Physical Therapy—The Science

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CHAPTER 106 Physical Therapy—The Science

Eric A.K. Mayer, MD, Julie Fritz, PhD, PT ATC

Physical therapy has long been the “backbone” in the care continuum to return patients with spine disorders or injuries to full function. Physical therapy lies at the heart of preoperative “conservative care,” postoperative rehabilitation, and the tertiary functional restoration. The specific therapeutic his interventions may very, but the goals of increasing range of motion and increasing strength are shared goals in each of these time periods. Injuries to the spine are often more complicated than musculoskeletal injuries to the extremities, and multiple factors can confound straightforward physical rehabilitation of muscles, joints, tendons, and ligaments. Spine injuries often do not respond to the standard recovery timeline seen in musculoskeletal injuries in the extremities. Factors that complicate spinal injury recovery include statutory vagaries, financial disincentives, charismatic practitioners, false beliefs, and erratically applied medical evidence.1,2 Scientific literature has helped to assuage fears about rehabilitation and functional capacity/limitation after injury. It is now recognized that minimizing bed rest and maximizing early activity return is not harmful and shows the greatest beneficial functional outcomes over “restful waiting.”3,4 Moreover, rehabilitation based on measured, progressive increases in resistance has demonstrated improvement in return to function, employment, social role, and reduction in symptoms.5–10 Unfortunately, there is an acknowledged lack of level I and II data as to the best type of therapeutic exercise to limit functional loss and to decrease the probability of chronicity. In the absence of clear and consistent research, rehabilitation has often relied on traditional patterns of practice that are not always evidence based. These traditional patterns have, at times, involved excessive reliance on modalities and passive intervention, rather than principles of active motion and strengthening.11,12 This chapter is a brief primer for the spine surgeon to maximize the chances of full benefit from conservative care and decrease the chances of creating a functional failure that progresses to disability.

Overview—Two Steps Forward, One Step Back

The past two decades have seen remarkable advances in spine surgical techniques and technology such as motion-sparing technology, muscle-sparing techniques, smaller surgical incisions, biomechanical stability, biologic restoration, and faster postsurgical recovery. Unfortunately, over the past 10 years total spine expenditures have increased by 82% while corresponding health status measures have declined. In 2006 (last available data), nearly 30% of the population reported physical limitations related to spinal problems (up from 20% in 1997).13 Disabling, benign spinal pain medication costs increased 139% nationwide, and the number of physician visits increased almost 300% in North Carolina.14,15 Approximately 65% of workers receiving a fusion in Washington State were disabled 2 years after surgery.16 Finally, the years 1991 to 2006 saw a staggering increase in “injured” workers dropping out and ceasing their societal contributions. The number of musculoskeletal disease claims awarded Social Security Disability Insurance rose from 15% to nearly 30%, making it the second highest group behind mental health.17 These metrics are an important indicator that physicians (and spine specialists in particular) are failing to provide the type of care that encourages function.

The answers behind this epidemiologic trend are not forthcoming. Cady and colleagues18 showed in 1979 that stronger, more physically fit individuals have fewer injuries. Their conclusion was that “… physical fitness and conditioning are preventive of back [spinal] injuries… .”18 Subsequent studies have shown that strong, aerobically fit individuals have fewer absences from “heavy” vocational or avocational activity. Furthermore, when physically fit individuals are injured, they tend to return to function more rapidly.19–22 Even with these findings in mind, there remains a lack of consensus on achieving flexibility, strength, balance, and overall fitness when rehabilitating spine injury. One consistent confounder has been the so-called “cumulative trauma” theory. This theory postulates that repetitive loading of the spine or postural effects such as driving significantly contribute to disc and facet joint degenerative changes that are themselves associated with pain. Recent studies seem to find little evidence that “cumulative trauma” is independent of genetics for sedentary work, heavy work, body weight, or work position.23–25

