If I had a nickel for every time a low back pain patient said they "slipped a disc"...
First, let's examine the anatomy of a spinal disc and explain what a "disc herniation" actually is.
Intervertebral discs are like jelly doughnuts; a tougher outer shell that surrounds a jelly center. They are obviously more complex than that, but for our purposes, we'll simplify it to that. The jelly substance on the inside of our discs (called the nucleus pulposus) is a bunch of complex proteins that loves to hold onto water. In fact, the nucleus is made up of nearly 80% water in some people! The denser outside layer of the disc is called the annulus and is made up of multiple overlapping layers of collagen fibers. Each fiber in a single layer is oriented in the same direction, while the fibers in the layer above and below it are oriented in a slightly different direction. This allows the disc to resist forces from all directions, but mostly resist the compression force from gravity and the weight of the spine and body pressing down on it. The most outside layer of the disc (the cartilaginous endplate for you nerds out there) is attached to the vertebrae above it and below it which prevents the disc from moving forward, backward, or side to side. These endplates are ULTRA important because they are how the discs get their nutrient supply! There is no direct blood flow to a disc to bring in nutrients, so the endplate allows some nutrients to flow into the disc via tiny pores. The front and back side of the disc are then covered by long dense ligaments called the anterior and posterior longitudinal ligaments which run the entire length of the spine and provide even more stability to the disc.
That was a lot of fancy terminology to describe a jelly doughnut huh? My point of that is to explain that there is A LOT of natural stability built around the discs. The common misconception that discs "slip" out of place is just wrong, so get that image out of your head. So what DOES happen then? Well, let's think back to our doughnut analogy. If you push down HARD AND FAST on a jelly-filled doughnut, the jelly is going to come smashing through the outside doughnut layer and squirt all over your shirt. The same can be said of a spinal disc. Too much compression too fast (like when you try to lift something WAY too heavy with bad form) will compress the disc so much that it will simply overpower the outside fibers of the annulus, they will rupture, and the nucleus will come spilling out. The difference is that instead of making your shirt dirty, that nucleus material is probably putting pressure on a spinal nerve or the spinal cord itself, causing the sharp, radiating back or neck pain most people associate with disc injuries. But this is the worst-case and oftentimes least likely scenario.
Disc Bulge Disc Herniation
Most times, all of the annulus fibers don't completely rupture and the compression isn't hard and fast. It is SLOW AND CONSTANT, for years and years at a time due to chronic poor posture, poor spinal stability, and poor nutrition/hydration to the discs. If you push down on the doughnut slow and steady, there won't be an immediate explosion of jelly, but after some time, the jelly will start to make it's way out as the dough gets deformed and compressed. Slow and steady compression of a disc due to gravity, improper disc loading, and poor nutrition/hydration will lead to a "flattening" of the disc because the disc is losing water, much like pushing down on a wet sponge. A few of the inside annulus fibers can be displaced outward as the nucleus material starts to push into the annulus, causing it to push outward slightly, aka a disc bulge. The constant pressure on the disc endplates will "close" the tiny pores where the nutrients flow to the disc, and the disc will start to degenerate over time. But that's normal, after all, we can't fight gravity 24/7. Compounded with poor nutrition, poor disc stability and loading strategies, and chronic poor posture, the disc degeneration will speed up and that bulge will continually get bigger. Some of the inner annular fibers can tear and the nucleus can now push into the annulus, but not all the way out of the disc yet. We call this a disc protrusion or herniation. At this point, we may start to see the disc getting close to a spinal nerve root or begin to push into the Posterior Longitudinal Ligament just in front of the spinal cord. Patients may start to experience intermittent pain, numbness or tingling, or a loss of muscle strength along the distribution of that particular nerve at this point. These discs are weaker than a healthy disc now, and it will take a less stressful activity to injure the disc. Instead of lifting 200 lbs with bad form to injure it, it might now take only 75-100 lbs.
If no intervention or treatment is done, the process continues until the nucleus finally breaks through the last layer of the annulus and now we have a disc extrusion or rupture. This is what most people think of as "slipping" or "blowing" a disc. They hear the characteristic "pop" sound and are in instant pain. That's because only the last outer few layers of the disc have nerve innervation to them, so when they tear, it's painful! The nucleus material is no longer bound by anything and is very hard to contain at this point. It is free to move into the spaces occupied by nerves. Little pieces of it may even break off and float away, and we call this a disc sequestration. These tend to be more serious and hard to manage cases, and MAY require surgery to remove the disc material from around the nerves.
Disc Extrusion/Rupture Disc Sequestration
So how do we prevent this stuff from happening in the first place?
The best strategy is to prevent early disc degeneration and injury in the first place!
Supplying the disc with good nutrition and hydration is key to maintaining proper tissue health and flexibility. Diets rich in inflammatory foods will lead to early tissue fibrosis and thus, the tissues being less healthy and flexible and more susceptible to injury.
Using proper disc loading strategies while exercising or performing normal daily activities will decrease the amount of stress placed on certain parts of a disc and allow the ENTIRE disc to resist the forces. Excessive anterior pelvic tilt and lumbar extension with a loaded spine like when carrying something heavy or squatting will create a shear force in the disc rather than a compressive force, which will load the disc unevenly and lead to problems!
Retraining proper disc and spinal stability is key to preventing overcompensation of muscles that improperly load the discs! Using our diaphragm to breathe and create Intra-Abdominal Pressure is the ONLY WAY to stabilize the spine and discs from the inside of the body. Without that pressure in front of the spine and discs, the low back and hip flexor muscles must take over stability, which puts the spine and pelvis into the vulnerable anterior pelvic tilt and excessive lumbar lordosis posture.
Lastly, don't let people scare you with findings on imaging!
If you don't have any pain, you can still have disc degeneration, bulges, and even herniations. It is a normal aging process that doesn't have a large correlation to pain! In fact, a study published by the American Journal of Neuroradiology shows that "The prevalence of disk degeneration in asymptomatic individuals increased from 37% of 20-year-old individuals to 96% of 80-year-old individuals. Disk bulge prevalence increased from 30% of those 20 years of age to 84% of those 80 years of age. Disk protrusion prevalence increased from 29% of those 20 years of age to 43% of those 80 years of age. The prevalence of annular fissure increased from 19% of those 20 years of age to 29% of those 80 years of age."
The most important word here is ASYMPTOMATIC! None of these 3110 study subjects had pain. Just because an MRI or x-ray shows the signs of disc degeneration does not mean you are doomed to a life of crippling back pain! YOU ARE NOT YOUR IMAGING! That is a static picture in time that tells us NOTHING about how you move, load, and stabilize your joints and tissues. Imaging should be used in conjunction with a good functional movement exam before determining need for further treatment!