Evaluation of Nerve Root Lesions Involving the Trunk and Lower Extremity
Manifestations of pathology involving the spinal cord and cauda equina, such as herniated disks, tumors, or avulsed nerve roots, are frequently found in the lower extremity. Understanding the clinical relationship between various muscles, reflexes, and sensory areas in the lower extremity and their neurologic levels (cord levels) is particularly helpful in detecting and locating spinal problems with greater accuracy and ease.
To make the relationship between the spine and the lower extremity clear, the neurologic examination of the lumbar spine is divided into tests of each neurologic level and its dermatomes and myotomes. Thus, for each neurologic level of the lower spinal cord, the muscles, reflexes, and the sensory areas that most clearly receive innervation from it is tested.
Testing of Individual Nerve Roots, T2-S4
Neurologic Levels T2-T12
Muscle Testing
Intercostals: The intercostal muscles are segmentally innervated and are difficult to evaluate individually.
Rectus Abdominis: The rectus abdominis muscles are segmentally innervated by the primary anterior divisions of T5-T12 (L1), with the umbilicus the dividing point between T10 and T11.
Beevor’s sign (Fig. 2-1) tests the integrity of the segmental innervation of the rectus abdominis muscles. Ask the patient to do a quarter sit-up. While the patient is doing this, observe the umbilicus. Normally, it should not move at all when the maneuver is performed. If, however, the umbilicus is drawn up or down or to one side or the other, be alerted to possible asymmetrical involvement of the anterior abdominal muscles. Lesions of the spinal cord or roots between T10 and T12 will cause weakness of the lower part of the muscle, and thus a positive Beevor’s side with the umbilicus moving upward during the quarter sit-up.
FIGURE 2-1 Beevor’s sign.
Sensory Testing
Sensory areas for each nerve root are shown in Figure 4-1. The sensory area for T4 crosses the nipple line, T7 the xiphoid process, T10 the umbilicus, and T12 the groin. There is sufficient overlap of these areas for no anesthesia to exist if only one nerve root is involved. However, hypoesthesia is probably present.
Neurologic Levels T12-L3
Muscle Testing
There is no specific muscle test for each root. The muscles that are usually tested are the iliopsoas (T12-L3), the quadriceps (L2-L4), and the adductor group (L2-L4).
Iliopsoas: (Branches from [T12], L1-L3): The iliopsoas muscle is the main flexor of the hip (Fig. 2-2). To test it, instruct the patient to sit on the edge of the examining table with the legs dangling. Stabilize the pelvis by placing your hand over the patient’s iliac crest and have the patient actively raise their thigh off the table. Now place your other hand over thedistal femoral portion of the knee and ask the patient to raise the thigh further as you resist (Fig. 2-3). Determine the maximum resistance the patient can overcome. Then repeat the test for the opposite iliopsoas muscle and compare muscle strengths. Because the iliopsoas receives innervation from several levels, a muscle that is only slightly weaker than its counterpart may indicate neurologic problems.
FIGURE 2-2B Iliopsoas.
Origin: Anterior surface of the bodies of all lumbar vertebrae and their transverse processes and corresponding intervertebral disks. Upper two-thirds of the iliac fossa.
Insertion: Lesser trochanter of femur.
FIGURE 2-3 Muscle test for the iliopsoas.
In addition to possible neurologic pathology, the iliopsoas may become weak as a result of an abscess within its substance; the patient may then complain of pain during muscle testing. The muscle may also become weak as a result of knee or hip surgery.
Quadriceps: L2- L4 (Femoral Nerve): To test the quadriceps functionally, instruct the patient to stand from a squatting position (Fig. 2-4). Note carefully whether the patient stands straight, with the knees in full extension, or whether one leg is used more than the other. The arc of motion from flexion to extension should be smooth. Occasionally, the patient may be able to extend the knee smoothly only until the last 10°, finishing the motion haltingly and with great
effort. This faltering in the last 10° of extension is called extension lag; it occurs because the last 10° to 15° of knee extension requires at least 50 percent more muscle power than the rest (according to Jacqueline Perry). Extension lag is frequently seen in association with quadriceps weakness. Sometimes, the patient may be unable to extend his knee through the last 10° with even the greatest effort (Fig. 2-5).
FIGURE 2-4B Rectus femoris.
Origin: Rectus femoris is a “two-joint” muscle that has two heads of origin. Straight head: from anterior inferior iliac spine. Reflected head: from groove just above brim of acetabulum. Insertion: Upper border of patella, and then into the tibial tubercle via the infrapatellar tendon.
FIGURE 2-4C Vastus intermedius.