These epidemiologic data strongly suggest that physical fitness, as well as the progressive resistance necessary to maintain fitness, is protective of injury and poses minimal independent risk of injury. Longitudinal industrial analysis of workers lifting over 5000 kg net per shift (observed over 2 years) concluded that although low back pain development was multifactorial, the best predictor of future back pain was decreased physical fitness at time zero.10 This study, although informative for preinjury planning, does not address postinjury treatment. The remainder of this chapter is devoted to discussing what to do after an injury has occurred. Physical therapists have several modes of treatment at their disposal, each with variable evidence as to efficacy. These modes include spinal manipulative therapy, stabilization (core exercise protocol), directional (McKenzie-type) exercises, and general reconditioning/strengthening exercises. In addition to the therapies listed earlier, cognitive behavioral therapy has an important, adjunctive role in rehabilitating a patient whose psychosocial factors prevent or delay improvement. Additionally, the thoughts and beliefs of clinicians including physical therapists and physicians can play an important role in patient recovery. Clinicians’ thoughts and beliefs may be the most important independent predictor of a patient’s perceptions of his or her own disability.26 In general, clinicians who want to manage expectations (to avoid patient anger and frustration if there is subsequent residual pain) should be wary of perpetuating beliefs that pain indicates ongoing harm or injury. There is a fine line between managing expectations of residual symptoms and feeding patient beliefs of permanent impairment. False ideas about persistent disability reinforced by interactions with clinicians are difficult to extinguish and may lead a patient to enter into expensive, tertiary-level care or the disability system.27,28 In summary, active physical reconditioning through physical therapy remains the mainstay of functional return after injury, with clinicians needing to remain cognizant of false perceptions of disability that may also need rehabilitation.

Evaluation and Treatment: Importance of Classification

One problem in developing evidence-based treatments for spinal conditions has been difficulty identifying the anatomic structure responsible for a patient’s symptoms. In fact, up to 90% of patients with back pain cannot be given a precise diagnosis on the basis of pathology.29 Instead, nonspecific diagnostic labels like “lumbago” or “lumbar strain” are common. This group of patients has historically been managed as a homogenous entity. More recently, many practitioners and some researchers have demonstrated that patients with nonspecific back pain are not a homogeneous group but instead consist of subtypes of patients who can be classified on the basis of specific signs and symptoms noted during the examination.30,31 Evidence suggests that patient classification that allows specifically tailored treatment based on a patient’s back pain subtype improves outcomes compared with giving all patients a stereotypical one-size-fits-all treatment regimen.32–34

Some investigators have proposed a treatment-based classification system for the evaluation and treatment of patients with low back pain.30,35 This system uses information gathered from the physical examination and from patient self-reports to guide patient management. Three basic levels of decision making or classification are required: (1) the patient is screened for medical “red flags” to ascertain his or her suitability for rehabilitation, (2) the acuity of the low back condition is determined, and (3) the patient is evaluated and placed into a classification that determines the treatment approach to be used.

Medical “red flags” are signs or symptoms that may indicate a serious underlying pathology such as spinal neoplasm, cauda equina syndrome, or infectious process. Specific signs and symptoms that have been identified include a history of cancer, widespread and progressive neurologic loss, unexplained weight loss, fever, chills, or a recent history of an infectious condition. More complete explanations of medical red flags for consideration in individuals with back pain can be found in other sources.36

The acuity of a patient’s back pain is an important consideration in determining the most appropriate treatment. Acuity is not simply a matter of number of days since the onset of symptoms but is also based on the nature of the patient’s course of back pain and the examination findings. The natural history of back pain tends to be one of periods of exacerbation and remission.37 A patient who experiences a new exacerbation may be considered in an acute stage. Patients in an acute stage will also have examination findings related to a classification category indicating the need for specific type of intervention (e.g., directional exercise, spinal manipulative therapy, stabilization exercises) as outlined later. In contrast, patients reporting persistent, unremitting low back symptoms and related disability are considered to have chronic symptoms. These patients often lack objective examination findings that indicate a specific classification and may be best managed with a strengthening and conditioning treatment strategy. Patients with chronic symptoms may also be more likely to have psychosocial risk factors that may respond favorably to a combination of physical and cognitive-behavioral approaches to rehabilitation.38

