Prosthetic hip infections

Prosthetic hip infections are one of the most severe complications of total hip arthroplasties. 

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:

• immunosuppression
  • immunosuppressive drugs
  • immunosuppressive conditions, e.g. poorly controlled diabetes mellitus, HIV, malnutrition
• inflammatory arthropathies
  • rheumatoid arthritis
  • ankylosing spondylitis
  • psoriatic arthritis
• lifestyle factors
  • obesity
  • intravenous drug use
  • alcoholism
  • 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:

• periosteal reaction
• 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. 

See also

• complications of total hip arthroplasty