Hello, I'm new on this forum and I need your help.

Last sunday, after a break of 3 weeks without cycling, I did 45 min on my home trainer and a knee pain immediatly appear after. The result: my doctor diagnostic me a tendinistis on the muscle behing my knee.

Here my background: around 10 years ago, I had a major surgery on my femur. At this moment, my right leg was 3'' shorter than the left one so the surgery consist on increasing my right femur lenght.

SO to summarize it: now, my both legs are equal BUT my right femur is around 2'' longer.

Or course, my bike positionning is done based on my left leg and that's why I'm having problem with my right knee.

Is there somebody with a similar problem (lenght discrepency) and what do you do to prevent injury (modification to your bike, exercice, see doctor etc).

Thank you very much for your help. I know my situation is complicated but I'm sure there is something to do.

I don't have an answer but I am curious if you could help your situation if you have different length cranks on one side such as run 170 on one side and 175 on the other. Pure speculation on my part.

You need to find a professional bike fitter, ideally one who has experience as a physical therapist and has done a lot of fitting on different riders.

Are your knees the same height? I have a similar problem with my left leg being shorter below the knee. I compensate by adjusting my shoes to make my legs as level as possible. I take the insole out of my right shoe and add insole to my left. (Before anyone suggests orthodics, if my left leg would keep its adjustment I would not have this problem)
The problem affects my right IT band especially from extended walking.

oldokie's suggestion is a great one too. Some crank arms are available in 172.5 mm length also.

You don't want to use different length cranks, because the pedal circumference will be different on each side. Instead you want to use the same length crank, but you either need spacers on your short leg or your longer leg needs a custom pedal drop extender that lengthens the reach. Think about it, it will have the same pedal circumference on both sides.

Speedplay pedals offer an reasonably priced way to add spacers between the shoe and pedal
https://www.speedplay.com/index.cfm?f...home.zeroshims

or check out the axle extenders here:
https://www.hscycle.com/Pages/cantsandwedges.html
these are expensive tho.

I don't think I get it. By using raisers the foot circumference would be equal using missized cranks OR spacers. Either way it would feel the same.

Maelstrom, here's a more elaborate explanation.

The crank length determines the pedal circumference. Using a shorter crank makes a smaller circle. However, using the same length cranks with a spacer (or a pedal drop extension) will have the same circle circumference. The spacer (or drop) is only changing the foot's OFFSET to the pedal.

Or think of it this way. Let's look at the side of the bike with the shorter leg.
Imagine taping a marker on the bottom of your shoe, marker facing to the side, away from the bike. Then imagine putting a sheet of white cardboard parralel to the bike, so the marker can draw a circle on it.

So using a shorter crank, draw a circle . Lets call this Circle A. (the bottom bracket will be the center of circle A)
Now put on a longer crank, the same size as the other side, and add a spacer between the marker and the pedal. ( with the spacer width the same as the crank length difference ). Now draw a new circle, let's call it Circle B.

This circle B will be larger and it will touch circle A at the bottom (near the ground). However, on the upstroke, circle B will come higher than Circle A. Or in other words both knees come to the same height on the upstroke.
If you used a shorter crank, the leg extension would be the same, but the knee would not come up as high as the other side.

Get it?

This is healthier for your body, because the muscles stay in symmetry and keep the same range of motion.

By the way, Benoit,
I reread your post more carefully and honestly i'm not sure what you should do, you have a case i've never heard of, and like eric said i'd get doctors advice.

Used to know a guy who had similiar problems....he ended up with 2 different crank lengths...but like was suggested in earlier post, I'd get the input of a good physical therapist...self treatment might make things worse....

good luck.

powercranks adjustable "adjustable length crank which easily changes from 85mm to 220mm"

www.powercranks.com

much less stress on your knees as you're reliant on a lot more muscles and the power is spread smoothly across the whole pedal stroke rather than just mashing or pedalling squares

https://www.pezcyclingnews.com/defaul...lstory&id=4331

https://www.bikeforums.net/showthread...ht=powercranks

Eddie Merckx had the same problem, and never knew it until his son was diagnosed with the problem. You can read about fit for leg length discrepancies in Andy Pruitt's Complete Medical Guide for Cyclists.

One of the problems I see here is the femur length is different. This would indicate that you need to have two different fore-aft seat positions. Having the saddle too far forward tends to hurt the ligament & tendons behind the knee above the calf. While having the saddle too far back tends to hurt the knees in front (above & below the kneecap).