TKR: Dangers of over-flexing

[Josephine]

When I play with the artificial knees on display in the doc's office, it appears that full flex is past the wear portion. Is there any chance that I could overflex and have it stick? That would be horrendous.

Of course you can get a full flex with the implants in your hand - there are no soft tissues to restrict them! Do remember this isn't just a mechanical issue. It's also biomechanical and that changes the goal posts extraordinarily. I could now write reams of stuff about the parts the muscles and ligaments play in this, not to mention the fascia, retinaculum, fat and skin but I won't! 155 is the extreme limit of the device outside the body. Inside you have to accept what your leg can allow. And as Kelly says, the risk of damage to the plastic insert is considerable at that angle so I would caution against it. The chances of it 'sticking' are remote.

My natural knee is hypermobile and slides a bit back during full flex alleviating so much stretching the ligaments. Will the extra flex be too much stretch and allow my knee to pop out?

Something you need to be aware of when flexing your knee is that the 'popping out' is only an issue if the flexion is too extreme and the plastic insert is squidged out of place like a seed out of a grape when you squeeze it!

But damaging the plastic insert is much more of an issue and a more realistic one at that.
Have a look at this to see the kind of thing that can happen!