Outcomes indicators and a risk classification system for spinal manipulation under anesthesia: a narrative review and proposal

Since the 1930’s, many forms of facilitated manipulation of the spine have been reported in the literature, with various anesthetic/sedative agents and techniques used [1]. In the 1990’s, in managing patients with chronic spine pain and related dysfunction, chiropractors began utilizing the conscious sedation variety of manipulation under anesthesia (MUA) [1]. During that era, the standards and protocols of the National Academy of MUA Physicians (NAMUAP) [2] were popularized and relied upon by many in determining clinical eligibility for MUA. A revised version of the original NAMUAP standards and protocols was put forth in 2012, as adopted by the newly established American Association of Manipulation Under Anesthesia Providers (AAMUAP). That document subsequently underwent a consensus-based review, in developing recommendations for the contemporary practice of MUA [3].

What may render a clinical guideline useful for individual patients is its reliance upon valid evidence in establishing decision points and risks of care [4]. An appraisal of risk is essential to clinical guideline development [5‐7]. Estimations of the balance of benefits against risks or harms helps to ensure guideline credibility for stakeholders [8]. A significant limitation with current SMUA guidelines, and the collective scientific knowledge on this subject, is inadequate recognition of the risk profiles and outcomes indicators that contribute to patient selection. This limitation relates to incomplete development of the relative/absolute contraindications to care and several known clinical, diagnostic, and litigation-related factors which may weigh against the option of SMUA.

For spinal manipulation under anesthesia, what remains ambiguous despite existing guidelines is when to move a patient toward treatment. The heterogeneity of primary research and the presence of mostly lower-level evidence pose inherent challenges to clinical decision making [9]. Moreover, the current SMUA literature and association-based protocol documents are without a corresponding evidence-informed resource that elucidates risk versus benefit. Even when individual patients have undergone all appropriate studies [10], weak levels of evidence for SMUA can lead to uncertainty in selection, dosing and patient safety. Although rare, sentinel events have been reported [11‐13]. It is with a rise in SMUA utilization in the United States in recent years that a constructive and critical analysis of these matters becomes essential. This paper reviews the evidence for SMUA in establishing a scale for the chiropractic clinician which categorizes risk and outcome potential. It considers risk and unfavorable outcomes indicators in the development of a risk classification system that identifies patient safety and quality of care interests for this advanced form of treatment. As such, it calls for an elevation in the standard of care and improved patient selection through the incorporation of specific indices from existing medical literature.

Within the existing SMUA literature, the principal mechanism theorized for procedural effectiveness is the disruption of soft tissue adhesions about the axial spine [2, 14‐17]. In 1948, Clybourne proposed that the cases most amenable to MUA treatment were those involving joint adhesions, with limited movement in all directions [14]. He posited that the careful selection of cases was the product of an in-depth knowledge of joint anatomy and pathology [14]. However, he acknowledged the scope and limitations of the MUA procedure, indicating that it was not a panacea for low back pain [14].

As the fundamental basis for SMUA, the adhesion-disruption theory remains clinically appealing. The term Fibrosis Release Procedures (FRP) is a broader designation for spinal manipulation under anesthesia which has been more recently introduced in the chiropractic literature and within the published AAMUAP guidelines [3]. This terminology establishes that mobilization (stretching) is the primary manual therapy component of the procedure.

The premise that reducing adhesions can increase joint flexibility, decrease pain, and improve quality of life is seemingly so elementary that utilizing approaches which aim to accomplish the like must be therapeutically beneficial. There is evidence, for example, that MUA for stiff knees after total knee arthroplasty (TKA) can significantly increase knee flexion in certain patients when administered during the postoperative period but within twelve weeks [18]. The circumstances by which adhesions may develop after knee replacement are self-evident, giving due consideration to the mode and scope of intervention. The proliferation of scar tissue about the knee joint is a well-known complication of TKA [19]. However, that clinical scenario differs greatly from one that involves the presence of chronically symptomatic and dysfunctional spinal joints due to repetitive postural strain, factors related to age, or a history of trauma that excludes vertebral fracture or reconstructive surgery after disc injury. Thus, the evidence that MUA may reduce TKA-related arthrofibrosis is not generalizable to chronic spine pain patients who have been managed non-surgically for lower-level injury or degenerative change. In the latter patient populations, the supposition that scar tissue explains any observed range of motion deficits may be presumptuous.

