Patients with an extension bias often assume a flexed posture or a flexed posture with lateral deviation of the trunk or neck, but during the examination sustained or repetitive extension maneuvers reduce or relieve their symptoms. These patients would benefit from early interventions that emphasize extension of the involved segments. The impairments may be due to a contained intervertebral disk lesion, fluid stasis, a flexion injury, or muscle imbalances from a faulty flexed posture. McKenzie developed a method of categorizing these patients based on the extent of their pain and/or neurological symptoms. He also described the phenomena of peripheralization and centralization that accompany an expanding and receding lesion, frequently attributed to intervertebral disk lesions.

Many of the techniques that were originally described by McKenzie and May to manage a patient with an acute disk lesion have been found to be beneficial in the management of patients who have a cluster of signs and symptoms that categorize them into the extension bias (extension syndrome).

Principles of Management

Because patients with signs and symptoms of a bulging intervertebral disk often fit into the “extension bias” category, a brief discussion of the response of the intervertebral disk is presented here.

Effects of Postural Changes on Intervertebral Disk Pressure
Relative changes in posture and activities affect intradiskal pressure. When compared to the level of pressure when standing, intradiskal pressure is least when lying supine, increases by almost 50% while sitting with hips and knees flexed, and almost doubles if leaning forward while sitting. Sitting with a back rest inclination of 120° and lumbar support 5 cm in depth provides the lowest load to the disk while sitting. Therefore, sitting with the hips and knees flexed or leaning forward should be avoided when there is an acute disk lesion. If sitting is necessary, there should be support for the lumbar spine by reclining the trunk 120°.

Effects of Bed Rest on the Intervertebral Disk
When a person is lying down, compression forces to the disk are reduced; and with time, the nucleus potentially can absorb more water to equalize pressures (imbibition). While lying down with the spine in flexion, the imbibed fluid accumulates posteriorly in the disk where there is greater space. Then, upon rising, body weight compresses the disk with the increased fluid, and intradiskal pressure greatly increases. The pain or symptoms from a disk protrusion are accentuated. To avoid exacerbating symptoms, absolute bed rest during the acute phase should be avoided. Bed rest during the first 2 days (when symptoms are highly irritable) may be needed to promote early healing, but it should be interspersed with short intervals of standing, walking, and appropriately controlled movement.

Effects of Traction on the Intervertebral Disk
Traction may relieve symptoms from a disk protrusion. It is proposed that separating the vertebral bodies may have the effect of placing tension on the annular fibers and posterior longitudinal ligament, thus have a flattening effect on the bulge; or it may decrease the intradiskal pressure. If traction relieves symptoms, the time of application must be short because with the reduced pressure fluid imbibition may occur to equalize the pressure. Then, when the traction is released, the pressure increases and symptoms are exacerbated.

Effects of Flexion and Extension on the Intervertebral Disk and Fluid Stasis
Rest in a slightly forward-bent position often lessens pain because of the space potential for the nucleus pulposus of the intervertebral disk. The patient may also deviate laterally to minimize pressure against a nerve root. Movement into extension initially causes increased symptoms. With acute disk lesions in which there is protective lateral shifting and lumbar flexion, techniques that cause lateral shifting of the spine opposite to the deviation followed by passive spinal extension (sustained or repetitive) to compress the protrusion mechanically have been found to relieve the clinical signs and symptoms in many patients.
Patients experiencing pain due to fluid stasis after being in a sustained flexed posture also experience relief with movement into extension.

Effects of Isometric and Dynamic Exercise
Isometric activities (resisted pelvic tilt exercises, straining, Valsalva maneuver) and active back flexion or extension exercises increase intradiskal pressures above normal. They therefore must be avoided during the acute stage of a disk lesion. Strong muscle contractions also exacerbate symptoms if a muscle has been injured. Therefore, active and resistive extension exercises are avoided during the acute stage.

Effects of Muscle Guarding
Reflex muscle guarding or splinting often accompanies an acute disk lesion and adds to the compressive forces on the disk. Modalities and gentle oscillatory traction to the spine may help decrease the splinting.

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