Spinal Manipulative Therapy

Spinal manipulative therapy is a treatment approach to spinal pain that has been practiced by some medical practitioners for several centuries. Research studies and evidence-based practice guidelines support early, limited use of spinal manipulation.39 Research further indicates that the subgroup of patients with back pain who may be most likely to benefit from spinal manipulation are those with recent onset of primary back pain or new exacerbation of axial pain without pain symptoms extending distal to the knee(s).40,41 Additionally, the presence of spinal stiffness, greater degrees of hip mobility in internal rotation, and low levels of psychologic distress may indicate a patient will benefit from spinal manipulation, especially when fear and avoidance beliefs are absent.42 Patients with the previously mentioned examination findings have been shown to respond favorably to a combined rehabilitation approach that includes spinal manipulation.43

Spinal manipulation treatment involves the application of a high-velocity, low-amplitude thrust force to the spine. Although it is not necessary for a successful manipulation, these techniques often result in an audible cavitation or “pop.”44 A variety of specific spinal manipulation techniques have been described by different types of clinical practitioners. Some have promoted the use of low-velocity, nonthrust procedures commonly called “mobilization procedures.” Recent research suggests that the use of a high-velocity, thrust manipulation technique is more likely to benefit patients fitting the “acute” classification category. The differences among high-velocity manipulation procedures appears negligible clinically.45 The goal of spinal manipulation treatments is to reduce the patient’s pain and permit the patient to proceed to a general conditioning/strengthening program. Therefore when applied to the appropriate patient, spinal manipulation may only be necessary for one to two treatment sessions before symptoms improve to a point where more aggressive exercises can be employed.43 Physicians should understand that it is appropriate to begin flexibility and strengthening exercises concomitantly with spinal manipulation treatment.

Spinal Stabilization Exercises

Strengthening the muscles of the lumbar spine is often the focus of exercise programs for patients with back pain. Research has indicated that the properties of muscular endurance, muscle balance, and neuromuscular control may be important considerations for rehabilitation of the trunk muscles.46–48 Some patients with LBP have also been observed to have morphologic changes that include atrophy and fatty infiltration in the lumbar multifidus and erector spinae muscles.49,50 Stabilization exercise programs are typically designed to address the deficits in strength, endurance, and function of the trunk musculature in patients with prolonged back pain and functional impairment. It is thought that improvements in trunk muscle function lead to a decrease in pain and disability by improving the motor control of spinal segments during movement. This hypothesis has been supported by studies showing stabilization exercise improving trunk muscle mobility, strength, and both radiologic and electromyographic morphology in individuals with low back pain.51–53

What the most effective stabilization exercise regimen is remains a subject of intense debate in the literature. Some studies have demonstrated the value of trunk stabilization exercises on specific deep muscles, particularly the transversus abdominis and multifidus.52,54 Other studies have demonstrated equivalence between stabilization exercise and more general trunk strengthening exercises.55,56 A systematic review of current literature concluded that stabilization exercises targeting the deep trunk muscles are more effective than usual care, but it was unclear whether or not they were more effective than other active/strengthening rehabilitation interventions.57 These findings seem to support the identification of patient subgroups likely to benefit from a particular exercise approach. Ongoing research indicates that subgroups who benefit from a focused program include younger individuals (younger than age 40), those with greater overall flexibility, those with lumbar segmental hypermobility, and those with possible physical examination signs suggesting instability.58,59

Directional Exercises

Robin McKenzie advocated repeated movements to the end range of a particular lumbar motion (e.g., extension, flexion, side-gliding) as a rehabilitation technique for patients with low back pain.60 The most common directional preference for individuals with low back pain is extension, particularly for those younger than age 60.61 Treatments include repeated exercises in the direction of the patient’s preference (i.e., direction of less pain) that progress by increasing the amount of force and increasing the range of motion to maximize symptom relief. It is important that patients perform directional activities frequently throughout each day. Additional adjuvant activities (e.g., postural education and mobilization) that promote movement in a patient’s preferred direction may also be beneficial.

