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Ultrasound detection of calcium pyrophosphate dihydrate crystal deposits in menisci: a pilot in vivo and ex vivo study
  1. Georgios Filippou1,
  2. Panagiotis Bozios1,
  3. Dario Gambera2,
  4. Sauro Lorenzini1,
  5. Ilaria Bertoldi1,
  6. Antonella Adinolfi1,
  7. Mauro Galeazzi1,
  8. Bruno Frediani1
  1. 1Department of Clinical Medicine and Immunology, Rheumatology Section, University of Siena, Policlinico le Scotte, Siena, Italy
  2. 2Department of Human Pathology and Oncology, Clinical Orthopedics and Traumatology Unit, University of Siena, Policlinico le Scotte, Siena, Italy
  1. Correspondence to Georgios Filippou, Department of Clinical Medicine and Immunology, Rheumatology Section, University of Siena, Policlinico le Scotte, Viale Bracci, 53100 Siena, Italy; g_filippou{at}virgilio.it

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Over the last decade, ultrasonography (US) has been demonstrated to be an excellent technique for detecting calcium pyrophosphate dihydrate (CPP)crystal deposits in joints and periarticular tissues.1,,8 The main difficulty in performing sensitivity and specificity studies for CPP crystal deposition disease is the definition of the gold standard for the diagnosis. The objective of our study was to define the sensitivity and specificity of US in detecting CPP crystal deposits in human menisci using polarised light microscopy as the gold standard.

In our study we enrolled all patients waiting to undergo knee replacement surgery due to severe osteoarthritis for two consecutive weeks. All patients underwent US examination of the knee on the day before surgery. Only the knee to be subjected to surgery was examined by an expert ultrasonographer. US scans were performed at the level of the medial and lateral meniscus with the knee completely extended, semiflexed and completely flexed, without raising the probe all the way along the medial and lateral rim. No other joint structures were examined and the sonographer did not ask the patients any questions. The sonographer gave a dichotomous score based on the absence/presence of CPP deposits in the meniscus, according to previously published criteria.4 A day or two after surgery, the same sonographer, who was blinded to the patient's identity, re-examined the menisci. The menisci were immersed in a gel bath and examined with longitudinal and transverse scans. The sonographer again gave a dichotomous score on the absence/presence of CPP deposits. When the US scan was positive, the sonographer indicated the exact position from where a sample should be collected for microscopic analysis by making an ultrasound-guided cut on the surface of the meniscus. An Esaote Mylab 70XVG (Esaote, Florence, Italy) scanner equipped with a 7–13 MHz linear probe was used for this study. For microscopic analysis, a small sample was collected from the surface of every meniscus, along with a sample from the location indicated by the sonographer. In the case of a negative ex vivo US scan, four random samples were collected from each meniscus: from the anterior horn, the mid-portion, the posterior horn and the surface. Each slide was observed under transmitted light microscopy and by compensated polarised microscopy. Previously published criteria were used for CPP crystal identification and differential diagnosis with basic calcium crystals and steroid deposits.9,,11 Microscopic analysis of the specimens was considered as the gold standard for the diagnosis.

We enrolled six patients in our study (five females). The mean age was 78 years (63–92 years). In one case, the lateral meniscus could not be entirely retrieved during surgery, so it was excluded from the study. Finally, we examined 11 menisci: 6 medial and 5 lateral. The results of the in vivo and ex vivo US examination are reported in table 1. US demonstrated a sensitivity of 44% and specificity of 50% in the in vivo study, compared with 67% and 100%, respectively, in the ex vivo study. In the samples collected after the ultrasound-guided cut, CPP crystals were found in all cases.

Table 1

Menisci positive and negative for the presence of calcium pyrophosphate dihydrate crystal deposits based on ultrasonography (US) and microscopic analysis

The sensitivity and specificity values obtained in this study are lower than those obtained previously by us6 or other researchers.7 We believe that this could be due to various reasons. First, the relatively small number of patients enrolled in this study. Second, the use of microscopic analysis as the gold standard; some of the patients in this study may have shown negative results on plain radiography or synovial fluid analysis and would therefore have been classified as normal if conventional methods had been used for diagnosis. Furthermore, we examined only two menisci for each patient. If we had examined the hyaline cartilage and both menisci of each knee, there would have been a higher likelihood of finding CPP deposits or excluding such a diagnosis, thus increasing the sensitivity and specificity values.

In conclusion, as demonstrated by the ex vivo US examination, US can be considered a reliable technique for the identification of CPP deposits in menisci. New studies should be carried out in order to further define aspects of CPP crystal deposits in fibrocartilage and cartilage tissues and to identify pitfalls that could lead to false interpretations.

References

Footnotes

  • Competing interests None.

  • Patient consent Obtained.

  • Ethics approval The ultrasonography examinations were carried out as a standard protocol during normal clinical practice.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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