Investigators have recognized that patient selection for SMUA could be enhanced by knowing more about the fibrotic adhesion concept [20]. One theory concerning adhesion development suggests that lumbar spine hypomobility may result in connective tissue adhesions of zygapophyseal joints [21]. While increased collagen deposition about the spine could explain the physical findings of palpable joint restrictions and decreased range of motion in chronic pain patients, there is no research that may assist in differentiating those with intraarticular adhesions from other manifestations of segmental dysfunction. In fact, validation of the adhesion concept and a related clinical role for SMUA would appear to have its greatest potential in cases of failed back surgery, in which advanced imaging reveals fibrosis in the region of prior intervention [16]. It has been estimated that as much as 20% to 36% of all cases of failed back surgery may be due to epidural fibrosis [22]. Nevertheless, for post-fusion lumbar pain there is limited evidence for the safety and efficacy of chiropractic treatment and no guidelines to aid with therapeutic decision-making [23].

Clinical research is lacking to support that the many historical accounts of successful SMUA treatment is due to the disruption of ligamentous, musculotendinous and/or epidural adhesions. The void of evidence in this area does not allow one to confirm or deny the theories that SMUA more effectively treats adhesions and that adhesion reduction increases flexibility [1]. With various spinal tissues known to account for pain and impaired function, it defies clinical logic that adhesions might serve as a pathological feature common to patients with chronic pain. Thus, what may account for a favorable response to SMUA treatment, and purportedly for numerous diagnoses [3], has yet to be elucidated. The genetic profiles that contribute to fibrosis and ligament hypertrophy in specific spinal conditions [24, 25], and how identifying the like may assist in patient selection/rejection for SMUA, are areas worthy of investigation. Nevertheless, recent evidence suggests that stretch does not have significant effects on joint mobility for people with or without neurological conditions, or short-term effects on pain or quality of life for people with non-neurological conditions [26].

In the development of treatment protocols for SMUA professional associations have relied upon numerous studies from the early medical literature. Advocates for the procedure frequently cite these same studies to support the use of SMUA for various diagnoses. In the more recent literature are reports of the indications for manipulation under anesthesia, including disc herniation/prolapse/protrusion/bulge, joint or spinal ankylosis, failed low back surgery, nonresponsive muscle contraction, compression syndromes with non-osteophytic entrapment, and whiplash-associated disorders [27, 28]. Most of these indications for care have been derived from the syllabi of chiropractic post-graduate MUA certification courses and the promotional materials of MUA proponents. However, numerous clinically significant findings from the same dependent literature base have yet to be given an appropriate level of attention. Several clinical, diagnostic, and litigation-related indices must now be recognized as predictors of unfavorable clinical outcomes or for potential adverse events. These indices, identified below, do not support the preservation of certain patient management concepts and selection criteria for SMUA, as initially developed before the era of evidence-based medicine.

In determining a patient’s candidacy for chiropractic treatment of an acute or chronic musculoskeletal condition, many core principles apply. These are not unique to clinical decision-making for SMUA. However, the same obligation exists for SMUA as with any modality or intervention being considered. For acute, non-specific low back pain, clinical practice guidelines consistently recommend patient reassurance of a good prognosis and educational instruction on self-care and remaining active [52]. Trajectory patterns for low back pain reveal that acute pain is often an episode or a flare-up of an ongoing condition, but pain in excess of three months would suggest a very different condition [53]. Once chronic, low back pain can be more difficult to manage and may require multimodal care [54]. Also, in the presence of widespread pain, chronic non-specific low back pain has a poorer prognosis than if pain is present only in the lower back [55].

