.”

Figure 26-3
Examination of thigh adduction (adductor) strength. Starting with the
patient’s thigh relatively parallel to the trunk, ask the patient to
resist you as you attempt to abduct his or her thigh. What you might
say as you test the strength: “Keep your thigh in the center, and don’t
let me pull it to the side.”

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Figure 26-4
Examination of knee flexor (hamstrings) strength. Starting with the
patient’s leg bent (flexed) at the knee, ask him or her to resist your
attempt to straighten the leg. What you might say as you test the
strength: “Don’t let me straighten your leg.”

Figure 26-5
Examination of foot dorsiflexor (tibialis anterior) strength. Ask the
patient to lift his or her foot up by bending at the ankle, and then
ask him or her to resist you as you attempt to push down on the foot.
What you might say as you test the strength: “Don’t let me push your
foot down.”

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Figure 26-6
Examination of large toe dorsiflexor (extensor hallucis longus)
strength. Ask the patient to lift his or her large toe upward, and then
ask him or her to resist you as you attempt to push the toe down. What
you might say as you test the strength: “Don’t let me push your toe
down.”

Figure 26-7
Examination of foot plantar flexion (gastrocnemius) strength. Ask the
patient to push his or her foot down, bending at the ankle (“as if you
are pushing on a gas pedal”) and then ask the patient to resist you as
you push upward on the sole. What you might say as you test the
strength: “Don’t let me push your foot up.”

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Figure 26-8
Examination of foot eversion (peroneus longus) strength. Ask the
patient to turn his or her foot outward and upward at the ankle,
lifting the lateral foot upward, and then ask the patient to resist you
as you attempt to push downward on the lateral foot. What you might say
as you test the strength: “Don’t let me push down on your foot.”

Figure 26-9
Examination of foot inversion (tibialis posterior) strength. Ask the
patient to turn his or her foot inward at the ankle, lifting the medial
foot upward, and then ask the patient to resist you as you attempt to
push downward on the medial foot. What you might say as you test the
strength: “Don’t let me push down on your foot.”

ADDITIONAL POINTS

The muscles described in this chapter are not inclusive
of all the muscles of the legs that may need to occasionally be tested
to localize a cause of weakness, but they do represent muscles that are
particularly helpful to have a working knowledge of for the majority of
neurologic examinations.