Chances of recurrence of septic arthritis in sternalclavicular joint. 2 surg to clean and debride and 1 surg removing cartilage 5 months IV antibiotic?

Low likelihood. Sternal clavicular septic arthritis is an unusual form of septic arthritis generally seen in diabetics. It is usually caused by Staphylococcus aureus though Gram negatives can cause this. Given the definitive procedure of washout and cartilage removal was performed, the risk of relapse is low. Work on addressing the risk factors that led this. Best wishes.
Low. If the joint itself was removed and any infected bone in the area debrided, and you were on 5 months of antibiotics; you would expect a surgical "cure" of the infection. Usually what is done us you follow a blood test to ensure it does not recur known as crp even for months after the antibiotics are given just to ensure it does not return.