REVIEW ARTICLE
Musculoskeletal Pain, Fear Avoidance Behaviors, and Functional Decline in Obesity Potential Interventions to Manage Pain and Maintain Function Heather K. Vincent, PhD,* Meredith C.B. Adams, MD,†‡§ Kevin R. Vincent, MD, PhD,* and Robert W. Hurley, MD, PhD*†‡§ Abstract: Individuals with musculoskeletal pain exhibit abnormal movement patterns, including antalgic gait, postural dysfunction, increased thoracolumbar stiffness, decreased proprioception, and altered activation of abdominal and extensor muscles. Additionally, aberrant or increased biomechanical forces over time produce joint or structural damage that results in pain. A large body habitus resulting from excessive weight can accelerate these musculoskeletal complaints. Irrespective of age, obesity contributes to chronic musculoskeletal pain, impairment of mobility, and eventual physical disability. Potential mechanisms that may mediate the relationships between obesityrelated pain and functional decline include skeletal muscle strength deterioration, systemic inflammation, and psychosocial characteristics (eg, pain catastrophizing, kinesiophobia, and depression). Treatment considerations for obese patients with musculoskeletal pain include assessment of kinesiophobia levels, biomechanical analysis, and pain medication use. Ideally, a multidisciplinary team of physicians, psychologists, and physical therapists should optimize the design of interventions specific to the patient. In some cases, the use of appropriate pain medications or intra-articular injectable agents may help control pain, fostering sustained activity, caloric expenditure, and weight loss. Morbid obesity is a medical condition that alters biomechanical forces on the tissues of the body. This condition provides the opportunity to examine accelerated development of musculoskeletal pain syndromes and etiology. The proposed therapeutic interventions can have multiple benefits in the obese population including weight loss, improved psychological outlook and self-efficacy, reduced kinesiophobia levels, reduced risk of functional dependence, and improved quality of life.
of the etiology of the pain syndrome. Studies on elderly adults, such as the Einstein Aging Study, indicate that among adults older than 70 years, abdominal adiposity increases the probability of developing chronic pain.2 The risk of developing painful musculoskeletal disease, such as OA, increases 36% with an increase of body mass index (BMI) by 2 U.3 The BMI also predicts onset of chronic low back pain4; shoulder and neck pain5; hand, hip, and knee OA6–8; and foot pain.9 Across all age groups, obesity contributes to chronic pain. Children with high BMI have an increased prevalence of musculoskeletal pain, knee pain, and complex regional pain syndrome compared with less heavy counterparts, and this pain severity is relatively high.10 Obese and severely obese elderly adults demonstrated a 2 and 4 times greater likelihood, respectively, of experiencing chronic pain compared with healthy weight individuals.11 Specifically, obesity is associated with higher pain burden and lower probability of sustained remission in persons with rheumatoid arthritis.12 In both young and old persons, obesity-related pain is associated with lower quality of life and relatively low psychosocial health when compared with normal-weight individuals.13,14 Thus, across the age spectrum, obesity is associated with painful musculoskeletal issues that can adversely affect psychological well-being and perceptions about staying physically active. This review will present the relationships between obesity, musculoskeletal pain symptoms, fear avoidance behaviors, and functional decline. Interventions that may redirect the pathway of obesityinduced pain and functional decline will be presented.
