The OP, Dick Howard mentioned his issue concerning range of motion after his knee replacement surgery and asked whether crank arm length may be the cause of his problem.
There have been a number of good suggestions but recovering range of motion can be a long long process especially with something as major as a full hip or knee replacement.
The intent of these kinds of orthopedic operations is to restore mobility and relieve chronic pain not necessarily athleticism.
When I asked my orthopedic surgeon about cycling after my operation, he thought it was a great idea, envisioning short rides around the block not 25-50 miles jaunts!
There are too many other possibilities besides crank arm length that should be considered first. I doubt that changing to 5mm shorter cranks - less than 1/4" difference - is going to make that much of a difference.
There are nerve endings throughout all of our joints that continuously send feedback to our brains tracking the position of the joint. With these kinds of orthopedic surgeries all of the nerves in the joints are removed along with the feed back to the brain.
No nerves, no more pain but there's also a reduction in balance, coordination and range of motion.
The human body is amazing and can compensate (to a degree) for these losses.
Dick didn't mention his height, bike size, type of riding, gearing, pedals, shoes, cleats and so on.
When getting back into riding (especially when over 40) it's wise to start off easy, riding lower gears on flat rides and avoiding hills until you build up strength.
You will probably have to alter your riding style too for example, more spinning and much less mashing.
You may need to try a pedal extender for the affected side.
Since there are no nerves in the area of the surgery, you can't feel if you are doing something wrong and can easily injure the new tissue attachments to the area.
The orientation of your lower leg compared to where it's been all of your life may have changed too. My right foot is splayed out about 10° more after my hip replacement.
I think that starting off with lower gears, lowering your seat and using pedals that allow your feet to move around are far more important than crank arm length.
When you hear hoof beats, think horses, not zebras!
Chas. Colerich Oakland, CA USA
RICHARD HOWARD wrote:
> I am 65 years old and have been using 175 mm cranks since my first real bike in
> 1967. I have had a total knee replacement and lost enough range of motion in
> the affected knee that it impacts on my ability to ride smoothly. The problem
> is mostly at the 12 o'clock position of the affected crank arm. It is a struggle
> to power over the top. I am thinking about switching to 170 mm cranks or even
> 165mm. Considering the skeletal shrinkage that also automatically comes with old
> age, I am thinking that 165 may be optimal. Has anyone else had a problem
> similar to this? Did you create any new problems for yourself while solving the
> targeted problem?
> Dick Howard
> Roanoke, Virginia
> USA