But, old fractures would be classified as antemortem (before death) trauma to the bones and the ME already stated that there was no evidence of this. What remains to be commented on by the ME is perimortem (at or near the time of death) and postmortem (after death) trauma to the bones.
Since the latter were never commented on in the ME's press conference there's a chance that the report could include evidence concerning these types of bone trauma.
Antemortem bone trauma is differentiated from the other types by evidence of healing having occurred, as in prior abuse. If trauma was found to be peri- or postmortem it is due to the lack evidence showing that healing has taken place. Further criteria differentiate peri from postmortem trauma.
A hypothetical situation could be that KC struck out at Caylee in a rage causing broken bones and massive internal hemmorhage. She died very quickly and the bones would show no evidence of healing. The ME couldn't rule the cause of death to be a broken rib or a broken ulna nor could she state that the cause of death was internal hemmorhage because she didn't have tissue with which to conclude this. She could, however, find perimortem trauma to bones. This, along with the duct tape placement would be enough for her to be confident in ruling the death a homicide.
She may even be able to give her opinion that the bones that were broken resulted from a force so great that trauma to other areas was likely and may have caused death. For instance, children rarely break a rib because they are very pliable. Most cases of broken ribs in children are the result of child abuse or mva. For a child to present with multiple broken ribs, major blunt force trauma to the chest wall would have to occur. This type of injury could result in any number of fatal injuries. KC wouldn't have a chance if the ME found multiple ribs with perimortem trauma. Nothing short of a massive blow could cause this.
Sorry to ramble but, since the As have tried to block the release of this autopsy I've thought of all kinds of things it could include. Until the ME rules out peri or post mortem trauma to the bones there are many possibilities. Something in that report has them very worried.