(Reg Anesth Pain Med 2013;38: 481–491)
T
he relationship between chronic musculoskeletal pain and functional decline is often discussed, but the associated mechanisms are poorly understood. Conditions with a component of osteoarthritis (OA), such as nonspecific axial low back pain, are prevalent. However, we lack treatments possessing a high likelihood of success for rehabilitation.1 Although our approaches to the treatment of musculoskeletal pain conditions may represent common sense, our incomplete success in treating these conditions may result from an imprecise understanding
From the *Departments of Orthopaedics and Rehabilitation, †Anesthesiology, ‡Psychiatry, and §Neurology, University of Florida, Gainesville, FL. Accepted for publication August 19, 2013. Address correspondence to: Robert W. Hurley, MD, PhD, Division of Pain Medicine, University of Florida, Gainesville, FL (rwhurley@ufl.edu). The authors declare no conflict of interest. This publication was made possible by Grant RO3 AR057552-10A1 from the National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health (HK Vincent, KR Vincent, and RW Hurley). Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the NIAMS or NIH. Copyright © 2013 by American Society of Regional Anesthesia and Pain Medicine ISSN: 1098-7339 DOI: 10.1097/AAP.0000000000000013
MUSCULOSKELETAL PAIN IN OBESITY Obesity-related musculoskeletal pain is a deterrent for adherence to exercise and physical activity recommendations.15 Severe obesity significantly affects the spine and lower extremity sites, such as the hip, knee, and ankle, by causing skeletal misalignment, joint compression, and progression of OA.16 Foot,17 knee,18 hip, and back pain all disrupt normal gait, walking indoors and outdoors, shopping, standing for a long period, and engagement in activities that require carrying body weight. An estimated 36% of obese adults are afflicted by painful arthritis. Moreover, obesity is a common barrier to consistent participation in physical activity.19 In adults older than 70 years, the likelihood of having chronic musculoskeletal pain is increased by 83% in persons with abdominal obesity compared with those without abdominal obesity.2 Even in elderly adults as old as 99 years, the odds ratio of having chronic pain was between 3 and 4 times higher in persons with mild to severe obesity when compared with their normal-weight counterparts.20 Potential mechanisms of obesity-related pain are unclear but are likely complex or bidirectional. Compared with other body fat distributions, abdominal or truncal obesity predicts higher total pain severity and doubles the risk for developing chronic pain. This may represent a unifying pathophysiology
Regional Anesthesia and Pain Medicine • Volume 38, Number 6, November-December 2013
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Copyright © 2013 American Society of Regional Anesthesia and Pain Medicine. Unauthorized reproduction of this article is prohibited.
Vincent et al
Regional Anesthesia and Pain Medicine • Volume 38, Number 6, November-December 2013
between metabolic syndrome and chronic pain, both of which are highly associated with truncal obesity.21,22 First, the presence of chronic pain may stimulate release of cortisol, which worsens truncal obesity.23 Second, visceral fat produces numerous substances including derived proinflammatory (adipocytokines and C-reactive protein) and insulin resistance–inducing molecules that may be related to osteoarthritic pain symptoms.24 Third, biomechanical stressors acting at the joint from excessive and aberrant loading patterns from obesity alter gait and likely contribute in part to pain onset and joint degradation.25–28 Cartilage lesions may develop in joints of obese individuals, even at an earlier time in life than previously thought. Specifically, 79% of imaged knees from morbidly obese adolescents have retropatellar lesions, 50% show lateral meniscal damage, and 87% show medial lesions.29 Fourth, muscle strength deficits exist in obese persons with chronic pain in the low back30,31 and in the knee.27,28 Inadequate strength may perpetuate poor biomechanics and joint malalignment. Inflammation, aberrant loading, and relatively low muscle strength, all of which are ideal conditions to sustain chronic pain, therefore characterize the collective musculoskeletal environment. Figure 1 illustrates the progressive changes in the collective physiological forces acting on the low back and other load-bearing joints. With normal weight, the mechanical forces and the opposing ground reaction forces acting on the foot, knee, hip, and low back are relatively low compared with the obese and morbidly obese persons. Adequate muscle strength and low systemic inflammation levels help preserve joint alignment and minimize the effects of aberrant loading and onset of painful joint disease. From obese to morbidly obese conditions, the progressive increase in systemic inflammation levels and magnitude of joint malalignment with added weight corresponds to musculoskeletal pain and joint disease.
