Spinal adjustment
Spinal adjustment and chiropractic adjustment are terms used by chiropractors to describe their approaches to spinal manipulation, as well as some osteopaths, who use the term adjustment.
Claims made for the benefits of spinal adjustments range from temporary, palliative (pain relieving) effects to long term wellness and preventive care. Some claims are controversial, particularly with regard to indications and health benefits. There is debate concerning the safety of some of the procedures used in spinal adjustments, particularly those including upper cervical manipulations.
The original spinal adjustment was a variation of a procedure known today as spinal manipulation. This form of treatment has documented use as far back as Hippocrates and the ancient Egyptians and was carried through the ages by families of bonesetters. The modern form of spinal manipulation techniques have characteristic biomechanical features, and are usually associated with an audible "popping" sound. There is strong evidence that this sound is the result of a phenomenon known as cavitation.

# Adjustment vs. manipulation
The difference between a spinal adjustment (only performed by chiropractors) and a spinal manipulation (as performed also by non-chiropractors) is essentially philosophical and concerns the intention behind the procedure. The intention of a chiropractic adjustment is to affect or correct the alignment, motion and/or function of vertebrae. Specifically, they are intended to correct "vertebral subluxations"; the term given to the signs and symptoms that are said to result from abnormal alignment of vertebrae. In contrast, manipulation is intended to improve the function of a joint. This makes the rationale for the use of an adjustment unique to chiropractors. This intention forms the legal and philosophical foundation of the profession, and is even formulated in US Medicare law as "manual manipulation of the spine to correct a subluxation."
While the terms "spinal adjustment" and "spinal manipulation" are often used interchangeably by chiropractors in their literature and research, most straight (foundational) chiropractors prefer to use the word "adjustment" to describe the nature of their work.
The International Chiropractors Association (ICA), which tends to represent the majority of straight chiropractors, makes the distinction as:
The word adjustment is also used by osteopaths trained at the European School of Osteopathy when referring to a technique called Specific Adjustment Technique, or SAT. The technique was developed by UK osteopath Tom Dummer.

# Adjustment methods
As the chiropractic profession engaged in the pursuit of improving health through adjustments to the nervous system, individual practitioners and institutions proposed and developed various proprietary techniques and methods.  While many of these techniques did not endure, hundreds of different approaches remain in chiropractic practice today.  Most cite case studies, anecdotal evidence, and patient testimonials as evidence for effectiveness.  These techniques include:
- Toggle Drop - this is when the chiropractor, using crossed hands, presses down firmly on a particular area of the spine. Then, with a quick and precise thrust, the chiropractor adjusts the spine. This is done to improve mobility in the vertebral joints.
- Lumbar Roll (aka side posture) - the chiropractor positions the patient on his or her side, then applies a quick and precise manipulative thrust to the misaligned vertebra, returning it to its proper position.
- Release Work - the chiropractor applies gentle pressure using his or her fingertips to separate the vertebrae.
- Table adjustments - The patient lies on a special table with sections that drop down. The chiropractor applies a quick thrust at the same time the section drops. The dropping of the table allows for a lighter adjustment without the twisting positions that can accompany other techniques.
- Instrument adjustments - often the gentlest methods of adjusting the spine. The patient lies on the table face down while the chiropractor uses a spring-loaded activator instrument to perform the adjustment. This technique is often used to perform adjustments on animals as well.
- Manipulation under anesthesia (MUA) - this is performed by a chiropractor certified in this technique in a hospital outpatient setting when the patient is unresponsive to traditional adjustments.

