To properly respond to one’s environment, the brain must know the status of the body and where the body is in space relative to the environment. Our central nervous system (CNS) receives, interprets, and integrates sensory information from our external (exteroceptive) and internal (interoceptive) environment so that a proper motor response is executed to maintain a controlled and upright posture. The visual, vestibular, and proprioceptive systems are the main sensory systems involved in postural control and balance. This allows us to move through space in a safe manner with less risk of falls or injuries.
Integration of sensory input by the CNS is multimodal (multisensory) and involves multiple circuits within the brain. One critical circuit involved in postural stability is between the cerebellum and the prefrontal cortex (PFC). The brain must constantly reassess and recalibrate one’s environment to adapt to the status of the body. The cerebellum is crucial for the recalibration of sensory predictions capturing the sensory consequences of one’s motor behavior. One of the functions of the PFC is to “turn on” the fine motor muscles close to the spine and skull needed for spinal stabilization. Therefore, it is imperative that the cerebellum and PFC receive proper afferent sensory information from the body to engage the muscles needed for spinal stabilization and postural control. Without this properly functioning sensory-motor loop, a person will be predisposed to spinal instability and increased risk of spinal injuries.
Chronic Pain
Spinal instability is a biomechanical entity, and an unstable structure is one that is not in an optimal state of equilibrium. In the spine, stability is affected by restraining structures that, if damaged or lax, will lend to altered equilibrium and thus instability.1 Movement within every joint in the body creates a sensory experience in the brain (proprioception). In the spine, even small intersegmental motor movement is interpreted by the brain as a sensory experience. In turn, the brain will use this information to direct the body on how to adapt and respond to this experience. If the spinal motor movement pattern is dysfunctional or subluxated, it can lead to compensatory sensory-motor responses and chronic musculoskeletal dysfunction, which can result in chronic pain syndromes.
Chronic pain stems from maladaptive responses to sensory experiences that create “memory maps” in the brain. The bioplastic model of pain looks at how the brain receives and interprets sensory information from the body related to trauma/injury and the emotional and cognitive responses to the trauma/injury. In other words, chronic pain is in the brain. Therefore, in so many cases, pharmaceutical approaches to chronic pain fail.
Opioids and Chronic Pain
Understanding the bioplastic model of pain is the wave of the future. This will help practitioners understand and manage chronic pain syndromes more effectively without the use of drugs.
Opioids are often the drug of choice prescribed for chronic pain, which is disconcerting given the opioid crisis in the United States. In one study that included 115 randomized controlled trials (RCTs), 40 observational studies, and seven studies of predictive accuracy, opioids were associated with small benefits versus placebo in short-term pain, function, and sleep quality. They found a small dose-dependent effect on pain, and effects were attenuated at longer (three to six months) versus shorter (one to three months) follow-ups.
Opioids were associated with an increased risk of discontinuation due to adverse events, gastrointestinal adverse events, somnolence, dizziness, and pruritus versus placebo. In observational studies, opioids were associated with an increased risk of an opioid abuse or dependence diagnosis, overdose, all-cause mortality, fractures, falls, and myocardial infarction versus no opioid use; there was evidence of a dose-dependent risk for all outcomes except fracture and falls. There were no differences between opioids and nonopioid medications in pain, function, or other short-term outcomes. Opioid plus nonopioid combination therapy was associated with little improvement in pain at short-term follow-up versus an opioid alone. Co-prescription of benzodiazepines or gabapentinoids was associated with an increased risk of overdose versus an opioid alone.2
Supporting the Foundation