FUNCTIONAL EFFECTS OF MUSCULOSKELETAL PAIN Ambulation and mobility tasks are adversely affected by musculoskeletal pain in obesity. Even before the development of overt pain-related functional disability, obese individuals with BMI values of 35 to 39.9 kg/m2 are up to 18 times more
likely to adopt different compensatory movement strategies while performing activities such as stair climbing and descending, chair rise, kneel to stand, and sitting to stand than individuals with lower BMI values.32 Other studies have documented altered movement patterns during functional tasks based on BMI. During a sit-to-stand task, for example, obese persons have less trunk flexion and demonstrate a posterior shift in movement of the feet compared with nonobese individuals.33 Biomechanically, this positioning reduces torque on the lumbar spine during the motion, and helps to suppress back pain symptoms while shifting loading and pain to the knees. Although these movement adaptations may temporarily diminish 1 pain generator, longer-term effects may include aberrant loading in other ways that may prematurely degenerate the compensating joints. Walking characteristics are influenced by the presence and severity of degenerative joint pain and obesity. In short- and long-distance walking tasks from a few seconds to 15 minutes in duration, obese individuals are characterized by slower gait velocity, shorter stride length, slower cadence, and a longer period in stance than nonobese individuals.34–36 There is a progressive decline in gait velocity with increasing BMI.37 The implications of this walking impairment in obesity are related to a lower daily activity level, reflected by fewer steps taken per day compared with healthy weight (3325 vs 7385 steps, respectively).38 The presence of obesity has been shown to be a significant negative predictor of community walking participation, but the presence of pain is the most significant negative predictor of walking capacity in persons with low back pain.39 When joint or chronic low back pain is present, the effects of obesity on gait parameter decline are amplified. For example, the gait velocity and stride length are progressively less in overweight and obese persons with moderate, symptomatic OA compared with asymptomatic counterparts.40 Aberrant knee joint motion (less knee flexion during the gait cycle, greater knee adduction moment) that occurs with the interaction of obesity and pain is associated with radiographic severity of OA and progression of OA.41,42 Other functional abilities are diminished with increasing BMI and pain. Tasks that involve considerable knee flexion
FIGURE 1. Physiological forces acting on the low back and load-bearing joints in healthy weight, obese, and morbidly obese persons. Ground force reaction is the force exerted by the ground on a body in contact with it; this force increases with increasing weight or mass.
482
© 2013 American Society of Regional Anesthesia and Pain Medicine
Copyright © 2013 American Society of Regional Anesthesia and Pain Medicine. Unauthorized reproduction of this article is prohibited.
Regional Anesthesia and Pain Medicine • Volume 38, Number 6, November-December 2013
coupled with eccentric or concentric loading (stair ascent, descent, chair rise, or timed-up-and-go activity) are particularly challenging. The odds risk of chair-rise debility increases nearly 6-fold in severely obese persons when compared with those who are not obese, and the ability to complete multiple chair rises diminishes with increasing adiposity.43 Obesity is related to a loss in stair ascent ability over time,44 and obesity increases difficulty of performing other tasks such as climbing a stool, cutting toenails, squatting, rising from a supine position from the floor, kneeling, rising from a squat, picking up coins from the floor, and 1-legged stance.45 In obese Japanese women, pain modulates the difficulty of performing daily movements such as walking more than an hour, sitting on the floor with legs beneath, and climbing stairs.46 Functional pain, therefore, interferes with numerous daily activities, diminishes quality of life, and leads to a negative psychological outlook and further functional deconditioning as highlighted later.
