A spinal cord injury at the fourth thoracic vertebra (T4) results in paraplegia. This injury, located in the upper-middle back, disrupts communication between the brain and lower body, leading to a loss of function and sensation below the chest. The severity of the injury, whether complete or incomplete, influences the degree of functional loss. A complete injury means a total loss of motor and sensory function below the injury site.
Level of Function and Sensation
An individual with a T4 spinal cord injury retains full function and feeling in their head, neck, shoulders, arms, and hands. This allows for a significant degree of independence in many daily activities, such as eating and personal grooming. The level of motor and sensory loss corresponds to the nipple line, which is aligned with the T4 dermatome. In a complete injury, sensation is absent from this point downward.
The paralysis also affects the abdominal and lower back muscles responsible for posture. Without the core muscles making constant adjustments to maintain stability, sitting upright without support can be a challenge. Individuals may initially need aids like a trunk brace or specialized seating in their wheelchair for support.
With dedicated physical therapy, many learn to use their upper body and arm positioning to help stabilize their trunk. This adaptation is a learned skill that compensates for the loss of core muscle function and allows for greater unsupported sitting balance.
Impact on Bodily Systems
A T4 spinal cord injury interrupts nerve signals that regulate several internal body systems, requiring new management strategies. Bladder and bowel control are affected because the nerves for these functions originate in the sacral region of the spinal cord. The brain can no longer receive signals that the bladder is full or control the sphincter muscles, a condition called neurogenic bladder.
Management involves using intermittent or indwelling catheters to empty the bladder on a regular schedule, preventing incontinence and kidney damage. Bowel function requires a structured program that may include dietary management, medications, and techniques like digital stimulation for regular movements.
Respiratory function is also altered, though individuals with a T4 injury can breathe independently. The diaphragm, the primary muscle for breathing, is controlled by nerves from the cervical spine and remains functional. However, the intercostal muscles between the ribs, which assist with deep breathing and coughing, are paralyzed, which can increase the risk of respiratory infections.
Sexual function changes for both men and women, as the injury disrupts nerve pathways for physical sensation and reflexive functions. While many can engage in sexual activity, the nature of the response is different. Medical interventions, including medications and devices, are available to address issues with erection, ejaculation, and fertility.
Understanding Autonomic Dysreflexia
A serious medical issue for individuals with spinal injuries at the T6 level or higher is autonomic dysreflexia (AD), making it a concern for anyone with a T4 injury. AD is a sudden, uncontrolled spike in blood pressure that can become life-threatening if not addressed quickly. The condition is a short-circuit in the autonomic nervous system, which controls involuntary functions like heart rate.
AD is triggered by a painful or irritating stimulus below the level of the injury. Because pain signals cannot reach the brain, they instead trigger an unchecked sympathetic nervous system response. This causes blood vessels below the injury to constrict, leading to a rapid rise in blood pressure.
Common triggers are often related to bladder or bowel issues, such as a full bladder from a blocked catheter, a urinary tract infection, or bowel impaction. Other causes can include tight clothing, pressure sores, or an ingrown toenail.
Symptoms of an AD episode include:
- A pounding headache
- Flushing and profuse sweating above the level of injury
- Goosebumps
- A stuffy nose
- Anxiety
The heart rate may slow as the body attempts to counteract the high blood pressure.
The first response is to sit the person upright to help lower blood pressure. The trigger must then be identified and removed, which often involves checking and emptying the bladder.
Rehabilitation and Daily Living
The rehabilitation process following a T4 spinal cord injury is focused on maximizing independence and function. Physical therapy concentrates on strengthening the upper body—the shoulders, arms, and chest—to improve mobility and facilitate transfers from a wheelchair to a bed, car, or other surfaces. Learning proper transfer techniques is important for safety and preventing strain on the upper body joints over time.
Occupational therapy plays a part in helping individuals adapt to performing everyday tasks. This can involve learning new ways to dress, bathe, and manage household activities. Therapists may also recommend home modifications, such as installing ramps, widening doorways for wheelchair access, or creating accessible bathrooms, to enhance independence and safety.
A wide range of adaptive equipment is available to support a high degree of autonomy. Most individuals with a T4 injury use a manual wheelchair for mobility, as they have the upper body strength required for self-propulsion. For driving, vehicles can be fitted with hand controls that allow for acceleration and braking without the use of foot pedals.