Research supports the benefits of directional exercises for a particular subgroup of patients with low back pain.61 Examination findings thought to identify patients in this subgroup include the presence of lower extremity symptoms, possibly accompanied by signs of nerve root compression. The principle findings originally described by McKenzie to identify patients likely to benefit from a directional exercise program include the ability to centralize pain with movement or a direction that reduces pain during the physical examination. Centralization is defined as a movement or position that abolishes pain or paresthesia in a limb or causes symptoms to move from a distal/lateral position in the buttocks and/or lower extremity closer to the midline of the lumbar spine. A concept related to centralization is directional preference. Directional preference occurs when a movement in one particular direction causes centralization of pain.60 When identified, the directional exercise prescription is in the direction that resulted in pain centralization or the directional preference during the examination.

Postoperative Rehabilitation

Postoperative rehabilitation of the spine is an understudied area in peer-reviewed literature. Postoperative morbidity and disability vary greatly between cervical and lumbar operative procedures. Moreover, lumbar fusion surgery seems to have a worse outcome and greater morbidity than lumbar microdiscectomy. Despite such variation in surgical outcome, rehabilitation interventions to improve outcomes have not been studied in depth. A recent meta-analysis of postsurgical spine rehabilitation yielded relatively few studies of variable quality.62 The analysis of postoperative efficacy has primarily focused on short- and medium-term pain scores with variable functional data and little focus on rehabilitation as protective of or causative for the development of postlaminectomy syndrome or failed-back syndrome. As stated earlier, this is likely a fertile area for observational or prognostic research with a growing number of postoperative patients entering the Social Security disability system.15 Observational evidence has shown that return to full function immediately after surgery is not associated with an increased risk of complications.63 One study compared intensive exercise with a light supine isometric postoperative protocol and found that the early exercise group had statistically superior range of motion at 12 weeks and fewer patients with pain at 6 and 12 weeks postoperatively.64 Another study compared high-intensity with low-intensity exercises begun 4 weeks after surgery and did not find a significant difference in sick leave or subjective pain disability.65 Three small studies have examined the effect of therapy compared with no treatment starting within 6 weeks of surgery.66–68 Overall, the studies showed short-term functional outcome gains in strength, range of motion, and positional tolerance in the exercise groups. There were weak associations for exercise creating greater pain relief than no treatment at 1 year postoperatively.66–68 In general, early rehabilitation does not seem to be harmful, with low and equivocal reoperation rates in the “high” activity groups. Because of its low risk of harm, and because of moderate evidence of short-term improvement, early postoperative exercises should likely be a part of most postsurgical plans.

Three studies looked at behavioral interventions, advice, and multidisciplinary activity “coaching” to return to activity.69–71 These interventions showed a greater rate of return to work with short-term changes to patient self-perception in the intervention groups that normalized between 1 and 2 years postoperatively.69–71 Another study reported that active exercise provided statistically greater benefit than passive modalities or manipulation in the postoperative period.72 In conclusion, the role of postoperative rehabilitation in improving outcomes remains an area ripe for research. The collaboration of physicians with physical therapists to return patients to early activity by aggressive rebuilding of lumbar musculature seems to pose no risk to the patient and appears to have a measurable short- to medium-term functional benefit.

Conclusion

Personal experience seems to indicate that a higher percentage of injured patients who engage in physical therapy and active exercises are able to return to function than those who cannot or will not participate in such treatment. Measuring the effects of such rehabilitation, however, has proven to be difficult. The lack of consensus and consistent evidence is seen in meta-analyses showing poor or insufficient blinded evidence to recommend physical therapy following surgical decompression or fusion, or in cases of spinal stenosis or spondylolisthesis.62,73–75 Optimizing the effects of physical therapy rehabilitation for patients considered to have “nonspecific” low back pain has also been difficult. The development and application of clinical decision-making processes to classify patients and target treatments most likely to benefit them may improve outcomes for these patients. It is important that spine surgeons take a greater interest in the postoperative rehabilitation of their patients to optimize the outcomes and improvement in quality of life that are associated with innovations in technology and surgical technique.

