Leukocyte esterase analysis in the diagnosis of joint infection: can we make a diagnosis using a simple urine dipstick?

PURPOSE: Analysis of joint fluid remains a key factor in the diagnosis of periprosthetic infection. Recent reports have shown that neutrophils in infected joint fluid release esterase, an enzyme that is a reliable marker for infection. Testing for leukocyte esterase is routinely done in the analysis of urine for the presence of urinary tract infection, by a simple "dipstick" method. We report our experience with this technique in the evaluation of patients suspected of having septic arthritis or periprosthetic joint infection (PJI) by comparing results of leukocyte esterase positivity with confirmed joint infection as defined by the American Academy of Orthopaedic Surgeons (AAOS). MATERIALS AND METHODS: We retrospectively reviewed leukocyte esterase test results performed on synovial fluid aspirated from 57 patients with prosthetic (52) and native (5) joints. Patients either presented with unexplained painful arthroplasties, routine testing of PROSTALAC (PROSthesis with Antibiotic-Loaded Acrylic Cement) orthopedic implants, or clinical suspicion of periprosthetic infection or septic arthritis. Synovial fluid was percutaneously aspirated using a standard technique. The patient age range was 31-91 years with a mean age of 69.1 years, consisting of 30 women (52.6 %) and 27 men (47.4 %). The "gold standard" for the presence or absence of infection at our institution and in the study group was based on the most recent recommendations of the AAOS. Positive culture remained the "gold standard" for native joint infection. RESULTS: Of the total 57 joints aspirated and included in the study, 20 (35.1 %) were read as positive (2+) on the leukocyte test strip and 37 (64.9 %) were read as negative (negative, trace, or 1+). PJI was diagnosed in 19 patients and native joint septic arthritis was identified in one patient. Sensitivities were excellent at 100 % with no false negatives in the entire cohort. There was one false positive in the periprosthetic group yielding a specificity, positive predictive value and negative predictive value of 97, 95, and 100 %, respectively. The results for the native joints showed markedly less specificity and positive predictive value at 50 and 33 %; however, its negative predictive value remained at 100 %. CONCLUSIONS: Our test results confirm that the leukocyte esterase test can accurately detect PJI and that it can be used as a part of the traditional PJI workup. In the assessment of native joints, its high negative predictive value suggests that it is a valuable tool in excluding native joint septic arthritis.

Accuracy of chemical shift MR imaging in diagnosing indeterminate bone marrow lesions in the pelvis: review of a single institution's experience.

OBJECTIVE: To re-assess the accuracy of chemical shift imaging in diagnosing indeterminate bone marrow lesions as benign or malignant. MATERIALS AND METHODS: We retrospectively reviewed our experience with MR imaging of the pelvis to assess the accuracy of chemical shift imaging in distinguishing benign from malignant bone lesions. Two musculoskeletal radiologists retrospectively reviewed all osseous lesions biopsied since 2006, when chemical shift imaging was added to our routine pelvic imaging protocol. Study inclusion criteria required (1) MR imaging of an indeterminate bone marrow lesion about the pelvis and (2) subsequent histologic confirmation. The study group included 50 patients (29 male, 21 female) with an average age of 67 years (range, 41-89 years). MR imaging results were evaluated using biopsy results as the "gold standard." RESULTS: There were 27 malignant and 23 benign lesions. Chemical shift imaging using an opposed-phase signal loss criteria of less than 20 % to indicate a malignant lesion, correctly diagnosed 27/27 malignant lesions and 14/23 benign lesions, yielding a 100 % sensitivity, 61 % specificity, 75 % PPV, 100 % NPV, and 82 % accuracy. The area under the receiver operator characteristic (ROC) curve was 0.88. The inter-rater and intra-rater agreement K values were both 1.0. CONCLUSIONS: Chemical shift imaging is a useful adjunct MR technique to characterize focal and diffuse marrow abnormalities on routine non-contrast pelvic imaging. It is highly sensitive in identifying malignant disease. Despite its lower specificity, the need for biopsy could be eliminated in more than 60 % of patients with benign disease.

Utility of percutaneous joint aspiration and synovial biopsy in identifying culture-positive infected hip arthroplasty.