PSYCHOSOCIAL FACTORS RELATING TO PAIN IN OBESITY Obesity negatively affects perceptions of the benefits of regular exercise and physical activity.47 Obese persons commonly experience discomforts during exercise, such as dyspnea, musculoskeletal pain, and joint pain. Patients with chronic pain conditions, such as ankylosing spondylosis, do not perceive exercise to be enjoyable and sedentary behavior is the norm.47 Individuals with knee OA do not often experience the positive feelings after performing exercise, as do healthy, younger, more active individuals. Repeated exposures to uncomfortable or painful exercise can acutely exacerbate joint pain with loading,48 and as a result of pain with activity an aversion to activity and exercise may develop.49 These fear behaviors are successfully treated by cognitive behavioral therapy, and this therapy is more successful than a systematic exercise regimen.50
Pain Catastrophizing Pain catastrophizing is defined as an “exaggerated negative orientation to noxious stimuli.”51 People who score highly on catastrophizing measures such as the pain catastrophizing scale51 have an exaggerated focus on pain, amplify pain sensations, and feel helpless when pain is present.52 Morbidly obese patients with OA are more likely to engage in pain catastrophizing behavior.52,53 Patients who have higher levels of catastrophizing typically engage in maladaptive behaviors that contribute to continued weight gain increase, such as physical inactivity.52,54 Also, persons within the BMI range of 38 to 60 kg/m2 who had high pain catastrophizing beliefs engaged in binge eating more frequently and demonstrated less control over overeating.52 Pain catastrophizing contributes to physical disability because catastrophizing reduces self-efficacy for performing physical tasks. Arthritis self-efficacy, defined as the conviction that one can successfully execute the behavior required to produce the outcomes, is positively correlated with positive health behaviors such as increased physical activity, healthy eating behaviors, and improved pain coping.55 High arthritis self-efficacy also lessens pain catastrophizing in obese persons with knee OA and increases physical activity.55,56 Avoidance of physical activity leads to additional weight gain and development of distorted or irrational thoughts or highly negative thinking.56 Treatment efforts include a restructuring of cognitive patterns and a modification of negative to positive thoughts. A recent randomized controlled trial examining psychological disability in obese OA patients found that the combination of pain-coping–skills training and behavioral weight © 2013 American Society of Regional Anesthesia and Pain Medicine
Biomechanics and Kinesiophobia
management resulted in significant reduction in negative psychological conditions including pain catastrophizing.53
Kinesiophobia Fear of movement due to pain, or kinesiophobia, can adversely impact mobility and responses to treatment for orthopedic conditions. Kinesiophobia predicts nonrecovery in persons diagnosed with specific nontraumatic arm, neck, or shoulder issues. Increased BMI also enhances prediction of persistence of pain complaints.57 Our laboratory has performed several studies in obese patients with orthopedic issues in the knee joint and low back. Patients seeking rehabilitation care for acute and chronic knee pain were stratified into groups based on BMI: nonobese (BMI, 40 kg/m2).58 Morbidly obese persons reported significantly lower scores on the SF-8 scale of physical function (QualityMetric, Lincoln, Rhode Island) compared with nonobese counterparts, whereas average Tampa Scale of Kinesiophobia (TSK) (Supplemental Digital Content 1, http://links.lww.com/AAP/A99) scores were 18.8% higher despite reporting lower baseline pain scores.58 This finding of lower pain scores in morbidly obese people when compared with nonobese subjects may be surprising; however, it relates to the patient selection for this particular study in which a convenience sample was obtained of those who had pain, irrespective of severity. The intent was to study fear of movement with pain and statistically control for pain severity.58 Straight leg raise and range of motion were not different among nonobese, overweight, obese, and morbidly obese patients. However, perceived knee function assessed with the International Knee Documentation Committee Scale59 was progressively worse for each group from nonobese to morbidly obese. Body mass index, pain, and kinesiophobia predicted International