Key Points

1 After acute injury, rest, particularly bedrest, for longer than 48 hours can be detrimental. Prolonged rest after spine injury is associated with greater rates of disability when compared with patients who are advised to remain active or engaged in an early, activity-based physical therapy program.
2 There is strong evidence that exercise reduces disability duration in employees who experience work- or activity-related exacerbation of low back pain.
3 Pain is a poor guide for determining therapeutic duration and intensity. Kool et al found that exercise programs the encouraged/required patients’ continuing with therapy when their pain increased had decreased work-related disability. Programs that encouraged pain to guide dosage and intensity of therapy fared worse in primary and secondary outcome measures. Patients who stopped therapeutic activities because of pain seemed to increase behaviors such as taking pain-killers, seeking health care, stopping work, limping, guarding, and talking about pain. These behaviors are hypothesized to lead to fear-associated belief about activity and work. The demonstration of pain intensity as a failure to guide therapy adds credence to the hypothesis that fear of pain may be more disabling than pain itself.
4 Pain “centralization” and a patient’s ability to obtain a directional preference with exercise are significant findings necessary to categorize patients for appropriate exercise. Categorizing patients and treating them appropriately result in a decrease in short-term (<3 months) pain and disability for patients with low back pain compared with other standard treatments, such as nonsteroidal anti-inflammatory drugs, educational booklet, and massage.
5 Compelling evidence exists that therapists finding subjective and objective evidence of clinical “instability” should treat patients with aggressive trunk strengthening and a stabilization exercise program.
6 In the patient with a subacute or chronically painful spine, the most effective strategy may be delivering individually designed exercise programs in a supervised format (regular therapist follow-ups that progress therapist-directed home exercises). The goal is encouraging adherence to achieve high dosage and progressively increasing intensity of stretching and muscle-strengthening exercises. These progressive programs, which depend on patient home participation, seem to be the most effective types of exercises for treating chronic low back pain. Studies show benefit from the early use of aggressive physical therapy (“sports medicine model”), training that is quota based and not pain based in its progression.
7 The use of active treatment modalities instead of passive treatments is associated with substantially better clinical outcomes. Case series of patients with acute low back pain treated by physical therapists who followed active therapy guidelines needed fewer treatment visits and had decreased cost, pain, and disability when compared with patients treated with a passive regimen of modalities and manipulation. In the active treatment protocol group, 64.7% deemed therapy a success compared with 36.5% for passive treatment.
8 Psychological support is important in overcoming fear beliefs about pain, injury, activity, and function. Moreover, active physical treatment, cognitive-behavioral treatment, and a combination of each resulted in statistically equivalent and significant improvement. All demonstrated a statistically significant improvement over no treatment. (The cognitive treatment focused on behavior reinforcement of increased physical activity.)
9 Patients with chronic low back pain who followed cognitive intervention and exercise programs improved significantly in muscle strength compared with patients either who underwent lumbar fusion or who were treated with placebo/passive massage.
10 Patients who fail timely, single-therapist active protocols should be considered for referral to a tertiary-level interdisciplinary functional restoration program. Delay in treatment is a leading cause of disability. Failure to improve with good, aggressive therapy does not necessarily imply a high surgical success rate for that patient. Please refer to Chapter 107, which discusses triage of patients with significant biopsychosocial overlay.

Key References

1 Staal JB, Rainville J, Fritz J, et al. Physical exercise interventions to improve disability and return to work in low back pain: current insights and opportunities for improvement. J Occ Rehabil. 2005;15:491-505.

Most important, physical exercises are not associated with an increased risk for injury recurrence. Despite numerous studies, more quantitative and qualitative investigations are needed to further clarify the requirements for a successful application and implementation of physical exercise interventions. The specific interventions and physical or behavior effects may vary depending on content-related factors (e.g., type of exercises, dosage, frequency, skills of the health care providers) and contextual factors (e.g., treatment setting, compensation system). Patients’ expectations and confidence in specific treatment also influence physical exercise outcomes. Timing and goal setting are important in targeting work return with early application of quota-based therapy during the acute phase of work absenteeism.

