The human spine is composed of individual bones, called vertebrae, stacked on top of each other. Between each two vertebrae is a spinal disc that absorbs shock, provides cushioning and contributes to movement of the spine. On either side of each vertebra are spinal nerves that supply sensation and motor power to different parts of the body. Bulging discs put pressure on these nerves, causing problems in the arms or legs.
Spinal nerves provide sensation to different parts of the body. The left and right L4 spinal nerves, which exit between the L4 and L5 vertebrae, provide sensation to the outside skin on the back of the upper thigh, coming around to the front of the knee to the inside of the lower leg and along the inside of the foot to the big toe. A bulging disc at L4-5 causes pain, tingling and eventually numbness in these areas of the leg on the side of the body that the disc is bulging toward.
Spinal nerves supply the muscles of the arms and legs. The L4 spinal nerve provides power to the muscles that bring the big toe and foot into extension, or up off the ground. With a bulging disc, these muscles become weak, which can cause a person to trip over the foot while walking. Prolonged pressure on the L4 nerve from a bulging disc can lead to "drop foot," a condition that causes the foot to point down to the floor when it is lifted up off the ground. This is a serious condition that must be addressed to prevent falls.
Conservative treatment often reverses the symptoms of an L4 bulging disc. Exercises are prescribed by a physical therapist or chiropractor to improve posture and increase flexibility of muscles that might be causing the disc to bulge. In addition, spinal manipulation may be performed. Moist heat can be applied to the back to decrease pain and stiffness. As pressure is relieved from the nerve, sensation and strength will return. An AFO (ankle-foot orthosis) can be worn to prevent foot drop and improve walking safety.
In severe cases, surgical intervention might be required to reduce pressure from a bulging disc. Several different types of surgery are performed to correct disc herniation, and the procedure is chosen based on the severity of the damage and other factors specific to the person's overall health. Microsurgery can be performed to remove small areas of damage. Invasive procedures like spinal fusion are performed when the disc is beyond repair and must be removed.