Epidemiology

Understanding the patterns of injury and clinical presentation of low back pain is important for the planning of therapeutic, rehabilitative, and preventive strategies. Low back disorders are prevalent in all societies and the etiology of these disorders is multifactorial including individual/intrinsic as well as external/extrinsic factors.

The annual incidence of low back pain in the general population is 5%, with many patients presenting between the ages of 30 and 50 years, and a significant number of cases resolving within 4 weeks of presentation. Of these patients, particularly the ones who present with pain at an early age, a significant number will present with recurrence of the symptoms, and some will develop chronic disability. Therefore, a functional rehabilitation program should be instituted early in the disease process.^6–8

Some individual risk factors for pain are modifiable and include obesity, cigarette smoking, and low fitness level.^9,10 Occupational factors associated with back pain include vibration, static work posture, flexed posture, frequent bending and twisting, lifting and material handling.^11,12 Psychosocial factors associated with back pain and recurrence of symptoms include dissatisfaction with work, long duration of initial treatment, recurrent treatment, and being disabled from work.^13–15 Other factors, such as heredity, may not be modifiable but also play a role in the development of low back pain. Familial predisposition to back pain and degenerative disc disease has been described and may be important in patients who present at an early age (Table 90.1).^16–19

Table 90.1 Risk Factors for Axial Low Back Pain

Sports and recreational activities are also associated with the development of back pain, wherein 10–15% of all sports injuries are related to the spine. Rotational, torsional, and compressive stresses to the spine are associated with the development of intrinsic disc disease.^20,21 Activities in daily life that involve frequent bending and lifting may also lead to back pain. Individuals caring for elderly or disabled family members present with an increased prevalence of back pain.²²

Functional anatomy and biomechanics

A review of the anatomy and biomechanics of the spine is beyond the scope of this chapter; however, an understanding of the functional anatomy as well as basic concepts of biomechanics of the lumbar spine is important for the clinician who treats and rehabilitates patients with low back pain.

The basic functional unit of the lumbar spine is the three-joint complex formed by two consecutive vertebra, the intervertebral disc, and the zygapophyseal joints. The anterior elements of the lumbar spine sustain the compression loads applied to the vertebral column including body weight and loads associated with contraction of the back muscles. The posterior elements regulate the passive and active forces applied to the vertebral column and regulate motion. The zygapophyseal joints are typical synovial joints endowed with cartilage, capsule, meniscoids, and synovial membrane. The articular facets exhibit variations in both the shape of their articular surfaces and their orientation. In the lumbar spine the only movement permitted is a sliding motion in a vertical direction, executed during flexion and extension.²³

Muscle function is very important for the lumbar spine since ligaments provide little static stability and in the absence of muscle activity the spine could buckle with low compressive loads. The erector spinae are composed of two major groups: the longissimus and iliocostalis. They are primarily thoracic muscles that act on the lumbar spine with a long moment arm ideal for lumbar spine extension. The small rotatores and intertransversarii muscles are basically length transducers and position sensors. The multifidi which cross 2 or 3 segmental levels are theorized to work as spinal stabilizers.²⁴

Other muscle groups important for low back function are the quadratus lumborum, which has a direct insertion in the lumbar spine and acts as a weak lateral flexor, and the abdominal muscles which include: the transversus abdominus, internal and external oblique, and rectus abdominus. These muscles are important in flexion of the trunk, lateral bending, but most importantly help to stabilize the lumbar spine. Pelvic muscles also play a role in the kinetic chain by acting on the lumbar spine and transmitting forces from the lower extremity to the trunk and upper extremities and include: the hip flexors such as the iliopsoas, and gluteal hip extensor, as well as abductor muscles.²⁵

The lumbar spine and related structures including ligaments and muscles receive an extensive nerve supply. The vertebral bodies, the intervertebral disc, the zygapophyseal joints, and the ligaments are all innervated and have the capacity to be pain generators, making it difficult for the clinician treating axial back pain to identify the origin of a patient’s symptoms.

