A 35-year-old female was referred to our center with right groin pain. She had undergone total hip arthroplasty (THA) four years ago due to ONFH following pregnancy. She had no history of fever and trauma. She received a high dose of corticosteroid following Covid-19 infection. The passive right hip range of motion was near full, although painful at extremes of movement. She had a painful weight-bearing with an antalgic gait. The neurologic examination was good, and no sign or symptom suggestive of spinal radiculopathy. The late-onset pain, the location, history, and examination grew us suspicious of a low-grade peri-prosthetic joint infection (PJI).

Her radiographs demonstrated a severe right acetabular sclerosis, and a radiolucent line around the acetabular component suggestive of loosening of the acetabular component (Figure 1).

Her ESR was 16, and her CRP was 14. 99m-Tc bone scan revealed mild hyper-flow at the right hip in angiography and blood pool images, and intense uptake in delayed images. Due to the unavailability of metal artifact reduction sequence (MARS) magnetic resonance imaging (MRI), in our center, it had not been done. In the next step, hip aspiration took place for her, which was negative for PJI.

So, we decided to do two-staged arthroplasty. After the acetabular component removal, we faced severe sclerosis of acetabulum, which was avascular. Several specimens were assembled for microbiology culture to assess peri-prosthetic joint infection (PJI) due to high suspicion, and pathology. A Cement spacer was also implanted. Post-op CT scan was done to evaluate the acetabulum also confirmed sclerosis (Figure 2).

The cultures were negative for PJI, and pathology confirmed the ONA (Figure 3).

After two weeks of antibiotic therapy the second stage was done. Acetabular reaming was associated with a lack of bleeding. Since, we decided to implant a cemented cup for her in that situation, by ONA diagnosis due to inappropriate bone ingrowth.

At one year postoperatively, the patient returned for a follow-up visit, and Radiographs were obtained at this time for routine monitoring (Figure 4). She had no complaints and her Harris hip score was 81.