Surgical technique: a cup-in-cup technique to restore offset in severe protrusio acetabular defects.

BACKGROUND: Severe medial and/or superior defects encountered in revision THA are currently managed with jumbo (≥ 66 mm) acetabular components and modular augments, with reconstruction cages, or with the cup-cage technique. Preoperative planning can indicate when these techniques may not restore vertical and horizontal offset. Failure to restore offset can lead to impingement, leg length inequality, abductor weakness, and dislocation.

SURGICAL TECHNIQUE: We developed a "cup-in-cup" technique in which a porous tantalum acetabular shell was impacted into supportive medial host bone. A second tantalum shell was then cemented in, and this shell's diameter could be selected based on preoperative planning to achieve restoration of horizontal and vertical offset.

PATIENTS AND METHODS: We implanted porous tantalum hemispheric shells in seven patients undergoing eight revision THAs. The average age was 73 years at the time of the procedure. Preoperative defects per the classification of Paprosky et al. were three IIC, four IIIA, and one IIIB. All patients were followed clinically and radiographically for a minimum of 12 months (average, 28 months; range, 12-50 months).

RESULTS: Abductor strength was either improved by one grade (four hips) or unchanged (four hips). Horizontal offset was increased an average of 10.5 mm (range, 8-16 mm), and vertical offset improved by an average of 18.4 mm (range, 10-29 mm). There was no evidence of loosening or migration at the time of final followup.

CONCLUSIONS: At short-term followup, the early experience cautiously supports the use of this construct. Long-term followup and a larger patient experience will be required to determine the durability of this novel technique.

LEVEL OF EVIDENCE: Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.