Exteroceptors and proprioceptors in the feet play an important role in postural control. The central nervous system uses ascending motor pathways that receive information from the feet to control the position of the body and coordinate posture in relation to the surrounding environment.3 The feet act as points of contact and sensory input between the ground and the body. Sensory information from the soles of the feet helps determine the position and motion of the body in space with information from the musculoskeletal system, which generates the forces necessary to control the body.4
In one study, they took 20 young and 20 older human adults and did proprioceptive mapping. They did foot tendon vibration and compared it with the vibration of a nearby bone in an fMRI environment to determine regions of the brain that were active in response to muscle spindle stimulation. Based on regression analyses, multiple clusters of voxels were identified, showing a significant relationship between muscle spindle stimulation-induced neural activity and maximum center of pressure excursion in the anterior-posterior direction. In this case, increased activation was associated with greater balance performance in parietal, frontal, and insular cortical areas, as well as structures within the basal ganglia. These findings support the notion that, beyond fundamental peripheral reflex mechanisms, central processing of proprioceptive signals from the foot is critical for balance control.5
In a study looking at the effects of custom three-arch shoe orthotics and chronic lower back pain, they divided subjects into three groups — shoe orthotic, plus, and waitlist groups. The shoe orthotic group received custom-made shoe orthotics that support all three arches of the foot. The plus group received custom-made orthotics plus chiropractic manipulation, hot or cold packs, and manual soft tissue massage. The waitlist group received no care. They found that six weeks of prescription shoe orthotics significantly improved back pain and dysfunction compared with no treatment. The addition of chiropractic care led to higher improvements in function.6
Summary
For both practitioners and patients, understanding that sensory input from the feet starts the chain of information that the brain needs to “see” the status of the body in space is an important concept in the bioplastic model of pain. The brain needs this input to move safely through space and minimize the risk of falls or injuries. The brain also requires proper sensory input from the body (interoception) for proper motor output to occur, such as proper motor control of the small spinal stabilization muscles next to the spine and skull necessary to minimize spinal injuries.
The use of custom three-arch foot orthotics has been shown to enhance proprioceptive information to the brain and help foster proper postural stability and balance control. They have also been found to be beneficial in the treatment of chronic lower back pain. The use of custom foot orthotics should be considered part of a natural, painless, and nonaddictive approach to managing chronic pain syndromes.
Dr. Monika Buerger, a 1991 graduate of Life Chiopractic College West, is the owner of Eagle Canyon Wellness & Sensory Development Center in Ammon, Idaho. She is a teacher, international lecturer, author, and the founder of lntersect4Life Educational Seminars and developing MINDS certification program in childhood and adolescent neurodevelopment. For additional information, visit www.intersect4life. com and www.devmindsu.com.
References
1. Pope MH, Panjabi M. Biomechanical definitions of spinal instability. Spine (Phila Pa 1976). 1985 Apr; 10(3):255-6. doi: 10.1097 00007632-198504000-00013. PMID: 3992345.
2. Chou R. Ha riling I). Turner J, Blazina I, Chan B. Levander X, McDonagh M, Selph S, Fu R, Pappas M. Opioid treatments for chronic pain. Comparative effectiveness review no. 229. (Prepared by the Pacific Northwest Evidence-based Practice Center under Contract No. 290-2015-00009-1.) AHRO Publication No. 20-EHC011. Rockville, MD: Agency for Healthcare Research and Quality; April 2020. DOI: 10.239 70 AHROEPCCER229.
3. Christovdo TC, Neto HP, Grecco LA, et al. Effect of different insoles on postural balance: a systematic review. J Phys Ther Sci. 2013,25(10): 1353-1356. doi: 10.1589jpts.25.1353
4. Mochizuki L, AmadioAC: The functions ofpostural control during stance. Sdo Paulo: Rev Fisio Univ, 2003, 10: pp 7-15.
5. Goble DJ, Coxon JP, Van Impe A, et al. Brain activity during ankle proprioceptive stimulation predicts balance performance in young and older adults. J Neurosci. 2011;31(45): 16344-16352. doi: 10.1523 JNEUROSCI. 4159-11.2011.
6. Cambron JA, Dexheimer JM, Duarte M, Freels S. Shoe orthotics for the treatment of chronic low back pain: a randomized controlled trial. Arch Phys Med Rehabil. 2017 Sep;98(9): 1752-1762. doi: 10.1016j.apmr2017.03.028. Epub 2017Apr 30. PMID: 28465224.