## Adjustment techniques
There are many techniques which chiropractors can specialize in and employ in spinal adjustments. Some of the most notable techniques include:
- Activator Methods - uses the Activator Adjusting Instrument instead of by-hand adjustments to give consistent mechanical low-force, high-speed clicks to the body. Utilizes a leg-length analysis to determine segmental abberation.
- Active Release Therapy (Active Release Technique) - soft tissue system/movement based massage technique that treats problems with muscles, tendons, ligaments, fascia and nerves.
- Blair Upper Cervical Technique - an objective upper cervical technique focusing primarily on misalignments in the first bone of the spine (Atlas) as it comes into contact with the head (Occiput).
- Cox Flexion-Distraction - a gentle, non-force adjusting procedure which mixes chiropractic principles with osteopathic principles and utilizes specialized adjusting tables with movable parts.
- Hole-in-one technique - developed by B.J. Palmer. He, at some point, claimed that the "pure, unadulterated & straight" chiropractors should only treat the upper two cervical vertebrae (C1-C2) , which is the cause of most, if not all, disorders by being misaligned.
- Directional Non-Force Technique - utilizes a diagnostic system for subluxation analysis consisting of gentle challenging and a unique leg check allowing the body to indicate the directions of misalignment of structures that are producing nerve interference. A gentle but directionally specific thumb impulse provides a long lasting correction to bony and soft tissue structures.
- Diversified - the classic chiropractic technique, developed by D.D. Palmer, DC. Uses specific manual thrusts focused on restoring normal biomechanical function. Has been developed to adjust extremity joints as well.
- Gonstead Technique - Developed by an engineer enthusiast turned chiropractor, this technique uses a very specific method of analysis by the use of nervoscopes, full spine x-rays and precise adjusting techniques that condemns "torquing" of the spine, which may harm the Intervertebral disc.
- Kale Technique (Specific Chiropractic) - gentle technique which utilizes a special adjusting table that helps adjust and stabilize the upper cervical region surrounding the brain stem.
- Logan Basic Technique - a light touch technique that works to "level the foundation" or sacrum. Its concept employs the use of heel lifts and specific contacts.
- NUCCA Technique - manual method of adjusting the atlas subluxation complex based on 3D x-ray studies which determine the correct line of drive or vector of force.
- Thompson Terminal Point Technique (Thompson Drop-Table Technique) - uses a precision adjusting table with a weighing mechanism which adds only enough tension to hold the patient in the "up" position before the thrust is given.
- Toggle Recoil Technique - a quick thrust and release to the upper cervical vertebra, the recoil is to allow the vertebra to oscillate into its proper position.

# Mechanisms and effects
The effects of spinal adjustment vary depending on the method performed.  All techniques claim effects similar to other manual therapies, ranging from decreased muscle tension to reduced stress.  Most of these effects can be attributed to theoretical neurological pathways that modulate pain and proprioception and therefore affect muscle tone and postural balance.  The mechanisms that are claimed to alter nervous system function and affect overall health are currently speculative in nature and range from mechanical pressure on nerve roots to autonomic reflexes altering Central Nervous System (CNS) function and therefore visceral function.  Some techniques use adjustments in an effort to restore proper posture and curvatures; suggesting that posture is related to health.  Whether these effects are placebo related is speculative as well.  Regardless of the technique used, most emphasize the repetitive use of adjustments over time in an effort to retrain the body's nervous system.
The effects of spinal manipulation have been shown to include: temporary relief of musculoskeletal pain and shortened time to recover from acute back sprains (Rand). There is evidence that spinal manipulation is effective for the treatment of acute low back pain, tension headaches and some musculoskeletal issues. Common side effects of spinal manipulative therapy (SMT) are characterized as mild to moderate and may include: local discomfort, headache, tiredness, or radiating discomfort.

# Safety issues
The World Health Organization states that when "employed skilfully and appropriately, chiropractic care is safe and effective for the prevention and management of a number of health problems." As with all interventions, there are risks associated with spinal manipulative therapy (SMT). Infrequent, but potentially serious side effects, include: vertebrobasilar accidents (VBA), strokes, spinal disc herniation, vertebral and rib fractures, and cauda equina syndrome.
A study on the chiropractic spinal adjustment published in the February 2002 issue of the Annals of Internal Medicine reviewed more than 160 reports and studies on chiropractic. With regard to the safety of neck adjustment, it states: "The apparent rarity of these accidental events has made it difficult to assess the magnitude of the complication risk. No serious complication has been noted in more than 73 controlled clinical trials or in any prospectively evaluated case series to date."
A New Zealand Commission report in 1979 said "We are satisfied that chiropractic treatment in New Zealand is remarkably safe... By the end of the inquiry we found ourselves irresistibly and with complete unanimity drawn to the conclusion that modern chiropractic is a soundly based and valuable branch of the health care in a specialized area.". However, the judge in the Wilk vs AMA case described this report as "unsatisfactory", and a review by the US Congress' Office of Technology Assessment (OTA) found 'serious problems' in its treatment of safety and efficacy issues.
In a 1993 study, J.D. Cassidy DC and co-workers concluded that the treatment of lumbar intervertebral disk herniation by side posture manipulation is "both safe and effective."