By Kyri Ioannou, MSc BSc (hons) GSR CPT
Next up in the joint pain series at Exercise Menu is a discussion about low back pain. The prevalence of low back pain in society is extremely high (1) and the condition is no longer unique to western society and developed countries (2-3). It is estimated that up to 80% of the population will suffer from low back pain (4). Unfortunately, most subjects will suffer having a relapse after the initial episode (5-6). Low back pain is a major problem for employers and insurance companies and costs millions in lost salaries, medical costs, and disability. The high prevalence and cost has led to a drastic increase in research and preventative measures to combat its effects. However, despite this it is still difficult to predict who will suffer an episode of low back pain (7-12).
Understanding the Relationship Between Anatomy and Low Back Pain
Before detailing specific conditions or common issues associated with low back pain, it is important to understand the anatomy and function of the lumbar spine and lower back. While the spine is divided into 5 sections (cervical, thoracic, lumbar, sacral, and coccyx), the lower back is commonly documented as spanning from thoracic vertebrae T10-T12 to sacral vertebrae S1-S2, not just the lumbar spine. The thoracic and sacral sections are included because of their influence on the lumbar lordotic curvature (13). The lumbar curve begins to move forward (or anteriorly) from the bottom three thoracic vertebrae. The curve typically reaches its maximum forward peak at the body of lumbar vertebrae L4 before beginning to move in a backward (or posterior) direction ending at the upper two sacral vertebrae. The health and function of the lower back and lumbar spine cannot be limited to solely the joints between these articulations. It is important to understand that lumbar spine health is greatly influenced by the sacro-iliac joints (the spine/hip articulations or connection), thoraco-lumbar fascia (soft tissue covering the lower thoracic and lumbar vertebrae), muscles of the hip and thigh, and muscles farther away.
The low back is the junction between lower and upper extremities. It permits the thigh and hip to move through vast ranges of motion. This connection also provides support for the upper limbs to lift and reach far outside the center of stability. The vertebrae of the low back are designed to bear load(s) and become bigger and progressively more weight bearing moving down the spine. The L5 vertebra is the largest and supports the most weight.
Attached to and between each round/crescent shaped vertebral body is an intervertebral disc. The disc is composed of outer fibrous rings with a softer nucleus structure in the middle. The disc is designed to mainly soften compressive loads, although it also has slight resistive properties to rotational forces. However, the discs are inherently weak and collapse or become injured easily (14).
Like a dome, the strongest structure on earth, the lower back has a functional anterior convex curve that assists in weight distribution and dispersion called the lordotic curve. The normal values relating to the angle of the lordotic curve have been widely debated and researched without definitive conclusions regarding the optimal curve angle that correlates with the lowest rates of low back pain (13). This possibly highlights less importance on curve angles (unless it is extreme) and greater importance of muscular stabilizers and support during loading and movement. Despite the seemingly advanced architectural structure, the lumbar spine has been shown to fail or buckle at loads between 2kg-9kg (4lbs-20lbs) without muscular support (15).
To aid in stability, the spine is equipped with supportive non-contractile tissues that include: one anteriorly positioned ligament (anterior longitudinal ligament) to resist extension movements and four posteriorly positioned ligaments (posterior longitudinal ligament, ligamentum flavum, interspinous ligament, supraspinous ligament) that resists flexion movements of the spine. It can be noted the lumbar spine is passively more supported to oppose forward movements. This may stem from developmental adaptations from the hunched posture of early humans.
The spine’s soft tissue structures are more likely to become injured during flexion movements and the body has adapted to provide further protective support. Another reason the low back is predominately more susceptible to flexion-type injuries is because vertebrae’s bony protrusions and structures limit extension movements. However, the spine can become injured during hyperextension and/or from external forces. Additionally, the lumbar spine has an attaching ligament from the posterior portion of the hip, the iliolumbar ligament, that provides extra support to the sacro-iliac joint. This helps to stabilize and control movements of the hip-spine junction that subsequently optimizes function of the lumbar vertebrae.