Poor outcomes with conventional conservative treatment can often be predicted. It is the provider’s duty to identify potential barriers to recovery. For example, Bigos et al. identified premorbid nonphysical factors such as job dissatisfaction to be the best predictor of reporting back pain at work [56]. Also, clinical prediction/decision rules have been proposed for patient responsiveness to lumbar stabilization exercises [57] and those at risk for developing chronic low back pain [58]. In these and other instances, use of clinical prediction rules may help to determine the most appropriate course of treatment or if manipulation should even be considered [59]. Attention to the patient history is particularly important, as the reliability of the information gleaned may be questionable when litigation potential or secondary gain are present [60, 61].

Absent from the MUA literature is insight regarding the significance of the patient’s attitudes, beliefs, and expectations of treatment. Factors such as secondary gain, somatization, illness-behavior, and physician dependence are essentially without mention, yet represent key components to the management of chronic musculoskeletal pain [54, 62]. Moreover, although it is known that behavioral treatment can prevent chronicity [55], related elements such as alcohol/illicit drug use may be overlooked during the patient history and ensuing course of care. In clinical and especially medicolegal circumstances, embellishment and symptom magnification are not uncommon [62]. If not recognized and addressed early on, these factors could affect the direction and outcome of care. Thus, a thorough clinical examination, with attention for non-physiologic responses, is paramount. Still bearing relevance today is this AHCPR appraisal on pain behavior and inconsistent findings:

“The patient who embellishes a medical history, exaggerates pain drawings, or provides responses on physical examination inconsistent with known physiology can be particularly challenging. A strongly positive supine straight leg raising test without complaint on sitting knee extension and inconsistent responses on examination raise a suspicion that nonphysical factors may be affecting the patient's responses. "Pain behaviors" (verbal or nonverbal communication of distress or suffering) such as amplified grimacing, distorted gait or posture, moaning, and rubbing of painful body parts may also cloud medical issues and even evoke angry responses from the clinician. Interpreting inconsistencies or pain behaviors as malingering does not benefit the patient or the clinician. It is more useful to view such behavior and inconsistencies as the patient's attempt to enlist the practitioner as an advocate, a plea for help. The patient could be trapped in a job where activity requirements are unrealistic relative to the person's age or health. In some cases, the patient may be negotiating with an insurer or be involved in legal actions. In patients with recurrent back problems, inconsistencies and amplifications may simply be habits learned during previous medical evaluations. In working with these patients, the clinician should attempt to identify any psychological or socioeconomic pressures that might be influenced in a positive manner. The overall goal should always be to facilitate the patient's recovery and avoid the development of chronic low back disability.” [63]

One of several concerns with SMUA utilization relates to proper patient selection beyond the factors of physical complaints and findings. This may be of greatest relevance in the personal injury setting, since patients within that setting represent the preponderance of SMUA recipients in the United States today. On the historical basis that spinal manipulation may be the “treatment of choice,” MUA proponents have considered SMUA to be the logical next step for chronic pain patients with limited response. Nonetheless, not all patients can be expected to respond to the treatment chosen by the attending provider. Furthermore, failure of one option to provide for measurable and objective clinical gains, such as conventional office-based manipulation, would rarely support advancing the patient to the SMUA setting. Numerous conservative treatment options exist. Those with more robust evidence should be considered first, as dictated by the best-interest principle [54].

