Movements of the lower extremity beyond a certain point will
stretch the lumbosacral plexus and associated nerve roots. Straight leg-raising
(i.e., passive flexion of the straightened leg on the hip), or the reverse,
extension of the leg on the hip, is used in an attempt to reproduce lower
extremity radicular symptoms in patients who are thought to have irritation or
damage to the lumbosacral plexus and roots. When the leg is flexed on the hip,
the nerve roots of the posterior-lying sciatic nerve, which originates in the
lower lumbar and upper sacral roots (L4-S2), begin to be stretched once the limb
has reached about 30 degrees of flexion. Extension of the leg on the hip (with
the patient lying on their side or prone) stretches the anterior-lying femoral
nerve, which originates from the middle lumbar roots (L2-4).
Any mass or inflammatory process impinging on the nerve, plexus,
or nerve roots is capable of binding or irritating these structures, causing
pain in the peripheral distribution of the nerve. This pain is often in the
muscle and bone distribution of the nerves as opposed to the skin or dermatomal
distribution. Buttock, posterior thigh, calf, as well as heel discomforts are
characteristic of sciatic system involvement, whereas groin and anterior thigh
pains are characteristic of femoral system involvement. If there is skin
involvement, loss of sensation occurs in appropriate dermatomes or peripheral
nerve distribution. However, loss of sensation or weakness will only occur if
the lesion is destructive. It is more common to have paresthesias
(pins-and-needles sensations) than actual loss of sensation when a nerve root is
damaged. A symptomatic irritative lesion may not cause any actual loss of nerve
function despite causing significant pain.
Herniated disk is the most common cause of lumbosacral
radiculopathy. The great majority of symptomatic intervertebral disks are
between the L4-5 or L5-S1 vertebral bodies. Because the L5 and S1 roots exist at
these spaces, straight leg-raising with the patient supine, causing sciatic
stretch, is the maneuver of choice. A relatively small percentage of lower spine
disk problems occur at L3-4 or L2-3, and a tiny number are found at L1-2 or
thoracic levels (although these have been recognized more frequently in the era
of magnetic resonance imaging). With the higher lumbar protrusions, femoral
stretching is the maneuver that is most likely to reproduce symptoms. It must be
noted that an increase of back pain, alone, is not considered an indication of
nerve root involvement and is considered a negative straight leg-raising test.
Such a "negative test" may still cause pain, but this is probably due to
stretching irritated tendons, joints and muscles in the back. Also, a true
positive test must be distinguished from tightness of the hamstring muscles,
which can produce discomfort during straight leg-raising.
Flexion of the head on the chest (chin to chest) pulls the
spinal cord upward and stretches the lumbosacral roots somewhat. Therefore,
lower extremity symptoms may be exacerbated in the patient with lumbosacral root
Meningitis can inflame the meninges and nerve roots at all
spinal levels. Therefore straight leg-raising is often positive with meningitis.
In fact, there may be involuntary flexion of the knees during attempted straight
leg-raise (Kernig sign).
Acute or chronic arthritis of the hip, on occasion, causes
referred pain in the knee and, less commonly, in the foot. Straight leg-raising
may irritate a damaged hip joint and may give a misleading impression of sciatic
root irritation. However, hip joint pathology is easily detected by rotating the
femur on the hip while the knee and hip are flexed. This flexion of the knee
puts slack on the sciatic and femoral nerves and should not put significant
stretch on the sciatic nerve roots. Pain and limitations of motion in internal
and external rotation of the flexed hip (Patrick maneuver) suggests hip disease,
and appropriate x-rays can confirm this suspicion.
Back pain is a common, nearly ubiquitous symptom. Pathologic
processes (degenerative, neoplastic, or inflammatory) in or near the spinal
column frequently give rise to local muscle spasm and pain. This may lead to
postural abnormality and/or palpable firmness and tenderness of muscles. When
the paraspinal muscles contract unilaterally, they bow the spine laterally; the
concave side of the bow appears on the side of increased muscle tension. This
lateral bowing is called scoliosis and can be observed most easily when the
patient is erect. Observation is further facilitated by making a mark with a pen
on the palpable top of the dorsal spinous processes of the vertebrae. The only
exception to the rule of contralateral bowing occurs at the lumbosacral junction
where the paraspinal muscles are broadly attached to the sacrum and the ilium.
The bowing occurs toward the side of the spasm in this instance.
Many neurologic conditions result in abnormal muscle tone. When
these begin early in life there may be associated skeletal abnormalities,
including severe scoliosis. Although many scolioses are "idiopathic," probably
related to problems of skeletal maturation, severe scoliosis, particularly when
accompanied by other signs such as pes cavus (high arched feet) should prompt
some neurologic examination. Progressive scoliosis, even when it does not result
from neurologic abnormality, can cause neurologic dysfunction if not arrested.
Most back pain is benign. Rarely, it can result from localized
serious pathology (infectious, neoplastic, hemorrhagic, etc). In many such
cases, percussion of the spine to elicit point tenderness often produces
localized pain. This percussion is carried out with the hypothenar portion of
the fist. Because a large area is covered with each blow to the spine and there
is diffusion to several vertebral segments, use of a percussion hammer to tap
each spinous process may more accurately localize the involved segments,
prompting some consideration of imaging.