Knee Documentation Committee Scale scores. From the TSK instrument, the 2 lower order factors, Somatic Focus (predicts perceived disability) and Activity Avoidance Focus (predicts actual physical performance, controlling for pain severity), were also the highest in the morbidly obese group compared with the nonobese group. These suggest that morbid obesity may induce a focus on limitations and fears induced by pain, and an avoidance of activities that could cause pain. Among patients with chronic low back pain, the associations between BMI, kinesiophobia, and pain-related low back disability were examined.14 In an initial analysis, patients seeking physical therapy for chronic low back pain issues were categorized into nonobese (BMI,
Musculoskeletal Pain, Fear Avoidance Behaviors, and Functional Decline in Obesity Potential Interventions to Manage Pain and Maintain Function Heather K. Vincent, PhD,* Meredith C.B. Adams, MD,†‡§ Kevin R. Vincent, MD, PhD,* and Robert W. Hurley, MD, PhD*†‡§ Abstract: Individuals with musculoskeletal pain exhibit abnormal movement patterns, including antalgic gait, postural dysfunction, increased thoracolumbar stiffness, decreased proprioception, and altered activation of abdominal and extensor muscles. Additionally, aberrant or increased biomechanical forces over time produce joint or structural damage that results in pain. A large body habitus resulting from excessive weight can accelerate these musculoskeletal complaints. Irrespective of age, obesity contributes to chronic musculoskeletal pain, impairment of mobility, and eventual physical disability. Potential mechanisms that may mediate the relationships between obesityrelated pain and functional decline include skeletal muscle strength deterioration, systemic inflammation, and psychosocial characteristics (eg, pain catastrophizing, kinesiophobia, and depression). Treatment considerations for obese patients with musculoskeletal pain include assessment of kinesiophobia levels, biomechanical analysis, and pain medication use. Ideally, a multidisciplinary team of physicians, psychologists, and physical therapists should optimize the design of interventions specific to the patient. In some cases, the use of appropriate pain medications or intra-articular injectable agents may help control pain, fostering sustained activity, caloric expenditure, and weight loss. Morbid obesity is a medical condition that alters biomechanical forces on the tissues of the body. This condition provides the opportunity to examine accelerated development of musculoskeletal pain syndromes and etiology. The proposed therapeutic interventions can have multiple benefits in the obese population including weight loss, improved psychological outlook and self-efficacy, reduced kinesiophobia levels, reduced risk of functional dependence, and improved quality of life.
of the etiology of the pain syndrome. Studies on elderly adults, such as the Einstein Aging Study, indicate that among adults older than 70 years, abdominal adiposity increases the probability of developing chronic pain.2 The risk of developing painful musculoskeletal disease, such as OA, increases 36% with an increase of body mass index (BMI) by 2 U.3 The BMI also predicts onset of chronic low back pain4; shoulder and neck pain5; hand, hip, and knee OA6–8; and foot pain.9 Across all age groups, obesity contributes to chronic pain. Children with high BMI have an increased prevalence of musculoskeletal pain, knee pain, and complex regional pain syndrome compared with less heavy counterparts, and this pain severity is relatively high.10 Obese and severely obese elderly adults demonstrated a 2 and 4 times greater likelihood, respectively, of experiencing chronic pain compared with healthy weight individuals.11 Specifically, obesity is associated with higher pain burden and lower probability of sustained remission in persons with rheumatoid arthritis.12 In both young and old persons, obesity-related pain is associated with lower quality of life and relatively low psychosocial health when compared with normal-weight individuals.13,14 Thus, across the age spectrum, obesity is associated with painful musculoskeletal issues that can adversely affect psychological well-being and perceptions about staying physically active. This review will present the relationships between obesity, musculoskeletal pain symptoms, fear avoidance behaviors, and functional decline. Interventions that may redirect the pathway of obesityinduced pain and functional decline will be presented.
