Letter to the Editor: Virtual McKenzie extension exercises for low back and leg pain: a prospective pilot exploratory case series. Journal of Manual and Manipulative Therapy, DOI:10.1080/10669817.2092822

The authors are to be commended for their work examining the potential benefit of a virtual, motor imagery directional preference treatment approach. Their case series bridges a common mechanical intervention with virtual motor imagery, and the acute effects of this intervention may have implications for the management of low back pain. Methodologically, case reports and case series are helpful in describing novel interventions and are generally intended to guide hypothesis generation. Case series designs are not intended to create generalizable knowledge given the lack of control or comparison groups among other factors [1].

Their investigation is relevant, as low back pain affects up to 80% of individuals within their lifetime and over 126 million adults in the United States have experienced pain over the last 3 months. Additionally, approximately 25.3 million adults are currently experiencing chronic pain, with the potential for psychosocial risk existing chronic low back pain subgroups [2,3]. Interventions, like the virtual motor imagery presented in this manuscript that address psychosocial risk factors associated with chronicity are in great need [4].

The authors included self-reported psychosocial assessment tools including the Fear Avoidance Belief Questionnaire (FABQ) and the Pain Catastrophizing Scale (PCS) to measure psychological impairments. It is well established that such assessment tools can identify psychosocial risk factors. Outcomes from these measures may allow the condition to be further subclassified and guide treatment approaches [3]. Statistical, but not clinically meaningful changes were described for fear avoidance and pain catastrophizing, suggesting virtual motor imagery may benefit some patients with low back pain. Reporting individual outcomes, as opposed to group data, as is commonly done in a case study or case series research design, would help readers understand patient characteristics in finer detail. These data would also be helpful to support the sub-grouping discussion points. For example, did individual patients with high fear have a better response to motor imagery or did any patients have an increase in pain or catastrophizing? These data would further describe the patients included in this study, may help clinicians determine the most appropriate intervention for patients, and would help guide future research.

Although trends were found that suggest the potential for this intervention, it was unclear how the outcomes assessor was blind to the patient’s status in this case series and given this was a clinician-derived outcome measure (not self-reported) there appears to be a potential for bias. Further limiting interpretation of the results was that the protocol cited in the study describes a control group, but the data for this group were not reported.

In a systematic review of patients with chronic low back pain, examination of pain measures and function indicated that the McKenzie method, also referred to as Mechanical Diagnosis and Therapy (MDT) may be efficacious in decreasing pain in the short term and may be effective in enhancing long-term function [5]. Exploring the potential for directional preference is integral to this approach, which has been found in other research to be associated with improving fear-avoidance beliefs, pain self-efficacy, depression, and psychological distress [6]. In relation to this case series, identifying a directional preference (DP), may allow patients to self-manage their condition [7] and the potential for supporting this process via motor imagery is extremely interesting.

The authors described directional preference as the ‘process of examining a patient with LBP and associated leg pain to a repeated movement direction, i.e. extension or flexion, and if it coincides with improvement, the test becomes part of the treatment.’ We would add that the patient-generated repeated movements are performed to end range, with close monitoring of patient response throughout the process.

In MDT, directional preference is operationally defined as the movement identified as the result of testing repeated end range movements performed by the patient that produces a positive symptomatic response, as well as a lasting improvement in previously established baselines. Although flexion and extension are common directions resulting in directional preference, repeated end range movements in other directions and planes of motion may determine a directional preference and changes in baselines as well. The baselines may include, but not be limited to favorable changes in range of motion, strength, and adverse neural tension. The authors found that the change in SLR measures exceeded the MCID and when a patient sees such a change in their baseline, they may be more likely to adhere to the directional preference exercise [8]. This phenomenon can foster self-efficacy in a person experiencing chronic pain as they see and appreciate changes early in the plan of care. As a point of note, the role of visualized repeated movements into extension appears to help address fear and catastrophizing but should not be confused with centralization given that the leg symptoms did not change significantly in this case series. However, this study provides some initial data to support using motor imagery to address initial psychological impairments. Identifying and specifically addressing psychological impairments in musculoskeletal pain has been shown to benefit patient outcomes [3,4] and the simple motor imagery technique described in this case series may be another treatment tool to this end.

In conclusion, the directional preference motor imagery described in this case series may be best suited to address psychological impairments or neural tension in patients with minimal levels of disability and pain durations less than 90 days given the baseline values of participants in this case series. Slight improvements in symptoms and function may show real change in some patients or may be part of measurement error. Furthermore, the changes in found in this study are parallel to outcome changes described as part of the examination process in Louw et al [9] and may represent the interaction with the physical therapist and be unrelated to the virtual motor imagery intervention. The inclusion of virtual motor imagery as a baseline intervention prior to movement-based interventions demonstrates some potential as a realistic, simple, and potentially effective first-line treatment for patients with low back pain.

Disclosure statement

.Ronald Schenk is the Chair of the McKenzie Institute USA and receives stipends for board meeting attendance of that institute. Craig Wassinger has no conflicts of interest to report.