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Background: Plain computed tomography (CT) and magnetic resonance imaging (MRI) are useful for diagnosing adverse local tissue reactions after metal-on-metal total hip arthroplasty (THA), but metal artifacts can hamper radiological assessments near the implants. We sought to clarify the usefulness of 18F-fluorodeoxyglucose positron-emission tomography (18F-FDG-PET) CT and MRI in the periprosthetic region, which is difficult to assess after THA due to metal artifacts., Methods: We performed preoperative 18F-FDG-PET/CT and 18F-FDG-PET/MRI, as well as plain CT and MRI, in 11 metal-on-metal THA patients who underwent revision surgery., Results: Most patients showed high FDG uptake in the metal artifact areas and pseudotumors in the 18-F-FDG-PET/CT and 18-F-FDG-PET/MRI scans. Intraoperative intra-articular macroscopic and histopathological intra-articular granulation tissue findings were suggestive of adverse local tissue reaction., Conclusions: The enhanced uptake in the metal artifact areas seemed to reflect adverse local tissue reaction. Therefore, 18F-FDG-PET/CT and 18-F-FDG-PET/MRI can be useful for the auxiliary diagnosis of adverse local tissue reactions after metal-on-metal THA., Competing Interests: CONFLICT OF INTEREST: No potential conflict of interest relevant to this article was reported., (Copyright © 2021 by The Korean Orthopaedic Association.)

We report herein the microstructure of the acetabular labrum obtained from a patient with stem loosening but without bipolar cup migration who had undergone hemiarthroplasty for femoral neck fracture 18 years ago. We used light and scanning electron microscopy to investigate the influence of bipolar cup on acetabular labrum in vivo. Deparaffinized blocks were treated with 2 N NaOH to digest the cell matrix, allowing the collagen fibers, constituting the acetabular labrum, to be observed under scanning electron microscopy. Although chondrocyte atrophy was seen, the basic structure was not different from the normal tissue images of the elderly. However, in the deep part of the acetabular labrum, there was an area that was not stained with Alcian blue observed with light microscopy, and there was an amorphous tissue without type II collagen fibrils observed with scanning electron microscopy. These findings proved that the acetabular labrum has partially degenerated over the long term after bipolar hemiarthroplasty, and that the acetabular labrum can survive in vivo in such a condition. Given that hemiarthroplasty has a possibility to preserve the face-to-face tissue in the long term in vivo, it may be one of the valuable options for modern or future joint reconstruction surgery.

The acetabular labrum is frequently damaged with advancing age. As collagen fibers are the main sources of strength, knowledge of their ultrastructure is important to determine the cause of age-induced changes. We aimed to investigate the ultrastructure of collagen fibers constituting the acetabular labrum using scanning electron microscopy (SEM). Acetabular labrum samples obtained during total hip arthroplasty were studied. The samples were specially prepared to observe the steric construction of collagen fibrils constituting the acetabular labrum under light microscopy followed by SEM. The acetabular labrum was mostly composed of cartilage tissue, consisting of chondrocytes and collagen type II, with a layer of collagen type I. In adults, chondrocytes with a rich cytoplasm were surrounded by a dense network of fine type II collagen fibrils, and small bundles of type I collagen fibrils were interposed in the cartilage layer. In elderly individuals, the chondrocytes atrophied and both type I and II collagen fibrils were sparse. We suggest that cartilage has three to five layers, consisting of type I and type II collagen fibrils with a solid cartilage substrate. In elderly individuals, the density of chondrocytes decreases and the cellular shape and architecture of collagen fibrils also changes.

Background: Acetabular component orientation, such as high placement and femoral head diameter influence joint stability in total hip arthroplasty (THA), wherein anterior inferior iliac spine (AIIS) shape could cause femoro-acetabular impingement. Little is known regarding the combined influence of these parameters, particularly in the context of developmental dysplasia of the hip. Therefore we conducted a computer simulation study based on computed tomography (CT) data to determine whether: (1) AIIS shape, (2) high placement of acetabular cups, and (3) ball head diameter influence the range of motion (ROM) after THA., Hypothesis: The decrease in ROM depends on AIIS shape and the ROM decreases even if the femoral head diameter is increased when high placement of acetabular cups., Patients and Methods: CT data from 14 hips of 14 patients were evaluated. Hips were categorized by Hetsroni classification type I (n=6), type II (n=6), and type III (n=2) depending on AIIS shape. ROM was evaluated using CT-based software. Cups were placed at and 5 and 10mm above the normal hip position. The femoral heads used were 28 (standard simulation), 32, and 36mm in diameter. ROM at impingement was measured under flexion (Flex), internal rotation (IR) at 90° flexion (IR at 90Flex), IR at 45° flexion with a 20° adduction (IR at 45Flex20Add), and external rotation at 10° extension (ER at 10Ext)., Results: The mean ROM standard simulation for Flex, IR at 90Flex, IR at 45Flex20Add and ER at 10Ext were: 119.8±5.4°, 31.0±11.3°, 70.0±11.9°, and 33.0±9.7° for type I; 118.5±5.5°, 31.5±2.9°, 71.3±2.2°, and 33.3±3.3° for type II; and 105.5±13.4°, 21.0±15.6°, 61.0±11.3°, and 34.5±2.1° for type III, respectively. There were no significant differences in the ROMs of each type (Flex, p=0.252; IR at 90Flex, p=0.461; IR at 45Flex20Add, p=0.261; and ER at 10Ext, p=0.655). For the high placement of acetabular cups, ROM increase was restricted despite the femoral head diameter increase., Discussion: Larger femoral head diameters increased ROM, with a lower increase in type III because of bony impingement. ROM decreased with higher cup placement. Expansion effects were minimal, even with larger ball head diameters, and were further decreased in types II and III. Attention should be paid to AIIS shape because bony impingements occur early with higher acetabular cup placement., Level of Evidence: VI Simulation study., (Copyright © 2018 Elsevier Masson SAS. All rights reserved.)