2 Martin BI, Turner JA, Mirza SK, et al. Trends in health care expenditures, utilization, and health status among US adults with spine problems, 1997-2006. Spine. 2009;34:2077-2084.

Expenditures related to supine care have increased by 82%, and well health measures have decreased in the 10-year interval between 1997 and 2006. Overall, nearly 30% of the population state that they are somewhat limited in vocational activities by spine pain. This increased from 20% in 1995.

3 Videman T, Sarna S, Battie MC, et al. The long-term effects of physical loading and exercise lifestyles on back-related symptoms, disability, and spinal pathology among men. Spine. 1995;20:699-709.

Body shape and habitus have a greater effect on disc desiccation then serial physical loading, type of work, vocational activity, or lifestyle when analyzed with radiologic criteria for desiccation or degenerative changes.

4 Rainville J, Pransky G, Indahl A, Mayer EK. The physician as disability advisor for patients with musculoskeletal complaints. Spine. 2005;30:2579-2584.

Physicians play a key role in determining whether patients return to work in a timely fashion through their advice. Evidence exists that educating physicians changes the population prevalence of disabling spine injuries. Educational efforts to modify physician belief about back pain, injury, and the relation of hurt and harm seem to improve population outcomes. Physicians should be adequately educated to prevent advice that is detrimental to the patient’s eventual functional recovery.

5 George SZ, Fritz JM, Bialosky JA, et al. The effect of a fear-avoidance based physical therapy intervention for patients with acute low back pain: results of a randomized clinical trial. Spine. 2003;28:2551-2560.

Patients with elevated fear-avoidance beliefs appeared to have less disability from fear-avoidance-based physical therapy when compared with those receiving standard care physical therapy.

6 Kool JP, Oesch PR, Bachmann S, et al. Increasing days at work using function-centered rehabilitation in nonacute nonspecific low back pain: a randomized controlled trial. Arch Phys Med Rehabil. 2005;86:857-864.

Pain is a poor guide to predict therapeutic efficacy. Patients were split into two groups: 1) a function-based group who were encouraged to continue with therapeutic exercises despite the pain and 2) a pain-based group who were told to cease exercises when they had pain. Patients who were trained by a therapist to stop exercising because of pain fared worse in all measures then the function-based group. Additionally, the pain-based group exhibited additional behaviors such as stopping work, limping, guarding, talking about pain, taking pain killers, and seeking additional health care.

7 Fritz JM, Delitto A, Erhard RE. Comparison of a classification-based approach to physical therapy and therapy based on clinical practice guidelines for patients with acute low back pain: a randomized clinical trial. Spine. 2003;28:1363-1372.

For patients with acute, work-related low back pain, the use of a classification-based approach with four classification subgroups resulted in improved disability and return to work status after 4 weeks. The work return was statistically significant when compared with therapy based on other clinical practice guidelines. Patients with subjection and objective evidence of clinical instability were treated with a strengthening and stabilization exercise program. Classification systems with four different treatment approaches based on findings are used by physical therapists, yet indications for their application have not been adequately studied.

8 Ostelo RW, Costa LO, Maher CG, et al. Rehabilitation after lumbar disc surgery: an update Cochrane review. Spine. 2009;34:1839-1848.

Pain and function that failed to improve through back surgery should be treated with physical therapy or a functional restoration program. There is strong evidence for intensive exercise programs for functional status and faster return to work, and there is no evidence that they increase the reoperation rate.

9 Videman T, Gibbons LE, Kaprio J, Battié MC. Challenging the cumulative injury model: positive effects of greater body mass on disc degeneration. Spine J. 2010;10:26-31.

Contrary to popular belief, heavier body weight between twins and greater physical activity do not seem to increase disc desiccation or degenerative changes when followed over time with MRI. In fact, heavier twins who were more physically active in avocational activities seem to preserve MRI disk signal L1 and L4. This finding challenges the long held belief in the “cumulative injury model.” The cumulative injury model seems to have no proof in favor of it, and there is fairly clear evidence with this article against this model.

