Tegwen Roderick from Abercanaid, Merthyr Tydfil, died from blood poisoning at Ysbyty Cwm Cynon, Mountain Ash, in May 2014.
Coroner Dr Sarah-Jayne Richards said her treatment was "substandard across several different levels of care".
The Aberdare inquest heard staff shortages had been blamed.
Dr Richards ordered a review of changes implemented by Cwm Taf health board following the death.
She said the case was "complex" as Mrs Roderick had many clinical problems, including dementia and a condition which led to the weakening of her bones.
"The view has been expressed that often nursing care was provided but simply not recorded or that writing was illegible - either way this is unacceptable and in breach of hospital policy and the duty of care that was owed to Mrs Roderick," she said.
The coroner said care was substandard, highlighting the monitoring of Mrs Roderick's fluids and dressing changes.
Her family also expressed concerns about staff knowledge of lifting and handling, nutrition, hydration and dementia.
Mrs Roderick was initially admitted to Prince Charles Hospital , Merthyr Tydfil on 3 April 2014 with a suspected broken left leg after a fall.
She was transferred to Ysbyty Cwm Cynon on 18 April with a view to her returning home.
But on 19 May an unexplained "open wound" fracture to her other leg was discovered and her health deteriorated.
Four people were arrested on suspicion of assault and conspiring to pervert the course of justice, but there was 'insufficient evidence to prosecute for gross negligence manslaughter', according to the Crown Prosecution Service.
The health board's assistant director Jason Roberts said staff levels were above national minimum guidelines and the manager of the ward has been put on a development programme.
An 88-year-old woman who died after being admitted to hospital with a broken leg received "deficient nursing care", an inquest has found.