K. Perera1, M. Armstrong1 1Eastern Health,Melbourne, VICTORIA, Australia
Introduction:
Septic arthritis is an emergency, potentially causing irreversible joint destruction and
disability. Synovial WCC and polymorphonuclear cell percentage is the best predictor of
septic arthritis likelihood. Yet, synovial WCC and differential are not routinely assessed.
We aim to investigate the incidence of this and develop correct synovial fluid analysis
practices.
Methods:
A retrospective analysis of native joints having had arthrocentesis for suspicion of septic
arthritis at Box Hill Hospital (BHH) between September 2011 and September 2013
inclusive. Recruitment was from the Eastern Health Decision Support Service (DSS), who
maintains a database compiled from all systems within Eastern Health; of which BHH is a
member.
The study was limited to large joints; this includes hip, knee and shoulder. All prosthetic
joints were excluded from the patient population.
All patient histories were examined for suspicion of septic arthritis and subsequent
arthrocentesis. Pathology records were accessed to determine incidence of cell count and
differential.
Results:
One hundred and thirty-six cases of joint aspirations were identified within the time frame,
of which sixty-seven fit our criteria for evaluation. All but two cases were delivered using
the DSS, which was limited to data compiled only until June 2013. The two remaining
cases were identified with a manual search of the radiology and pathology databases from
June to September 2013.
22 of the 67 joint aspirates studied did not have a cell count carried out. Four of these 22
cases had a diagnosis of septic arthritis. In five aspirates, there was a failure to confirm a
definite diagnosis and were thus conservatively treated as a septic joint. The remaining
acute joints in which no cell count was done were gout (7 cases), pseudogout (5 cases) and
rheumatoid arthritis (1 case).
Cell counts were not routinely detected for a variety of reasons. Eleven aspirates were
deemed too viscous, and in eight cases the sample had clotted prior to pathologist
assessment. Two cases had insufficient volume, and one sample was too bloodstained to
calculate a cell count and differential; likely due to traumatic aspiration.
Conclusion:
33% of acute monoarthritis’ evaluated over the study period failed to have a synovial fluid
WCC and differential. This may be due to inadequate samples, or lack of appropriate
collection tube. Better education is required for appropriate collection and test requesting
wherein a diagnosis of septic arthritis is in question.