Stabilization Exercises Versus Flexion Exercises in Degenerative Spondylolisthesis: A Randomized Controlled Trial

Abstract

Objective

Exercise is the mainstay of treatment in individuals with low back pain and the first-line option in degenerative spondylolisthesis (DS); however, there is still no consensus surrounding the superiority of any specific exercise program. Thus, the primary aim of this study was to compare the effectiveness of lumbar stabilization exercises and flexion exercises for pain control and improvements of disability in individuals with chronic low back pain (CLBP) and DS.

Methods

A randomized controlled trial was conducted in a tertiary public hospital and included 92 individuals over the age of 50 years who were randomly allocated to lumbar stabilization exercises or flexion exercises. Participants received 6 sessions of physical therapy (monthly appointments) and were instructed to execute exercises daily at home during the 6 months of the study. The primary outcome (measured at baseline, 1 month, 3 months, and 6 months) was pain intensity (visual analog scale, 0–100 mm) and disability (Oswestry Disability Index, from 0% to 100%). Secondary outcomes were disability (Roland-Morris Disability Questionnaire, from 0 to 24 points), changes in body mass index, and flexibility (fingertip to floor, in centimeters) at baseline and 6 months, and also the total of days of analgesic use at 6-month follow-up.

Results

Mean differences between groups were not significant (for lumbar pain: 0.56 [95% CI = −11.48 to 12.61]; for radicular pain: −1.23 [95% CI = −14.11 to 11.64]; for Oswestry Disability Index: −0.61 [95% CI = −6.92 to 5.69]; for Roland-Morris Disability Questionnaire: 0.53 [95% CI = −1.69 to 2.76]).

Conclusion

The findings from the present study reveal that flexion exercises are not inferior to and offer a similar response to stabilization exercises for the control of pain and improvements of disability in individuals with CLBP and DS.

Impact

Exercise is the mainstay of treatment in individuals with CLBP and DS; however, there is still no consensus surrounding the superiority of any specific exercise program. This study finds that flexion exercises are not inferior to and offer a similar response to stabilization exercises.

Lay Summary

Exercise is the mainstay of treatment in individuals with CLBP and DS, but there is no consensus on the superiority of any specific exercise program. If you have DS, flexion exercises may provide similar effects to stabilization exercises.

Chronic Low Back Pain, Conservative Treatment, Degenerative Spondylolisthesis, Exercise, Physical Therapy, Spondylolisthesis

Introduction

Degenerative spondylolisthesis (DS) is the acquired displacement of a vertebra over the subjacent vertebra due to degenerative changes.^1,2 The etiology of DS is multifactorial, but the disorder is common in individuals over 50 years old and is 4 times more common in women than in men. The most commonly affected spine level is L4 to L5, and the displacement rarely exceeds 25% to 30% of the width of the underlying vertebra.¹ Due to the mechanical commitment of the central canal and foramina, individuals may develop symptoms of chronic low back pain (CLBP), radiculopathy, or neurogenic claudication during the natural course of the disease.^3,4

Treatment is initially conservative (in the absence of severe neurological symptoms), and surgical treatment is indicated only for those who have been refractory to nonsurgical options for at least 3 to 6 months.^5,6 Exercise is the intervention with the highest level of evidence related to the improvement of CLBP and is superior to all other interventions in terms of improving pain and function.^7,8

Lumbar stabilization exercises became popular over 30 years ago, and unlike other programs, these exercises prioritize the conscious and progressive training of stabilizing muscles of the trunk.⁹ Previous evidence suggested that lumbar stabilization exercises were a useful and superior option for treating individuals with nonspecific CLBP through exercise.^10–13 However, certain recent literature reviews have created controversy in the field due to the lumbar stabilization exercises’ contradictory results compared with other types of exercises.^14,15 A previous study demonstrated the effectiveness of stabilizing exercises or exercises aimed to control the neutral mid-range for pain control and functional improvement in DS; however, these exercises were not compared with other types of exercise to allow for judgment on the superiority of the stabilization program.¹⁶

One of the most popular exercise routines for the management of individuals with CLBP—used since the 1930s—is the Williams flexion exercises, simply referred to as flexion exercises. Williams originally designed these exercises for CLBP in young individuals (<50 years) with lumbar hyperlordosis and decreased lumbar intersomatic spaces¹⁷. The primary objective of the exercises is to activate the abdominal muscles and relax the paraspinal lumbar muscles.¹⁷ The classic flexion exercise routine has been adapted over time, most notably to be used in populations older than 50 years of age and with CLBP.¹⁸

Considering the information mentioned above and with evidence suggesting the superiority of the lumbar stabilization exercise program, the present study was conducted to compare the effectiveness of lumbar stabilization exercises with flexion exercises in terms of pain control and functional improvement in individuals with CLBP and DS.

