A chiropractic adjustment, formally known as spinal manipulative therapy (SMT), is a hands-on, non-invasive procedure used by practitioners to address restricted movement in joints, particularly in the spine. This controlled technique involves applying a precise force to a joint that is not moving properly, with the goal of restoring its normal range of motion. The process is a focused physical intervention designed to improve mechanical function and influence the body’s nervous system. The procedure is a systematic approach, beginning with careful preparation and culminating in a specific, rapid action.
The Preparation and Setup
The adjustment process begins with a careful physical assessment of the patient’s spine and joints to identify the specific area of restricted movement. The practitioner uses palpation to feel for subtle changes in the position or tension of the individual joints and surrounding soft tissues. This evaluation isolates the target joint for manipulation.
Once the target joint is identified, the patient is positioned on a specialized padded table, often lying prone or side-lying, depending on the area being treated. Correct patient positioning is employed to stabilize the rest of the body. This helps localize the force of the adjustment to the intended joint, preventing the force from being absorbed by adjacent segments.
A technique called pre-loading or tensioning is then applied, where the chiropractor gently guides the joint to the end of its passive range of motion. This controlled tensioning takes the slack out of the joint capsule and surrounding connective tissue. This crucial step prepares the joint to be moved past its normal physiological limit but safely within its anatomical boundary.
The Mechanism of Spinal Manipulation
The core action of the adjustment is the application of a High-Velocity, Low-Amplitude (HVLA) thrust, which is a quick, shallow, and highly specific impulse. This force is delivered by the chiropractor’s hands or a small instrument, causing a momentary separation of the joint surfaces. The speed of the thrust is a defining characteristic, as a fast rate of force application is needed to produce the desired joint gapping with the least amount of total force.
The physiological goal of this manipulation extends beyond simple joint movement; the specific thrust stimulates mechanoreceptors, which are sensory nerve endings located in the joint capsule and surrounding deep muscles. This sudden bombardment of sensory input is sent to the central nervous system. The immediate neurophysiological effect of this stimulation is thought to alter motor control signals and potentially reduce muscle hypertonicity and pain perception.
By moving the joint slightly beyond its typical end range of motion, the adjustment works to release entrapped folds of the synovial membrane, known as meniscoids, that may be causing joint irritation. The overall biomechanical outcome is an increase in the joint’s range of motion, which can contribute to a reduction in local pain. This controlled movement is performed with precision to ensure the joint remains within its anatomical integrity.
Understanding the Joint Sound
Many people associate the adjustment with an audible “pop” or “crack,” a phenomenon known scientifically as cavitation. This sound is a common side effect of the joint separation that occurs during the HVLA thrust. The joint capsule contains synovial fluid, a viscous liquid that lubricates the joint and contains dissolved gases.
When the joint surfaces are rapidly separated by the adjustment, the volume inside the joint capsule increases, causing a sudden drop in pressure. This reduction in pressure forces the dissolved gases to rapidly form a temporary gas bubble within the fluid. The characteristic sound is produced by this sudden physical event.
It is important to understand that the sound is a physical event related to fluid dynamics, not the grinding or fracturing of bones. Furthermore, the presence or absence of this audible release is not considered a measure of the adjustment’s success. The therapeutic benefits can occur whether or not a cavitation sound is heard.
Immediate Post-Adjustment Responses
Following an adjustment, the body can exhibit several immediate physical sensations as it adapts to the restored joint mobility. The most commonly reported response is temporary, mild muscle soreness in the treated area, similar to the feeling after an unaccustomed workout. This soreness typically resolves within 24 to 48 hours.
Some individuals may experience a temporary feeling of lightness or mild lightheadedness, particularly after a neck adjustment. A small percentage of patients may also report feeling tired or fatigued, which is thought to be the body’s natural response to the neurophysiological changes. These post-treatment effects are transient and considered normal.
To support the body’s response, practitioners often advise light movement and increased hydration immediately following the session. Drinking water helps flush the system and assists the muscles and connective tissues in adapting to their new functional state.