cause of acute Back pain with chills in legs

15 days back my mother F-65, has undergone angioplasty primary PTCA 1stent. for 1st 10 days she had mild fever (98.5 F to 100.5). which came with back pain along with occasional chill and pain in legs. No recurrance of chest pain,cough, breathing discomfort. she was put on a 6 day course of antibiotics.

Now since last 5 days fever has gone but there is acute back pain and ocasional chill in lower legs.

She is daibetic with Fasting sugar level at 225 and PP at 345 levels, BP is 135 - 68, and she has thyroid problem with Free T3 is 2.42 pg/mL Free T4 is 0.9 ng/dl and TSH is 4.64 microIU/ml, her currect Hb level is 7.4 Gm/dl

blood test and urine tests and an ultrasound of place of incersion were negative for any infection.

Can anyone suggest?

[Cleveland Clinic]

The only way that the PTCA caused the fever, is if in the closure of the arterial wall a closure device was used which subsequently got infected. I would look at his groins to make sure there was no infection ( redness, swelling or tenderness).
There are other causes of fever, possibly relating to lung problems, or urinary tract infection, possibly related to the foley catheter used.