References

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2 Hadler NM, Carey TS, Garrett J. The influence of indemnification by workers’ compensation insurance on recovery from acute backache. Spine. 1995;20:2710-2715.

3 Deyo R, Diehl A, Rosenthal M. How many days of bed rest for acute low back pain? N Engl J Med. 1986;315:1064-1070.

4 Staal JB, Rainville J, Fritz J, et al. Physical exercise interventions to improve disability and return to work in low back pain: current insights and opportunities for improvement. J Occ Rehab. 2005;15:491-505.

5 Manniche C, Lundberg E, Christiansen I, et al. Intensive dynamic back exercises for chronic low back pain. Pain. 1991;47:53-63.

6 Risch SV, Norvell NK, Pollock ML, et al. Lumbar strengthening in chronic low back pain patients. Physiologic and psychological benefits. Spine. 1993;18:232-238.

7 Kankaanpaa M, Taimela S, Airaksinen O, et al. The efficacy of active rehabilitation in chronic low back pain. Effect on pain intensity, self-experienced disability, and lumbar fatigability. Spine. 1999;24:1034-1042.

8 Mannion AF, Taimela S, Muntener M, et al. Active therapy for chronic low back pain part 1: Effects on back muscle activation, fatigability, and strength. Spine. 2001;26:897-908.

9 Kaser L, Mannion AF, Rhyner A, et al. Active therapy for chronic low back pain: part 2: Effects on paraspinal muscle cross-sectional area, fiber type size, and distribution. Spine. 2001;26:909-919.

10 Mannion AF, Junge A, Taimela S, et al. Active therapy for chronic low back pain part 3: Factors influencing self-rated disability and its change following therapy. Spine. 2001;26:920-929.

11 DeLorme TL. Restoration of muscle power by heavy resistance exercises. J Bone Joint Surg. 1945;27:645-667.

12 DeLorme T, Watkins A. Progressive Resistance Exercise: Technic Medical Application. New York: Appleton-Century-Crofts, Inc.; 1951.

13 Martin BI, Turner JA, Mirza SK, et al. Trends in health care expenditures, utilization, and health status among US adults with spine problems, 1997-2006. Spine. 2009;34:2077-2084.

14 Martin BI, Deyo RA, Mirza SK, Turner JA, et al. Expenditures and health status among adults with back and neck problems. JAMA. 2008;299:656-664.

15 Freburger JK, Holmes GM, Agans RP, et al. The rising prevalence of chronic low back pain. Arch Int Med. 2009;169:251-258.

16 Maghout Juratli S, Franklin GM, Mirza SK, et al. Lumbar fusion outcomes in Washington State workers’ compensation. Spine. 2006;31:2715-2723.

17 Social Security Administration. Annual Statistical Report on Social Security Disability Insurance Program. Baltimore, MD: Office of Research Evaluation and Statistics; 2007.

18 Cady LD, Bischoff DP, O’Connell ER, et al. Strength and fitness and subsequent back injuries in firefighters. J Occ Med. 1979;21:269-272.

19 Storheim K, Brox JI, Holm I, et al. Predictors of return to work in patients sick listed for sub-acute low back pain: a 12-month follow-up study. J Rehab Med. 2005;37:365-371.

20 Stevenson J, Weber C, Smith JT, et al. A longitudinal study of the development of low back pain in an industrial population. Spine. 2001;26:1370-1377.

21 Gibbons LE, Videman T, Battie MC. Determinants of isokinetic and psychophysical lifting strength and static back muscle endurance: a study of male monozygotic twins. Spine. 1997;22:2983-2990.

22 Videman T, Sarna S, Battie MC, et al. The long-term effects of physical loading and exercise lifestyles on back-related symptoms, disability, and spinal pathology among men. Spine. 1995;20:699-709.

23 Videman T, Gibbons LE, Kaprio J, et al. Challenging the cumulative injury model: positive effects of greater body mass on disc degeneration. Spine J. 2010;10:26-31.