(Reg Anesth Pain Med 2013;38: 481–491)
T
he relationship between chronic musculoskeletal pain and functional decline is often discussed, but the associated mechanisms are poorly understood. Conditions with a component of osteoarthritis (OA), such as nonspecific axial low back pain, are prevalent. However, we lack treatments possessing a high likelihood of success for rehabilitation.1 Although our approaches to the treatment of musculoskeletal pain conditions may represent common sense, our incomplete success in treating these conditions may result from an imprecise understanding
From the *Departments of Orthopaedics and Rehabilitation, †Anesthesiology, ‡Psychiatry, and §Neurology, University of Florida, Gainesville, FL. Accepted for publication August 19, 2013. Address correspondence to: Robert W. Hurley, MD, PhD, Division of Pain Medicine, University of Florida, Gainesville, FL (rwhurley@ufl.edu). The authors declare no conflict of interest. This publication was made possible by Grant RO3 AR057552-10A1 from the National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health (HK Vincent, KR Vincent, and RW Hurley). Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the NIAMS or NIH. Copyright © 2013 by American Society of Regional Anesthesia and Pain Medicine ISSN: 1098-7339 DOI: 10.1097/AAP.0000000000000013
MUSCULOSKELETAL PAIN IN OBESITY Obesity-related musculoskeletal pain is a deterrent for adherence to exercise and physical activity recommendations.15 Severe obesity significantly affects the spine and lower extremity sites, such as the hip, knee, and ankle, by causing skeletal misalignment, joint compression, and progression of OA.16 Foot,17 knee,18 hip, and back pain all disrupt normal gait, walking indoors and outdoors, shopping, standing for a long period, and engagement in activities that require carrying body weight. An estimated 36% of obese adults are afflicted by painful arthritis. Moreover, obesity is a common barrier to consistent participation in physical activity.19 In adults older than 70 years, the likelihood of having chronic musculoskeletal pain is increased by 83% in persons with abdominal obesity compared with those without abdominal obesity.2 Even in elderly adults as old as 99 years, the odds ratio of having chronic pain was between 3 and 4 times higher in persons with mild to severe obesity when compared with their normal-weight counterparts.20 Potential mechanisms of obesity-related pain are unclear but are likely complex or bidirectional. Compared with other body fat distributions, abdominal or truncal obesity predicts higher total pain severity and doubles the risk for developing chronic pain. This may represent a unifying pathophysiology
Regional Anesthesia and Pain Medicine • Volume 38, Number 6, November-December 2013
481
Copyright © 2013 American Society of Regional Anesthesia and Pain Medicine. Unauthorized reproduction of this article is prohibited.
Vincent et al
Regional Anesthesia and Pain Medicine • Volume 38, Number 6, November-December 2013
between metabolic syndrome and chronic pain, both of which are highly associated with truncal obesity.21,22 First, the presence of chronic pain may stimulate release of cortisol, which worsens truncal obesity.23 Second, visceral fat produces numerous substances including derived proinflammatory (adipocytokines and C-reactive protein) and insulin resistance–inducing molecules that may be related to osteoarthritic pain symptoms.24 Third, biomechanical stressors acting at the joint from excessive and aberrant loading patterns from obesity alter gait and likely contribute in part to pain onset and joint degradation.25–28 Cartilage lesions may develop in joints of obese individuals, even at an earlier time in life than previously thought. Specifically, 79% of imaged knees from morbidly obese adolescents have retropatellar lesions, 50% show lateral meniscal damage, and 87% show medial lesions.29 Fourth, muscle strength deficits exist in obese persons with chronic pain in the low back30,31 and in the knee.27,28 Inadequate strength may perpetuate poor biomechanics and joint malalignment. Inflammation, aberrant loading, and relatively low muscle strength, all of which are ideal conditions to sustain chronic pain, therefore characterize the collective musculoskeletal environment. Figure 1 illustrates the progressive changes in the collective physiological forces acting on the low back and other load-bearing joints. With normal weight, the mechanical forces and the opposing ground reaction forces acting on the foot, knee, hip, and low back are relatively low compared with the obese and morbidly obese persons. Adequate muscle strength and low systemic inflammation levels help preserve joint alignment and minimize the effects of aberrant loading and onset of painful joint disease. From obese to morbidly obese conditions, the progressive increase in systemic inflammation levels and magnitude of joint malalignment with added weight corresponds to musculoskeletal pain and joint disease.
