Paraplegia is a form of paralysis affecting the lower half of the body, commonly resulting from a spinal cord injury. This condition leads to a significant loss of motor function and sensation in the legs and sometimes the lower trunk. Understanding the physiological changes in the legs after such an injury helps grasp the daily realities faced by individuals with paraplegia. This article will explore the biological consequences, unexpected movements and sensations, associated health complications, and interventions designed to manage these changes.
The Physiological State of Paraplegic Legs
A spinal cord injury disrupts nerve signals between the brain and the lower body. When the spinal cord is damaged, messages that control voluntary movement and transmit sensory information are interrupted below the injury level. While leg muscles and tissues remain biologically alive, they lose their direct connection to the brain for conscious control and feeling.
Over time, this disconnection leads to disuse atrophy. The muscles in the legs, no longer receiving signals to contract or bear weight, begin to shrink and lose mass. This can result in a significant decrease in muscle cross-sectional area, sometimes by 18% to 46% within the first six weeks following the injury. Even with significant size reduction, their basic cellular structure can be maintained for many years.
Involuntary Movements and Sensations
Despite the loss of voluntary control, individuals with paraplegia often experience involuntary movements and sensations in their legs. One common manifestation is spasticity, characterized by uncontrolled muscle stiffness and spasms below the injury level.
Spasticity arises because reflexes within the spinal cord below the injury can no longer be properly regulated by the brain. Inhibitory messages that normally descend from the brain to temper these reflexes are blocked, leading to exaggerated and uncoordinated muscle responses. This can present as sudden, jerky movements, hyperactive reflexes, or persistent muscle tightness that makes movement difficult. This involuntary muscle activity begins around six weeks after the initial spinal cord injury.
Individuals may also experience abnormal sensations, known as neuropathic pain. This pain is not caused by physical damage to the leg itself but by misfiring signals from damaged nerves in the spinal cord. The brain misinterprets these aberrant nerve signals, resulting in sensations often described as burning, stabbing, tingling, or electric shock-like pains. These sensations can occur even in areas of the legs where normal touch or temperature sensation is absent.
Health Complications and Management
Immobility and reduced sensation associated with paraplegia can lead to health complications in the legs. Pressure sores, also known as decubitus ulcers, are a common concern. They develop when continuous pressure on the skin, particularly over bony areas like the sacrum, heels, or buttocks, restricts blood flow and causes tissue breakdown. Individuals with complete spinal cord injuries face a higher risk, with about 30% developing pressure ulcers compared to 10.5% in those with incomplete injuries.
Deep vein thrombosis (DVT) is another complication, involving blood clot formation in the deep veins of the legs. Reduced movement leads to venous stasis, where blood pools in the lower limbs, increasing the risk of clot formation. Edema, or swelling, in the legs can also occur due to poor circulation.
Joint contractures, a shortening of muscles, tendons, or ligaments around a joint, limit its range of motion and can begin to develop as early as one week post-injury. These are caused by prolonged immobility, muscle imbalances, and spasticity. Management focuses on prevention, including regular repositioning schedules and diligent skin inspections to avoid pressure sores. Passive range-of-motion exercises, performed manually or with assistance, help maintain joint flexibility and prevent contractures. Anticoagulant medications and compression stockings may also be used to reduce the risk of deep vein thrombosis.
Therapeutic and Technological Interventions
Therapeutic and technological advancements offer ways to manage and improve the physiological state of paraplegic legs. Functional Electrical Stimulation (FES) is a widely used technique that applies low-level electrical currents to paralyzed nerves or muscles. Electrodes placed on the skin stimulate these nerves, causing muscles to contract.
FES helps maintain muscle mass, improve circulation, and can reduce spasticity and disuse atrophy. This technology can also enable functional activities, such as cycling on a stationary bike, by coordinating muscle contractions to produce movement. FES can contribute to improved muscle size, strength, range of motion, and bone density.
Beyond FES, assistive technologies like standing frames provide support for weight-bearing, which benefits bone health and circulation. Robotic exoskeletons represent another innovation. These wearable devices incorporate motors and sensors to provide powered assistance for leg movement. Exoskeletons enable individuals with paraplegia to stand, walk, turn, and in some cases, even climb stairs, by mimicking natural gait patterns. These systems can also positively influence spasticity, trunk control, and bladder and bowel function, offering a higher degree of independence and mobility.