A spinal cord injury disrupts communication between the brain and the body below the injury site, affecting far more than movement. Depending on where the damage occurs, it can alter breathing, heart rate, blood pressure, bladder and bowel function, bone density, skin integrity, and mental health. About 18,000 people in the United States sustain a traumatic spinal cord injury each year, most commonly from vehicle crashes (37.5%), falls (31.7%), or violence (15.4%).
Why the Level of Injury Matters
The spinal cord is organized into segments, and the location of the damage determines which body systems lose function. Injuries are classified as complete (no motor or sensory function preserved below the injury) or incomplete (some function remains). But the label “complete” or “incomplete” alone doesn’t tell you much without knowing the level.
A complete injury in the lower lumbar spine might cause bowel or bladder problems and foot drop while leaving a person otherwise able to walk and live independently. An incomplete injury in the upper cervical spine, even though some function is technically preserved, can still leave someone unable to move all four limbs and dependent on full-time support. The combination of level and severity shapes every aspect of how the body is affected.
Breathing and Respiratory Function
The diaphragm, the primary muscle for breathing, is controlled by nerves that exit the spinal cord at the C3, C4, and C5 levels in the neck. Injuries above this point paralyze both the muscles of inhalation and exhalation, making a person dependent on a ventilator or a device that electrically stimulates the nerve controlling the diaphragm.
Injuries below C5 spare the diaphragm but typically knock out the muscles between the ribs and the abdominal muscles. This creates an unusual breathing pattern: the upper chest wall actually moves inward during inhalation instead of expanding outward, because the rib muscles aren’t there to hold it in place while the diaphragm pulls down. The result is lung capacity dropping to 20 to 50 percent of normal and a severely weakened cough. That weak cough is a major problem because it makes clearing mucus from the lungs difficult, raising the risk of pneumonia and other respiratory infections.
Heart Rate and Blood Pressure Instability
The spinal cord carries signals that regulate how fast the heart beats and how tightly blood vessels constrict. A high thoracic or cervical injury interrupts these pathways, and the consequences show up in two opposite directions.
In the acute phase, the most common issue is a persistently slow heart rate. Nearly all people with severe cervical injuries experience sustained heart rates below 60 beats per minute. Blood pressure tends to run low because the blood vessels below the injury lose their ability to tighten on command, allowing blood to pool in the legs and abdomen. This pooling is also why sitting or standing up can cause a sudden drop in blood pressure, a condition called orthostatic hypotension. Compression stockings, abdominal binders, and thigh cuffs help by physically preventing blood from settling in the lower body.
Autonomic Dysreflexia
In people with injuries at or above the T6 level, a dangerous condition called autonomic dysreflexia can develop during the chronic phase. Something as seemingly minor as a full bladder, constipation, a pressure sore, tight clothing, or even an ingrown toenail sends pain signals up toward the brain. Those signals can’t get past the injury, so instead they trigger an uncontrolled flood of nerve activity below the injury that constricts blood vessels throughout the lower two-thirds of the body. Blood pressure spikes, sometimes to life-threatening levels (systolic pressure above 150 mm Hg or more than 40 mm Hg above baseline). The brain tries to compensate by slowing the heart and dilating vessels above the injury, but it can’t override the constriction below it. Bladder distension alone accounts for roughly 85% of all episodes. Recognizing and removing the trigger quickly is the most important step.
Bladder and Bowel Control
The nerves controlling the bladder and bowel run through the lowest segments of the spinal cord, so injuries at virtually any level can disrupt these functions. How they’re disrupted depends on whether the injury is above or below the nerve centers in the lower spine.
An injury above these centers (an upper motor neuron pattern) produces what’s called a reflexic bladder and bowel. The bladder may empty on its own at unpredictable times because the reflex arc is still intact but the brain can no longer regulate it. The bowel develops increased muscle tone and sphincter tightness, which promotes constipation but preserves some ability to move stool forward with the help of suppositories or stimulation techniques.
An injury at or below these nerve centers (a lower motor neuron pattern) produces an areflexic bladder and bowel. The bladder loses the ability to contract, and the bowel loses coordinated movement. Sphincter tone becomes lax, which means both constipation and incontinence become problems. Manual removal of stool is often part of the daily routine. In both patterns, bowel management programs involve scheduled routines, dietary adjustments, medications to regulate stool consistency, and abdominal massage.