Methods

A randomized controlled trial was conducted at the Luis Guillermo Ibarra Ibarra National Institute of Rehabilitation in Mexico City. This particular tertiary care hospital only accepts individuals who have been referred from another care facility in Mexico. As such, its patients come from diverse parts of the country and present a wide range of socioeconomic, demographic, and clinical characteristics.

The research protocol was approved by the institute's Ethics and Research Committee (registration number 19/15) and registered in the clinicaltrials.gov database (ID NCT02664688). All procedures performed on the participants were in accordance with the Committee's ethical standards and with the 1964 Helsinki Declaration and its later amendments. All participants provided written informed consent before study commencement and received a printed copy for their records. This study conforms to all CONSORT guidelines for reports RCT (see Checklist at Suppl. Digital Content 1).

Study Participants

For the present study, the inclusion criteria included being a first-time patient at the research institute's Spinal Rehabilitation Outpatient Department, being older than 50 years of age, having a radiologic confirmation of DS at L4 to L5 intervertebral segment, and having suffered from CLBP for more than 3 months with or without radicular pain. Individuals with a history of lumbar surgery, rheumatic inflammatory diseases or diabetic polyneuropathy, cauda equinae symptoms, or ischemic heart disease were excluded. People with rheumatic inflammatory diseases or diabetic polyneuropathy were excluded because they could suffer from back pain or nonradicular neuropathic for nonmechanical reasons, and people with ischemic heart disease were excluded because of their need to be supervised closely by health professionals while exercising. Individuals were also excluded if they had received previous exercise treatment of any type; individuals could have received passive therapies in another institution prior to their inclusion in the study, such as the use of physical agents for pain control, but not a structured exercise program for CLBP management.

Clinical Evaluation

All of the individuals included were interviewed and evaluated in a private and quiet evaluation room at a specially scheduled time for them. All interviews were performed by a single physician with extensive experience in CLBP evaluation and treatment who was blinded to the exercises. The interview included a full medical history and physical examination. Lumbar spine clinical images were used to measured sagittal displacement and classified according to the Meyerding Classification.¹⁹

The questionnaire specifically gathered information on disease-evolution time, body mass index (BMI), flexibility (fingertip to toe, in centimeters), comorbidities (including their history of smoking, diabetes, depression, and anxiety), and use of analgesics. Participants, under medical supervision, could use 1 of 3 analgesics: non-steroidal anti-inflammatory drugs, paracetamol, or (in some cases) pregabalin. Because the information on the frequency of use of analgesics varied widely, this information was only collected at baseline (number of total days of analgesic intake in the previous 30 days) and at follow-up (total number days of medication use in the previous 6 months).

The information gathered was divided into primary and secondary outcomes to facilitate statistical analysis. Primary outcome (measured at baseline, 1 month, 3 months, and 6 months) was pain intensity (visual analog scale [VAS], from 0 to 100 mm) and disability (Oswestry Disability Index 0 to 100%).²⁰ Secondary outcomes were disability (Roland-Morris Disability Questionnaire, from 0 to 24 points),²⁰ changes in BMI, flexibility (fingertip to floor, in centimeters) at baseline and 6 months, and also the total of days of analgesic use at 6-month follow-up.

Sample Size

The sample size was calculated using the mean difference formula and supposing the superiority of the lumbar stabilization program. Previous studies have shown that the difference acceptable as minimally clinically relevant changes for low back pain is a difference of 20 mm on the VAS and 10 percentage points on the Oswestry Disability Index.²¹ This calculation yielded a sample of 46 individuals per group with a 95% confidence level, 80% statistical power, and an assumption of 20% of individuals lost to follow-up.

