[read time ~ 5 minutes]
Paul sat across the table from me at our favorite restaurant. He slumped to one side, gazing down at his empty appetizer plate and moved a few remaining crumbs around with his fork. It seemed obvious that something was bothering him, so I asked if anything was on his mind.
“Yeah, my knees hurt; they really hurt. And I don’t know why.”
Paul was semi-retired. He worked as a consultant and loved to travel. He recently returned from a two week backpacking trip that included both camping and fishing--two activities that he loved.
My immediate reaction was empathy. “Oh, man, I’m sorry… When did that start?”
“Yesterday,” Paul responded, sitting up a bit. “I don’t get it. I was fine on my last trip and I’ve felt fine landscaping my yard since I’ve been back.”
“Oh, that’s right,” I said, as I remembered he was having a load of mulch and some small limestone boulders delivered last Saturday. “How does your yard look?”
Paul brightened up a bit: “It looks fantastic. Just in time for this great weather we’re having. It’s so nice to sit out there in the evenings. But now, my knees are aching so much….” He looked down again with disgust.
“So you felt fine on your trip, and you felt fine last weekend when you were weeding, mulching, and arranging the rocks?”
I felt myself shifting into detective mode. “So when exactly did your knees start hurting?”
A little anger crept into his voice. “Monday evening when I was doing nothing! My wife and I were just sitting outside on the patio...” Paul paused, shaking his head. His knee pain seemed rather mysterious.
One of the most frustrating things about hurting is not knowing why you hurt.
If you step on something sharp while walking barefoot, the pain causes you to spontaneously lift your foot away from the sharp object. This is because there are a lot of sensors in skin. And these sensors are connected to pathways called nerves--the structures that serve as the information superhighways of our bodies-- delivering messages to the brain. Nerves also deliver messages from muscles and from bones.
Pain is felt when messages from the sensors within various body parts travel via nerves to the brain.
But some body parts can be harmed without immediate pain because some body parts don’t have nerves.
Without nerves, there is no way to immediately tell the brain that harm is happening. Cartilage is an example of a body part without nerves.
Cartilage is a tough substance that covers the end of the bones in your body—found in your hip, shoulder, knee, and other joints. So you can be hurting your cartilage without knowing it--at least for a while.
When harm happens to the cartilage incredibly tiny particles of cartilage shear off. They are microscopic and too small to initially be seen on imaging studies like X-rays or MRIs. These tiny particles of cartilage float around inside the joint until they eventually contact the joint lining. It may take several hours or as long as a couple of days for this to happen.
When the tiny particles of sheared-off cartilage contact the joint lining, they cause irritation and inflammation. Since the joint lining has access to nerves, messages about this irritation and inflammation are sent to the brain, and pain is finally felt.
When cartilage is damaged, pain results, but not necessarily right away. (That’s why it often feels mysterious.)
Paul probably harmed the cartilage in his knees during his weekend landscaping project. What likely happened is microscopic particles of cartilage inside his knee sheared off as he was squatting and lifting heavy rocks. He didn’t immediately feel pain because cartilage doesn’t have nerves to deliver pain messages to the brain.
However, a day or two later, the tiny particles of cartilage that sheared off contacted the joint lining--a body part that does have nerves. And by Monday evening, the nerves from the joint lining delivered pain messages to the brain at a moment when he wasn’t doing anything harmful--when he was simply relaxing in his backyard.
The Mystery of Delayed Pain, Explained:
Pain is felt immediately when the body part being harmed has access to nerves (the superhighways that deliver pain messages to the brain).
Body parts that don’t have nerves--like cartilage--can be hurt without immediately knowing it.
When cartilage is harmed, eventually sheared-off microscopic pieces of the cartilage irritate the nearby joint lining, and this joint lining sends pain messages to the brain via nerves.
Read more about delayed knee pain: The 90 Day Knee Arthritis Remedy.