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We report the observation of the soft tissue recurrence of an osteoid osteoma (OO) in a 26-year-old man initially complaining of post-traumatic pain and swelling of the right ankle. A first arthroscopic resection was performed after the misdiagnosis of "bone irregularities" observed on computed tomography (CT) and magnetic resonance imaging (MRI). The diagnosis of OO was made by histological analysis of the resection material. The patient became asymptomatic for 5 years until the symptoms progressively recurred. Follow-up MRI and CT studies demonstrated a nodular bony focus within the periarticular soft tissues of the ankle. The lesion was removed, and histological analysis confirmed the diagnosis of a whole viable OO. This observation likely resulted from the displacement of the initial lesion during the initial arthroscopic procedure. This case report highlights the possibility of recurrence of OO in the soft tissues.

Aim: To assess the topology of bone and cartilage microfractures in osteonecrotic femoral heads., Method: Sixteen resected human femoral heads with collapsed osteonecrosis (ON, n = 11) or osteoarthritis (OA, n = 5) were imaged at μCT with 12 μ nominal resolution. Forty-seven histological sections and μCT reformats with (n = 30) or without (8 from ON and 9 from OA femoral heads) osteonecrotic lesions were obtained and divided in 2 × 2 mm segments by a superposed grid. A radiologist and a pathologist separately assessed the presence of bone and cartilage microfractures in each segment on μCT and histological images, respectively. We determined the frequency and distribution of segments with bone microfractures according to a zonal distribution. Matrix analysis was performed by using Matlab to calculate the connectivity index and long/short axis ratios of clustered segments with microfractures., Results: Segments with bone microfractures but not with cartilage microfractures were found more frequently in ON than in OA femoral heads. In the 38 matched μCT and histological images from ON femoral heads, 86%/82% of segments with cortical microfracture, 91%/96% of segments with trabecular microfractures involved ON lesions at μCT/histology. At histology, 83% of segments with cartilage microfractures involved ON lesions. In the 30 paired μCT and histological images containing necrotic lesions, the frequency of segments with trabecular microfractures in the superficial layers (55% at μCT/51% at histology) was statistically significantly higher than in the deep layer (25% P < 0.0001/35%; P = 0.0006). Clustered segments with cortical/trabecular microfractures, exclusively found in osteonecrotic lesions, had a connectivity index >2.0/20.0 and mean long/short axis ratio > 2.35/2.2, respectively., Conclusion: Segments with bone microfractures predominate in necrotic lesions. Segments with trabecular microfractures form elongated clusters near the femoral head surface., (Copyright © 2020 Elsevier Inc. All rights reserved.)