Surgical Technique: A Cup-in-Cup Technique to Restore Offset in Severe Protrusio Acetabular Defects

Abstract

Background Severe medial and/or superior defects encountered in revision THA are currently managed with jumbo (C 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).

The Use of Augment Devices in Revision Acetabular Surgery

“…In this setting, a second porous metal shell, placed in appropriate inclination and anteversion, is cemented into the first shell. Early results show no failures in eight hips, but the average follow-up time was less than two years 25 .…”

Cup-on-cup technique to manage severe protrusio acetabular defects

“…Previously published studies have reported the application of cup-in-cup technique in the management of severe protrusio acetabular defects. [3][4][5] In comparison, the cup-on-cup First, the creation of initial stability and the anchoring concepts are different. Cup-in-cup technique using two porous tantalum acetabular cups: one larger medial cup is placed on to supportive host bone in a cementless fashion to buttress large defects, establish the initial stability, increase the horizontal offset and restore the vertical offset.…”

Revision Total Hip Arthroplasty in the Setting of a Well-Fixed Cup: Early Report on the Cup-in-Cup Technique

“…While our early clinical measures are promising, longer follow-up is needed to determine if cement debonding and loosening risks increase as loading and torsional stresses accumulate over time from the longer moment arm created by increasing leg length and offset. 14,20 In cases of acetabular component malposition, the cup-incup construct can be used selectively in cases where substantial retroacetabular bone loss exists, and cup explantation would cause imminent discontinuity and/or drastically alter the surgeon's ability to reconstruct the socket due to loss of superomedial support. Previously placed cups in a neutral orientation or mild retroversion (no more than 10°) are not necessarily excluded as long as they meet the minimum dimensions requirement, and the degree of their malposition does not cause further impingement when the new inner cup is placed in the targeted position (►Fig.…”

“…17 Offset was measured on an anteroposterior (AP) radiograph of the affected hip using the technique described by Berstock et al 18 and Merle et al 19 For the cup-in-cup radiographs, horizontal offset was designated as a horizontal line connecting the mid-point of the best fitting circle of the prosthetic head and the ilioischial line. 20 Leg length ("vertical offset") estimates were determined on AP pelvis radiographs as the perpendicular difference in millimeters between a line connecting the inferior aspect of the ischial tuberosities and the most prominent medial tip of the lesser trochanter. 21 Basic statistical analysis using Fisher's exact testing was conducted to analyze categorical data pre-and postoperatively given our small sample size.…”