Pathophysiology of injury

Flexion of the lumbar spine, which involves sagittal rotation and translation, is well tolerated by the lumbar elements. Compression of the lumbar spine occurs by adding body weight, muscular contraction, and the loads that are lifted by the individual. Excessive compression may injure the anterior vertebral elements, particularly the endplates. When flexion and compression are combined with rotation, shear applied to the intervertebral disc results in injury to this structure. Vertebral extension is limited primarily by bony impaction of the spinal processes or the inferior articular facet against the lamina below, and repeated extension as well as rotation activities may lead to injury of the posterior elements such as the pars intercularis.²⁶

Lumbar disc disease associated with axial back pain is multifactorial in origin. Aging, apoptosis, abnormalities in collagen, vascular ingrowth, loads placed on the disc, and abnormal proteoglycan all contribute to disc degeneration.²⁷ Repetitive or continuous axial overloading, associated with disc fatigue, is key in the pathogenesis of lumbosacral degenerative disease.²⁴ Vigorous occupational activity and competitive athletic participation associated with end-range flexion and frequent turning predispose the disc to herniation and accelerated degeneration.²⁸

These changes in the disc, which progress from herniation to subsequent internal disruption and resorption, may affect more than one functional unit and compromise spinal motion. The combined changes in the posterior joint and discs lead to arthritis, lateral recess stenosis, and central stenosis.^29–31

Low back pain may result from compression of nerve tissue, inflammation of the nerve root, and the facet joint, as well as damage to the anulus fibrosus. Inflammatory mediators, such as prostaglandins and substance P, have been identified in patients with disc disease and are associated with pain in the absence of a compressive lesion.^28,32

Increasing age has been associated with progressive disc degeneration which can be asymptomatic in some individuals. Changes in trabecular bone morphology and inappropriate disc matrix may be related to apoptosis, or programmed cell death, in the patient with disc disease.^27,33

Clinical presentation

In the individual with axial back pain, the history and physical examination are very important in the planning of a functional rehabilitation program. Pertinent information that should be obtained from the history include: the type of pain, the mechanism of injury, exacerbating and mitigating factors, and previous injuries and response to treatment strategies. The physical examination should identify limitations of motion, direction of pain exacerbation, lack of flexibility, muscle weakness and imbalance, ligamentous laxity, and neurologic as well as proprioceptive deficits. This information combined with pain diagrams, diagnostic imaging, and injection procedures allows the clinician to recognize specific characteristics of different clinical subsets.³⁴ Clinical subsets of axial back pain include patients with acute annular tears, intrinsic disc disease, facet joint degeneration, or posterior element injury.

Patients with axial back pain associated with disc disease may present with acute symptoms, chronic symptoms, or acute exacerbation of chronic symptomatology. The patient with an acute annular disc injury will present with axial pain, limited lumbar motion, intolerance to sitting, and exacerbation of symptoms with attempted flexion of the spine. The physical examination of these individuals may reveal a lateral trunk list, pain with flexion of the spine, normal neurologic examination, and typically no evidence of spinal nerve root irritation.

The patient with chronic discogenic disease will present with axial back pain, intolerance to sitting as well as pain upon arising from a chair, limited capability to lift, bend, or twist.³⁵ Physical examination will reveal soft tissue inflexibility of paravertebral muscles, fascia and ligaments as well as some muscle spasm. There may be evidence of lumbar segmental hypomobility, loss of lumbar lordosis, and pain with flexion and rotation. The neurologic examination is usually normal with no evidence of root irritation.³⁶ Individuals who present with an acute on chronic injury give the history of an excessive load or sudden trauma superimposed on previous discogenic symptoms. The physical examination is usually similar to patients that presents with an acute annular tear.