FUNCTIONAL EFFECTS OF MUSCULOSKELETAL PAIN Ambulation and mobility tasks are adversely affected by musculoskeletal pain in obesity. Even before the development of overt pain-related functional disability, obese individuals with BMI values of 35 to 39.9 kg/m2 are up to 18 times more
likely to adopt different compensatory movement strategies while performing activities such as stair climbing and descending, chair rise, kneel to stand, and sitting to stand than individuals with lower BMI values.32 Other studies have documented altered movement patterns during functional tasks based on BMI. During a sit-to-stand task, for example, obese persons have less trunk flexion and demonstrate a posterior shift in movement of the feet compared with nonobese individuals.33 Biomechanically, this positioning reduces torque on the lumbar spine during the motion, and helps to suppress back pain symptoms while shifting loading and pain to the knees. Although these movement adaptations may temporarily diminish 1 pain generator, longer-term effects may include aberrant loading in other ways that may prematurely degenerate the compensating joints. Walking characteristics are influenced by the presence and severity of degenerative joint pain and obesity. In short- and long-distance walking tasks from a few seconds to 15 minutes in duration, obese individuals are characterized by slower gait velocity, shorter stride length, slower cadence, and a longer period in stance than nonobese individuals.34–36 There is a progressive decline in gait velocity with increasing BMI.37 The implications of this walking impairment in obesity are related to a lower daily activity level, reflected by fewer steps taken per day compared with healthy weight (3325 vs 7385 steps, respectively).38 The presence of obesity has been shown to be a significant negative predictor of community walking participation, but the presence of pain is the most significant negative predictor of walking capacity in persons with low back pain.39 When joint or chronic low back pain is present, the effects of obesity on gait parameter decline are amplified. For example, the gait velocity and stride length are progressively less in overweight and obese persons with moderate, symptomatic OA compared with asymptomatic counterparts.40 Aberrant knee joint motion (less knee flexion during the gait cycle, greater knee adduction moment) that occurs with the interaction of obesity and pain is associated with radiographic severity of OA and progression of OA.41,42 Other functional abilities are diminished with increasing BMI and pain. Tasks that involve considerable knee flexion
FIGURE 1. Physiological forces acting on the low back and load-bearing joints in healthy weight, obese, and morbidly obese persons. Ground force reaction is the force exerted by the ground on a body in contact with it; this force increases with increasing weight or mass.
482
© 2013 American Society of Regional Anesthesia and Pain Medicine
Copyright © 2013 American Society of Regional Anesthesia and Pain Medicine. Unauthorized reproduction of this article is prohibited.
Regional Anesthesia and Pain Medicine • Volume 38, Number 6, November-December 2013
coupled with eccentric or concentric loading (stair ascent, descent, chair rise, or timed-up-and-go activity) are particularly challenging. The odds risk of chair-rise debility increases nearly 6-fold in severely obese persons when compared with those who are not obese, and the ability to complete multiple chair rises diminishes with increasing adiposity.43 Obesity is related to a loss in stair ascent ability over time,44 and obesity increases difficulty of performing other tasks such as climbing a stool, cutting toenails, squatting, rising from a supine position from the floor, kneeling, rising from a squat, picking up coins from the floor, and 1-legged stance.45 In obese Japanese women, pain modulates the difficulty of performing daily movements such as walking more than an hour, sitting on the floor with legs beneath, and climbing stairs.46 Functional pain, therefore, interferes with numerous daily activities, diminishes quality of life, and leads to a negative psychological outlook and further functional deconditioning as highlighted later.