Randomization

Treatment was assigned through simple randomization with the use of a computer-generated random numbers list. After the initial evaluation, a sealed envelope was given to each participant with either “lumbar stabilization exercises” or “flexion exercises” written on a letter inside. The envelopes were opened by the physical therapist (not blinded) who taught the exercise program to each individual and verified that the participant was executing the routine correctly; participants received 6 sessions of physical therapy (monthly appointments) and were instructed to execute them daily at home during the 6 months of the study. Only 2 physical therapists participated in this study and were previously standardized to ensure consistency in the exercise programs they taught to the participants. Each participant maintained the same physical therapist from baseline through the 6-month follow-up to ensure consistent education and promote therapeutic adherence and continuous communication. The participants were instructed to perform the assigned program once per day, and each participant received a sheet with instructions on how to perform their daily home exercises. Although it was entirely possible that participants could have discovered their assignation (eg, by searching the internet for this particular sequence of exercises), the research team encouraged participants to simply focus on the exercises instead of seeking out additional surrounding information. Participants were also encouraged to avoid discussing their exercises with peers, and all sessions were held individually with their physical therapist to avoid comparisons. Also, participants were encouraged to avoid adding any other kind of exercise routine.

Intervention

Before signing informed consent, participants were advised that participating in this study would involve voluntarily giving up other types of exercise or physical agents during the 6 months of follow-up. Likewise, those participants with a history of previous exercise practice—such as running, walking, or other activities—were asked to refrain entirely from this practice during the 6-month follow-up. Because the study’s first author was also the participants’ coordinating physician, she reviewed all additional interventions (such as guided steroid injections for pain), ensuring that none of the final study participants had received treatments that would have constituted an exclusion criterion.

The lumbar stabilization exercise group was considered the experimental group. The home exercise program started with an initial warm-up: applying therapeutic heat for 15 minutes at the lumbosacral region via a hot pack. After the warm-up, the participants engaged in stretching exercises of the thoracolumbar fascia, hip flexors, and hamstrings and the initial stage of stabilization exercises. This program was aimed at stabilizing motor patterns and establishing a neutral spine position, with a goal of controlling the transverse and internal oblique abdominis, multifidus, pelvic floor muscles, and diaphragmatic breathing control. In subsequent weeks, participants were instructed to progress further in their stabilization exercises by adding lateral and anterior bridges, leg raises in a supine position, and arm and leg lifts in a quadruped position (“bird-dog”). A detailed description of the progression is in Supplementary Appendix 1.

The flexion exercise group was considered the control group. The home flexion exercise program included the same initial warm-up phase as the experimental group. The flexion exercises were continued without progression for the 6 months. The participants in this group were then instructed to execute the Williams’s flexion exercise routine, described in detail elsewhere¹⁷ and in Supplementary Appendix 2.

Adherence

Each participant received a monthly log specifically designed to record the number of days of the month that the exercises were performed. This log has been previously used in a population at the same institute population to assess therapeutic adherence.²²

Statistical Analysis

Data were first summarized and examined through descriptive analysis. A Kolmogorov–Smirnov test was performed to verify the normality of the quantitative variables. Descriptive data were presented as means and SDs. An intention-to-treat analysis and per protocol analysis were performed. Student t tests for unrelated samples and chi-squared tests were used to compare variables at baseline between groups of treatment. Student t tests for related samples and a linear mixed model for repeated measures were used to analyze changes in time in the main variables. Correlation analysis was used to test the relationships between pain and BMI, evolution time, and age and then between disability and the same 3 variables. An alpha of .05 was selected as the cutoff for significance in this study, and all statistical findings were also reported together with appropriate confidence intervals. All statistical analysis was performed using SPSS software v.21.0 (IBM SPSS Statistics, IBM Corp, Chicago, IL, USA).

Results

Eighty-five participants, 42 from the experimental group and 43 from the control group, completed the trial. Figure 1 details the flow of participant selection and monitoring during the study. The baseline characteristics of the groups are presented in Table 1, where the values show that both groups of treatment were homogenous in terms of anthropometric and clinical characteristics at baseline. Pain and disability were not influenced by the variables of BMI, age, evolution time, smoking, diabetes, depression, anxiety, or degree of spondylolisthesis. Pain was not influenced by sex, but men showed disability scores significantly lower than the women (Oswestry Disability Index [ODI]: P = .021; Roland Morris Questionnaire (RMQ): P = .031).

Figure 1

Flow diagram of the study.

