A spinal cord injury (SCI) occurs when damage to the spinal cord disrupts communication between the brain and the body below the injury site. An injury at the fourth thoracic vertebra (T4) results in paraplegia, which is the loss of motor and sensory function in the lower half of the body. This is considered a high thoracic injury, meaning paralysis begins in the upper torso. Understanding the level and its consequences is the first step in managing the medical and functional changes that follow a T4 SCI.
Defining the T4 Segment and Level of Paralysis
The T4 segment is located in the upper back, within the thoracic spine. Damage at this level interrupts nerve signals high on the trunk. The sensory demarcation line, representing the lowest point of normal sensation, typically runs horizontally across the mid-chest, often aligning with the nipple line. Below this line, there is usually a significant loss of feeling, including the abdomen, hips, and legs.
A T4 injury is categorized as high paraplegia. The motor level defines the lowest spinal segment with normal muscle function, which at T4 includes control over the upper trunk muscles. While cervical spine muscles remain unaffected, the muscles of the lower rib cage and abdomen lose their connection to the brain. The degree of loss is determined by whether the injury is complete or incomplete, affecting the prognosis for movement and sensation below the injury site.
Functional Capacity: What Movement is Retained
Individuals with a T4 spinal cord injury retain full use of their arms, hands, shoulders, and neck muscles. This preserved upper body strength is important for independence in daily activities. The muscles of the upper chest and the diaphragm, necessary for breathing, are typically spared, allowing for normal respiratory capacity.
However, muscle control is lost below the T4 level, including the abdominal and intercostal muscles of the lower trunk. These muscles provide core stability and trunk balance, which are necessary for sitting upright without support. Without this core strength, a person may struggle with unsupported sitting and often requires back support to maintain posture. The inability to use these torso muscles also impacts the ability to generate a strong cough, affecting respiratory health.
Managing Systemic Health and Autonomic Issues
Autonomic Dysreflexia (AD)
A high thoracic SCI, such as at T4, places an individual at risk for Autonomic Dysreflexia (AD), a serious medical condition involving the involuntary nervous system. This occurs when a noxious stimulus below the injury level (e.g., a full bladder or bowel) triggers an exaggerated sympathetic nervous system response. This uncoordinated response leads to a sudden and potentially dangerous spike in blood pressure, often accompanied by a headache, sweating, and flushing above the injury level.
Neurogenic Bladder and Bowel
Management of the neurogenic bladder and bowel is necessary due to the loss of voluntary control and sensation. Routine protocols, such as intermittent catheterization and timed bowel programs, are implemented to prevent distention, the most common trigger for AD. Adherence to these plans prevents serious complications like urinary tract infections or high blood pressure episodes.
Thermoregulation
Impaired ability to regulate body temperature (thermoregulation) is a concern because sympathetic control is disrupted below the T6 level. The body struggles to cool itself in hot environments since sweating is minimal or absent below the injury, leading to overheating risk. Conversely, the body has difficulty retaining heat in cold environments because the ability to constrict blood vessels and shiver is compromised.
Pressure Injury Prevention
The lack of sensation below the mid-chest, combined with the necessity of a seated position, creates a high risk for pressure sores (pressure injuries). The body loses the natural warning signals of pain that prompt a change in position, making routine pressure relief essential. Individuals must perform weight shifts every 15 to 30 minutes while seated to allow blood flow to bony areas like the tailbone and hips. Skin integrity must be monitored daily, as redness that does not fade quickly can indicate serious tissue damage.
Adapting to Daily Life and Mobility
The preserved strength in the arms and hands makes a manual wheelchair the primary method of mobility for most people with a T4 SCI. An ultralightweight, rigid-frame manual wheelchair is often recommended to maximize efficiency and conserve energy during propulsion. Learning proper technique is important to reduce the risk of repetitive strain injuries to the shoulders and wrists.
Achieving independence relies on mastering safe transfers, which involves moving between the wheelchair and surfaces like a bed, car, or toilet. Rehabilitation focuses on using strong upper body muscles to perform these movements, often with a sliding board. Adaptive equipment, such as grab bars, transfer benches, and modified vehicles with hand controls, facilitates self-sufficiency. The combination of retained upper body function and specialized equipment allows many individuals with a T4 injury to live independently and participate in work and community life.