Synovial fluid leukocyte count and differential for the diagnosis of prosthetic knee infection

doi:10.1016/j.amjmed.2004.06.022

The American Journal of Medicine

Volume 117, Issue 8, 15 October 2004, Pages 556-562

https://doi.org/10.1016/j.amjmed.2004.06.022 Get rights and content

Purpose

Criteria for the interpretation of synovial fluid are well established for native joint disorders but lacking for the evaluation of prosthetic joint failure. Our aim was to define cutoff values for synovial fluid leukocyte count and neutrophil percentage for differentiating aseptic failure and prosthetic joint infection.

Methods

We performed a prospective study of 133 patients in whom synovial fluid specimens were collected before total knee arthroplasty revision between January 1998 and December 2003. Patients with underlying inflammatory joint disease were excluded.

Results

Aseptic failure was diagnosed in 99 patients and prosthetic joint infection was diagnosed in 34 patients. The synovial fluid leukocyte count was significantly higher in patients with prosthetic joint infection (median, 18.9 × 10³/μL; range, 0.3 to 178 × 10³/μL) than in those with aseptic failure (median, 0.3 × 10³/μL; range, 0.1 to 16 × 10³/μL; P <0.0001); the neutrophil percentage was also significantly higher in patients with prosthetic joint infection (median [range], 92% [55% to 100%] vs. 7% [0% to 79%], P <0.0001). A leukocyte count of >1.7 × 10³/μL had a sensitivity of 94% and a specificity of 88% for diagnosing prosthetic joint infection; a differential of >65% neutrophils had a sensitivity of 97% and a specificity of 98%. Staphylococcus aureus was the only pathogen associated with leukocyte counts >100 × 10³/μL.

Conclusion

A synovial fluid leukocyte differential of >65% neutrophils (or a leukocyte count of >1.7 × 10³/μL) is a sensitive and specific test for the diagnosis of prosthetic knee infection in patients without underlying inflammatory joint disease.

Section snippets

Patient selection and definitions

A prospective study was performed on patients with a total knee arthroplasty who had undergone synovial fluid aspiration for preoperative evaluation of arthroplasty failure at Mayo Clinic, Rochester, between January 1998 and December 2003. Patients with underlying inflammatory joint diseases (e.g., rheumatoid arthritis, psoriatic arthritis), crystal-induced arthropathy, or connective tissue diseases were excluded. Each patient was included only once. Medical records of study subjects were

Results

A total of 133 synovial fluid specimens from 78 men and 55 women (median age, 71 years; range, 26 to 99 years) with total knee arthroplasties were studied. In all subjects, the prosthesis had been implanted more than 6 months before arthrocentesis. Ninety-nine patients had aseptic failure and 34 patients had prosthetic joint infection (Table 1). The causative microorganism was found in the synovial fluid or tissue cultures of 31 patients (91%) with prosthetic joint infection and included

Discussion

We found that a synovial fluid leukocyte differential of >65% neutrophils (or a leukocyte count of >1.7 × 10³/μL) was the optimal cutoff value for identifying patients with prosthetic joint infection. These cutoff values are considerably lower than those used to diagnose infection in native joints, probably reflecting the lower virulence and biofilm phenotype of microorganisms causing prosthetic joint infection (4, 5, 8, 9, 10, 11).

High cutoffs for synovial fluid cell counts suggested in

Acknowledgment

The authors would like to thank Dr. Shreyasse Amin for her thoughtful review of the manuscript, and Kerryl E. Piper, Emily A. Vetter, Vicky M. Soppa, and Dean S. Strain for their help in preparing the manuscript.

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: This work was supported by the Mayo Foundation, the Minnesota Chapter of the Arthritis Foundation, and the Roche Research Foundation.

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Synovial fluid leukocyte count and differential for the diagnosis of prosthetic knee infection

Purpose

Methods

Results

Conclusion

Section snippets

Patient selection and definitions

Results

Discussion

Acknowledgment

Rheum Dis Clin North Am

Rheum Dis Clin North Am

Am J Med

J Arthroplasty

J Arthroplasty

A Practical Handbook of Joint Fluid Analysis

Diagnostic value of synovial fluid microscopy: a reassessment and rationalisation

Ann Rheum Dis

Acute monoarthritis

N Engl J Med

Synovial Changes in Joint Disease

Arthritis and Allied Conditions

Guidelines for the initial evaluation of the adult patient with acute musculoskeletal symptoms. American College of Rheumatology Ad Hoc Committee on Clinical Guidelines

Arthritis Rheum

Acute septic arthritis

Clin Microbiol Rev

Synovial fluid

Primer on the Rheumatic Diseases

Synovial analysis and synovial biopsy

Knee replacement underused, says panel: useful option when nonsurgical therapies fail

JAMA

Prosthetic joint infection