It is pretty simple to understand

the cushioned linings of my knees are pretty much gone - the upper and lower parts of the knee rub bone on bone. That works OK but feels 'kinda gritty and "not quite right" as I walk. I've learned to ignore most of the slightly unpleasant symptoms and feelings.

occasionally a small piece of bone or something else breaks or chips off inside the knee joint. That chip (I've commonly heard them called "joint mice") tears the lining of the knee. The knee then fills up with fluid and knee motion becomes very limited due to hydraulic locking. The knee joint can't bend because the fluid in it will not compress.

If I have really bad luck the chip lodges in the joint and mechanically locks the joint. If I wiggle and flex the knee enough (painful!) the chip moves to a less painful location.

From the outside the knee begins to look swollen and eventually resembles a small American football. The pressure in the knee is somewhat painful while the knee is stationary and becomes progressively more severe as I try to bend it.

For example - two weeks ago today I was sitting in the cockpit of my boat replacing the tube in one of my mountain bike tires. I was pumping up the tire while seated. The tube blew up with a very loud bang which startled me. I jumped to my feet and it felt like someone had stuck an ice pick in the back of my knee. When I tried to wiggle the knee the ice pick sensation intensified.

Within 24 hours the knee was so swollen I had only about 60 degrees of motion in the knee. Walking is very difficult when the knee will not come within 15 degrees of going straight. Typically the swelling continues to worsen for about 36 hours. If the swelling is too great I go to my bone doc who sticks a really big needle in the joint and drains off a coffee cup of bloody fluid. That is a huge relief,

By Tuesday afternoon the swelling was down enough I could limp along without to much distress and that is when I raised my bike seat and started gently spinning the pedals.

By the next Saturday (8 days after the ice pick) I rode 62 miles on the road bike with only minor distress in the knee.

These episodes of joint mice tearing the knee lining occur with no apparent cause in both knees.

As long as I keep my weight down and ride the bikes a lot the knee swelling only occurs once or twice a year.

The big problem is when the joint mice bite the knee during a bike ride. That has happened several times and is a real problem.

five years ago - 30 miles from home on my road bike - in the country where I had not seen a house or car for five minutes - I stopped to take a picture - pushed off with my right foot and POW - my right knee locked - I could only bend it about 20 degrees. I was able to wiggle and flex my knee enough to get the offending piece in the knee to move to a less painful and motion limiting location. I was able to take a 22 mile short cut home. Next day the knee was the most swollen I have ever seen it.

20 years ago on the mountain bike - in the Cascade mountains 10 miles from the trailhead a knee locked up and would not loosen up. It was mostly downhill but I could not bend the knee enough to put in on the pedal. I was riding by myself so I could whine and cry all I wanted as I rode with one leg or limped on one leg using the bike as a crutch.

Bottom Line - 99% of the time my knees are sore but work OK - occasionally one or the other knee locks up, either mechanically or hydraulically, and I have 3 to 6 days of sore stiff annoyance.

Here is a link to an X-ray of a knee joint with a chip lodged in it - it is part of an article by a long distance bicyclist and his problems with knees

http://www.google.com/imgres?hl=en&s...r:15,s:0,i:105