Table 1

Group Characteristics at Baseline^a

Characteristic	Stabilization Exercise Group (n = 46)	Flexion Exercise Group (n = 46)
Sex, womenb	39 (84.7)	39 (84.7)
Age, y	60.20 (7.51)	61.78 (7.79)
Evolution time, y	2.75 (4.8)	2.18 (2.5)
Meyerding grade Ib	34 (73.9)	26 (56.5)
Smokingb	11 (23.9)	13 (28.2)
Diabetesb	5 (10.8)	9 (19.5)
Depressionb	5 (10.8)	4 (8.6)
Anxietyb	4 (8.6)	3 (6.5)
BMI, kg/m2	30.09 (4.66)	30.53 (4.55)
Fingertip to floor, cm	14.32 (8.39)	12.80 (10.34)
VAS, lumbar, mm	55.21 (24.49)	61.78 (17.67)
VAS, radicular, mm	46.28 (34.08)	42.5 (32.72)
Analgesic use, d	12.19 (11.32)	9.97 (10.23)
ODI, %	29.93 (13.02)	33.97 (13.63)
Roland-Morris Disability Questionnairec	11.25 (4.8)	11.82 (4.53)

^aData are reported as mean (SD) unless otherwise indicated. BMI = body mass index; ODI = Oswestry Disability Index; VAS = visual analog scale.

^bReported as number (percentage) of participants.

^cFrom 0 to 24 points.

Both treatment groups showed good adherence to the home-based program, with an average execution of 143.17 (SD = 36.94) days (80.03% of 178 total days) for the lumbar stabilization exercise group versus 145.57 (SD = 38.5) days for the flexion exercise group (81.4% of 178 total days), without differences between groups (P = .72). No differences were found between groups in terms of analgesic intake: the stabilization exercise group participants took analgesics for a mean of 39.77 (SD = 33.73) days during the previous 6 months, and the flexion exercise group participants took analgesics for a mean of 33.76 (SD = 30.36) days in the same period (P = .37). During the 6 months of follow-up, both treatment groups showed progressive improvements in disability (ODI) and reduction in pain (VAS), as shown in Figures 2, 3, and 4 of the repeated-measures analysis for these variables. These changes were shown to be clinically relevant for lumbar pain (reduction of >20 mm on the VAS) in 44 study participants (20 from stabilization exercise group and 24 from flexion exercise group) and for improvement in disability (changes of >10 points in the ODI) in 53 study participants (26 from the stabilization exercise group and 27 from the flexion exercise group). Table 2 presents the intergroup comparison of the main variables. No significant differences were found between the groups of lumbar stabilization and flexion exercises in terms of pain (VAS), disability (RMQ and ODI), or other measured variables, such as flexibility (fingertip to toe, in centimeters). Regression logistics models were carried out for principal outcomes considering as covariate age, evolution time, BMI, flexibility, gender, and use of analgesics without significance.

Figure 2

Changes in lumbar pain (VAS) for both groups of treatment at 6-month follow-up.

Figure 3

Changes in radicular pain (VAS) for both groups of treatment at 6-month follow-up.

Figure 4

Changes in functionality (ODI) for both groups of treatment at 6-month follow-up.

Table 2

Mean Changes at 6 Months^a

Parameter	Analysis	Stabilization Exercise Groupb	Flexion Exercise Groupb	Mean Difference (95% CI)	P
VAS, lumbar, mm	PP	23.69 (29.63)	24.25 (26.16)	0.56 (−11.48 to 12.61)	.53
	ITT	24.70 (29.27)	24.89 (25.47)	0.19 (−11.17 to 11.56)	.40
VAS, radicular, mm	PP	16.14 (30.59)	14.90 (29.09)	−1.23 (−14.11 to 11.64)	.54
	ITT	15.89 (29.80)	14.85 (29.36)	−1.1 (−13.38 to 11.12)	.40
ODI, %	PP	12.59 (15.79)	11.97 (13.39)	−0.61 (−6.92 to 5.69)	.42
	ITT	12.61 (15.14)	12.76 (13.36)	0.15 (−5.7 to 6.06)	.83
Roland-Morris Disability Questionnairec	PP	3.92 (5.85)	4.46 (4.39)	0.53 (−1.69 to 2.76)	.68
	ITT	3.72 (5.64)	4.65 (4.40)	0.93 (−1.16 to 0.03)	.43
Fingertip to floor, cm	PP	7.23 (7.38)	5.93 (8.83)	−1.30 (−4.8 to 2.20)	.23
	ITT	7.15 (7.1)	6.35 (8.74)	−0.80 (−4.11 to 2.50)	.53

^aITT = intention-to-treat analysis; ODI = Oswestry Disability Index; PP = per-protocol analysis; VAS = visual analog scale.

^bReported as mean (SD).

^cFrom 0 to 24 points.

