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June 11, 2019
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Hip Replacement

Hip Replacement

Hip replacement is a surgical procedure in which the hip joint is replaced by a prosthetic implant, that is, a hip prosthesis. Hip replacement surgery can be performed as a total replacement or a hemi (half) replacement. Such joint replacement orthopaedic surgery is generally conducted to relieve arthritis pain or in some hip fractures. A total hip replacement (total hip arthroplasty or THA) consists of replacing both the acetabulum and the femoral head while hemiarthroplasty generally only replaces the femoral head. Hip replacement is currently one of the most common orthopaedic operations, though patient satisfaction short- and long-term varies widely. Approximately 58% of total hip replacements are estimated to last 25 years.[1] The average cost of a total hip replacement in 2012 was $40,364 in the United States, and about $7,700 to $12,000 in most European countries.[2]

Risks

Risks and complications in hip replacement are similar to those associated with all joint replacements. They can include infection, dislocation, limb length inequality, loosening, impingement, osteolysis, metal sensitivity, nerve palsy, chronic pain and death. Weight loss surgery before a hip replacement does not appear to change outcomes.[3]

Infection

Infection is one of the most common causes for revision of a total hip replacement, along with loosening and dislocation. The incidence of infection in primary hip replacement is around 1% or less in the United States.[4] Risk factors for infection include obesity, diabetes, smoking, immunosuppressive medications or diseases, and history of infection.

Modern diagnosis of infection around a total knee replacement is based on the Musculoskeletal Infection Society (MSIS) criteria.[5] They are:

1.There is a sinus tract communicating with the prosthesis; or 2. A pathogen is isolated by culture from at least two separate tissue or fluid samples obtained from the affected prosthetic joint; or

Four of the following six criteria exist:

1.Elevated serum erythrocyte sedimentation rate (ESR>30mm/hr) and serum C-reactive protein (CRP>10 mg/L) concentration,

2.Elevated synovial leukocyte count,

3.Elevated synovial neutrophil percentage (PMN%),

4.Presence of purulence in the affected joint,

5.Isolation of a microorganism in one culture of periprosthetic tissue or fluid, or

6.Greater than five neutrophils per high-power field in five high-power fields observed from histologic analysis of periprosthetic tissue at ×400 magnification.

None of the above laboratory tests has 100% sensitivity or specificity for diagnosing infection. Specificity improves when the tests are performed in patients in whom clinical suspicion exists. ESR and CRP remain good 1st line tests for screening (high sensitivity, low specificity). Aspiration of the joint remains the test with the highest specificity for confirming infection.

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