case_images: PMC11722162_01
case_images: Zone of interest of anteroposterior radiographs of the pelvis showing the right hip (A-D), respectively corresponding faux-profile (A') or axial radiographs (B'-D'). The oldest radiographs available are from 11 years after THA, respectively 9 years after the first revision of the cup, 13 years before the revision described (A,A'). Note the metal-polyethylene-sandwich cup and the small-diameter metal-on-metal bearing, as well as the improper placement of the reinforcement ring. The hook normally should engage the acetabular fossa to reduce the risk of dislocation (arrow). Dislocated hip implant 3 months before revision illustrated in (B,B'). Postoperative radiographs after revision are illustrated in (C,C'). Note successful reconstruction of the centre of rotation and of the leg length. Follow-up 3 years after revision in (D,D').
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case_images: Eighteen years after the first revision, aseptic loosening of the reinforcement ring was noticed (Figure 1), causing the cup to tilt and migrate over time. The cup had been correctly oriented initially, with an inclination of 32  and a radiologic anteversion of 19  (Figure 1A). However, the reinforcement ring may have lacked proper support, as the distal hook did not engage the distal end of the acetabular fossa and as the lateral flange was placed medially to the lateral wall of the acetabular roof (Figure 1A). Reconstruction of the hip is illustrated in Figure 1.
case_images: Macrophotographs of the retrievals. In (A) implant head and neck with a posteriorly situated wear defect, measuring 13 mm in width, 4.4 mm from proximal to distal, with a depth of 4.25 mm. Total volume loss thus measured approximately 162 mm3, considering the defect as a half-cylinder. In (B), illustration of the cup, showing a posterior wear defect. In (C), illustration of both the cup and the stem assembled, showing posterior component impingement. The defect zones align perfectly. The edge of the cobalt-chromium-alloy cup of the metal-polyethylene-sandwich cut into the softer titanium alloy of the stem during repetitive impingement, whereas the neck caused a defect of the softer polyethylene (red arrows).
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case_images: As a previously not identified indentation of the neck of the stem was observed (Figure 2), estimated to be critical regarding fatigue fracture risk based on size and location, as the head could not be removed and as exposure was insufficient for reconstruction of the acetabulum despite extension of the approach along the iliac crest, conversion to a transfemoral approach was performed. Upon retrieval of the implant, component impingement (wear mode 4A) was obvious, resulting in severe wear of the Ti-alloy stem articulating against the rim of the CoCr-polyethylene-sandwich liner (Figure 2).
case_images: In (A), macrophotograph of the sectioned periarticular solid black necrotic tumor, which was located posteriorly to the hip joint, having a diameter of 3.8 cm after fixation, surrounded by adipose tissue. In (B,C), microphotograph at high magnification (hematoxylin and eosin staining x200 in (B) and x400 in (C), depicting proliferated macrophages showing basophilic stained oval nuclei and expanded cytoplasm, containing numerous phagocyted black metal microparticles (two macrophages delineated with a dotted white line).
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case_images: A significant, mostly solid ARMD pseudotumor (Figure 3A) was present posterolaterally to the hip joint, which had not been present on the CT-scan performed 3 months preoperatively, causing complete destruction of the external rotators. Histology showed that the periarticular black mass (Figure 3A) consisted of extensive necrosis containing black microparticular debris without birefringence in polarized light, identifying the material as non-ferrous metal particles. The necrotic tumor was demarcated by a marked macrophage reaction demonstrating phagocytosis of the metal particles (Figure 3B,C), some bone sequesters and siderophages indicating older haemorrhage.
case_images: Heat maps showing bearing surface wear based on metrology data collected with an optical coordinate measuring machine (RedLux, Ortholux). (A) shows a narrow wear scar on the head's bearing surface, which is characteristic for edge loading. The wear of the head amounted to 32.34 mm3. The wear scar of the metal liner is shown in (B), located at the rim and was associated with 8.02 mm3 of material loss. Total wear of the bearing surfaces amounts to 40.36 mm3, which is only a fourth of the defect size of the neck of the implant.
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case_images: The wear of the head amounted to 32.34 mm3, while wear of the metal liner was 8.02 mm3, summing up to 40.36 mm3 (Figure 4).
case_images: Graphical illustration of the titanium concentrations in whole blood over time observed in the patient described. Expected concentrations were extrapolated from the individual measurements, not considering the last two values, as an unexplained secondary increase was observed. The calculated elimination half-life of titanium in the blood in this patient thus was 2 years and 233 days. Without this secondary increase, normalisation of the titanium concentration would not have been expected before 14 years postoperatively. The dotted line at 1 microg/L marks the normal reference value.
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case_images: Ti at 406,100 microg/kg. The Ti blood levels slowly decreased over time (Figure 5).
case_images: In (A), high magnification photomicrograph demonstrating dense metal debris within macrophages (haematoxylin and eosin, x600). In (B), backscattered scanning electron micrograph of the same metal particle-containing area as in A (x4000). In (C), EDS spectrum of the bright 882 nm particle marked in (B) (yellow arrow), showing an elemental composition corresponding to the titanium alloy (TiAlNb) of the stem. In (D), EDS mapping of the area within the white box of (B), showing the location and composition of the particles seen in (A,B).
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case_images: Particles containing Cr and phosphorous were also identified in the tissue, especially intracellularly (Figure 6).