Discussion

The findings from the present study reveal that flexion exercises are not inferior to and offer a similar response to stabilization exercises. The similarity of response between both exercise programs (at least in terms of pain control and functional improvement) may derive from the ability of the flexion exercise program to perform a mechanical release of the posterior structures of the spine (where facet degeneration is observed as 1 key primary pathophysiology point in DS). In the late 1980s, Dr Sinaki proposed that flexion exercises were superior to extension exercises in terms of spine biomechanics and discouraged the use of extension programs.²³

The reduction in pain and increase in disability after executing a home-based program coincide with previous studies conducted in a population at the same institute and suggest that an active conservative program must be the first-line of treatment before other options.¹⁶

The natural evolution of DS in most cases is benign,^2–4 primarily in those with axial pain and/or mild radicular pain. Few studies on DS treatment and management compare exercise interventions against other exercise interventions, thereby complicating direct comparisons between the present study and others. However, the Spine Patient Outcomes Research Trial (SPORT) multicenter study,²⁴ a central project in this field, published controversial findings that surgical treatments provided better results in the study period. However, because the SPORT study suffered from high levels of nonadherence—evident from notable differences in results of the “intention to treat analysis” versus the as-treated analysis²⁵—the findings of this study should be interpreted with caution. In addition, the SPORT participants may not be representative of all individuals with DS, perhaps only those with more severe conditions. Indeed, the SPORT exclusion criteria outline how only individuals who had failed previous conservative treatment were enrolled (“insufficient trial of non-surgical treatment” and “dramatic improvement with non-surgical care”).²⁶

Several exercise modalities have been shown to be effective for DS; however, there is a lack of strong evidence for exercise in treating DS, and most studies do not separate individuals with DS from 1 or more other pathologies.²⁷

Demir-Deviren et al²⁸ demonstrated that a comprehensive nonsurgical treatment with exercise programs, patient education, transforaminal epidural injections, and/or medications could generate a positive therapeutic response. This therapeutic response was measured at 3 years post treatment by participants’ self-reported pain relief and the choice to have surgery or not. Despite the fact that the study has a slightly different design from the one presented here, these similarities highlight how conservative treatment can yield desirable outcomes. Indeed, the present study also found optimal outcomes with conservative treatment. Although the current study design included an official follow-up visit only at 6 months, all participants continue to attend annual clinical reviews at the same institute, and, at 48 months after the completion of this study, only 4 of the 85 study participants had requested a surgical procedure.

Another recently published study included 24 participants randomly assigned into the stabilization (n = 12) and general exercise (n = 12) groups. Both groups performed the exercises 2 times a week for a period of 2 months. Pain and disability were improved in both stabilization and general exercise groups. Although the study does not clarify this, its inclusion criteria accepted participants from 20 to 60 years of age (averages of 48–51 years younger compared with our study), which makes us think that it is probably associated with low-grade spondylolisthesis (dyplastic or lytic) and not proper to DS, which was the main reason for study of our research.²⁹

Limitations

Although the current study provides valuable information on the benefits of exercise in individuals with DS, it also has certain limitations. First, although it was not planned as a selection criterion for this study, our participants all had mild-to-moderate clinical presentations (mean VAS in both groups <70 mm). Because proper execution of any exercise program requires that individuals be active participants, individuals with severe pain or dysfunction may not be in condition to tolerate independently executing a home-based program. Our department does not habitually receive individuals in acute crises or severe pain, because those individuals typically go through our hospital’s urgent care center to receive spinal infiltration treatment and/or through our surgical department for spinal surgery before being referred to our rehabilitation services. Another limitation is that there may have been a bias toward including only individuals who were able to attend the sessions; this might have indirectly selected only highly motivated participants. This bias may affect the generalizability of the results, because not all individuals in clinical practice are as motivated to perform physical exercises.