Patients who present with axial back pain may also have involvement of posterior elements such as the facet joints. These individuals may present with pain in the back which may radiate to the buttocks or thighs that could worsen with extension activities such as walking downhill, prone lying, and prolonged standing. Other patients may present with a different history such as pain with flexion that is not exacerbated by sitting and still have facet joint pathology. The physical examination may reveal inflexibility of the lumbar soft tissues, hypomobility of spine segments, and pain with extension or flexion as well as rotation maneuvers. The neurologic examination and special maneuvers to identify root irritation are usually normal, and injection procedures may be required to clearly identify the facet joint as the pain generator.³⁷

In sports, the patterns of back injury will depend on several factors which include the patient’s age and sport-specific demands. Athletes involved in sports that require trunk rotation and hyperextension usually present with axial back pain associated to posterior element injury. Repeated stresses associated to gymnastics, diving, and wrestling places the athlete at increased risk of pars interarticularis injury such as spondylolisis. These athletes may present with acute or gradual onset of pain and limited motion which restricts activity.³⁸

Older individuals who exercise vigorously or participate in sports will generally present with injuries of the vertebral endplate and the intervertebral discs. These individuals usually present with symptoms associated to repeated flexion and trunk rotation. They may present with episodes of axial back pain and limited motion which may be accompanied by leg symptoms.³⁹

Psychosocial factors

Psychologic and social issues should be addressed in the individual with axial back pain because they may affect rehabilitation, and include coexisting anxiety, depression, family or work related stress, and lack of social support. Work dissatisfaction, fear of recurrence of pain with activity, and pending compensation are also factors that may be impediments to return to normal activity.¹⁴

Complete diagnosis of musculoskeletal injury

Prior to starting rehabilitation, attempts should be made to reach a complete diagnosis of the patient with back pain including the pain generator and the biomechanical deficits. In the authors’ practice, a modification of the musculoskeletal injury model described by Kibler is used for this purpose. This model identifies the anatomic site of injury, the clinical symptoms, and the functional deficits (Table 90.2).⁴⁰

Table 90.2 Framework for Musculoskeletal Injuries

Phases of rehabilitation

Musculoskeletal rehabilitation combines therapeutic modalities and exercise in order to return the individual to normal function. It should start early in the disease process in order to reduce the deleterious effects of inactivity and immobilization. A medical rehabilitation program should state the goals and objectives of treatment specific for each phase of rehabilitation. The treatment should focus on optimizing the healing process, restoring the biomechanical relations between the normal and injured tissue, and finally preventing recurrence of pain and chronic disability. A functional rehabilitation program emphasizes therapeutic exercise and physical activity while monitoring for exacerbation of symptoms. Rehabilitation of the patient with back pain can be divided into acute, recovery, and functional phases (Table 90.3).

Table 90.3 Goals in Rehabilitation of Musculoskeletal Injury

The acute phase addresses the clinical symptom complex and should focus on treating tissue injury. The goal at this stage should be to allow tissue healing while reducing pain and inflammation. Reestablishment of nonpainful range of motion, prevention of muscle atrophy, and maintenance of general fitness should be emphasized. Symptom control and patient education about the condition should be accomplished prior to progressing to the next rehabilitation phase.

The subacute or recovery phase should focus on obtaining normal passive and active range of motion, improving muscle control, achieving normal muscle balance, and working on core strength as well as proprioception. Biomechanical and functional deficits including inflexibilities and inability to bend or lift should begin to be addressed. Functional activities should be initiated in this stage and progression without recurrence of symptoms is required prior to advancing to the next stage.

The functional or maintenance phase should focus on increasing power and endurance while improving neuromuscular control. Rehabilitation at this stage should work on the entire kinematic chain, addressing specific residual functional deficits. The individual should be pain free, exhibit full range of motion, normal strength, and muscle balance prior to returning to full activity.

After return to activity, disease prevention and ‘prehabilitation’ strategies to avoid recurrence of symptoms in the previously injured individual should be developed. Exercise programs which combine flexibility, stabilization, dynamic strengthening, and balance training, as well as appropriate biomechanics should be encouraged in the patient who has recovered from low back pain.