The Modular Cup-in-Cup Construct in Revision Total Hip Arthroplasty.

BACKGROUND: The modular cup-in-cup technique, in which a modular primary acetabular component is cemented into a highly porous monobloc tantalum revision shell, provides the intraoperative flexibility to change bearings if subsequent re-revision is required. This study seeks to characterize the early outcomes of this technique. METHODS: A single-center retrospective review was performed of all patients who underwent revision total hip arthroplasty (rTHA) utilizing a modular acetabular component cemented into a highly porous monobloc tantalum revision shell. Preoperative and postoperative radiographs were assessed to quantify bone loss, cup position, and aseptic loosening. All-cause reoperation, revision for aseptic loosening, and revision for instability were estimated using the Kaplan-Meier method. RESULTS: In total, 27 hips were identified with a mean follow-up of 21.6 months. The most common indication for revision was aseptic loosening (48.1%). Preoperatively, 16 (59.3%) hips had Paprosky 3A defects, 7 (25.9%) had Paprosky 3B, 2 (7.4%) had Paprosky 2C defects, and 1 (3.7%) had a Paprosky 2A defect. In total, 4 (14.8%) patients underwent reoperation, 3 (11.1%) for instability and 1 (3.7%) for irrigation and debridement. All patients revised for instability were converted from a dual mobility articulation to a constrained liner. No radiographic loosening was observed at final follow-up. Estimated 3-year survivorships for all-cause reoperation and revision for instability were 84.6% (95% confidence interval: 46.6-95.6%) and 88.5% (95% confidence interval, 48.8-97.6%), respectively. CONCLUSIONS: The modular cup-in-cup technique is a viable option for rTHA patients at increased risk of instability. This technique provides surgeons the flexibility to exchange the articulation if recurrent instability occurs.