PMC6410446_01
Preoperative ranges of motion. Elbow extension (a) and flexion (b). Forearm supination (c) and pronation (d).
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A physical examination revealed elbow contracture with a maximal extension of -20  and flexion of 125  (Figures 1(a)-1(d)).
Preoperative radiographic images. The anteroposterior radiograph (a) and computed tomography images (b: axial, c: sagittal) depict a nidus comprising central sclerosis with circumferential radiolucency (arrowhead) at the olecranon/coronoid fossa of the humerus.
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Plain radiograph and CT images taken at our clinic revealed a nidus at the olecranon/coronoid fossa of the distal humerus (Figures 2(a)-2(c)).
Axial T1-weighted (a), T2-weighted (b), and gadolinium-enhanced (c) images on preoperative magnetic resonance imaging. The round lesion shows slightly hyperintense signals compared to adjacent muscles on T1-weighted imaging and hyperintense to intermediate-intensity signals on T2-weighted sequences, with heterogeneous enhancement (arrowhead).
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Magnetic resonance imaging was then performed, showing that the central lesion had slightly hyperintense signals compared to adjacent muscle on T1-weighted sequences and hyperintense to intermediate-intensity signals on T2-weighted sequences, with heterogeneous enhancement (Figures 3(a)-3(c)).
Arthroscopic findings. Proliferated synovial tissues were shown via anteromedial (a) and posterolateral (b) portals. The lesion was excised as an en bloc specimen (c, d, e). The margin was carefully treated to eliminate all traces of the tumor (f).
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fig4
Severe proliferation of synovial tissues was observed throughout the joint space (Figure 4(a)). Posterolateral and posteromedial portals were also created to treat the synovium located at the posterior capsule (Figure 4(b)). The lesion was excised as an en bloc specimen using a bone chisel and cupped forceps (Figures 4(c)-4(e)). The margin was carefully debrided using the shaver and radiofrequency devices to eliminate all traces of the tumor (Figure 4(f)).
Histologic findings. Incompletely mineralized trabeculae rimmed by scattered osteoclasts (blue arrowhead) and irregularly shaped osteoblasts (yellow arrowhead). The intervening stroma (asterisk) is loose and fibrovascular (Hematoxylin-Eosin stain, bar represents 100 mum).
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fig5
A histologic examination confirmed the diagnosis of OO (Figure 5).
Ranges of motion at one-year follow-up. Elbow extension (a) and flexion (b). Forearm supination (c) and pronation (d).
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At the 12-month follow-up, the patient had no recurrence of elbow limitation or pain (Figures 6(a)-6(d)).