What can be done if a hip deteriorates rapidly after a steroid injection?

If someone has rapid progressive joint deterioration after a steroid injection there are several possible explanations. 

1)    The most likely explanation is that the steroid injection was undertaken when the deteriorating joint was becoming progressively more symptomatic.  The injection partially masked this deterioration for a few weeks.  When the effect of the steroid began to wear off, the patient became aware of the further deterioration and attributed this to the steroid injection rather than the natural progression of their joint disease.

2)    There are reports of the metabolism of cartilage cells being adversely affected by some steroids. While most of the data on this phenomenon comes from laboratory studies and tissue culture specimens, there are rare clinical cases where rapid loss of joint space is observed on serial x-rays and the term chondrolysis is applied to this change.  While it is hard to say whether this process has been triggered or accelerated by steroid injections, if all other possibilities are excluded, it may be the explanation.

3)    If an infection has found its way into the joint, either through the bloodstream or when the steroid injection was undertaken, there is a risk that the infection remains in the tissues after hip replacement surgery and the infection settles on the new hip implants.  If this occurs, further surgery is usually required, and revision of the implants may be necessary.

What can be done to find out if there is/was an infection in a hip prior to hip replacement surgery?

If the possibility of an infection is being considered prior to primary hip replacement, the following strategies are available to help identify whether or not an infection is/was present prior to surgery.

1)    Pre-operative blood tests can be undertaken. These include:

a.      Full blood count (FBC)

b.     C-Reactive protein (CRP)

c.     Erythrocyte sedimentation rate (ESR)

d.     Procalcitonin (PCT)

2)    Joint aspiration under ultrasound or image intensifier guidance with 

a.     Alpha Defensin Lateral Flow Test on synovial fluid obtained from the joint.

b.     Microscopy and culture of fluid +/- tissue biopsies from the joint.

3)    Microscopy & culture of multiple tissue specimens obtained during surgery in aerobic and anaerobic environments with standard and enhanced culture media. 

What are the options if hip replacement is undertaken when there is continueing suspicion of infection in the joint but investigations have failed to identify an infecting organism?

 

If all pre-operative tests have failed to deliver an organism but there is still a significant index of suspicion that an infection is present in the joint, the following strategies can be followed:

1)     Intra-operative microscopy of tissue specimens from the joint is available at some centres. If greater than five neutrophils per high-power field, in five high-power fields, are observed on histologic analysis of periprosthetic tissue at ×400 magnification, the possibility of infection should be seriously considered.

2)     A single stage procedure can be undertaken with thorough joint debridement, irrigation of the tissues with antiseptics and implantation of a hip replacement. If one or both of the components are being fixed using cement, a cement option that is normally reserved for revision (redo) cases can be used. This will have a different antibiotic to the normal gentamycin impregnated cement, that is preferred for first time (primary) hip replacements.  If uncemented components are used, antibiotic can be put into the joint cavity prior to wound closure. The patient can then be kept on antibiotic therapy, at least, until the tissue culture results are known.

3)     A two-stage procedure can be undertaken.  In the first stage the joint is debrided, multiple soft tissue and bone biopsies are obtained. The joint can be irrigated with antiseptics and then reclosed.  Alternatively, the femoral head can be removed and an antibiotic loaded cement spacer can be put in its place, prior to wound closure.  If the latter option is taken, traction will need to be applied to the affected leg until the joint becomes comfortable enough to allow transfers to a chair.  If tissue culture does confirm the presence of an infection, discussion with the microbiology team will provide guidance on appropriate antibiotic therapy and the timing of the second for implantation of the new hip.

 

What are the risks of undertaking a hip replacement if there is a pre-existing infection in the joint?

In addition to the normal risks of joint replacement surgery, there is the risk that bacteria in the tissues prior to surgery are not completely removed prior to implantation of the new hip, are not killed by antiseptics used during surgery and are not killed by the antibiotics given during surgery or the antibiotics in the cement that may be used to secure one or both of the new hip components.  

Any residual bacteria may find their way onto the surfaces of the artificial hip. Once on the components, the bacteria can divide, form colonies, become protected by a biofilm and be inaccessible to the body’s white blood cells or antibiotics that may be given.  If the bacteria are of low virulence and struggle to survive in the tissues, the patient may never know that their implants are infected.  Alternatively, if the bacteria are able to divide and flourish the patient will develop the symptoms and signs of an infected hip replacement. These can include:

1)    Pain

2)    Swelling in the tissues around the hip.

3)    Breakdown of the wound with discharge of pus.

4)    Formation of a discharging sinus tract from the infected joint to the skin.

5)    Spread of the infection into the bloodstream (Septicaemia)

6)    Spread of the infection to other tissues.

7)    Malaise, night sweats, a low grade or swinging pyrexia and death.

Approximately 80% of all joint infections present within the first year of surgery.  If the infection becomes apparent with the first four to six weeks of the hip replacement, a DAIR procedure can be undertaken. This involves debridement of the joint, antibiotic therapy and implant retention. Beyond the first four to six weeks, an infected joint is best treated by removal of the components, implantation of a new hip replacement and course of antibiotic therapy. Revision can be undertaken as a single or two-stage procedure depending on the infecting organism and the condition of the tissues.  Overall, revision for infection has a slightly better than 90% chance of eradicating the infection and providing a well-functioning joint.