I also just got back from the mall. The mall has many slopes and stairs. Not cripple friendly.
I hate slopes. Both slopes going up, and down. They are evil in their own way.
Stairs are safer for me than slopes. I have a physio appointment next Tuesday. I want her to help me with slopes.
By law, any "handicap friendly" slope can not be more than 4.8 degrees steep. One foot rise for 12 feet distance.
4.8 degrees feels very steep to me. Whether I am in a wheelchair, or using a prosthetic leg. Unfortunately the 1 in 12 is also the normal. That is the most economical for builders, so they tend to make all slopes 1 in 12.
To understand why slopes are bad for a prosthetic leg, you need to understand how a prosthetic leg works like a normal leg.
Here is a normal gait while walking.
My prosthetic knee is called a Mauch SnS. Mauch is pronounced "Mawk". The SnS stands for Stance and Swing. I can vary both the stance resistance and the swing resistance.
When the weight is on the heel, (the beginning of the "Stance" phase), the knee is a tiny bit over center, and won't collapse. This is called "extension". At the beginning of a step, when the heel strikes the ground in front of me, my knee is theoretically locked at full extension.
As I move forward, I must use my buttocks muscles to keep back pressure on the knee to make sure it stays extended and locked as I put more weight on it.
As I move forward, the weight gradually shifts to the toe. Weight on the toe pushes the knee farther back into hyper extension. The Mauch knee is designed with a tiny pendulum inside that detects when the leg is pushed into hyper extension. This pendulum unlocks the knee and allows it to flop about loose. The knee isn't 100% floppy. There is a resistance setting for the resistance of the bending of the knee, as I move forward. This is called "flexion" resistance. To little resistance and the knee will try to kick me in the ass. To much resistance and the knee won't bend far enough to use its weight to swing all the way forward when it is time for that. We are now at maximum flexion and enter the "Swing" phase.
Now the leg is free to swing forward. The resistance that I set for extension determines the resistance to the knee flopping forward. If this resistance is too little, the leg will snap forward with force. Like a kick. It makes me look like a Nazi goose stepper.
To much resistance and the leg won't swing far enough, and it won't be locked in full extension when I put weight on it when the heel hits. This is a guaranteed fall.
To me the swing forward is the most dangerous period of a gait. It the foot swinging forward touches the ground or is blocked, it will stop, and when I move my weight onto what I hope is a locked knee, there is no leg in front of me, and I will fall hard. This is called a "stumble".
If everything goes right, and I have the extension resistance set right, the leg swings forward into extension just as the heel hits the ground. End of swing phase.
Now lets see what happens on a down slope.
The heel strikes and locks the knee. But because of the down slope, the toe never touches the ground as I move forward, and the knee never goes into hyper extension, and never unlocks into swing mode. This means that as I am trying to swing the knee forward, it is still locked in full extension. The leg stays stiff, and I must swing it off to the side in an arc to get it around in front of me so I can put weight on it.
So on a down slope the leg will never get into swing mode.
On an up slope, the toe hits early, and the knee unlocks into swing mode while I am still putting weight on it, thinking I am still in the stance mode. Halfway into a step, the knee unlocks and I will fall if I am not expecting it.
This also will happen if there is an uneven floor. The toe may be on a rock or a raised tile. it will unlock early while I have weight on it, and am still thinking it is locked.
The opposite is also true. If the floor is uneven, and there is a depression where the toe should hit, then the knee will not go into hyper extension, and unlock. I will be trying to swing the leg forward, but it will still be locked straight.
One good feature of the Mauch Knee is that I can set it to stay in a mode.
I can make it stay in extension mode, so it will never bend. This is very secure and safe mode. I use it when I am standing for a long period of time, like doing dishes.
I can also make it stay in swing mode. This is useful for cycling.
There are many prosthetic knees on the market. They all are different, and do things in different ways. One I will get to test soon is the Total Knee 2000. It has a device that jams the knee whenever there is weight on the heel. Weight onto the toe releases the jam and allows the leg to swing. It is harder to use, but many athletes run with it.
The one feature it has that sets it apart, is that the mechanical linkages make the leg shorter on swing forward. This drastically reduces the chance of a stumble.
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18:00
I just got all padded up, and walked up and down the street in front of my house. .5km. I get very tired.
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