Prosthetic hip infections are one of the most severe complications of total hip arthroplasties.
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Epidemiology
Prosthetic hip infections complicate around 0.57% of total hip arthroplasties 1.
Risk factors
Risk factors for prosthetic hip infections can be separated into pre-operative and post-operative risk factors.
Pre-operative risk factors may include:
existing underlying infection
previous local surgery
Post-operative risk factors may include:
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immunosuppressive drugs
immunosuppressive conditions, e.g. poorly controlled diabetes mellitus, HIV, malnutrition
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inflammatory arthropathies
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lifestyle factors
alcohol use
smoking
Clinical presentation
pain at the site of the arthroplasty
stiffness of the prosthetic joint
swelling around the site
overlying skin redness
tenderness
Pathology
The main methods by which a prosthetic joint can become infected are:
directly during implantation
hematogenous spread
reactivation of a latent infection 2
The most common causative micro-organisms are Gram-positive bacteria, including Staphylococcus aureus, Staphylococcus epidermidis and coagulase-negative Staphylococcus. Infections may also be caused by fungi such as Candida 3.
Radiographic features
Plain radiograph
Plain radiographs are the main imaging method utilized in diagnosis of prosthetic joint infections. Signs that may be seen include:
wide band of radiolucency at the cement-bone or metal-bone interface
patchy osteolysis
implant loosening
bone resorption around the implant
transcortical sinus tracts 3,5,6
CT
CT is useful in helping to distinguish between septic and aseptic loosening of the joint 3.
Nuclear medicine
Bone scintigraphy (Tc-99m)
Bone scintigraphy is a highly sensitive method for diagnosing prosthetic joint infections, but it is not very specific, as increased periprosthetic bone activity can be due to a variety of causes 4.
PET
The use of PET in prosthetic joint infections is a relatively novel application. FDG-PET is thought to be highly sensitive and specific for diagnosis infection in hip prostheses, and may aid pre-operative planning 5,9.
Treatment and prognosis
Orthopedic surgery is indicated in most cases, unless the patient is not fit for surgery. Surgical options include:
polyethylene exchange with component retention and intravenous antibiotic therapy
one-stage replacement arthroplasty
two-stage replacement arthroplasty 8
resection arthroplasty
In very severe cases, amputation may be necessary.