Internal bras had always been composed of lattice (pigskin) sewn into the epidermal skin on the underside of the implant in a sling like form. The opposing ends are supported by braided suture that is normally affixed to bone with titanium screws. While the medial screw is often placed in the first rib close to the sternum for support, the lateral is usually in rib depending upon the height of the implant.
That said, when implants are above a subjective weight, the stress on a lateral rib could prove too much, so the anterior shoulder would prove a far sturdier structure.
Beshine has never to my knowledge acknowledged having an internal bra, only saying that she does not require support from her bras, essentially admitting that her implants are affixed to bone. These are not traditional expanders in size or structure, but the weight would have them sagging extremely today if not anchored. In one OF video, she goes into exactly what her custom made bras are designed to do and it has nothing to do with lifting.
You probably noticed the right medial cord under her skin; it is that raised thin line going from her breast to the first rib. Normally, it should be pressing against her ribs, but I have hypothesized that the lattice slipped out of place before it naturally grew into her skin. This would also explain the wide indentation on her lateral (sideboob) that reflected the typical width of lattice used in a bra.
The right medial cord has been visible all along and in some videos, you can see it move under the skin when she moves in a way where her breast would sway one way or another. Like I said, it is like a sling or hammock; the breast can swing left or right or even upward, but not downward below what the suture cords allow. Hence, as she has expanded her implants, expansion will be seen in every direction except downward; the crest of her boobs is inches higher than in the picture from 2011, despite her forearms boosting them higher.
You virtually never see the lateral cords today, but in the early years, even in 2011, if she used her arms to hoist her boobs higher, you could suddenly see those thin suture lines, heading right for the anterior shoulder, just like the literature mentions for securing really heavy implants.
I would bet that Beshine sought out a very competent surgeon who fully understood the size and weight each implant would become if she filled them to capacity. Sutures are common in surgery, using braided suture is not, but I was told it can be made to hold a few hundred pounds reliably if necessary. Still, I cannot imagine any surgeon would be willing to insert implants of this potential size without being dissolved of all potential legal complications. Someone asked how she found a surgeon and her reply was along the lines that it isn't difficult when you offer enough money. Obviously, the same can be said for her implants; no one else has found a manufacturer willing to make enormous custom implants, but they probably haven't been starting the conversation from a no bargaining "I want custom implants regardless of cost."
I would also expect that she did get a second pair of implants, just in case.