Table 4

Studies providing direct adverse event classification system only (n = 20).

Author, year, citation	Study Design	Classification system
Stern et al. 1995 [73]	Case Report / series	A minor complication was defined as increasing symptoms as reported by the patient.
		A major complication was defined as emergency surgery after the treatment.
Hendry et al. 2002 [74]	Survey	Minor: benign and transient
		Moderate: reversible and serious
		Major / serious: irreversible
UK BEAM Trial Team 2004 [75]	Trial	Serious adverse events: treatment related events leading to hospital admission or death within one week
Gibbons et al. 2006 [76]	Other design	Transient: begin within 4 hours of receiving treatment and typically resolve within the next 24 hours.
		Substantive reversible impairment
		Serious non-reversible impairment
Thiel et al. 2007 [77]	Survey	Minor adverse events: worsening of presenting symptoms or onset of new symptoms, immediately, and up to 7 days, after treatment
		Significant (serious) event: referred to hospital and/or severe onset/worsening of symptoms immediately after treatment and/or resulted in persistent or significant disability/incapacity.
Haneline et al. 2009 [78]	Observational Study	Serious adverse events: events resulting in death, life-threatening situations, the need for admittance to a hospital, or temporary or permanent disability.
Carnes et al. 2010a [23]	Consensus	‘Mild’ and ‘not adverse’ adverse events: short term and mild, they are non-serious, the patient’s function remains intact, they are transient/reversible and no treatment alterations are required because the consequences are short term and contained.
		‘Moderate’ adverse events: the same as ‘major’ adverse events but only moderate in severity.
		‘Major’ adverse events: medium to long term, moderate to severe and unacceptable; they normally require further treatment and are serious and distressing.
Carlesso et al. 2011 [79]	Other design	Not Adverse: short term duration, acceptable severity, intact function and no other explanation possible
		Mild: short term (hours to 2 days) duration, 0.5–2 on NRS severity, intact function and no other explanation possible
		Moderate: medium term (1–5 days) duration, 1–2 on NRS severity, modified function, no other explanation possible
		Major: longer term (>2 days/next visit) duration, >3 on NRS severity, unacceptable symptoms, impaired function, no other explanation possible
Carlesso et al. 2013 [25]	Survey	Mild: acceptable and short-term, no functional impact, lasting up to 2 days
		Major events: impacting on function
Carlesso et al. 2013 [24]	Trial	Mild: No impact on function; lasts less than 24 hours
		Moderate: Function modified but intact, may require alteration in treatment, lasts between 24 hours to 1 week
		Major: Function absent, requires medical intervention, lasts over 1 week
Hebert et al. 2015 [80]	Review	Serious adverse event was defined as an untoward occurrence that results in death or is life threatening, requires hospital admission, or results in significant or permanent disability
Keating et al. 2015 [81]	Protocol	Significant adverse event presents progressive neurological signs; or emerging medical red flags or cervical spondylotic myelopathy
Kressig et al. 2016 [82]	Other design	Serious adverse events: symptoms with immediate onset after treatment and with persistent or significant disability.
Lisi et al. 2018 [83]	Consensus	Serious adverse event: resulting in death, life-threatening symptoms, hospitalization, or disability or requiring intervention to prevent permanent impairment or damage.
Frydman et al. 2018 [84]	Protocol	Serious adverse events are defined as events that are fatal, life-threatening or lead to hospitalisation.
Smith et al. 2019 [85]	Review	Serious adverse events associated with manipulative therapies are defined as conditions that lead to hospital admission, permanent damage or death.
Yao et al. 2020 [86]	Trial	Nonserious adverse events: self-limited, and no permanent injuries occurred
		Serious adverse events: caused death, were life threatening, or necessitated admission to the hospital
Gross et al. 2002 [87]	Clinical Practice guideline	Minor: relatively common benign transient side effects, lasting less than 24 hours
		Moderate: reversible serious complications
		Major complications: irreversible serious complications
Skelly et al. 2020 [88]	Review	Minor adverse events: mild symptoms and time-limited
		Nonserious treatment-related adverse events: worsening of symptoms, mild, self-limiting back or joint pain
		Serious adverse events: involving death, hospitalization, persistent disability, requiring intensive medical attention or a life-threatening risk
Funabashi et al. 2020 [89]	Protocol	Serious adverse events: any unfavorable sign, symptom, or disease temporally associated with the treatment, whether or not caused by the treatment that results in death or is life-threatening or results in inpatient hospitalization or prolongation of existing hospitalization for more than 24 hours with a persistent or significant incapacity or substantial disruption of the ability to conduct normal life functions.

NRS: numeric rating scale.