Another concern relates to the circumstance of offering the option of SMUA relatively early in care. This likely occurs more frequently than it should despite that the procedure lies low in the hierarchy of evidence-based treatment. As early patient advancement to SMUA stands apart from the existing literature on patient management, additional risk/benefit issues arise. The concepts that hurt isn’t always harm and that some patients get better with or without treatment must be given adequate consideration relative to the natural course of an injury. An individual who is likely to demonstrate additional improvement based on time alone may have no need for exposure to the added risk of medication assisted manipulation, even if that risk is minor. At times, a particular patient may be predestined to receive a full complement of therapeutic services and diagnostic tests early on, only to be followed by a treatment option of “last resort” if symptoms remain after a few weeks. But with that is the failure to incorporate unique anatomic, physiologic, and psychosocial variables in clinical decision making. Setting the individual patient’s expectations that the only way to improve is by way of treatment “x” undermines both the contemporaneous treatment being pursued and the available alternatives. Under these circumstances, the patient preference/value component of the evidence-based practice model [54] becomes prone to the influences of provider habit, preference, and assuredness for treatment “x”.

In the office setting, the risks associated with spinal manipulative therapy (SMT) are relatively low as compared with common modes of medical treatment [54]. However, a recent systematic review found inadequate reporting of adverse events with spinal manipulative therapy (SMT), whether catastrophic or otherwise [64]. Swait and Finch report that serious adverse events with manual treatment of the spine appear to be rare, making it difficult to estimate risk level [65]. They note that pre-existing pathology may increase the risk of some events and call for enhanced knowledge through clinician use of patient safety incident reporting systems [65]. Cassidy et al. reported no evidence of increased risk of vertebrobasilar artery (VBA) stroke [66] or carotid artery stroke [67] associated with chiropractic treatment versus primary care, suggesting coincidental occurrence. Thus, the possibility exists for a cervical arterial stroke to be the cause of neck pain rather than the result of manual intervention [65‐67]. Although it has been proposed that neck hyperextension during intubation may lead to vertebral artery dissection (VAD) [68], any specific association between VAD and vascular mechanical stress during neck manipulation under anesthesia has yet to be studied. Cadaveric studies have shown that chiropractic manipulation of the neck does not cause vertebral arterial strain or internal carotid arterial strain in excess of the strains incurred with ordinary movements [69, 70]. As for lumbopelvic spine manipulation-related cauda equina syndrome (CES), a recent systematic review cites it as the most common of the serious adverse events reported but excludes the assessment of cases involving manipulated under anesthesia [71]. Nevertheless, manipulating the lumbar spine under anesthesia may present an increased risk for CES over manipulation alone, as per anecdotal reporting that sixteen of twenty-nine identified CES cases involved manipulation under narcosis or ether anesthesia [72].

Medical malpractice carrier statistics on adverse events with MUA are proprietary and unavailable for analysis in the public domain. The SMUA literature contains mostly retrospective case reports and case series with selective focus on the benefits of treatment. Thus, the incidence for failed treatment or adverse events cannot be determined. With the rate of minor to serious complications remaining unknown, better case reporting and investigative efforts on the safety profile of SMUA are needed. For the chiropractic clinician who may not be particularly expert on certain aspects of the individual patient’s medical history, concurrent conditions, and prescription/illicit drug use, clinical decision making for SMUA should be reserved until all appropriate consultations are pursued. Any area of concern or uncertainty identified should result in a referral to a specialist who has the needed expertise to determine risk level and is best positioned to provide for medical clearance.

Spinal manipulation under anesthesia brings additional risk exposure beyond office-based conscious manipulation. Prior to anesthetization, it is incumbent upon the chiropractor to be aware of these risks and overall patient fitness for SMUA. For example, it is known that poor general health increases the risks inherent to anesthesia. General health risk categories for anesthesia have been established by the American Society of Anesthesiologists (ASA) [73], with which SMUA providers must be familiar when directing patients through pre-procedure screening evaluations. Also, consideration must be given by the chiropractor to the risks and contraindications for the manual therapy component of the MUA procedure. These expand from those associated with office-based manipulation. As mitigation and outcomes optimization strategies for the manual therapy component of the MUA procedure, Table 2 provides examples of clinical predictors of risk and outcome potential. The elements therein have been placed on a scale similar to that established by the ASA for predictors of perioperative mortality rates, and as adopted by the American College of Physicians for predictors of postoperative pulmonary and cardiac complications [74]. As with the ASA Physical Status Classification System, it has been shown that offering examples for each category aids with proper patient assignment [75].

