A. The Safety of Cervical Adjusting
No one pays closer attention to injury statistics than Malpractice Insurance carriers.
Scott Haldeman, MD, DC reviewed malpractice claims records for a 10-year period between 1988 and 1997. In reviewing the outcomes following the application of 134.5 million cervical manipulations (commonly referred to as the chiropractic adjustment), the records indicated that there were 23 reported cases of stroke or vertebral artery dissection (VAD).  Of this group, 10 of the patients had the complicating factors of high blood pressure, use of oral contraceptives, or a history of smoking, all of which are associated with vascular disease. The actual incidence of stroke or VAD following cervical manipulation was found to be one per 5.85 million cervical adjustments. That means that the average chiropractor could work for 1430 years (or practice 48 full chiropractic careers!) before they might be involved with this type of litigation.
Other reports, listing a higher frequency of adverse events, have been compromised by the tendency of those authors to inappropriately list the pracitioner as a chiropractor, even when it turned out that the injury was caused by a medical doctor, a physical therapist or a hairdresser! , 
Rather than raising concerns about the safety of chiropractic, these statistics emphasize that spinal manipulation, in the hands of unskilled practitioners, is dangerous, and the practice must be closely regulated.
The World Health Organization recently released a comprehensive set of guidelines that clearly states that chiropractic is a separate profession, rather than a set of techniques that can be learned in short courses by other health professionals. They also make it clear that medical doctors and other health professionals, in countries where the practice of chiropractic is not regulated by law, should undergo extensive training to re-qualify as chiropractors before claiming to offer chiropractic services. In some countries there have been recent efforts by medical groups to provide short courses of approximately 200 hours in chiropractic technique.
WHO’s guidelines indicate that a medical graduate should a require an additional minimum of 1800 class hours, including 1000 hours of supervised clinical training, before claiming to offer chiropractic services.
B. The Safety of Low Back Adjusting
Lower back injury alleged to have occurred following spinal manipulative therapy has been reported in patients with pre-existing disc herniation or prolapse. While it is suggested that the forces required to cause a disruption of the annular fibers of the healthy intervertebral disc well exceed that of a rotational manipulative thrust, some disc herniation/protrusion may certainly be aggravated by an inappropriately applied manipulative maneuver, as it may be by other simple activities of daily living such as bending, sneezing, or lifting. The most frequently described severe complication is compression of the cauda equina by massive midline nuclear herniation at the level of the 3rd, 4th or 5th intervertebral disc.
Of the 30 cauda equina complications associated with manipulation reported in the French, German and English literature over an 80 year period, only 8 were allegedly related to chiropractic treatment.