So What are the Causes of Back Pain?
There are many causes of back pain and we really need to evaluate the area of pain and get an understanding of what’s causing the specific type of pain to really answer the question “What causes back pain?“. With nearly 90% of people experiencing back pain in their lifetime the prevalence of back is quite high and there are various reasons one might experience back pain.
There are various structures in the back that can potentially hurt and there are a number of things that give rise to back pain, but the first thing to note is that there are three basic types of nerves and two of the nerves can convey a sense of pain. In this blog I’m going to cover most of the areas you would experience back pain, symptoms, as well as different types of back pain and their characteristics.
Understanding Nerve Types
The three nerve types are motor, sensory, and sympathetic. Motor nerves are responsible for conducting electrical impulses to muscles so they will contract for the purpose of moving something or holding something still. Sensory nerves provide several types of information from various tissues throughout the body. Sensory nerves can transmit different kinds of information to the brain. This information can include temperature, pressure, position in space, and pain.
Sympathetic Nerves and Pain
Sympathetic nerves are the most elusive of all the nerve networks and are most associated with unconscious background activity such as control of heart rate, blood pressure, body temperature, respiratory rate, dilation and constriction of pupils, intestinal activity and a great deal more. The sympathetic nerves are not usually associated with pain from an injury, but might contribute to painful situations with an abnormal response to healing and inflammation. An example of this is referred to as reflex sympathetic dystrophy (RSD) or complex regional pain syndrome (CRPS).
Stimulation of Sensory Nerves
The next thing to think about is what can stimulate the sensory nerves that give rise to the sensation of pain. The two most obvious sources of stimulation are physical injury or mechanical pressure and chemical stimulation. Examples are bumping a nerve will give pain and so will pouring acid on a nerve.
Anatomical Structures and Injuries That Cause Back pain
Now that we understand what is transmitting the sense of pain, let’s look at what anatomical structures can be injured and cause pain. You must also keep in mind that age and the history affect the likelihood of one problem versus another is causing your pain.
The Spinal Disc: A Major Source of Low Back Pain
The lumbar disc is probably the most common source of low back pain and is always a major consideration when talking about back pain. There are 5 lumbar discs and they support the entire weight or load of the upper body. The next feature of the lumbar spine discs is that they never hold completely still, they are always moving, even when sleeping at night.
Complex Structure and Function
The disc is a complex structure that has to limit twisting and rotation as well as act like a shock absorber. The structure of the disc is complex in order to fulfill its requirements. The tough covering of the disc is called the annulus and can be compared to a radial tire with its fibers crossing in different directions to accommodate the different forces it is exposed to, such as flexion, extension, bending and rotation.
Annulus and Sensory Nerves
The annulus will accommodate and restrict motion past a certain point. The annulus is full of sensory nerves that let the brain know where the back is in 3-dimensional space as well as when too much motion is being attempted (pain). The annulus is a very tough structure that constantly in motion and has a rather poor blood supply that limits the nutrition, oxygen delivery and speed of healing.
Back Pain from Annulus Injuries
The annulus is constantly moving to support the weight of the body and resist excessive motion. The annulus can generate serious back pain when injured or torn.
The Disc’s Center: Cartilage Cushion
The center of the disc is made of cartilage that acts like a cushion or shock absorber. The disc has a softer center (almost like a Bismark jelly donut) that is held in place by the annulus. There aren’t really any nerves in the center of the disc where the nucleus is and there isn’t really a blood supply either.
Disc Bulges and Protrusions
If a large piece of the cartilage breaks off, it can herniate to the periphery and can put pressure on the annulus causing pain (disc bulge or protrusion).
Soft Tissues – Muscles, Ligaments, and Tendons
The muscles, ligaments, and tendons are what control and stabilize the back, and of course the whole body. The muscles, ligaments, and tendons have a rich sensory nerve supply that keep the brain informed about where everything is in 3-dimensional space as well as generating pain if things are moving beyond where they are supposed to.
The muscles have the ability to contract and relax to stabilize and control motion, but muscles need a way to attach to the bone. The way that muscle can attach strongly to a bone is to have a transition tissue like a tendon be able to attach to the muscle on one side and the bone on the other.