In addition to the previously mentioned study-specific limitations, there are certain limitations inherent to this field of rehabilitation research. Therapeutic adherence is an ongoing challenge for the field of physical therapy in general, because it is difficult to know if an individual is following their recommended therapy plan at home exactly as proposed. This could be better assessed in the near future with emerging technologies (such as platforms to video-record exercise sessions or online sessions to perform programs from home). However, we would like to emphasize that at the moment the study was designed, and considering the daily practice of public institutions that treat people with limited resources (many without internet access), it was not an option to apply this type of technology; for this reason, we decided to choose a printed therapeutic diary for this project. Also, there is an inherent and fundamental discord between standardized randomized trials and the need for individualized and adapted treatment for individuals. Although the program’s progression was not conducted individually, we did make sure to increase the program’s difficulty at each stage (as described in Suppl. Appendix 1), thus increasing the requested load. We believe that clinical providers should interpret these results and use them as input to tailor their patients’ programs. We hope that the standardized exercise programs in this study will allow for certain conclusions that will be translated to individual clinical practice in the future. Despite the limitations, we consider that the results of the present study are very close to the conditions for providing treatment through public institutions where individuals do not have the possibility of daily individual sessions with a physical therapist, due to either the distance to the care center or lack of financial resources. Moreover, evidence has shown that individuals who take an active role in exercise and treatment have better outcomes than those who rely on passive treatments; therefore, we believe that any rehabilitation should have a robust at-home component for individuals to allow for complete participant involvement and responsibility. Lastly, another limitation associated with the study design (and indeed with any physical activity clinical trial) was the impossibility of blinding the physical therapists and participants. This could very well change the participants’ perception of the effectiveness of the exercise, because the stabilization exercises are more complex, have a progression through the stages, and modify the routine over time in contrast with flexion exercises. We believe that showing how neither of these exercise routines is inferior to the other highlights that more “sophisticated” or complex routines should not be favored over those perceived to be older or simpler routines.

At this time, it is not possible to conclude that there are no long-term differences between exercise programs. Therefore, further research should build on our study by analyzing recurrences of acute pain, neurological deterioration, the need for surgical management, and differences between clinical conditions (low back pain, radicular pain, or pseudo-claudication).

Both lumbar stabilization exercises and flexion exercises offer a similar response for controlling pain and improving disability in individuals with CLBP and DS, with no statistically significant difference between the types of exercises indicated over 6 months. This lack of statistical differences should not be considered a detriment to the evidence; indeed, it allows for broadened options to be used at clinicians’ discretion. For example, the flexion exercise program may be a good option for individuals who do not tolerate positions with weight placed on joints, while stabilization exercises could be ideal for individuals who wish to scale-up their exercise loads even further and incorporate them into other popular exercise activities. We believe that the selection of spinal stabilization exercises is useful for safely treating older individuals with chronic pain and DS who require learning a home program and will be able to perform it independently. It is still necessary to study the outcome of variations over time to determine if exercises with greater demand (such as increased weight use to the extremities or inclusion in multidisciplinary treatment programs) could confer more significant gains in the variables of interest. Lumbar stabilization exercises have been widely used and accepted for several decades to treat CLBP, and this study finds that, for individuals with DS, flexion exercises are not inferior.

Author Contributions

Concept/idea/research design: T.I. Nava-Bringas, L.O. Romero-Fierro, Y.P. Trani-Chagoya, S.I. Macías-Hernández, E. García-Guerrero, M. Hernández-López, R. Coronado-Zarco

Writing: T.I. Nava-Bringas, L.O. Romero-Fierro, Y.P. Trani-Chagoya, S.I. Macías-Hernández, E. García-Guerrero, M. Hernández-López, R. Coronado-Zarco

Data collection: T.I. Nava-Bringas, L.O. Romero-Fierro, Y.P. Trani-Chagoya, S.I. Macías-Hernández, M. Hernández-López, R. Coronado-Zarco

Data analysis: T.I. Nava-Bringas, L.O. Romero-Fierro, S.I. Macías-Hernández

Project management: T.I. Nava-Bringas, L.O. Romero-Fierro, R. Coronado-Zarco

Providing participants: T.I. Nava-Bringas, L.O. Romero-Fierro, Y.P. Trani-Chagoya, S.I. Macías-Hernández, E. García-Guerrero, M. Hernández-López, R. Coronado-Zarco

Providing facilities/equipment: R. Coronado-Zarco

Consultation (including review of manuscript before submitting): T.I. Nava-Bringas, S.I. Macías-Hernández, E. García-Guerrero, M. Hernández-López, R. Coronado-Zarco

Funding

There are no funders to report for this study.

Ethics Approval

This study was approved by the Instituto Nacional de Rehabilitation Luis Guillermo Ibarra Ibarra Ethics and Research Committee (No. 19/15). All procedures performed on the participants were in accordance with the committee’s ethical standards and with the 1964 Helsinki Declaration and its later amendments. All participants provided written informed consent before study commencement and received a printed copy for their records.

Clinical Trial Registration

This study was registered in clinicaltrials.gov (NCT02664688).

Disclosures and Presentations

The authors completed the ICMJE Form for Disclosure of Potential Conflicts of Interest and reported no conflicts of interest.

This research was previously presented as a poster at: Annual Meeting of the Association of Academic Physiatrists; February 2019; Puerto Rico. The poster was published in: Am J Phys Med Rehabil. 2019; 98:a1–a158.