Assessment, investigation, and management of acute monoarthritis

Molecular Imaging of Periprosthetic Joint Infections

Infection is an infrequent complication of lower extremity prosthetic joint surgery. Approximately one third develop within 3 months (early), another third within 1 year (delayed), and the remainder more than 1 year (late) after surgery. The diagnosis of periprosthetic joint infection is not always straightforward. Pain, the most common symptom, is present in 90%-100% of patients. The presence of fever is more variable, ranging from less than 5% to more than 40% of patients with infection. Erythema and joint swelling are often present in acute infections, but are less common in chronic infections. Erythrocyte sedimentation rate, C-reactive protein and interleukin-6 levels are useful "rule out" tests, while peripheral blood leukocyte count and serum tumor necrosis factor α are not helpful. The diagnosis of periprosthetic joint infection often requires a combination of blood, synovial fluid, and tissue sample tests, as well as imaging. Plain radiographs lack sensitivity and specificity. Molecular imaging is useful for evaluating painful joint replacements. Bone scintigraphy is most useful as a screening test. If it is negative then infection and aseptic loosening are unlikely. Combined labeled leukocyte/bone marrow imaging is a very specific test for diagnosing lower extremity joint arthroplasty infection; sensitivity is more variable. Despite more than two decades of investigation, there still is no consensus on the value of ¹⁸F-FDG for diagnosing periprosthetic joint infection. Differing test probabilities, an inability to discriminate between infection and inflammation secondary to physiologic reactions, and lack of standardized interpretative criteria are obstacles to incorporating ¹⁸F-FDG into the routine diagnostic imaging workup of periprosthetic joint infection. Preliminary results for gallium-68 citrate, fluorine-18, and technetium-99m labeled antimicrobial fragments are encouraging but no large scale trials with these agents have been conducted. Limited data suggest that labeled leukocyte/bone marrow SPECT/CT and ¹⁸F-FDG-PET/CT are specific but not sensitive for diagnosing periprosthetic infection of shoulder arthroplasties. There are minimal data on molecular imaging for monitoring treatment response in periprosthetic infections.

Septic Arthritis in Immunosuppressed Patients: Do Laboratory Values Help?

Previous studies have recommended synovial fluid cell count thresholds of 50,000 cells/mm^-3 to diagnose septic arthritis; however, data to support this are limited. It is also unknown if this value is valid in immunosuppressed patients.

Methods

We retrospectively reviewed 33 immunosuppressed patients treated at our institution from 2008 to 2018. We compared culture-positive patients with culture-negative patients.

Results

We found no statistically significant differences in synovial fluid cell count, percent synovial fluid neutrophils, erythrocyte sedimentation rate, or C-reactive protein between the groups (all P = 0.081). The median synovial fluid cell count in the culture-positive cohort was 29,000 cells/mm^-3, with only 31.2% having >50,000 cells/mm^-3.

Conclusion

Traditional synovial fluid cell thresholds are not a reliable method of diagnosing septic arthritis in immunosuppressed patients.

Corticosteroids as adjunctive therapy with antibiotics in the treatment of children with septic arthritis: a meta-analysis

Purpose

We performed a meta-analysis to systematically assess the effect of adjunctive administration of dexamethasone with antibiotic therapy in the clinical course of septic arthritis (SA) in children.

Method

Potential academic articles were identified from the Cochrane Library, Medline, PubMed, Embase, ScienceDirect, and other databases. The time range we retrieved from was from the inception of electronic databases to January 2018. The reference lists of identified studies were manually checked to identify other potentially eligible trials. The STATA version 11.0 (Stata Corporation, College Station, TX, USA) was used to analyze the pooled data.

Results

Three randomized controlled trials, and one retrospective cohort study were included in the meta-analysis. There were significant differences in the days of hospitalization (mean difference [MD] = -4.226, 95% CI: -4.785 to -3.667, P=0.001), the days of intravenous antibiotics treatment (MD = -3.593, 95% CI: -4.825 to -2.361, P=0.001), the days of oral antibiotics treatment (MD = -1.658, 95% CI: -2.539 to -0.777, P=0.001), and the days to normalization of C-reactive protein (MD = -3.075, 95% CI: -3.362 to -2.788, P=0.001).

Conclusion

The present meta-analysis base points strongly toward a beneficial effect for corticosteroids in SA. Corticosteroids as adjunctive therapy with antibiotics in the treatment of children with SA could shorten the number of days of hospitalization, the days of intravenous antibiotics treatment, the days of oral antibiotics treatment, and the days to normalization of C-reactive protein. We recommend corticosteroids as adjunctive therapy with antibiotics in the treatment of children with SA.

Critical orthopedic skills and procedures

Musculoskeletal injury and diseases are common presentations in the Emergency Department. Emergency physicians must be versed in the critical procedural skills necessary to diagnose joint infection, manage fractures and dislocations, and assess for compartment syndrome. Arthrocentesis, splinting, dislocation reduction, and the evaluation of limb compartment syndrome are reviewed.