A ligament is a tissue that connects bones to other bones, providing stability and support to joints.
Soft Tissue Injuries
The soft tissues can be injured when doing something “wrong” or during an injury. A common example would be a motor vehicle accident where excessive motion can’t be resisted by the soft tissues, so they tear or are pulled off their attachment. The same kind of injury can occur with practically any sport that is overdone or inadequately prepared for in terms of strengthening or stretching. The result is injury, inflammation, and pain. The good thing about the soft tissues is that they usually have a pretty good supply, so healing can be more rapid than a disc injury.
There are two common situations that can give rise to back pain. One is an auto accident and the other is a sports injury. Although the mechanisms of injury might be different and affect different muscles, tendons, and ligaments, the final result is the same. There will be injury and inflammation of the soft tissues that stimulate sensory nerves that give the sensation of pain.
Facet Pain and Other Causes of Low Back Pain
Facet Pain: An Overview
The facets probably represent the second most common cause of back pain. The facets are small joints that are formed by small bones that protrude off the back of each vertebra. When these small bones touch each other, they form a joint called the facet joint and there is a right and left facet joint for each vertebra.
Facet Joint Formation and Function
Since there is a bony contribution from two vertebrae to make the joint, the facets are referred to with a pair of numbers, for example lumbar 4-5 facet on the right or left. The facet joints have relatively flat surfaces that allow sliding, rather than a ball and socket configuration. The facet joints are a bony extension of bone to the back of the vertebrae and help to stabilize the spine and limit twisting, flexion, and extension motions.
Causes of Facet Pain
Facet pain can be generated acutely by injury or chronically by wear and tear. The most common acute injury results from a motor vehicle accident, but falls or twisting injuries can injure the facet joints and tear the capsule too. The capsule contains the sensory nerves that cause pain. Facet pain can also result from degenerative or wear and tear changes.
Sacroiliac pain is the third most common cause of low back pain. The sacroiliac joint is where the upper body is attached and connected to the lower body (buttocks and legs). The pain originates from the sacroiliac joint itself or from the many tendons and ligaments associated with the joint.
Soft Tissue Envelope
The fourth most common cause of low back pain arises from the soft tissues surrounding the vertebra and discs that is sometimes referred to as “the soft tissue envelope” which includes the muscles and ligaments. Muscles help to control the overall movement of the spine, while the ligaments help to hold the individual bones to each other as well as to coordinate and limit spine motion.
Another cause of back pain is pinched nerves. There are numerous ways to pinch a nerve, but it usually comes down to pinching a nerve with soft tissues like a herniated disc or from bony overgrowth and narrowing of a tunnel that the nerve passes through (stenosis).
Different Types of Back Pain and Their Characteristics
The description of back pain can be as varied as there are people describing it. Most people just have a complaint of back pain in a general way, they have never really thought about a way to objectively describe it. In addition to the inherent difficulty to describe pain, there is not a way to objectively measure it. However, there are some key components in the description of back pain that can have relevance, such as the location of pain.
- Pain Location A good place to start when trying to describe your pain is to use your finger to point to where you feel it and you could even consider using a magic marker to mark it.
- Deep Middle Pain Is the pain deep in the middle or is it a little off to the sides? Pain that is deep in the middle often means the pain is coming from an injured disc. The description of “my back going out” is often related to a bad disc.
- Pain Off to the Side If the pain is off to the side, how far off to the side? Pain that is focal and an inch or two off to the side suggests that the pain may be from an inflamed facet joint (facet syndrome). If the pain is a few inches off to the side, it can sometimes indicate a pinched nerve or a muscle in spasm. If the pain is larger and diffuse, it suggests a musculotendinous problem that is more general and described as aching.
- Pain Traveling to the Buttock, Thigh, Leg, or Foot Does the pain travel from the back into the buttock and thigh, leg, or foot? If so, this may indicate a pinched nerve. The quality of the pain might be described as intense, sharp, or electrical.
- Importance of Pain Description The description of pain is highly subjective but can give some indication of the underlying problem. If you know what the underlying problem is (the diagnosis), it can improve your choice of what to do to relieve that pain.