General description of the studies
We found 13 original articles, in which the issue of maintenance care was investigated. Eleven could be described as surveys and have been briefly described in Table 1 [Additional file 1]. Eight were cross-sectional [4, 5, 9–14], one was a file inspection study , one was a prospective study , and one was a one-year multi-centre prospective outcome study, in which the prevalence of maintenance care was retrospectively investigated at the one-year follow-up . The two non-survey articles consisted of a case-report  and a preliminary randomized controlled clinical trial, investigating the efficacy of maintenance care in patients with chronic LBP . The first of the studies was published in 1976 with data collected in 1973–4  and the last 30 years later .
Five of the surveys were from Australia, three from the USA, two from UK, and one from Norway (Table 1 [Additional file 1]). The clinical trial would have been carried out in Canada , whereas it is unclear in which country the case-report was produced . The sample sizes ranged from a case-report of 1 patient  to 2056 case files .
Five of the 11 surveys had low response rates: 20% , 22% , 35% , 44% , 51% , and in one survey the response rate does not appear to have been reported . In the file inspection study, the proportion of participants was higher (71%) than the percentage of practitioners whose files were inspected (35%) . Two of the surveys with higher response rates included specific study samples that nevertheless probably did not represent the general chiropractic profession; one of recently graduated Australian chiropractors  and one in which Australian chiropractors were included on the basis of whether they practised in a chiropractor-dense area or not .
In summary, there were only few studies, covering a wide time-period, unevenly distributed across the world, and the study participants were often unlikely to be representative of their target populations.
Definitions of maintenance care
The definitions of maintenance care that we found were not based on scientific evidence of the clinical validity of maintenance care but perhaps more on opinion and consensus.
Because there is a conviction among some chiropractors that spinal adjustments/manipulations have a preventive effect not only on musculoskeletal problems but also on the general state of health, it is not surprising that one "officially recognized and approved" definition of maintenance care that we found was rather vague. This would allow the chiropractor to apply it according to his/her own scope of practice. The definition is "Appropriate treatment directed toward maintaining optimal body function. This is treatment of the symptomatic patient who has reached pre-clinical status or maximum medical improvement, where condition is resolved or stable" .
Another definition found in the literature is "...a regimen designed to provide for the patient's continued well-being or for maintaining the optimum state of health while minimizing recurrences of the clinical status" in brief also "continuing care" . These definitions resemble that used by Breen, when reporting his study, in 1976: "... treatment, either scheduled or elective, which occurred after optimum recorded benefit was reached, provided there was no evidence of relapse." . But on the other hand, according to a recent British study of chiropractors, osteopaths and physiotherapists, at least 10% of each profession reported that they sometimes continue to treat patients with low back pain who show almost no improvement . Therefore, it appears that maintenance care is also offered to patients who have not improved. Boline and Sawyer  report on "regular chiropractic care", which we interpreted as meaning maintenance care.
Other authors, who studied this subject, did not define maintenance care at all [9, 13, 16, 17] and in one study such non-definition was stated to be purposeful, in order to prevent bias of the investigation process .
Indications for maintenance care
There was only sparse information in the literature on the indications for maintenance care and there was no information on specific indications for particular conditions.
The chiropractors in a North-American study by Rupert  generally agreed that the purposes of maintenance care were to minimize recurrence or exacerbation, maintain or optimize state of health, prevent conditions from developing, provide palliative care for "incurable" conditions, and determine and treat subluxations (all statements with over 80% agreement). Fifty-six percent meant that the purpose of maintenance care was to prevent subluxations, and this was confirmed in a similar study of Australian chiropractors . Most of these statements reflect secondary or tertiary preventive approach. Nevertheless, some could also be interpreted as referring to a primary preventive approach.
Interestingly, the concept of "prevention and health promotion" was used in a North American study of maintenance care in relation to chiropractic patients aged at least 65 . Boline and Sawyer explored similar concepts, also in a study from North America, in which they investigated attitudes among chiropractors in relation to counselling of patients on a healthy lifestyle, i.e. including elements of primary prevention, as well as regular chiropractic care. . This shows that they mean that chiropractors should participate in health promotion and prevention of disease, outside the realm of the purely musculoskeletal.
According to a prospective multicenter study of 115/205 Norwegian chiropractors and 832 patients with persistent low back pain, patients, who after one year reported definite improvement, were treated only a few times and those with poorer outcome had a larger number of consultations over a period of one year. This might indicate that tertiary prevention is offered to and accepted by some of those patients with persistent low back pain, who fail to recover, but that secondary prevention in patients with more satisfactory outcome is less common . This information is the only indication of how maintenance care is actually employed in clinical practice.
The nature of the use of maintenance care
According to the Mercy Guidelines , spinal adjustments are central in maintenance care. However, the research literature is vague on the contents of a maintenance care consultation and the frequency of treatments required for different types of patients.
Rupert  asked his North-American study subjects to describe the therapeutic components of maintenance care and concluded that they were adjustments/spinal manipulation, exercises, proper eating habits, patient education, and vitamin supplementation. This finding was confirmed in a similar a study of Australian chiropractors  and in another study of Rupert et al in North American patients, aged 65 or older .
