Como dizer "ceder o silicone" em inglês

A palavra mais usada no momento quando uma operação foi feita de forma errada é botched. Inclusive é nome de uma série popular de TV. Mas de forma geral podemos falar:

"a botched breast implant."
"a botched boob job." (informal)
"a breast augmentation gone wrong."
"breast implant complications."

Tecnicamente pode-se falar de Implant Malposition, e no caso de ficar mais baixo do que deveria, pode-se falar:

Low Malposition
An implant that sits too low, called bottoming out, can occur when the implant pocket is formed too low on the chest. It can also occur when an implant pushes down on the breast tissues, despite a properly placed pocket. This can occur if the breast lacks strong support attachments in the breast fold or if these attachments were released too much during surgery. Large implants have a greater risk of bottoming out due to their weight.

Fonte: 77plasticsurgery

Agora para sua pergunta

Quando colocamos prótese de silicone no seio e ela cede… como dizemos isso em inglês?

Se for uma queda natural, conforme texto Low Malposition acima, destaco a seguinte parte:

"It can also occur when an implant pushes down on the breast tissues, despite a properly placed pocket." Podemos falar mais tecnicamente, conforme figura acima, também de:
"Bottoming out"
"Capsule contracture"
"Mastopexy augmentation"
"Fold malposition"

Fonte: doctorcorey Quando o implante cede com o tempo, devido à idade, gravidez, integridade da pele, etc:

"breast droop"

Fonte: brisbaneplasticsurgery

Espero ter ajudado

Some of the likely complaints or complications studied about silicone implants/prostheses:
Assimetry - in terms of shape, size, and breast level.
Contracture - tightening around the tissue around the implant capsule. It is a stretching of the skin, somehow.
Deflation - due to leakage, sometimes one breast seems to have sagged or is asymmetrical.

I think the "ceder" you have mentioned could be just a "displacement" (the silicon implant has somehow shifted/moved around a bit), so it has to be readjusted by the plastic surgeon.