Biomechanics of the Spine PDF

Biomechanics of the Spine Introduction The spine, or vertebral column, is a complex structure critical for supporting the body, protecting the spinal cord, and enabling movement. Composed of 33 vertebrae, it is divided into five regions: cervical, thoracic, lumbar, sacral, and...

Biomechanics of the Spine Introduction The spine, or vertebral column, is a complex structure critical for supporting the body, protecting the spinal cord, and enabling movement. Composed of 33 vertebrae, it is divided into five regions: cervical, thoracic, lumbar, sacral, and coccygeal. Biomechanics of the spine involves understanding its structure, function, and the forces it encounters during movement and posture. Anatomy Overview Vertebrae: Cervical (7 vertebrae): Highly mobile; supports the head. Thoracic (12 vertebrae): Less mobile; connected to ribs. Lumbar (5 vertebrae): Large and robust; bears the majority of body weight. Sacral (5 fused vertebrae) and Coccygeal (4 fused vertebrae): Provide stability and attachment points for ligaments. Intervertebral Discs: Fibrocartilaginous structures between vertebrae. Consists of an outer annulus fibrosus and an inner nucleus pulposus. Act as shock absorbers and facilitate movement. Ligaments: Provide stability by connecting vertebrae. Key ligaments include the anterior longitudinal ligament, posterior longitudinal ligament, and ligamentum flavum.  Muscles: Intrinsic muscles (e.g., multifidus, rotatores) stabilize the spine. Extrinsic muscles (e.g., erector spinae, latissimus dorsi) enable movement. Nerves: The spinal cord, housed within the vertebral canal, gives rise to spinal nerves. Each spinal nerve exits the spinal column through an intervertebral foramen. Nerves are critical for transmitting sensory and motor signals between the brain and the body. Key regions: Cervical nerves: Control neck, shoulders, arms, and diaphragm. Thoracic nerves: Serve the chest and abdominal muscles. Lumbar and sacral nerves: Innervate the legs, pelvis, and lower body. Compression or irritation of spinal nerves (e.g., from disc herniation or stenosis) can result in pain, weakness, or sensory deficits. Biomechanical Functions Load Bearing: The spine supports the weight of the head, trunk, and upper limbs. Load distribution varies by region, with the lumbar spine bearing the most load. Flexibility and Mobility: Enables movements such as flexion, extension, lateral flexion, and rotation. Range of motion varies by region: cervical spine is highly mobile, while thoracic and lumbar regions are less so. Protection: The vertebral canal houses and safeguards the spinal cord. Intervertebral foramina allow for the safe passage of spinal Forces Acting on the Spine Compression Forces: Occur during weight-bearing and axial loading activities. Managed by the vertebrae and intervertebral discs. Shear Forces: Arise from horizontal or tangential forces. Controlled by facet joints and ligaments. Tensile Forces: Experienced during activities like stretching or hanging. Counteracted by ligaments and muscles. Torsional Forces: Result from rotational movements. Managed by intervertebral discs and facet joints. Spinal Curvatures and Biomechanics The spine exhibits natural curvatures: Cervical and lumbar regions: Lordotic (inward curve). Thoracic and sacral regions: Kyphotic (outward curve). Curvatures enhance the spine’s shock-absorbing ability. Deviations (e.g., scoliosis, hyperlordosis) can alter biomechanics and lead to dysfunction. Clinical Relevance Intervertebral Disc Herniation: Excessive compression or torsion can cause disc rupture. Results in nerve impingement and pain. Osteoarthritis: Degeneration of facet joints leads to reduced mobility and pain. Spondylolisthesis: Forward displacement of one vertebra over another. Affects spinal stability. Postural Issues: Poor posture can lead to imbalanced forces and chronic pain. Key Concepts in Spinal Stability Intrinsic stability: Provided by ligaments, discs, and joint architecture. Extrinsic stability: Maintained by muscles and neural control. Neutral zone: Range of motion within which the spine maintains stability with minimal resistance. Assessment and Measurement Tools such as radiography, MRI, and motion analysis systems are used to assess spinal biomechanics. Functional assessments (e.g., range of motion tests) help in diagnosing biomechanical dysfunctions. Next intro lecture