The father, who cannot be identified, pleaded guilty yesterday to recklessly causing grievous bodily harm and two counts of assault.

The offences occurred in the family's home in the Port Stephens area last year.

The father will be sentenced in September.

He initially took an active role in the baby's care, but started to suffer what he called "brain snaps" when the baby cried, a statement of facts said.

The offender told his wife that he shouldn't be left alone with the baby because of his anger, but his wife told him he was being melodramatic.

The father, who now lives in Lake Macquarie, admitted to twisting the girl's leg and arm on separate occasions.

He was changing the baby in May last year when the girl urinated on a change table and continued crying.

The father twisted the girl's ankle and heard a "pop" sound near her knee.

The girl was later examined by a doctor and found to have a fracture in her leg.

The father initially denied any knowledge of how the girl suffered the injury, but confessed to police three days later.

The girl was removed from the mother's care, but has since been returned, the statement said.

The girl's ability to walk was reportedly delayed, but she was not expected to suffer any long term problems.