Shoulder arthroplasty complications: infection

Authors: P. Hoffmeyer

References: SECEC 2005, Rome

 

EPIDEMIOLOGY:

Shoulder replacements are reports to have a good record of postoperative infections as to compared to other arthroplasties.  The prevalence of deep infections is reported to be between 0 and 3.9% for unconstrained arthroplasty and between 0 and 15.4% for constrained arthroplasty (Sperling et al).  these results may be attributed to a number of factors of which:

Minimally traumatic operating techniques, adequate intraoperative anaesthetic care, targeted perioperative antibiotic prophylaxis and an ultraclean air environment.  There are however associated factors that tend to favour onset of infection amongst which: Rheumatoid arthritis, diabetes, advanced age, malnutrition, immunosuppressive chemotherapy and remote sites of infection.

 

PATHOGENESIS:

Infections associated with prosthetic joint replacements are typically caused by micro-organisms that produce and grow in biofilms (polymeric matrix).  The biofilms induce a stationary growth phase and protect the micro-organisms from antimicrobial agents and host immune responses (Zimmerli et al).  in the presence of an implant granulocytes also tend to be inactivated due to the phagocytation of wear particles (UHMW PE) and by more complex interactions involving the prosthetic surfaces (Bernard et al).  these various mechanisms tend to diminish the bacterial inoculum necessary to produce an infection and this makes the implant susceptible to sepsis for the whole of its lifetime.

 

DEFINITIONS:

Acute Infection:       (<3 months after surgery)    ¡V S aureus, Gram-

                                                                             negative bacilli

Delayed Infection:    (3-24 months after surgery)           - Coag-neg

                                                                             staphylococci, P. acnes

Late Infection:         (>24 months after surgery)  - Coag-neg

                                                                             staphylococci, P. acnes

 

LABORATORY STUDIES:

Serial postoperative measurements of C-reactive protein

Synovial fluid neutrophil count > 1700 mmƒV or more than 65%

Histopathology: >1-10 neutrophils per high power field at a magnification of 400

Gram staining: High specificity but low sensitivity

Aspiration and culture: Pathogen identified in 45-100% of cases (Specificity +++)

Periprosthetic cultures x3: Sensitivity 65-94% (Specificity +++)

Implant sonication for identifying fastidious organisms

 

NB: In the specific case of SHOULDER ARTHROPLASTY: Propionibacterium acnes causes infection more frequently than it does after replacement of other joints (16% vs. <2%) (Sperling et al).

 

IMAGING STUDIES:

Plain RX, Arthrography, Scintigraphy, PET, CT, MRI: (Non-specific)

NB: MRI only for non ferro-magnetic implants (Titanium or Tantalum)

 

TREATMENT:

Medical therapy

Choice of antimicrobials depends on: Bacterial sensitivity; bactericidal activity against surface adhering, slow growing and biofilm producing organisms; tolerance for prolonged use; possibility of oral administration.  Combinations of antibiotics should be used (Zimmerli et al, Bernard et al).  sometimes IV delivery devices may be necessary for prolonged outpatient parenteral administration.  Rarely, it may be necessary to instore a purely suppressive treatment using the most appropriate and well tolerated antibiotics.  In all cases, it is strongly recommended to obtain specialised infectious diseases consultation before embarking on prolonged antibiotic therapy.

 

Surgical therapy

The mainstay of prosthetic infection is surgical debridement thereby diminishing the bacterial inoculum.  The modalities available vary considerably in surgical aggression and include:

-        Disarticulation: Life threatening end stage situation with overwhelming infection.

-        Fusion: Loss of cuff and deltoid function in the face of adequate bone stock

-        Resection arthroplasty: Extensive soft tissue and/or bony damage

-        One or two stage exchange arthroplasty

-          One stage:    Acute or delayed infection with little soft tissue damage and a non resistant bacteria

-        Two stage:    Resistant organism (MRSA etc), tissue damage, sinus tract

-        Spacer:         Maintenance of length, some mobility, issue of stability

          No Spacer:    Very resistant organisms where treatment in the absence of any foreign body is preferable.

-          Interval to reoperation varies from two to eight weeks depending on the magnitude of the infectious process and the response to therapy (Clinical, CRP, WBC).  If the pathogen is known and if the infection is not threatening, appropriate antibiotics may be given two to three weeks prior to the operation.

-        Debridement with prosthetic retention: Acute infections setting with little soft tissue attrition.

 

However, most studies or general reviews pertain to infections of hip or knee arthroplasties.

-                     Specific to the shoulder are the following discussions:

TSA_TSA; TSA_HA; HA_HA; TSA or HA_Inverted; Inverted_

Many factors including the expectations and demands of the patients, the presence of ongoing infection, the amount of bone stock destruction at the glenoid or the humerus, the existence of neurovascular dysfunctions and the importance of soft tissue damage involving the rotator cuff or the deltoid muscle come into play for guiding treatment strategies and surgical tactics in these particularly complex situations.

 

LITERATURE:

1.                  Zimmerli et al.  N Engl J Med 2004, 351: 1645-1654

2.                  Bernard et al. J Antimicrobial Chemotherapy 2004, 53:127-129

3.                  Bernard et al. Biomaterials 2005, 26:5552-5557

4.                  Sperling et al.  Clin Orthop Rel Res 2001, 382:206-216

5.                  Coste et al.  J Bone Joint Surg B 2004, 86:65-69