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(A) The G7 dual mobility acetabular system (ZimmerBiomet, Inc, Warsaw, IN) device includes a vitamin-E infused highly crosslinked polyethylene outer head and Delta ceramic inner femoral head. The titanium alloy acetabular cup is a 3D porous cup with a mean pore size of 475 microns, 70% porosity, and a coefficient of friction of 1.25. A multi-hole design for the acetabular cup was used in this case.
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To reduce this risk, we selected a G7 dual mobility system (50 mm multi-hole cup, 40 mm outer-head; vitamin-E infused crosslinked polyethylene, 28 mm inner-head; Delta ceramic, Taperloc 123  #11 cementless stem, ZimmerBiomet, Warsaw, IN, USA) (Fig. 1, Fig. 2A).
(A) Postoperative radiographs obtained immediate after left total hip arthroplasty. (B) Plain radiograph showing postoperative posterior dislocation just one month after surgery. (C) Postoperative radiographs obtained 28 months after dry revision hip arthroplasty. Both retaining cup and stem remained stable.
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Unfortunately, postoperative dislocation occurred twice within 2 months after that surgery (Fig. 2B). Postoperative radiographs obtained 28 months after the revision surgery showed the implants were stable (Fig. 2C).
Evaluation of the implant alignment (A) Radiographic inclination of the cup (B) Anatomical anteversion of the cup (C) Operative anteversion of the cup (D,E) Anteversion of the stem.
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Implant alignment was acceptable, with the cup showing radiographic anteversion of 31 , radiographic inclination of 41 , anatomical anteversion of 45 , operative anteversion of 44 , and stem anteversion of 19  (Fig. 3A-E).
(A) Intraoperative image showing removal of the metal liner by tapping the edge of the cup. (B) The metal liner was easily removed from the cup. (C) The Freedom constrained liner (Zimmer Biomet, Inc, Warsaw, IN) system comprises a highly crosslinked polyethylene liner and (D) 36-mm cobalt chromium modular femoral head. The unit has a flat equatorial section at 15  to the vertical axis along the sides. (E) The unique 36-mm cobalt chromium head was compatible with the retaining stem; both stem and head were manufactured by the same manufacturer. (F) Intraoperative image after reduction.
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During surgery, the metal liner of the G7 dual mobility construct was easily removed by tapping on the edge of the cup (Fig. 4A, B), and the G7 cup and the Taperloc stem were well fixed to the bone. We then embedded the Freedom constrained liner in the G7 cup and placed the uniquely shaped Co-Cr metal head on the femoral neck of the original stem (Fig. 4C-F).
Range of motion of the left hip at most recent follow-up (A) Flexion (B) Abduction (C) External rotation (D) Internal rotation.
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The range of motion (ROM) in her left hip was good: flexion 110 , abduction: 30 , external rotation 30 , internal rotation 15  (Fig. 5A-D).