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My father, now in his 70's, had a left knee replacement several years ago. He has limited movement in that knee - probably about 85 degrees on a good day. His knee can extend fully, but cannot bend as much as it should. As a result, he cannot pedal a bike he cannot get his left leg over the top of the pedal stroke.

He is desperate to get back onto a bike, he knows he won't be ripping up the road and winning races like the old days, but wants the freedom to go for a slow easy rides.

Does anyone have suggestions as to a solution to the problem. We don't mind spending money if we know the solution will work, but he can't afford to throw big money at wild ideas that may or may not work. If we find a solution, a new bike is likely.

We have access several mountain bikes in a range of sizes to trail ideas, and we have all the tools and skills to build bikes up from parts and rearrange things as needed.

EDIT: Thanks everyone - all great suggestions. What am am going to do is got tto the LBS and get hold of a cheap set of short cranks for around $30- probably from a kids bike, in the 120-150 size range, and see if he can ride that. Depending how he goes, I'll try a standard right crank and a short left crank. If all else fails, we will go for the Power Cranks

UPDATE: In case anyone else has similar problems. Got some 152mm cranks for $30. Set an old mountain bike up with the seat as far back as possible. The old man is able to ride reasonably comfortably, now has a smile from ear to ear - any suggestions how to remove it - doesn't fit with the grumpy old man image :)

Has got me wondering how many people with minor knee problems would benefit from short(er) cranks.......

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You wondered how many people have this problem; I haven't had a knee replaced, but I have the same problem- I can't bend my knee enough at the top of the stroke to ride. I bet there are many out there w/ the same problem. –  user7321 Jun 26 '13 at 23:51
    
Really glad to hear this worked out. –  JamesBradbury Jun 27 '13 at 7:31
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3 Answers

up vote 5 down vote accepted

Look at Power Cranks. They are a crank set with the ability to freewheel independently of each other.

It allows a slow build to fully articulated movement if additional rehab is still a goal, and using each crank independently means using a bike is still possible, even if doing so uses a pedaling motion which would be awkward for someone who had an option for full movement.

They also have adjustable crank lengths on each independent arm, which would allow you to use a shorter crank on the leg with the limited movement.

They are often used as a rehab tool, are a real, readily available, and not ridiculously priced product, and are install-able with normal bicycle tools.

One caveat: They are shifting to a new poly carbonate fixing cap. If you order, I recommend requesting the old alloy fixing caps. The last set of poly caps I installed broke easily.

FTR, I have installed and used this product, and have no relationship with the manufacturer, nor will I be compensated in any way for this post.

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That's a brilliant suggestion. The reduced length should really help with reducing the angle required for knee bend. –  Mac Apr 20 '12 at 6:49
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Their website is hideous though! –  Mac Apr 20 '12 at 6:49
    
Thanks, the price may be a bit high, but otherwise looks like exactly what I am after. –  mattnz Apr 20 '12 at 7:07
    
@Mac: They are a brilliant product. The design is simple, mechanically, but ridiculously effective for rehab or training. They could definitely do with an image and marketing consultant though. :) –  zenbike Apr 20 '12 at 7:20
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I have also seen pictures, many years ago in an old bike book, of a crank with a pivoting piece. Basically, imagine the crank cut off at about the 2/3rds point, and then the cut-off piece reattached with a pivot. The crank would go down to the bottom of the stroke, but only come up a little over midway. (Kinda like a car on a Ferris wheel.)

Unfortunately, I have no idea if this is still made, or where you might find it.

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Is this any use? Very similar solution to the power cranks (I think) http://www.sjscycles.co.uk/thorn-crank-shorteners-prod239/

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Here's a similar product. –  R. Chung Apr 20 '12 at 15:47
    
Both of these product are effective for deciding on crank length if you want to try multiple length variations, but I wouldn't really trust them for a long term use installation. –  zenbike Apr 21 '12 at 9:20
    
You could probably get someone with the right tools to cut down a standard crank to the proper length, or just leave it at length and drill a new hole. –  Kibbee Jun 27 '13 at 1:04
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