Referred Knee Pain
Let's talk today about the concept of referred knee pain, that is, pain that seems to be coming from
the affected knee joint, but in reality is coming from somewhere else. Many times in my practice, I would see a patient that complained of
knee pain, only to find,
after a thorough workup, that there was no observable knee pathology. These cases were invariably frustrating for both the patient and for me.
If you're the patient, all you know is that your knee hurts and here's this guy telling you that it isn't your knee. What are you supposed to think?
The first principle is that all joint pain, like water, flows "downhill." In other words, the cause of the
referred pain has to come from ABOVE the affected joint. An injured ankle generally doesn't refer pain
up to the knee, unless you've also injured that knee. With this principle in mind, let's consider a few other problems that are known to mimic knee pain.
Back problems, especially herniated discs, can refer pain to the knee on the
side of the herniation. This is most common at the L3-4 or L4-5 levels in the lumbar spine. That means that the disc that lies between
the 3rd and 4th lumbar vertebrae has squished out its jelly-like core (the "nucleus pulposis"), like toothpaste out of a tube, into the spinal canal, or the foramen ("window" in Latin) where the nerve
roots emerge. This herniated disc material applies pressure on the spinal cord, or a specific nerve root,
on its way to the knee. You would then feel the pain in the knee joint, because the nerves going
into the joint are irritated or compressed, even though there's no pathology in the knee joint.
In the same way, a tendinitis, an inflammation of the long muscle in front of your thigh,
femoris, (Figure 1-E) can present with knee pain. A doctor can often differentiate this from true knee
pain by examining the upper attachment of the muscle tendon at the "point" of the hip (the anterior
inferior iliac spine). Its next door neighbor, the Sartorius muscle (Figure 1-D), is attached just above it, at
the anterior superior iliac spine, and it, too, can refer pain to the inner (medial) side of the knee joint
The hip joint, too, can refer pain to the knee. In fact, one of the most common errors made by Family
Practicioners, Internists, Chiropractors and even some orthopaedists, is to fail to evaluate and x-ray the
hip joint, when a patient comes in for a knee problem. It was always a favorite Orthopaedic Board Exam
I can't tell you how many times I found unsuspected arthritis of the hip, when a patient came in
complaining of knee pain. They were always skeptical when I recommended x-rays of the hip joint
in addition to those of the knee (probably figured I was "padding" their bill), but they were always
amazed when I solved their problem, by identifying and then treating hip disease that everyone else
The most common reason that it had been missed is "Tunnel Vision." It's very common for everyone,
including the doctor, to focus on the apparent site of pain, and fail to consider the other possible
sources of those symptoms. So, if you are ever in to see the doctor for your painful knee, be sure he or
she at least considers, and preferably examines, your hip and your back, especially if your knee exam
and x-rays don't readily disclose the reason for your pain. If they don't, you haven't had a complete
evaluation of your knee. If they don't look, they won't find the cause in those few cases where the pain