What causes a shoulder joint replacement to get infected? My sister had this surgery two months ago and it’s been nothing but trouble due to an infection.

Joint infection after joint replacement is not very common. When it does happen, the results can be very serious. Most of the time, infections are caused by the immune system failing to do its job. When the immune system is not functioning properly, it’s called immunosuppression.

Many health conditions can actually impair the immune system and keep it working overtime or not at all. This can include diabetes, rheumatoid arthritis, and lupus. Other outside causes of joint infection include chemotherapy for cancer or corticosteroid drugs for chronic inflammatory conditions.

Several studies report repeated local injections with steroids into the joint can also lead to joint infection.

Infections can occur in the acute phase (right away up to three months after the operation) or years later. Pain and altered lab values are the most common signs and symptoms of this condition.