Origin: Upper two-thirds of anterior and lateral surface of femur. Insertion: Upper border of the patella with the rectus femoris tendon and then via the infrapatellar tendon into the tibial tubercle.
Vastus lateralis.
Origin: Capsule of hip joint, intertrochanteric line, gluteal tuberosity, linea aspera.
Insertion: Proximal and lateral border of patella, and into tibial tubercle via the infrapatellar tendon.
Vastus medialis.
Origin: Lower half of intertrochanteric line, linea aspera, medial supracondylar line, medial intermuscular septum, tendon of adductor magnus.
Insertion: Medial border of patella and into tibial tubercle via the infrapatellar tendon.
FIGURE 2-5 Extension lag. (Hoppenfeld, S.: Physical
Examination of the Spine and Extremities. Norwalk, CT: Appleton-Century-Crofts, 1976.)
To test the quadriceps manually, stabilize the thigh by placing one hand just above the knee. Instruct the patient to extend his knee as you offer resistance just above the ankle joint. Palpate the quadriceps during the test with your stabilizing hand (Fig. 2-6). Note that the quadriceps weakness can also be due to a reflex decrease in muscle strength following knee surgery or to tears within the substance of the muscle itself.
FIGURE 2-6 Muscle test for the quadriceps.
Hip Adductor Group: L2-L4 (Obturator Nerve): Like the quadriceps, the hip adductors can be tested as a massive grouping (Fig. 2-7). Have the patient lie supine or on their side and instruct the patient to abduct the legs. Place your hand on the medial sides of both knees and have the patient adduct their legs against your resistance (Fig. 2-8). Determine the maximum resistance they can overcome.
Reflexes
Although the patellar tendon reflex is supplied by L2-L4, it is predominantly L4 and will be tested as such.
Sensory Testing
Nerves from L1 to L3 provide sensation over the general area of the anterior
thigh between the inguinal ligament and the knee. The L1 dermatome is an oblique band on the upper anterior portion of the thigh, immediately below the inguinal ligament. The L3 dermatome is an oblique band on the anterior thigh, immediately above the kneecap. Between these two bands, on the anterior aspect of the mid thigh, lies the L2 dermatome (Fig. 2-9).
FIGURE 2-7B Adductor brevis (center).
Origin: Outer surface of inferior ramus of pubis.
Insertion: Line extending from lesser trochanter to linea aspera and upper part of linea aspera.
Adductor longus (left).
Origin: Anterior surface of the pubis in the angle between crest and pubic symphysis.
Insertion: Linea aspera, middle half of medial lip.
Adductor magnus (right).
Origin: Ischial tuberosity, inferior rami of ischium and pubis. Insertion: Line extending from greater trochanter to linea aspera. The entire length of linea aspera, medial supracondylar line, and adductor tubercle of the femur.
FIGURE 2-8 Muscle test for hip adductors.
Sensory testing, with its bands of individual dermatomes, is a more accurate way of evaluating neurologic levels T12-L3 than motor testing, which lacks individual representative muscles. There are also no representative reflexes for these levels, making it even more difficult to diagnose an exact neurologic level. Neurologic levels L4, L5, and S1 are represented by individual muscles, dermatomes, and reflexes, and are easier to diagnose.
Neurologic Level L4
Muscle Testing
Tibialis Anterior: L4 (Deep Peroneal Nerve): The tibialis anterior muscle is predominantly innervated by the L4 segmental level; it also receives L5
innervation (Figs. 2-10 and 2-11). To test the muscle in function, ask the patient to walk on his heels with his feet inverted. The tendon of the tibialis anterior muscle becomes visible as it crosses the anteromedial portion of the ankle joint and is quite prominent as it proceeds distally toward its insertion. Patients with weak tibialis anterior muscles are unable to perform this functional dorsiflexion inversion test; they may also exhibit “drop foot,” or steppage gait.
FIGURE 2-9 Dermatomes of the lower extremity.
To test the tibialis anterior manually, instruct the patient to sit on the edge
of the examining table. Support his lower leg, and place your thumb in a position that makes him dorsiflex and invert his foot to reach it. Try to force the foot into plantar flexion and eversion by pushing against the head and shaft of the first metatarsal; palpate the tibialis anterior muscle as you test it (Fig. 2-12).
FIGURE 2-10 Neurologic level L4.
FIGURE 2-11B Tibialis anterior.
Origin: Lateral condyle of tibia, upper two-thirds of the anterolateral surface of tibia, interosseusmembrane. Insertion: Medial and plantar surfaces of medial cuneiform bone, base of 1st metatarsal bone.
FIGURE 2-12 Muscle test for the tibialis anterior.
Reflex Testing