Evidence-based diagnostics: adult septic arthritis

BACKGROUND

Acutely swollen or painful joints are common complaints in the emergency department (ED). Septic arthritis in adults is a challenging diagnosis, but prompt differentiation of a bacterial etiology is crucial to minimize morbidity and mortality.

OBJECTIVES

The objective was to perform a systematic review describing the diagnostic characteristics of history, physical examination, and bedside laboratory tests for nongonococcal septic arthritis. A secondary objective was to quantify test and treatment thresholds using derived estimates of sensitivity and specificity, as well as best-evidence diagnostic and treatment risks and anticipated benefits from appropriate therapy.

METHODS

Two electronic search engines (PUBMED and EMBASE) were used in conjunction with a selected bibliography and scientific abstract hand search. Inclusion criteria included adult trials of patients presenting with monoarticular complaints if they reported sufficient detail to reconstruct partial or complete 2 × 2 contingency tables for experimental diagnostic test characteristics using an acceptable criterion standard. Evidence was rated by two investigators using the Quality Assessment Tool for Diagnostic Accuracy Studies (QUADAS). When more than one similarly designed trial existed for a diagnostic test, meta-analysis was conducted using a random effects model. Interval likelihood ratios (LRs) were computed when possible. To illustrate one method to quantify theoretical points in the probability of disease whereby clinicians might cease testing altogether and either withhold treatment (test threshold) or initiate definitive therapy in lieu of further diagnostics (treatment threshold), an interactive spreadsheet was designed and sample calculations were provided based on research estimates of diagnostic accuracy, diagnostic risk, and therapeutic risk/benefits.

RESULTS

The prevalence of nongonococcal septic arthritis in ED patients with a single acutely painful joint is approximately 27% (95% confidence interval [CI] = 17% to 38%). With the exception of joint surgery (positive likelihood ratio [+LR] = 6.9) or skin infection overlying a prosthetic joint (+LR = 15.0), history, physical examination, and serum tests do not significantly alter posttest probability. Serum inflammatory markers such as white blood cell (WBC) counts, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) are not useful acutely. The interval LR for synovial white blood cell (sWBC) counts of 0 × 10(9)-25 × 10(9)/L was 0.33; for 25 × 10(9)-50 × 10(9)/L, 1.06; for 50 × 10(9)-100 × 10(9)/L, 3.59; and exceeding 100 × 10(9)/L, infinity. Synovial lactate may be useful to rule in or rule out the diagnosis of septic arthritis with a +LR ranging from 2.4 to infinity, and negative likelihood ratio (-LR) ranging from 0 to 0.46. Rapid polymerase chain reaction (PCR) of synovial fluid may identify the causative organism within 3 hours. Based on 56% sensitivity and 90% specificity for sWBC counts of >50 × 10(9)/L in conjunction with best-evidence estimates for diagnosis-related risk and treatment-related risk/benefit, the arthrocentesis test threshold is 5%, with a treatment threshold of 39%.

CONCLUSIONS

Recent joint surgery or cellulitis overlying a prosthetic hip or knee were the only findings on history or physical examination that significantly alter the probability of nongonococcal septic arthritis. Extreme values of sWBC (>50 × 10(9)/L) can increase, but not decrease, the probability of septic arthritis. Future ED-based diagnostic trials are needed to evaluate the role of clinical gestalt and the efficacy of nontraditional synovial markers such as lactate.

How sensitive is the synovial fluid white blood cell count in diagnosing septic arthritis?

OBJECTIVE

This study was conducted to determine the sensitivity of the current standard for synovial fluid leukocytosis analysis in diagnosing infectious arthritis or a septic joint. How accurate is the standard synovial fluid white blood cell (WBC) cutoff of 50,000 WBC/mm3 to rule out septic arthritis?

METHODS

We conducted a retrospective study at an urban tertiary care medical center with 50,000 adult emergency department visits per year. The study population consisted of patients with infectious arthritis confirmed by synovial fluid culture growth of a pathogenic organism. The study period lasted from January 1996 to December 2002. Extracted data included synovial fluid leukocyte count, Gram's stain, culture, past medical history, and discharge diagnosis. Fisher exact test was used to compare proportions. Sensitivity and means were calculated with 95% confidence intervals (CI).

RESULTS

There were 49 culture-positive synovial fluid aspirates in the 6-year study period. Nineteen (39%) of 49 patients (95% CI, 25%-52%) had a synovial WBC of less than 50,000/mm3 and 30 (61%) of 49 patients (95% CI, 48%-75%) had a synovial WBC of more than 50,000/mm3. The sensitivity of the 50,000 synovial WBC/mm3 cutoff was 61% (95% CI, 48%-75%). Twenty-seven (55%) of 49 patients had a negative Gram's stain (95% CI, 41%-69%) and 15 (56%) of 27 patients (95% CI, 37%-74%) with negative Gram's stain had a synovial WBC of less than 50,000/mm3.

CONCLUSION

A synovial fluid WBC cutoff of 50,000/mm3 lacks the sensitivity required to be clinically useful in ruling out infectious arthritis.