8.2 Spinal Adjustive Techniques

High-Velocity, Low-Amplitude (HVLA) Thrust Mechanics

A high-velocity, low-amplitude (HVLA) adjustment is a specific, controlled manual thrust delivered at or just beyond a joint's passive end range of motion, characterized by high speed of force application and a very small (low-amplitude) displacement of the joint itself. The goal is to move the joint a short distance, quickly, into what has been described as the paraphysiological space -- a small zone beyond the normal passive range but short of the anatomic limit (ligamentous end-range) that produces the audible/palpable release, or cavitation.

Cavitation is the tribonucleation phenomenon in which a rapid drop in intra-articular pressure causes dissolved gas (largely carbon dioxide) within the synovial fluid to form a gas bubble, producing the characteristic joint 'crack' or 'pop.' Cavitation is associated with, but not strictly required for, a successful segmental release; it correlates with a measurable, temporary increase in joint range of motion and a drop in paraspinal muscle activity immediately following the thrust. A joint that has recently cavitated typically requires a refractory period of roughly fifteen to twenty minutes before it can cavitate again.

Every HVLA adjustment, regardless of named system (Diversified, Gonstead, Thompson, or others), is built from the same core components that Part III exams isolate individually:

• Patient position: the posture (side-posture, prone, supine, seated) that pre-tensions the joint and locks out segments above/below the target to localize force
• Doctor position/stance: body mechanics that allow the doctor to deliver force through the body rather than the arms alone, protecting the doctor and improving accuracy
• Segmental contact point: the specific bony landmark (e.g., mammillary process, transverse process, spinous process, articular pillar, pisiform contact) where force is applied
• Line of drive (LOD): the vector along which the thrust is delivered, determined by the facet plane and the direction needed to correct the identified joint restriction/listing
• Pre-stress/tension (set-up): taking the segment to its passive end range/tissue tension point before the thrust, minimizing the amplitude needed
• The thrust: a high-velocity, low-amplitude, and typically low-force impulse delivered along the line of drive once set-up is complete

Because the amplitude of a correct HVLA thrust is small, most of the corrective force comes from precise localization (contact point and set-up) rather than from raw force -- a distinction Part III frequently tests by pairing a described dysfunction with the most specific rather than the most forceful corrective option.

Segmental contact selection follows the local anatomy available at each region: the mammillary process and transverse processes are the common lumbar contacts, the transverse and articular processes are used in the mid-to-lower thoracic spine, the articular pillar is the typical cervical contact, and the spinous process is used for some central thoracic and lumbar techniques. The part of the doctor's hand used to contact the patient -- pisiform, hypothenar, thenar, or a reinforced index/thumb contact -- is chosen to match the size and orientation of the target bony landmark and to allow the force to be delivered cleanly along the line of drive without slipping or spreading force to adjacent segments.

Named Technique Systems at the Part III Level

Part III does not test brand-name marketing claims; it tests the underlying biomechanical logic each system uses to select contact point, patient position, and line of drive.

Diversified Technique is the most broadly taught system and the de facto default against which Part III case scenarios are usually written. It uses a wide variety of patient positions (side-posture, supine, prone, seated) and a listing system (commonly a short letter code describing the segment's position, such as posterior, left/right, and superior/inferior relative to the segment below) to describe the direction of joint dysfunction and derive the corrective line of drive. Contacts vary by region -- a pisiform contact on the transverse process for a lumbar side-posture thrust, for example.

Gonstead Technique emphasizes an extensive, structured analysis before any thrust: static palpation, motion palpation, visualization, instrumentation (such as paraspinal thermography), and full-spine X-ray line analysis to identify a specific listing. Gonstead-specialized contacts are largely on the mammillary process (lumbar) or lateral mass, and the line of drive is deliberately kept free of a rotational component -- the classic Gonstead teaching is a straight posterior-to-anterior, lateral-to-medial vector without added rotation, intended to reduce shear at the facet. Gonstead uses distinctive equipment, including the knee-chest table (used for disc lesions and to unload the lumbar spine in patients who cannot tolerate prone positioning) and the Gonstead pelvic bench (a stepped table that allows a hip drop for side-posture work).

Thompson (Thompson Terminal Point) Technique uses a segmented drop-piece table: each section of the table is pre-tensioned to a specific resistance, and the doctor's thrust releases the table section a fraction of a second after force is initiated, adding a distraction/traction assist to the segment while reducing the force required from the doctor. Thompson technique pairs closely with a supine leg-length analysis used to identify which side or level is dysfunctional before the drop-thrust is applied. The doctor feels for a distinct terminal point -- the sensation of the joint reaching the endpoint of its available motion -- as the target endpoint of the thrust.