PATHOGENESIS OF LOW BACK PAIN
The cause of LBP is controversial. A rational hypothesis,described by Kirkaldy-Willis and Bernard,8 is outlined below.
I. Three major factors predispose a client to an
episode of LBP:
1. Emotional upset, such as tension, stress, anxiety,fear, resentment, uncertainty, and depression.
Emotional upset causes local areas of vasoconstriction and sustained muscle contraction that leads to muscle fatigue. These changes result in altered patterns of muscle contraction and movement.
2. Abnormal function of the muscles of the lumbopelvic
girdle creates abnormal movement patterns and excessive stresses on the facets and disc. The result of these changes is that movement
becomes restricted and painful. These painful restrictions of movement lead to fibrosis around the joint.
3. Facet joint hypomobility (fixation). As mentioned,this loss of the normal gliding characteristics has reflexive changes in the surrounding muscles, setting up a continuing cycle of muscle dysfunction and further joint dysfunction.
II. Muscle dysfunction occurs in a predictable pattern in LBP. In the lower back, the paraspinal muscles tend to be tight. Sustained muscle contraction decreases the blood supply to the muscles, which leads
to an accumulation of waste products, and eventual muscle fatigue.
III. The multifidus is especially important in LBP. Its fibers interweave with the joint capsule. Sustained contraction adds a compressive load to the joint,and weakness decreases the stability of the lower
back; both of these conditions accelerate the degeneration process.
IV. The client then reports a minor incident, such as gardening, or reaching for a light object, and experiences an episode of acute LBP either at the time, or within a day or two. There are twodifferent mechanisms of injury:
(1) a rotational strain that typically injures the facet joints, and
(2) a compression force in flexion, which typically injures the disc. It is important to realize that in any given injury, the muscles, facets, and disc are all involved to some degree.
V. This minor trauma leads to inflammation of the synovial
lining of the capsule, called synovitis, and to sustained hypertonic contraction in the paraspinal muscles, usually on one side of the lower back. The inflammation releases enzymes that cause minimal
degeneration of the articular cartilage.
VI. This phase of dysfunction is often followed by a of instability, which is demonstrated by abnormal,increased movement of the facets. There is laxity in the joint capsule and the annulus of the disc,and subluxation (partial dislocation) of the facets.
VII. The last phase of pathogenesis is the stable phase, in which the body responds to the continuing degeneration by laying down connective tissue and bone.
VIII. Continuing degeneration leads to bony spurs under
the periosteum, enlargements of the inferior and superior facets, periarticular fibrosis, and loss of motion.
IX. Changes in the disc begin in the dysfunctioning phase with small circumferential tears in the annulus that become larger and form a radial tear that passes from the annulus to the nucleus. These tears
increase until there is internal disc disruption,which can lead to a disc herniation in which the nucleus shifts position.
X. With further degeneration the normal disc height is reduced owing to the loss of proteoglycans and water.
FACTORS PREDISPOSING TO LOW BACK
DYSFUNCTION AND PAIN
1. Functional factors: Posture, joint dysfunction, muscle imbalances, deconditioning, fatigue, altered movement patterns, or emotional tension.
2. Structural factors: rheumatologic, endocrine or metabolic, neoplastic (tumors), and vascular diseases; infection; congenital anomalies; referred pain from pelvic and abdominal disorders.
DIFFERENTIATION OF LOW BACK PAIN
LBP can be caused by many conditions in addition to
functional problems, injury, or degeneration in the
musculoskeletal system. These other causes are diverse but may be categorized as follows:
1. Visceral diseases such as kidney stones or endometriosis
2. Vascular diseases such as aneurysms
3. Tumors, especially cancer that has metastasized from another site
4. Stress-related disorders, such as adrenal exhaustion
The vast majority of LBP is caused by a mechanical disorder, a problem of function, and not pathology. The precise cause of the mechanical LBP can be difficult to determine. Sometimes it is a case of a frank injury, but more often there is an underlying chronic muscle imbalance,poor posture, or emotional stress. Assuming
that the client’s pain is caused by a mechanical disorder,
there are two fundamental types of pain that refer into the leg(s): sclerotomal and radicular. The two types are differentiated by the quality of pain. These two types of referral are important to distinguish, because it helps you differentiate a simple mechanical disorder from a serious condition, such as a herniated disc.
Sclerotomal pain, the first type of referred pain, is caused by an injury to the paraspinal muscle, ligament,facet joint capsule, disc, or dura mater and can manifest locally and be referred to an extremity. For example,pain from a muscle strain in the lumbar region may be felt as a pain in the thigh in addition to the lower back. Usually, the sclerotomal referred pain is described as deep, aching, and diffuse.
Radicular pain, the second type of referred pain, is caused by an irritation of the spinal nerve root. If the sensory (dorsal) root is irritated, sharp pain, numbing,or tingling that is well-localized in dermatomes occurs.
If there is compression of the motor (ventral) nerve root, in addition to the pain, numbing, and tingling,there may be a weakness in the muscles supplied by that nerve root (myotome) and a decrease in the response in the corresponding reflex. The most common cause of nerve root irritation is disc herniation. Nerve root pain is much more serious and requires an assessment by a doctor.
With these two categories in mind, we can enumerate nine common types of LBP. Note that these are artificial categories and that an injury or dysfunction usually has several of these causes of pain at the same time. For example, with a simple overuse injury of the lower back during gardening, muscles, ligaments (including joint capsule), and joint dysfunction would all typically be involved.
These categories should be used as a guide to help differentiate simple from more complex problems.