Walker agreed that CPR attempts the night she collapsed could be responsible for the abnormal readings on the ribs. The bone in the back, L1, could have been broken then too. The L1 was the only fracture as confirmed by xrays. In his testimony, Walker concedes that this was the only broken bone in the scope of the bone scan he reviewed. Bone scans are based on a body's metabolism and not bone structure.
Other causes of abnormalities in the bone scan were given on the report.
"Additional possibility would be neoplastic bone disease, widespread disseminated infectious bone disease or multiple bone infarcts from abnormal hemoglobin."
As stated in the autopsy, Terri had a markedly reduced hemoglobin as a result of treatment given her immediately following her collapse.
Dr. Walker is talking about possibilities, not known facts. All perfectly reasonable, docs consider various causes. But keep in mind that while such injuries via CPR are possible, the probability that it happened that way is near zero. (Same with "bulimia" -- the odds against it were absolutely astronomical.)
Now think a bit. Suppose it was CPR -- then we don't have a cause for Terri's collapse. Why would she need CPR, if not for the injuries shown by the bone scan? No other cause is known or even suspected.
The bone scan offers a solid explanation. It is fully consistent with all the known facts and with Occam's razor. You don't need to look further and try to evade the obvious.