135 - Microarchitectural and Histological Analyses of Myositis Ossificans

Poster Board Number: 135
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Abstract Body : Introduction: Myositis ossificans (MO) is a benign ossification that most frequently develops secondary to trauma within the elbow, shoulder, pelvis, and thigh musculature. Despite reports of MO lesions dating to the 1600s, microstructural analysis of MO architecture in humans is limited. This study examines a case of MO via morphometric, histologic, and micro-CT analysis to augment existing microstructural knowledge of MO.

Methods: A MO discovered within the left adductor longus muscle of an ethically obtained human cadaveric donor was photographed (iPad Pro, Apple Inc.), measured (8-inch Adoric Digital Caliper, Model DWQ), weighed (Ohaus Micro Balance, Model AR3130), and three-dimensionally modeled (Blender software, V3.1.2). Four regional samples (S1-S4) of the MO were collected, scanned via micro-CT (Bruker SkyScan 1172, Kontich, Belgium), three-dimensionally reconstructed (NRecon software), and microarchitectural parameters quantified (CTan software). Subsequently, S1-S4 samples underwent decalcification (Leica Surgipath Decalcifier I) prior to processing, embedding, sectioning, and staining. Staining included H&E and endothelial CD31 immunohistochemistry (IHC) (ThermoFisher: eBioscience anti-CD31, 14-0319-82 and Alexa Fluor 488, A-11001). Light and polarized microscopy (Nikon Optiphot Series) were used for histological analysis, and comparisons were made to typical bone parameters.

Results: The length, thickness, and weight of the MO were 102.19 mm, 6.47 mm, and 9.70 g, respectively. A calcified perimeter was consistently found along the entire parameter of the MO, which, based on the micro-CT imaging, averaged 0.14 ± 0.06 mm in thickness, ranging from 0.04 mm to 0.28 mm. Microarchitectural analysis revealed an average: percent bone volume (BV/TV) of 6.29 ± 1.19%, trabecular pattern factor (Tb.Pf) of 12.72 ± 72 / mm, structure model index (SMI) of 2.12 ± 0.20, trabecular number (Tb.N) of 0.60 ± 0.10 / mm, trabecular thickness (Tb.Th) of 0.11 ± 0.01 mm, and trabecular separation (Tb.Sp) of 0.79 ± 0.05 mm. Compared to typical bone, the MO had low bone volume and decreased structural integrity based on BV/TV, Tb.Pf, SMI, Tb.Th, Tb.N, and Tb.Sp. Light and polarized microscopy revealed that the MO consisted of lamellar bone, mature osteocytes, and functional osteons along the perimeter with trabecular spindles and vascularized adipose throughout the core.

Conclusions: This study evaluates MO bone quality by comparison to typical bone parameters. Correlations from morphometric, histologic, and micro-CT analysis suggest the case in study was a mature MO lesion. These findings may aid bone and mineral scientists in elucidating MO development and characterization of stage progression while assisting healthcare providers with diagnosing and treating soft tissue lesions.