Unlike the days when life was simpler and we slept soundly awakened by the sun, many things contribute to our modern epidemic of poor sleep. That said, I think most of us can agree that pain makes sleep very difficult. Given what the vast majority of our patients present with, this study on knee and back pain and sleep caught my attention.
It would seem that lying down, rather than being erect would be much more comfortable for people with back pain, and is for many. It really depends on what’s causing the back pain. There are specific back problems like Spinal Stenosis, or Ankylosing Spondylitis (where back vertebrae fuse together) that are more painful when lying down. But other issues like inflammation can be made worse by being in a prone position for long periods of time as well. With arthritis, joint linings can become congested with excess fluid whose purpose is to bathe the cells, and protein waste products, when joints are not moving for long periods of time. While these waste products are normal byproducts of the joint, they’re routinely flushed away. However, due to immobility, these processes are slowed down at night and can lead to pain and stiffness in your arthritic knees, or arthritic back, awakening you, or preventing you from falling asleep in the first place.
There are also other issues like instability, which can make lying down all night in certain positions more painful for knees or backs. Your spine is like a series of blocks threaded on a string. Muscles and ligaments hold the vertebrae in position as we move. When muscles like the multifidus and ligaments that work like duct tape to hold the vertebrae in place are severely stretched or injured, the vertebrae can move ever so slightly out of position. When erect, gravity is pulling downward, with your vertebrae stacked like a tower. When lying down however, muscles relax and gravity is pulling the vertebrae laterally. If there is enough lack of stability caused by loose ligaments, atrophied multifidus muscles, or degenerated discs, this micro-movement while lying down can be quite painful in of itself and also cause painful spasms. A mattress that can create enough external support may help.
With knees, while the symptoms may only be felt in the knee, knee pain often originates in the back due to misfiring nerves caused by a host of issues. One of those issues is with the L5 nerve which goes to the outside hamstring muscle also known as the biceps femoris. If there is a disc bulge at L5-S1 it irritates the exiting L5 nerve which makes the lateral hamstrings tight, which in turn impacts how the knee joint works. While getting up to a standing position, the tight hamstrings muscle doesn’t allow the femur to get out of the way of the meniscus effectively, pinching the meniscus. Left untreated, this type of problem often causes a tear and cartilage defect in the lateral posterior meniscus and femoral condyle, not a pretty picture, so treating these problems is essential. If you do have night time knee pain, putting a pillow under your knee to keep it supported in a slightly bent position, may provide enough support to make sleeping more comfortable.
The new research was a large questionnaire study of 9,611 subjects ages 39-67. 29% of the subjects had knee pain, 42% had back pain and 17.6% had both knee and back pain. Lack of sleep was defined as less than 6 hours a day, and both sleep quality and knee pain and back pain were evaluated by Yes and No questions and metrics were applied to correlate the results. Unsurprisingly, both knee pain and back pain negatively affected both duration and quality of sleep. In addition, having both knee and back pain had an additive correlation and created the most negative effect on sleep.
The upshot? There is a lot going on there. This was a study to determine the general effect of knee and back pain on sleep. There were no indications on the sources of knee or back pain, or any attempt to determine how particular knee or back problems affect sleep. There are a few organ related medical issues that can also cause worsening back pain when lying down, so if the problem gets worse and you don’t have a known back problem, getting cleared by a physician could be a good idea. In the meantime, handle small back and knee issues when they come up, so they don’t become bigger ones!