Synovial Fluid Analysis and Microscopic Assessment of Macrophage Quantities and Morphology in Equine Septic Arthritis

Abstract

Objective Research and provision of data on macrophages by cytological synovial fluid analysis and light microscopy in horses with septic arthritis

Material and methods Records of 167 synovial fluid samples were evaluated and subdivided into different groups: (1) non-septic, (2) haematogenous septic arthritis in foals and (3) traumatic/iatrogenic septic arthritis. The effect of joint lavage on synovial fluid cytology and on the occurrence of macrophage phenotypes was investigated.

Results Regardless of aetiology and age of the horse, macrophage concentrations in synovial sepsis are decreased to a median of 5–6 % (unaffected joints: 23.5 %) and further diminished by joint lavage. Microscopic assessment led to the identification of 4 phenotypes. Morphological characteristics of type 1 showed similarities to monocytes and predominated in unaffected and in septic joints after lavage.

Conclusion and clinical relevance Macrophages are highly versatile by altering their phenotype. A morphological assessment by light microscopy is easily applicable. Type 1 presumably contributes to joint homeostasis.

Zusammenfassung

Gegenstand und Ziel Erfassung von Daten über Makrophagen durch zytologische Synoviaanalyse und Lichtmikroskopie bei Pferden mit septischer Arthritis

Material und Methoden 167 Synovialpunktate und zugehörige Patientenakten wurden ausgewertet und in 3 Gruppen eingeteilt: (1) nicht septisch, (2) hämatogen septische Arthritis beim Fohlen und (3) traumatisch/iatrogen verursachte septische Arthritis. Der Einfluss arthroskopischer Gelenkspülung auf die Synoviaanalyse und auf Makrophagen-Phänotypen wurde gruppenspezifisch untersucht.

Ergebnisse Unabhängig von Ätiologie und Alter des Pferdes sinkt der Anteil synovialer Makrophagen bei septischer Arthritis auf Medianwerte von 5–6 % (nicht septisch: 23,5 %) und wird durch Gelenkspülung weiter verringert. Lichtmikroskopisch wurden 4 Makrophagen-Phänotypen identifiziert. Typ 1 weist morphologische Ähnlichkeiten zu Monozyten auf und überwiegt in nicht erkrankten Gelenken sowie nach Lavage.

Schlussfolgerung und klinische Relevanz Die Plastizität von Makrophagen zeigt sich durch Alternierung ihres lichtmikroskopisch leicht beurteilbaren Phänotyps. Typ 1 trägt vermutlich zur intraartikulären Homöostase bei.

Schlüsselwörter

Pferd - septische Arthritis - Synovia - Makrophagen - Phänotypen - Gelenkspülung - Mikroskopie

Key words

Horses - joint disease - synovial fluid - macrophages - phenotypes - arthroscopic lavage - microscopy

Publication History

Received: 29 June 2022

Accepted: 08 August 2022

Article published online:
14 December 2022

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