PURPOSE: Percutaneous synovial biopsy has recently been reported to have a high diagnostic value in the preoperative identification of periprosthetic infection of the hip. We report our experience with this technique in the evaluation of patients undergoing revision hip arthroplasty, comparing results of preoperative synovial biopsy with joint aspiration in identifying an infected hip arthroplasty by bacteriological analysis. MATERIALS AND METHODS: We retrospectively reviewed the results of the 110 most recent revision hip arthroplasties in which preoperative synovial biopsy and joint aspiration were both performed. Revision surgery for these patients occurred during the period from September 2005 to March 2012. Using this study group, results from preoperative cultures were compared with preoperative laboratory studies and the results of intraoperative cultures. Synovial aspiration was done using an 18- or 20-gauge spinal needle. Synovial biopsy was done coaxially following aspiration using a 22-gauge Chiba needle or 21-gauge Sure-Cut needle. Standard microbiological analysis was performed on preoperative synovial fluid aspirate and synovial biopsy. Intraoperative tissue biopsy bacteriological analysis results at surgical revision were accepted as the "gold standard" for the presence or absence of infection. RESULTS: Seventeen of 110 (15 %) of patients had intraoperative culture-positive periprosthetic infection. Of these 17 cases, there were ten cases where either the synovial fluid aspiration and/or the synovial biopsy were true positive (sensitivity of 59 %, specificity of 100 %, positive predictive value of 100 % and accuracy of 94 %). There were seven cases where aspiration and biopsy results were both falsely negative, but no false-positive results. Similar results were found for synovial fluid aspiration alone. The results of synovial biopsy alone resulted in the identification of seven infected joints with no false-positive result (sensitivity of 41 %, specificity of 100 %, positive predictive value of 100 %, and accuracy of 91 %). CONCLUSIONS: Standard microbiological analyses performed on percutaneous synovial biopsy specimen during the preoperative evaluation of patients undergoing revision hip arthroplasty did not improve detection of culture-positive periprosthetic infection as compared to synovial fluid aspiration alone.

Anatomically based guidelines for core needle biopsy of bone tumors: implications for limb-sparing surgery.

Diagnostic image-guided needle biopsy plays a vital role in the work-up and treatment of patients with extremity bone tumors. The radiologist and the orthopedic oncologic surgeon should take a team approach to this procedure, especially when the bone lesion might be a primary sarcoma for which limb-sparing surgery (LSS) would be considered. A set of anatomically based guidelines were developed that can be used by the radiologist, in combination with case-by-case consultation with the surgeon, to plan image-guided core needle biopsies of extremity long bone lesions that may be treatable with LSS. By using these guidelines, along with the aforementioned consultation, the radiologist will be able to preserve the patient's chances of receiving optimal surgical treatment.

"Absent middle facet": a sign on unenhanced radiography of subtalar joint coalition.

OBJECTIVE: We compared the accuracy of the previously unevaluated "absent middle facet" sign with the more commonly used "talar beak" sign and C sign for the detection of coalition of the subtalar joint middle facets on lateral foot radiographs obtained with the patient standing. MATERIALS AND METHODS: Three musculoskeletal radiologists graded the visibility of these three signs on standing lateral radiographs of 32 feet that had been proven to have coalitions of the middle facets of the subtalar joint and 62 feet that had normal subtalar joints. The reviewers were unaware of the presence or absence of subtalar coalitions in these feet. RESULTS: The absent middle facet sign had a sensitivity, specificity, and accuracy of 75%, 98%, and 90%, respectively, for the diagnosis of subtalar joint coalition in this patient population, whereas these values were 56%, 100%, and 85% for the C sign and 53%, 90%, and 78% for the talar beak sign, respectively. A finding of either a positive absent middle facet sign or a positive C sign resulted in a sensitivity, specificity, and accuracy of 84%, 98%, and 94%, respectively. CONCLUSION: In this study population, the absent middle facet sign was more sensitive than and nearly as specific as the talar beak sign and C sign for diagnosing subtalar coalition on standing lateral foot radiographs. The highest accuracy was obtained when a finding of either a completely absent middle facet or a complete C sign was considered as a positive indicator of a subtalar coalition.

Imaging of osteoid osteoma with dynamic gadolinium-enhanced MR imaging.

PURPOSE: To compare dynamic gadolinium-enhanced T1-weighted magnetic resonance (MR) imaging with nonenhanced T1-weighted and T2-weighted MR imaging and thin-section computed tomography (CT) for the demonstration of osteoid osteomas. MATERIALS AND METHODS: The images of 11 patients with pathologically proven osteoid osteomas who underwent nonenhanced MR imaging, dynamic gadolinium-enhanced MR imaging, and CT were retrospectively reviewed. Images obtained with all three techniques were scored for conspicuity of the osteoid osteoma relative to the surrounding bone. Time-enhancement curves were generated from signal intensity measurements of these lesions and the adjacent bone marrow. The mean imaging scores of the four techniques were compared, and the statistical significance was calculated by using a linear model with terms for method and patient. Pairwise comparisons were made by using the Tukey-Kramer adjustment for multiple comparisons. RESULTS: Compared with CT, dynamic gadolinium-enhanced MR imaging demonstrated the osteoid osteoma equally well in eight of 11 patients and with better conspicuity in three of 11 patients, although this difference was not statistically significant (P =.69). The dynamic gadolinium-enhanced MR images demonstrated the osteoid osteomas significantly better than the nonenhanced T1-weighted (P <.001) and T2-weighted (P <.001) MR images. On the dynamic gadolinium-enhanced MR images, nine (82%) of 11 patients had peak enhancement of the osteoid osteoma in the arterial phase with early partial washout, compared with slower, progressive enhancement of the adjacent marrow. This resulted in greatest lesion to marrow contrast material enhancement in the arterial phase. One osteoid osteoma had peak enhancement in the venous phase, and one showed progressive enhancement through all phases to 150 seconds. CONCLUSION: Osteoid osteomas can be imaged with greater conspicuity by using dynamic gadolinium-enhanced instead of nonenhanced MR imaging and with conspicuity equal to or better than that obtained with thin-section CT.