Basically, Terri had serious injuries (fractured femur, etc.) for which there is no apparent innocent explanation, and which Michael, when he discovered them, was unconcerned about.
Terri's bones suffered damage somehow, and the most plausible explanation would be that Michael damaged them.
Was this before or after her brain damage caused by the "chemical imbalance"?
This is very significant. And it reminds me of the flaw in the "heart attack" theory. She had such a vulnerable heart at 26? But no problems since? Same with the bones. If she had such vulnerable bones in 1990, then there should have been plenty more pathology in the years that followed. Bone diseases don't go away.