"About 20 per cent of these children have other fractures as well, especially rib fractures.
"Outpatients - usually brought in by CYF [Child, Youth and Family] or the police - are usually older children who present with soft-tissue injuries: black eyes, bruising, patterned marks from being slapped or struck with an object."
Dr Kelly said the perpetrator of the abuse was "very variable".
"Like most centres, our anecdotal experience is that male offenders are more common than female offenders, and non-biologically related males - 'stepfathers' - are disproportionately represented," he said.
"However, with very young infants the offender sometimes cannot be reliably identified, and in very young infants the mother can often be the offender, particularly if there are issues like postnatal depression."
Dr Kelly said the cause of most of the abuse-related deaths at the Starship was head injuries "by far".
"Second would be abdominal trauma - children who are kicked or stomped on, but these children tend not to survive to [be admitted to] hospital and come to the pathologists," he said.
Those children were not included in the statistics because the victims were not treated or admitted.
Dr Kelly said it was hard to say why the number presenting at the Starship hospital with injuries consistent with abuse was increasing. "What is clear is that despite all the societal angst and all the expressed interest in intervention and prevention, the incidence is certainly not going down," he said.
Possible contributing factors were family violence, the increase in social inequality in New Zealand and alcohol abuse stemming from a "flood of cheap alcohol".
"We are not good at early intervention," he added.
In 2003 a Unicef Innocenti Research Centre report card, published to monitor the performance of nations in meeting the needs of their children, put New Zealand near the bottom of the OECD countries.
Said Dr Kelly: "As far as I am aware that hasn't changed significantly."