Several months ago I blogged a study that showed that patients who got a knee replacement and who had low back pain were less likely to have a good outcome. The connection between low back and knee pain didn’t surprise us one bit, as we’ve known for about this relationship for years. Now yet another study shows the same thing: if you have back pain and want a knee replacement, your results won’t be as good.
The Prior Study
Let’s first review the prior study that showed lesser knee replacement outcomes in patients with back pain. The study data was collected via a spine-function questionnaire completed by almost 700 patients with knee replacements. Over half of the patients (54%) questioned responded that they had low-back pain daily. Further, patients who did not report back pain reported good replacement results, while patients who did report low back pain reported knee replacement outcomes that were significantly poorer than those without back pain. Another interesting finding is that before the knee replacement, patients with low back pain also had a lower function score in the knee and more pain.
Many orthopedic surgeons, when working up a knee, ignore the low back and don’t determine if it might have something to do with the knee pain. So as a patient, it’s important to understand that poor knee replacement outcomes can result when the knee issue is accompanied by low back pain.
How Low Back and Knee Pain Are Connected
While knee pain symptoms may only be felt in the knee, the back is often the culprit due to misfiring nerves and a variety of spinal issues. The L5 nerve, for example, branches off the spine down along the hip and hamstrings past the knee and all the way down into the foot. So you can see how a disc bulge at L5–S1 could irritate the nerve at the spine, but this irritation can travel through the entire nerve branch, causing issues in the hamstrings, knee, and even into the foot. It’s easy to see why a knee replacement won’t be able to address your pain if your knee pain is caused by a problem in your spine. So could your back be causing your knee pain? There are three signs you should look for:
Do you have pain or occasional twinges in your low back and knee pain? The lower-extremity nerves branch off of the lower spine. So a pinched nerve or disc problem, for example, could send pain signals down that branch of nerves and into the knee. It’s important to note here that back pain will not always be felt (I had an issue with knee pain that was due to my back, though back pain wasn’t a big issue), despite irritated back nerves causing knee pain. So you should have a physician that understands these connections check your spinal nerves regardless of whether or not you have back pain.
Are you experiencing any tightness in your hamstrings? The L5 nerve branches off the lumbar spine and down through the outside hamstring muscle. So tight, inflamed, or painful hamstrings can be one of the first signs there is a nerve issue in your back. This chronic tightness can lead to knee problems, as the hamstrings are supposed to pull the knee meniscus out of the way during movement. When this doesn’t happen, the meniscus can get crunched.
Do you have bunions? If you have low back issues accompanied by bunions, you may also have knee pain. The lower lumbar nerves travel down from the spine to muscles that stabilize the foot. The stabilizing muscles in the foot can weaken when there is a problem in the low back, and this can cause bunions. This same lack of stability in the foot can lead to the forces in the knee that can wreck it over time.
The New Study
The new study involved patients over the age of 65 who had either knee arthritis with preoperative low back pain or knee arthritis with no back pain. The study looked at the knee replacement outcomes of both groups. Those patients with preoperative low back pain reported worse results and less satisfaction following surgery, and this was related to the intensity of the back pain, drawing a clear connection between the status of the back and the knee.
The upshot? Many times, low back and knee pain are connected, but one or the other is often ignored. You may not feel you have a back problem, but that doesn’t mean that irritated nerves in the spine aren’t messing with how the knee functions. Hence, if you have a low back problem, get that issue handled before you consider getting your knee treated!