Introduction

Since the 1980’s, spine stabilization exercises have been the most popular exercise routine for treating patients with non-specific chronic low back pain (CLBP). While spine stabilization exercises were thought to be superior over other exercise therapies, recent literature reviews have cast doubt in the field, finding that spine stabilization exercises may not in fact be superior to other exercises.¹,²,³

While extensive evidence associates the atrophy of the stabilizing muscles-primarily the multifidus- with the persistence of CLBP,⁴,⁵ few studies compare the effects of spine stabilization exercises against other exercises in multifidus trophism. Those that have, used magnetic resonance imaging or computed tomography in people with chronic non-specific pain or healthy controls.¹,⁶ In degenerative spondylolisthesis, a previous study demonstrated that lumbar stabilization exercises and flexion exercises offer a similar response for controlling pain and improving disability; however, trophic changes in response to the exercise program were not analyzed.⁷

Ultrasound is an increasingly popular and affordable alternative for evaluating the musculoskeletal system,⁸ and has proven to be a reliable and accurate tool for the measurement of muscle thickness of the lumbar segment.⁹,¹⁰ The present study therefore aimed to evaluate-by ultrasound-the changes of the thickness of the main lumbar stabilizing muscles after twelve weeks of performing spine stabilization exercises and to compare these changes with another classical exercise routine (flexion exercises) in patients with CLBP and lumbar spondylolisthesis.

Material and methods

A nested longitudinal and observational study with three months of follow-up was conducted at the «Luis Guillermo Ibarra Ibarra» National Institute of Rehabilitation (INRLGII, for its initials in Spanish) in Mexico City. The protocol was approved by the institute’s Ethics and Research Committee prior to commencing the recruitment process in January 2017, and was conducted as a add-study research in a randomized clinical trial already in the active recruitment phase evaluating the clinical response of the spine stabilization exercises vs flexion exercises (registration number 19/15 and clinicaltrials.gov database (ID NCT02664688).⁷

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.

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 above 50 years of age, having a radiologic confirmation of degenerative spondylolisthesis at L4-L5 intervertebral segment, and having suffered from CLBP. Patients with a history of lumbar surgery, rheumatic inflammatory diseases or diabetic polyneuropathy, cauda equinae symptoms, or ischemic heart disease were excluded. Patients were also excluded if they had received previous exercise treatment of any type.

Exercise program. The treatment assignment was made based on the RCT in progress, by simple randomization with the delivery of a sealed envelope to each participant that contained in the exercise program what could be the «lumbar stabilization exercises» or the «Williams flexors exercises». The envelopes were only opened by the physical therapist that taught the exercise program to each patient. Only two physical therapists participated in the study, with a designated therapist for each participant to ensure consistency. The therapists taught each participant the assigned exercise program in a three 60-minute private sessions (spaced 4 weeks apart), and instructed the participants to continue daily at home with the program learned until completion at 12 weeks follow-up. Both programs were preceded by the use of a hot pack for 15 minutes in the lumbosacral region.

Ultrasound evaluation. Two medical specialists in musculoskeletal ultrasound performed all ultrasound measurements. Siemens Acuson Antares^® equipment with a 7 MHz linear probe was used. The muscle thickness of the transverse abdominal, internal oblique, external oblique, and multifidus at L5 were measured bilaterally in greyscale at rest and contraction and recorded in millimeters. Abdominal and lumbar multifidus muscle measurements were performed in accordance with Wilson et al.¹¹ The inter and intra-reader reliability of the ultrasound was evaluated by repeated measurement on two occasions by both physicians.

Results

Twenty-one participants (17 women and 4 men), thirteen from the stabilization group and eight from the flexion exercise group, completed the follow up. Baseline results on clinical characteristics and ultrasonographic measurements did not show significant differences between treatment groups as shown in Table 1. No differences were found considering sex, for any of the variables (p ≥ 0.05). According to the Meyerding Classification, spondylolisthesis was grade I for 12 patients and grade II for 9 patients, without finding grade III or IV cases.

Ultrasonographic measurements obtained intra-reader kappa values of 0.76 (95% CI 0.58-.94) and inter-reader kappa values of 0.66 (95% CI 0.34-0.84), both reliable measures according to Landis and Koch’s classification.

After twelve weeks of treatment, all participants presented significant changes in the multifidus size as measured by ultrasound, but none in abdominal muscles (Table 2). No significant differences were found between the exercises groups for any of the variables of interest (p ≥ 0.05).

Discussion

Although exercise is known to be the most effective intervention for treating CLBP, the superiority of any particular program is still in debate.¹² This has been because few studies compared the effects of the spine stabilization exercises program on muscle thickness against other therapeutic exercises. To our knowledge, this is the first study to do so in CLBP and degenerative spondylolisthesis.

In the present study, all participants showed significant changes in multifidus thickness, however, no differences were found between exercise groups, as Akbari et al.¹³ reported in their eight-week clinical trial for patients with a diagnosis of non-specific CLBP. In counterpart, no differences were found in abdominal muscles in this study, which differed from previous studies that found detectable changes in the abdominal muscles after executing exercise routines.¹⁴,¹⁵,¹⁶ The divergence could be attributed to variations in follow-up time between the studies, and the fact that patients with chronic nonspecific pain are typically younger than patients with degenerative spondylolisthesis, or that previous reports of abdominal muscles has been performed comparing people with CLBP vs healthy population,¹⁷ and the present study did not include a group of asymptomatic participants.

While our results confirm the usefulness of ultrasound for detecting early changes in multifidus thickness and serve as a preliminary comparison between types of exercises, it also has certain limitations. A small sample and a short follow-up time of 12 weeks were our main limitations and implied that we were unable to conclude if there are no long-term differences between exercise programs. Further studies are needed with larger sample sizes and longer follow-up periods to evaluate muscle thickness, clinical characteristics, and other variables of interest.

Conclusion

All participants presented significant changes in the thickness of the multifidus muscles without difference between spine stabilization exercises and flexion exercises. Not significant changes were detected for the rest of the evaluated muscles at twelve weeks of follow up.