Wenban described the outcome in relation to the various outcomes measures used when treating one female patient with a complaint of uncomplicated chronic low back pain . His indications for treatment were "tenderness of the patient's vertebral spinous processes, S2 spinous process, and the superior aspect of the posterior superior iliac spines". According to the author, this indicated a "subluxation", and providing that there were no other "more serious indicators" (not further specified), treatment was provided. The treatment consisted of adjustments only, using a combination of diversified and sacro-occipital techniques (a reference is provided to two textbooks].
Wenban also described the frequency of visits, after a 12 weeks intensive care period, as 2 times per week for 6 weeks, 1 time per week for 2 weeks, and 1 time per 2 weeks for the reminder of the study period of 5.5 months. In addition, Jamison offers some information on this subject. According to the participants in one of her studies: "Maintenance adjustments should be offered on a basis of once a month to once every three to four months" . According to one of Rupert's studies, North American patients who agree to receive maintenance care, average 14 visits per year , and in another study, elderly maintenance care patients (65+ years of age) average 17 visits per year . This amounts to a little more than one visit per month.
There were no studies of different types of strategies in relation to different types of patients or conditions.
Beliefs among chiropractors and acceptance among patients
Boline and Sawyer in a 1987-survery of North American chiropractors noted that 98% of their participants believed that "regular chiropractic care would be important for the 'average' person" . Jamison found that 93% of Australian chiropractors considered that at least some patients would require maintenance care (and that 41% thought that all patients would) . In another survey, she found that 92% believed that spinal adjustments promote health in asymptomatic patients .
However, the last two studies dealt primarily with the concept of spinal adjustments and the prevention of endocrine, visceral and autonomic dysfunction, which may have incited chiropractors of specific opinions to participate and, indeed, the very low response rates (22% and 20%, respectively) indicate that this may have been the case.
These beliefs are underpinned by the finding in the study by Rupert , in which 40% of the chiropractic respondents believe that there is adequate research to support the concept of maintenance care. The Australian respondents were less naïve, with only 22% supporting this statement .
We found no information on the patients' perspective of maintenance care. However, in one study it was stated that 79% of patients are recommended for maintenance care and that 34% of those "elect to receive these services" . It is not clear, whether these estimates are based on an objective count of patient files or on the participating chiropractors' opinions. However, the figure of 34% does not appear unreasonable, given the personal experience of many chiropractors that only some patients are willing and able to continue treatment past the acute event.
Even among patients with persistent low back pain, maintenance care might not be attractive. Of the 832 participants in a large Norwegian multi-centre prospective outcome study, all with persistent low back pain at base line, only 14% were reported by their chiropractors to have received some type of maintenance care during the subsequent year .
In summary, it is possible that most chiropractors believe in maintenance care but data from unbiased samples are missing. The opinion of patients is unknown, although it might be less positive, as a relatively low percentage of patients seem to accept to continue treatment past the initial treatment program.
Prevalence of use and factors associated with its use
Although the concept of maintenance care seems to be firmly ensconced in the chiropractic profession, the frequency of its use has not been clearly described.
Breen reported in 1976 that 36% of 2987 case files belonged to patients who received maintenance care . These patients were obtained from a sample belonging to 24 British chiropractors, i.e. 35% of the practitioners at that time. They had been selected to give a proportional representation of practitioners in the British hospital regions, and a 20% randomly selected sample of up to 1000 case files was taken from each practice. There were proportionally fewer files from newly established practices. Most of these chiropractors were educated in North America, practising at a time when there were relatively few manipulating practitioners but also at a time when chiropractic was relatively unknown. It was noted that most patients consulted for "rheumatic conditions and in particular low back pain" whereas non-musculoskeletal problems were very rare. This appears to be the first investigative study on this subject, and it probably provides a fair picture of the use of maintenance care in the UK at that time.
Others have reported the proportion of patients who receive maintenance care in the literature. Webb and Leboeuf in 1987 found that 44% of newly graduated Australian chiropractors estimated that at least 34% of their patients were on maintenance care .
A similar estimate was obtained in another Australian study published two years later . In both these two studies, only 6% of the respondents reported that more than 2/3 of their patients received maintenance care. However, although the response rates were better in these, two studies (65% and 82%, respectively); their estimates were based on the practitioners' opinion rather than exact counts of patient files.
Obviously, the use of maintenance care will affect the clinic income. According to Rupert's participants, 23% of practices' incomes was generated from maintenance care . That the use of maintenance care can affect the patient turnover was shown in the Leboeuf et al study from Australia .
We were unable to find any information on which factors play a role, when a chiropractor decides to offer a maintenance care program to a patient, and no information seems to be available on what considerations patients take into account when deciding to accept such a program.
Efficacy and cost-effectiveness for various types of conditions
It remains also to study the efficacy and cost-effectiveness of maintenance care for various types of conditions.
To our knowledge, it has only been attempted to test the efficacy of maintenance care in one well-designed pilot study, in which 29 patients with chronic low back pain were randomly allocated to either a non-maintenance care group or a maintenance care group (for a 9-month treatment after one initial month of treatment). At follow-up, there was no difference in pain but the group that received maintenance care had lower disability scores than the control group . A full-scale trial is presently underway on patients with neck pain (personal communication – M. Descarreaux).