As noted across the early SMUA publications and within the consensus statement put forth by the American Academy of Osteopathy (AAO), the single-dose approach is most common [9]. Under AAO criteria, if a second procedure dose is to be considered, it is usually after a three-week period [76]. Such would permit sufficient time to gauge the outcome of the initial procedure and to determine if it was sufficiently restorative in scope to represent clinical endpoint. With the SMUA approach put forth by the AAMUAP, it has been proposed that customary use of serial dosing provides for increased safety through gentler treatment (with “better control of biomechanical force,” when administered over three consecutive days) [3]. Nevertheless, each anesthesia exposure event would carry its own separate risks, whether inherent to the anesthetic agent or for the successive encounters during which the unconscious patient is unable to alert the provider to a painful and potentially injurious maneuver.

The ambulatory surgical center setting (ASC) in which SMUA is typically performed presents its own risk concerns. First, it must be established that patients are free from mental impairment and have an intellectual status permitting for adherence to ASC-related pre-procedural and post-procedural instructions. Second, it is required that patients have social support by way of a companion for transportation/observation, in adhering to procedural logistics and the at-home recovery period following ASC discharge. Last, because the ASC simply does not have the operational depth to meet that of a large medical center, it is not as well positioned to manage patients with poorly compensated or incompletely evaluated systemic disease, issues of acute substance abuse, an abnormal airway predisposing to difficult intubation, or patients having a personal or strong family history of anesthesia-associated malignant hyperthermia.

SMUA is an elective procedure. As a treatment option for a non-life threatening disorder, it is scheduled in advance. This provides adequate time for informed consent and/or patient pursuit of a second opinion from a specialist not involved in MUA. As put forth by Globe et al. informed consent is defined as a communication process between doctor and patient that leads to the patient agreeing to undergo a specific intervention [54]. Material risks of the intervention and available treatment options should be explained to the patient, along with the risks of no treatment [54]. It is the responsibility of the doctor to disclose information that is known and that the patient would find important in deciding whether to undergo a particular procedure [77]. Clinicians who perform spinal manipulation under anesthesia, or make referrals for the like, are obligated to understand the state of the evidence, procedural contraindications/risks, and the conditions and indicators that are predictive of adverse or unfavorable outcomes. As such, that information may be communicated to patients as they contemplate which of the available treatment options to pursue.

This paper adds to the body of knowledge for SMUA by evaluating the existing evidence in a unique way. It addresses outcome potential in several areas, identifies prognostic factors for complication, and qualifies where primary research efforts are needed for improved patient selection. As a primer, a new risk classification system is introduced which may serve as a guide for use in clinical practice. No longer can treatment standards be reliant upon anecdotal reports of satisfied patients, proclamations of the various conditions amenable to SMUA, preconceptions of permanent therapeutic benefit, a philosophy that calls for serial and multiregional treatment applications, and/or the fact that the procedure has had a historically good safety record. As health care professionals committed to the public interest, chiropractors who perform or make referrals for SMUA are obligated to remain current and put forth accurate information in the public domain on the state of the evidence, known procedural contraindications/risks, and the conditions and indicators that may predict an adverse or unfavorable clinical outcome. When chiropractors lack a comprehensive understanding of that information, or advocate for the procedure by preference, patients may be unable to make informed decisions about their health care options in submitting to appropriate consent. With a new perspective on the evidence for SMUA, this analysis can assist clinicians who are seeking to identify key decision points in care in enhancing risk management strategies and optimizing patient outcomes.