These authors sought to determine the sensitivity of frozen section histology in identifying patients with Propionibacterium acnes infection during revision total shoulder arthroplasty and investigate various diagnostic thresholds of acute inflammation that may improve frozen section performance.
They reviewed the results of forty-five patients who underwent revision total shoulder arthroplasty. Patients were divided into a non-infection group (n = 15), a Propionibacterium acnes infection group (n = 18), and an other infection group (n = 12).
Using the traditional thresholds for grading frozen section histology, the sensitivity was lower for the Propionibacterium acnes infection group (50%) compared with the other infection group (67%). The specificity of frozen section was 100%.
Using a receiver operating characteristics curve, an optimized threshold was found at a total of ten polymorphonuclear leukocytes in five high-power fields. Using this threshold, the sensitivity of frozen section for Propionibacterium acnes was increased to 72%, and the specificity remained at 100%.
Comment: It is now well recognized that a failed arthroplasty requiring surgical revision may be culture positive for Propionibacterium even though the usual symptoms, blood tests, and surgical findings do not suggest an infection. Because they are not finalized until weeks after the surgery, data from intra-operative cultures cannot be used to determine whether a prosthesis exchange and immediate vigorous antibiotic therapy is indicated. Thus at the time of the revision, the surgeon has inadequate data on which to base these therapeutic decisions.
Comment: It is now well recognized that a failed arthroplasty requiring surgical revision may be culture positive for Propionibacterium even though the usual symptoms, blood tests, and surgical findings do not suggest an infection. Because they are not finalized until weeks after the surgery, data from intra-operative cultures cannot be used to determine whether a prosthesis exchange and immediate vigorous antibiotic therapy is indicated. Thus at the time of the revision, the surgeon has inadequate data on which to base these therapeutic decisions.
The study reviewed above is helpful in that it demonstrates that a positive frozen section has high specificity for infection - thus, if the frozen section is positive, the shoulder is best treated as if it is infected. This study also shows that a negative frozen section cannot exclude the possibility of an infection: even with the revised threshold identified by the authors, 28% of the cases culture positive for Propionibacterium would not be identified.
Our approach to intraoperative decision making in revision arthroplasty is shown below:
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Considerations in revision arthroplasty
I. Obvious infection
Typical characteristics
Draining sinus
Classic signs (fevers, chills, erythema, elevated WBC, ESR, CRP)
Massive osteolysis
Gross purulence
Prosthetic revision: Hold perioperative antibiotics until five tissue/explant cultures are obtained and submitted for Propionibacterium specific cultures. Treat with explant of all components, vigorous debridement and irrigation, topical antibiotics, lightly fixed antibiotic spacer and IV antibiotics via PICC line X 6 weeks; initially ceftriaxone and Vancomycin. Antibiotics modified according to culture results. 6 months oral antibiotics after IV course complete. At 6 months can consider reimplantation of prosthesis
II. High suspicion for stealth infection – red protocol
Typical characteristics
Honeymoon period (onset of otherwise unexplained pain and stiffness after a period of usual post op course ranging from months to years)
Patient at increased risk: young active male patient with prior surgery
Rest pain
Loose components (especially early humeral loosening), osteolysis
Synovitis, >5 wbc/hpf, cloudy joint fluid, humeral membrane
Prosthetic revision: Hold perioperative antibiotics until five tissue/explant cultures are obtained and submitted for Propionibacterium specific cultures. Treat with explant of all components, vigorous debridement and irrigation, topical antibiotics, single stage exchange to impaction allografted hemiarthroplasty and IV antibiotics via PICC line X 6 weeks; initially ceftriaxone and Vancomycin. Antibiotics modified according to culture results. 6 months oral antibiotics after IV course complete. If cultures negative at 3 weeks consider discontinuing antibiotics.
III. Lower suspicion for stealth infection – yellow protocol
Typical characteristics
Female patient
No osteolysis
Pain only with activity
Suspect prosthesis failure is strictly mechanical
Prosthetic revision: Hold perioperative antibiotics until five tissue/explant cultures are obtained and submitted for Propionibacterium specific cultures. Prosthesis revision as indicated by surgical findings. Oral antibiotics (Doxycycline or Augmentin) for 3 weeks. Antibiotics modified according to culture results. If cultures are positive and if revision fails to produce a satisfactory clinical result, consider repeat surgery with red protocol or spacer.
See prior related post here and a diagram of the protocol here.
See prior related post here and a diagram of the protocol here.
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