PSYCHOSOCIAL FACTORS RELATING TO PAIN IN OBESITY Obesity negatively affects perceptions of the benefits of regular exercise and physical activity.47 Obese persons commonly experience discomforts during exercise, such as dyspnea, musculoskeletal pain, and joint pain. Patients with chronic pain conditions, such as ankylosing spondylosis, do not perceive exercise to be enjoyable and sedentary behavior is the norm.47 Individuals with knee OA do not often experience the positive feelings after performing exercise, as do healthy, younger, more active individuals. Repeated exposures to uncomfortable or painful exercise can acutely exacerbate joint pain with loading,48 and as a result of pain with activity an aversion to activity and exercise may develop.49 These fear behaviors are successfully treated by cognitive behavioral therapy, and this therapy is more successful than a systematic exercise regimen.50
Pain Catastrophizing Pain catastrophizing is defined as an “exaggerated negative orientation to noxious stimuli.”51 People who score highly on catastrophizing measures such as the pain catastrophizing scale51 have an exaggerated focus on pain, amplify pain sensations, and feel helpless when pain is present.52 Morbidly obese patients with OA are more likely to engage in pain catastrophizing behavior.52,53 Patients who have higher levels of catastrophizing typically engage in maladaptive behaviors that contribute to continued weight gain increase, such as physical inactivity.52,54 Also, persons within the BMI range of 38 to 60 kg/m2 who had high pain catastrophizing beliefs engaged in binge eating more frequently and demonstrated less control over overeating.52 Pain catastrophizing contributes to physical disability because catastrophizing reduces self-efficacy for performing physical tasks. Arthritis self-efficacy, defined as the conviction that one can successfully execute the behavior required to produce the outcomes, is positively correlated with positive health behaviors such as increased physical activity, healthy eating behaviors, and improved pain coping.55 High arthritis self-efficacy also lessens pain catastrophizing in obese persons with knee OA and increases physical activity.55,56 Avoidance of physical activity leads to additional weight gain and development of distorted or irrational thoughts or highly negative thinking.56 Treatment efforts include a restructuring of cognitive patterns and a modification of negative to positive thoughts. A recent randomized controlled trial examining psychological disability in obese OA patients found that the combination of pain-coping–skills training and behavioral weight © 2013 American Society of Regional Anesthesia and Pain Medicine
Biomechanics and Kinesiophobia
management resulted in significant reduction in negative psychological conditions including pain catastrophizing.53
Kinesiophobia Fear of movement due to pain, or kinesiophobia, can adversely impact mobility and responses to treatment for orthopedic conditions. Kinesiophobia predicts nonrecovery in persons diagnosed with specific nontraumatic arm, neck, or shoulder issues. Increased BMI also enhances prediction of persistence of pain complaints.57 Our laboratory has performed several studies in obese patients with orthopedic issues in the knee joint and low back. Patients seeking rehabilitation care for acute and chronic knee pain were stratified into groups based on BMI: nonobese (BMI, 40 kg/m2).58 Morbidly obese persons reported significantly lower scores on the SF-8 scale of physical function (QualityMetric, Lincoln, Rhode Island) compared with nonobese counterparts, whereas average Tampa Scale of Kinesiophobia (TSK) (Supplemental Digital Content 1, http://links.lww.com/AAP/A99) scores were 18.8% higher despite reporting lower baseline pain scores.58 This finding of lower pain scores in morbidly obese people when compared with nonobese subjects may be surprising; however, it relates to the patient selection for this particular study in which a convenience sample was obtained of those who had pain, irrespective of severity. The intent was to study fear of movement with pain and statistically control for pain severity.58 Straight leg raise and range of motion were not different among nonobese, overweight, obese, and morbidly obese patients. However, perceived knee function assessed with the International Knee Documentation Committee Scale59 was progressively worse for each group from nonobese to morbidly obese. Body mass index, pain, and kinesiophobia predicted International Knee Documentation Committee Scale scores. From the TSK instrument, the 2 lower order factors, Somatic Focus (predicts perceived disability) and Activity Avoidance Focus (predicts actual physical performance, controlling for pain severity), were also the highest in the morbidly obese group compared with the nonobese group. These suggest that morbid obesity may induce a focus on limitations and fears induced by pain, and an avoidance of activities that could cause pain. Among patients with chronic low back pain, the associations between BMI, kinesiophobia, and pain-related low back disability were examined.14 In an initial analysis, patients seeking physical therapy for chronic low back pain issues were categorized into nonobese (BMI,