24 Wai EK, Roffey DM, Bishop P, et al. Causal assessment of occupational bending or twisting and low back pain: results of a systematic review. Spine J. 2010;10:76-88.

25 Roffey DM, Wai EK, Bishop P, et al. Causal assessment of awkward occupational postures and low back pain: results of a systematic review. Spine J. 2010;10:89-99.

26 Rainville J, Pransky G, Indahl A, et al. The physician as disability advisor for patients with musculoskeletal complaints. Spine. 2005;30:2579-2584.

27 Dersh J, Mayer T, Theodore BR, et al. Do psychiatric disorders first appear preinjury or postinjury in chronic disabling occupational spinal disorders? Spine. 2007;32:1045-1051.

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29 Abenhaim L, Rossignol M, Gobeille D, et al. The prognostic consequences in the making of the initial medical diagnosis of work-related back injuries. Spine. 1995;20:791-795.

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31 Fritz JM, Cleland JA, Childs JD. Subgrouping patients with low back pain: evolution of a classification approach to physical therapy. J Orthop Sports Phys Ther. 2007;37:290-302.

32 Brennan GP, Fritz JM, Hunter SJ, et al. Identifying sub-groups of patients with “non-specific” low back pain: results of a randomized clinical trial. Spine. 2006;31:623-631.

33 Fritz JM, Delitto A, Erhard RE. Comparison of a classification-based approach to physical therapy and therapy based on clinical practice guidelines for patients with acute low back pain: a randomized clinical trial. Spine. 2003;28:1363-1372.

34 Long AL, Donelson R. Does it matter which exercise? A randomized trial of exercise for low back pain. Spine. 2004;29:2593-2602.

35 Fritz JM, George S. The use of a classification approach to identify subgroups of patients with acute low back pain: Inter-rater reliability and short-term treatment outcomes. Spine. 2000;25:106-114.

36 Deyo RA, Rainville J, Kent DL. What can the history and physical examination tell us about low back pain? JAMA. 1992;268:760-765.

37 Hestbaek L, Leboeuf-Yde C, Manniche C. Low back pain: what is the long-term course? A review of studies of general patient populations. Eur Spine J. 2003;12:149-165.

38 George SZ, Fritz JM, Bialosky JA, et al. The effect of a fear-avoidance based physical therapy intervention for patients with acute low back pain: results of a randomized clinical trial. Spine. 2003;28:2551-2560.

39 Chou R, Huffman LH. Nonpharmacologic therapies for acute and chronic low back pain: a review of the evidence for an American Pain Society/American College of Physicians clinical practice guideline. Ann Intern Med. 2007;147:492-504.

40 Flynn T, Fritz J, Whitman J, et al. A clinical prediction rule for classifying patients with low back pain who demonstrate short term improvement with spinal manipulation. Spine. 2002;27:2835-2843.

41 Fritz JM, Childs JD, Flynn TW. Pragmatic application of a clinical prediction rule in primary care to identify patients with low back pain likely to respond quickly to spinal manipulation. BMC Fam Pract. 2005;6:29.

42 Crombez G, Vlaeyen JW, Heuts PH, et al. Pain-related fear is more disabling than fear itself: evidence on the role of pain-related fear in chronic back pain disability. Pain. 1999;80:329-339.

43 Childs JD, Fritz JM, Flynn TW, et al. Validation of a clinical prediction rule to identify patients with low back pain likely to benefit from spinal manipulation. Ann Intern Med. 2004;141:920-928.

44 Flynn TW, Childs JD, Fritz JM. The audible pop from high-velocity thrust manipulation and outcome in individuals with low back pain. J Manip Physiol Ther. 2006;29:40-45.

45 Cleland JA, Fritz JM, Kulig K, et al. Comparison of the effectiveness of three manual physical therapy techniques in a subgroup of patients with low back pain who satisfy a clinical prediction rule: a randomized clinical trial. Spine. 2009;34:2720-2729.

46 Lee JH, Hoshino Y, Nakamura K, et al. Trunk muscle weakness as a risk factor for low back pain: A 5-year prospective study. Spine. 1999;24:54-61.

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