Question

A 75 year-old man with a history of rheumatoid arthritis underwent a left hip replacement two weeks ago. Initially, the wound was healing, but over the past 2-3 days, he noticed increased pain in the area, along with redness and swelling. Yesterday, he noticed a small blister over the middle of the incision, and today that area opened up and began to drain purulent fluid. He does not have any fever or chills. Upon examination, he is well-appearing, but has difficulty bearing weight on his left leg due to the pain. His temperature is 100.5F, heart rate = 86 beats/min, blood pressure = 180/78, respiratory rate = 18 breaths/min. He has no oral or skin lesions, his chest sounds clear, and the cardiac exam has no murmurs, rubs, or gallops. The remainder of the exam is unremarkable except for his left leg. There is severe pain upon rotation of his hip. The incision is warm, erythematous, indurated, and tender. There is a small area where the skin has split open where the purulent fluid is coming from. A joint aspirate yields 20 mL of thick, cloudy fluid

a. Give all of the possible organisms and why those organisms are possibilities for causing the patient’s symptoms.

Answer 1

Answer :

Possible organisms :

1) Staphylococcus aureus

2) Staphylococcus epidermidis

3) Streptococcus pyogenes

4) Corynebacteria

5) Salmonella

6) Pseudomonas

7) Escherichia coli

8) Bacteroids.

These bacteria are possible causes because they are commonly found on skin surfaces as commensals which become pathogenic after breach of protective skin barrier (as in surgery). Most commonly Staphylococci are responsible for hip replacement infections. Some of these bacteria especially Enterobactericae such as E.coli are commonly found in perianal and perineal area and are very near to operated site and thus can also complicate hip replacement surgeries.

Discussion and explanation :

Rheumatoid arthritis is a multisystem autoimmune disorder mainly effecting joints eroding cartilages and underlying bones resulting in pain and deformity.

Hip replacement surgery also called hip arthroplasty is done if hip joint involvement interferes with daily life activities and non-surgical treatment options have failed.

Infection is a common possible complication due to skin breach and implant made up of artificial material. Infection can reach the operated site by three common ways :

1) By direct contamination during joint surgery

2) By contact with a neighbouring infected site

3) By hematogenous or lymphogenous seeding of pathogens.

Most commonly encountered pathogens are :

* Staphylococcus

* Streptococcus

* Enterobactericae

* Corynebacterium

* Mycobacterium

* Actinomycetes

* Bacteroids

* Fungi such as Candida

Treatment :

Proper antibiotics after microbiological studies and if needed surgical intervention.