Bone Loss and Muscle Changes
Without regular weight-bearing and muscle contraction, the skeleton below the injury begins losing density rapidly. Bone loss is steepest in the first one to two years, but it doesn’t necessarily stop there. At sites rich in the spongy interior bone (like the ends of the shin bone near the knee), losses can range from less than 1% to as high as 80% within two years. The denser outer bone along the shaft of the leg may continue thinning progressively for more than a decade. This makes fractures from minor impacts, like a transfer from a wheelchair, a real concern.
Muscles below the injury atrophy because they’re no longer receiving regular signals to contract. Less muscle mass lowers the body’s resting metabolic rate, which means fewer calories are burned at rest. If food intake stays the same, fat accumulates. Reduced nerve activity to blood vessels in the lower body further slows metabolism. These metabolic shifts increase the long-term risk of obesity, diabetes, and cardiovascular disease.
Spasticity
In the days and weeks immediately after injury, muscles below the injury site go limp during a period called spinal shock. Once that phase passes, many people develop spasticity: involuntary muscle stiffness, spasms, and exaggerated reflexes. This happens because the nerve circuits in the spinal cord below the injury are still functional but no longer receive the calming, regulating signals from the brain. Over time, the nerve cells below the injury become increasingly excitable, and the connections between sensory nerves and motor nerves reorganize in ways that amplify reflexes. The result is muscles that tighten or jerk in response to stimuli that wouldn’t normally cause a reaction, like a light touch or a change in position.
Spasticity isn’t always unwanted. Some people find that a degree of muscle tone helps with transfers, standing, or circulation. When it interferes with sleep, positioning, or daily function, medications that reduce nerve excitability or muscle contraction are typically the first approach.
Skin Breakdown and Pressure Injuries
When you can’t feel pressure or shift your weight naturally, the skin and tissue over bony prominences (the tailbone, hips, heels, shoulder blades) are at constant risk. Sustained pressure cuts off blood flow to the tissue, and without the discomfort signal that would normally prompt you to adjust your position, damage can begin within hours.
Pressure injuries range from intact but persistently reddened skin (stage I) to full-thickness wounds exposing bone, tendon, or muscle (stage IV). The standard prevention guideline is straightforward: relieve pressure over bony areas for five minutes every two hours when in bed, and perform brief pressure reliefs (lifting or leaning for about 10 seconds) every 10 minutes while sitting in a wheelchair. These intervals are based on the minimum time needed to restore adequate blood flow to compressed tissue.
The Secondary Injury Cascade
The initial trauma to the spinal cord is only the beginning. Within hours, a wave of biochemical damage expands the zone of injury well beyond the original impact site. The blood-spinal cord barrier breaks down, and the body mounts an intense inflammatory response. Immune signaling molecules surge within the first 3 to 6 hours and remain elevated for days. Immune cells flood the area, and while their job is to clean up damaged tissue, they also damage healthy neighboring cells in the process.
This cascade is why the amount of function someone has in the first hours after injury doesn’t always match their long-term outcome. Swelling and inflammation can temporarily silence nerve pathways that aren’t permanently destroyed, and some recovery may occur as that inflammation subsides over days to weeks. Conversely, the spreading damage can claim cells that survived the initial impact. The window in which this secondary damage unfolds, particularly the first 24 to 72 hours, is a critical period for medical intervention.
Mental Health After Injury
In the first year after a spinal cord injury, an estimated 12 to 40 percent of people experience clinical depression. That range is wide because it depends on factors like the severity of injury, pre-existing mental health, social support, and access to rehabilitation. The psychological impact goes beyond grief over lost function. Sleep disruption from spasticity or repositioning schedules, chronic pain, loss of independence, changes in relationships, and the daily burden of managing bladder, bowel, and skin care all compound the strain.
Life Expectancy
People with spinal cord injuries are roughly two to three times more likely to die prematurely compared to the general population, and the higher and more complete the injury, the greater the gap. For a 25-year-old with a complete cervical injury at C1 to C3, life expectancy drops to about 50% of what would be expected for the general population. At the C5 level, it’s roughly 59%. For injuries at C6 to C8, around 68%. Paraplegia carries a significantly better prognosis, with life expectancy reaching about 88% of the general population for injuries from T1 downward.
On average, people with paraplegia survive about 34 years after injury, compared to 25 years for those with tetraplegia. Those with high cervical injuries average about 17 years. These numbers have improved substantially over past decades as respiratory care, infection prevention, and cardiovascular management have advanced, but the gap with the general population persists.