A Novel Distractive and Mobility-Enabling Lumbar Spinal Orthosis for Treating Mechanical Low Back Pain
Authors:   ,   University of Tennessee Health Science Center, Hilyard Daniel 
Published: January 2022

Introduction: Lumbar spinal orthoses (LSOs) are often used as non-surgical treatment and serve to support the spine and alleviate low back pain. More recently, dynamic orthoses claiming to decompress the spine have been introduced. Currently, there is an unserved population of people that suffer from mechanical low back pain (LBP) conditions, such as degenerative disc disease or lumbar foraminal stenosis, that would benefit from spinal decompression and mobility. A previously-developed prototype of dynamic mobility orthosis (DMO1) was designed that provided a distractive load across the lumbar spine but required higher sagittal bending moments and was unable to maintain spinal off-loading throughout extended ranges of movement. The research objectives were to a) Design a new orthosis that reduced bending moment build up and sustained spinal off-loading throughout daily living ranges of flexion and extension movement, b) Test the new orthosis prototype in a controlled laboratory environment, and c) Organize and carry out a clinical pilot study with patients suffering from mechanical LBP to determine the immediate and short-term effects of the new orthosis prototype on LBP and overall patient quality of life. Methods: A mechanical analog upper torso model and programmable robotic testing platform were used to design features of the new prototype (DMO2): a mobility-enabling component (MEC) and a distractive force component (DFC). The DMO2 prototype was tested in a robotic testing platform (RTP) under a 300 N applied vertical torso load over a range of 25° flexion to 10° of extension utilizing a previously-developed protocol. For DMO2, loads carried by the brace were determined throughout flexion and extension. Applied moments to upper torso model and transferred moments to spine were measured. The difference in applied and transferred moments represented brace moment effects. It was determined that DMO2 had limitations, primarily with providing a distractive force to actual human subjects. Because of this, a new orthosis prototype (DMO3) was developed that improved upon the design of the DMO2 MEC and DFC. The DMO3 prototype was designed to provide a constant distractive force with minimal resistance to bending while effectively providing a distractive force to the wearer that could be felt. Also, the MEC of DMO3 included both flexion and extension as well as axial rotation. The DMO3 prototype was tested in the RTP under a 150 N applied vertical load over a range of 25° flexion to 10° of extension utilizing a previously-developed protocol. Also, the DMO3 prototype was tested in the RTP under simulated axial rotation without an applied vertical torso load. For this test, a measurement was made that determined how much axial rotation DMO3 allowed. A clinical study was organized in which two patients with LBP wore the DMO3 prototype during six physical therapy (PT) treatment sessions. Before the treatment sessions began, the patient had a radiograph (x-ray 1) taken and the patient completed a Modified Oswestry Disability Questionnaire (mODI). During each treatment session, a pain score was taken before wearing DMO3 and after completing exercises for 30-40 minutes while wearing the DMO. Additionally, on the last treatment session, a radiograph (x-ray 2) was taken. The lumbar disc height at the diseased and adjacent lumbar levels were measured on x-ray 1 and x-ray 2 and compared. Also, the mODI scores were compared before and after treatment. Results: The DMO2 prototype improved spinal off-loading capacity from 172 N to 290 N at end range flexion and from 247 N to 293 N at end range extension compared to the original DMO1 prototype. End range applied moments (flexion-DMO1: 32.4 Nm / DMO2: 21.7 Nm; extension-DMO1: 15.0 Nm / DMO2: 10.9 Nm) and brace moments (flexion DMO1: 18.6 Nm / DMO2: 6.6 Nm; extension-DMO1: 15.0 Nm / DMO2: 4.4 Nm) were also reduced. The DMO3 prototype was able to support 100% (at vertical stance), 104% (at end range flexion), and 97% (at end range extension) of the applied vertical torso load during simulated flexion and extension. Also, the DMO3 prototype contributed 0 of the 4.1 Nm (at end range flexion), and 4.4 of the 6.6 Nm (at end range extension) of the total bending moment. During simulated axial rotation, the DMO3 prototype was able to achieve 10 degrees of axial rotation in both the clockwise and counterclockwise directions. The DMO3 prototype immediately reduced pain for both patient 1 (p < 0.001) and patient 2 (p = 0.005) during all PT treatment sessions that they participated in. Patient 1 showed an of 2 mm (resolution 0.14 mm) of lumbar disc height at the L5-S1 level between the start and end of the treatments with DMO3. Similarly, patient 2 showed an increase of 0.5 mm at both the L4-L5 and L5-S1 levels. Patient 1 and patient 2 showed a decrease in mODI scores from 70 % to 62% and from 46% to 22%, respectfully. Discussion: An advanced testing assembly was used in this study to carry out the design of two prototypes of a novel dynamic spinal orthosis having the unique design goal of providing spinal offloading while enabling mobility. Two prototype models (DMO2 and DMO3) were built and tested under simulated DLAs in a controlled laboratory environment. Throughout the development of the DMO, each prototype demonstrated significant improvements compared to its predecessor. The means by which the DMO3 prototype produced a distractive force allowed the force output of the DMO to remain constant even with minor fluctuations in vertical displacement as might be experienced in normal flexion and extension motions. Preliminary testing found DMO3 prototype completely removed all pain from patient 1 at five of her six PT treatment visits. Conclusion: A novel dynamic spinal orthosis was designed that maintained spinal off-loading throughout extended ranges of flexion and extension movement without buildup of adverse bending moments. Additionally, the novel orthosis was able to achieve enough axial rotation required for most daily living activities (DLAs). Preliminary testing found this orthosis was also effective on human subjects as pain was reduced during all PT treatment sessions for both patients. An orthosis that provides distraction and mobility has not been designed and the proposed spinal orthosis provided the first evidence of its clinical effectiveness on human subjects. Because of the efficacy of this orthosis, a larger clinical study is warranted to see if the DMO can have short-term and long-term effects on mechanical LBP.