Teaching Case

An 80-year-old female patient presented with a four-month history of painful right total hip replacement. She had restricted hip movements and pain on weight bearing. Patient had history of hospital admission for urosepsis prior to presentation.  Imaging confirmed infected total hip replacement. She was treated with two-stage hip revision surgery.

Fig. 1: Initial post-operative radiographs following Hip replacement shows a cemented total hip replacement with no evidence periosteal reaction, or lysis suggesting infection.

Fig.2: The radiographs following urosepsis demonstrated periosteal reaction and irregularity of the femoral cortex along with translucent areas around the acetabulum.  These findings on radiographs indicate evidence of infection and loosening.

Fig.3 (Indium-111) White cell label scan of the hip shows increased uptake around the stem and acetabular components in the delayed phase.  This confirms the diagnosis of peri-prosthetic joint infection.

The most common causes of painful hip replacement are aseptic loosening or instability. [1] The aseptic loosening usually happens over 10-15 years following the life span of hip replacements. The painful hip following infection is common in the early stages after hip replacement. Late presentation is not common, and usually associated with secondary infection. [2] Urosepsis was the source of infection in our case.

In aseptic loosening, the radiographs show osteolysis around the hip prosthesis, between the bone and cement or cement and implant. However, there wouldn’t be any signs of periosteal reaction, which is suggestive of infection.

Indium labelled white cell scan, shows an increased uptake of Indium-111 around the acetabulum and femoral stem confirming a peri-prosthetic infection. This is represented by the white patches on the scan.

The diagnosis of an infected hip replacement is made by the combination of clinical, biochemical and radiological findings. The clinical features include pain, swelling, erythema, and effusions. The biochemical tests show raised inflammatory markers. The radiographs, white cell scan and on occasions SPECT scan confirms the infection. [3,4]

The pain from peri-prosthetic joint infections are caused by the release of inflammatory mediators by macrophages within the joint and the direct action by macrophages that stimulates osteoclasts to initiate bone resorption. This causes the loosening of the prosthesis. [4]

Our patient presented with hip pain two months following the urosepsis. The hip infection was confirmed with radiographs and white cell scan. The hip aspiration grew same organism that caused urosepsis suggesting the bacteraemia during the urosepsis is the source of infection. She underwent successful two stage revision hip replacement. [5]

Revision hip arthroplasty is the gold standard treatment for an infected hip replacement as there is a 90% eradication of infection.  The first stage revision includes debridement of infected tissue and bone, removal of all components and adding an antibiotic loaded cement spacer. The patient is also given systemic antibiotics in conjunction for six weeks and then an antibiotic free period to ensure the removal of the infection. Then once blood serum and inflammatory markers are assessed, a second stage revision with debridement, removal of cement spacer and insertion of the prosthetic joint. [6,7]

Take home message –
Delayed peri-prosthetic joint infections caused by secondary infections. The radiographs and indium-labelled white cell scan have important role in diagnosing the infection. These infections are treated with two-stage revision surgery as gold standard.

Written informed patient consent for publication has been obtained.