Emerging Techniques Address Massive Acetabular Bone Loss in Revision Hip Arthroplasty

Revision of a failed acetabular component with associated bone loss can present substantial reconstructive challenges for the arthroplasty surgeon. The goals of this surgery include restoring acetabular bone stock for the purpose of providing acetabular cup stability and restoring the hip center of rotation. Traditionally, massive acetabular defects have been managed with structural allograft, which is susceptible to complications including infection, resorption, and fracture. This article reviews current strategies and emerging techniques for managing massive acetabular bone loss in revision hip arthroplasty.

The Paprosky classification provides a framework for characterizing these acetabular defects. View the Sidebar for more details on the classification system.

Severe bone loss can result in an osteolytic transverse acetabular fracture called pelvic discontinuity (Fig. 1). This “fracture” is different from a traumatic fracture in that a pelvic discontinuity has very poor healing potential. The healing potential drives treatment considerations. Patients with minimal to moderate acetabular migration and only minimal osteolysis (i.e., Paprosky types I, IIA, and IIB) and even those with some type III defects without pelvic discontinuity can achieve biologic fixation with a hemispheric shell with or without highly porous metal augments. Generally, augments are used to treat oblong type IIIA defects. However, patients with more severe acetabular migration, progressive ischial osteolysis, and massive bone loss (i.e., types IIC, IIIA, and IIIB) benefit from larger, more stable constructions due to poor healing potential. If pelvic discontinuity is also present in these type III defects, conventional cup reconstruction, even with augments, is more likely to fail. However, recent studies have shown promising short-term results with posterior plating of an acute discontinuity and implantation of a highly porous cup. Alternative revision constructs used for severe acetabular bone loss include a cup-cage construct and custom triflange acetabular component. These constructs are effective in treating pelvic discontinuity with good midterm follow-up.

A cup-cage construct consists of a highly porous metal shell that is fixed to the acetabulum with multiple screws. A cage is then placed over the shell to secure the shell to the ilium and ischium. A liner is then cemented into the cage in the appropriate version. In effect, the cage protects the shell while it achieves bony ingrowth. This construct has the advantage of being built intraoperatively without customized components; however, given that it assembles multiple modular pieces, there is a concern for implant failure if any one piece fails.

Two recent studies showed that the cup-cage construct can treat severe acetabular bone loss. In a 2024 study in the Journal of Arthroplasty, Chaudhry et al examined survivorship, complications, and functional outcomes of 131 hips treated with a cup-cage construct. Seventy-five of the cases had massive bone loss. The mean age was 68 years, and the mean follow-up was 7.7 years. Survivorship due to all-cause failure was 75 percent at 10 years and 70 percent at 15 years. The revision rate for aseptic loosening of the cup and/or cage was 3.8 percent (five of 131 hips). The revision rates for infection and dislocation were 9.1 percent (12 of 131 hips) and 7.6 percent (10 of 131 hips), respectively.

A 2024 study in Clinical Orthopaedics and Related Research from Mu et al examined functional outcomes, survivorship, and complications of 30 hips with pelvic discontinuity reconstructed with a cup-cage construct. The mean age was 61 years with a median follow-up of 7.6 years. Harris Hip Scores improved significantly from a preoperative median of 39 to a postoperative median of 76. Survivorship without radiographic aseptic loosening or migration of components was 100 percent at 115 months. Likewise, survivorship was 100 percent with revision for any reason as the endpoint. Complications included two dislocations, one femoral stem loosening, and one infection.

Custom triflange components
The second option for massive acetabular bone loss is a custom triflange acetabular component, which is designed directly from a patient’s pelvic CT scan (Fig. 2). This process can take more than 6 weeks and involves creating a plastic model followed by the actual implant. This construct has the advantage of requiring less intraoperative assembly because it is one unit. However, given the delay from pelvic CT scan to operation, additional bone loss may occur. This bone loss often is over the posterior column, leading to increased acetabular retroversion and subsequent dislocation.

A 2023 study from Christie et al in the Journal of Arthroplasty examined complications in 88 hips treated with a custom triflange construct with 10-year follow-up. All defects were type IIIA or B with or without pelvic discontinuity. Forty-three hips (49 percent) had complications leading to revision. Ten revisions (11 percent) were for failure. Seven of those were for infection and three for aseptic loosening. Overall, the custom triflange component was retained in 89 percent of cases.

Another 2023 study in the Journal of Arthroplasty, by Meding et al, examined functional outcomes and complications of 40 hips treated in a custom triflange with 6- to 13-year follow-up. All hips had Paprosky type IIIA or IIIB acetabular bone loss. Thirty-eight hips (95 percent) were considered radiographically stable at final follow-up. Complications included two hips with deep infections (5 percent), one hip requiring femoral component revision for recurrent dislocations, and one hip with femoral aseptic loosening.

Reconstruction of aseptically loose acetabular components with massive bone loss continues to pose major challenges in terms of addressing bone loss and associated pelvic discontinuity. Pelvic discontinuity can greatly increase difficulty of the operation because of the need to manage the transverse acetabular fracture. More recent studies have described favorable outcomes with techniques to manage pelvic discontinuity, ranging from plating the defect to peripherally distracting the defect and placing the acetabular component in the defect. The elastic recoil of the pelvis provides initial mechanical stability and bone ingrowth. As more hip arthroplasties are being performed in younger, more active patients, revisions with substantial acetabular bone loss will be encountered more frequently by arthroplasty surgeons.

Andrew Palosaari, MD, is an orthopaedic house physician at New York–Presbyterian/Lower Manhattan Hospital.

Michael DeRogatis, MD, MS, is an orthopaedic surgery resident at St. Luke’s University Health Network in Bethlehem, Pennsylvania.

Paul S. Issack, MD, PhD, FAAOS, FACS, is a clinical associate professor in the Department of Orthopaedic Surgery, Weill Cornell Medical College, and a trauma and adult reconstruction orthopaedic surgeon at New York–Presbyterian/Lower Manhattan Hospital. He is also a member of the AAOS Now Editorial Board.

The Paprosky classification

The Paprosky classification categorizes acetabular bone loss into three types based on severity and anatomical factors.

• Type I defects have minimal acetabular bone loss, do not have acetabular migration, and have an intact acetabular rim.
• Type II defects have distortion of the acetabulum with increasing degrees of bone loss.
  • Type IIA defects have superomedial migration of the acetabulum (<3 cm) and an intact acetabular rim.
  • Type IIB defects have superolateral migration of the acetabulum (<3 cm) and an obliterated superior acetabular rim.
  • Type IIC defects have isolated medial migration of the acetabulum with an intact acetabulum rim.
• Type III defects demonstrate disruption of the acetabular columns.
  • Type IIIA defects have superolateral migration (>3 cm) of the acetabulum and bone loss around the acetabular rim from 10 a.m. to 2 p.m. (“up and out”).
  • Type IIIB defects have superomedial migration (>3 cm) of the acetabulum, with bone loss around the acetabular rim from 9 a.m. to 5 p.m. (“up and in”).

• Type IIA defects have superomedial migration of the acetabulum (<3 cm) and an intact acetabular rim.>
• Type IIB defects have superolateral migration of the acetabulum (<3 cm) and an obliterated superior acetabular rim.>
• Type IIC defects have isolated medial migration of the acetabulum with an intact acetabulum rim.
• Type IIIA defects have superolateral migration (>3 cm) of the acetabulum and bone loss around the acetabular rim from 10 a.m. to 2 p.m. (“up and out”).
• Type IIIB defects have superomedial migration (>3 cm) of the acetabulum, with bone loss around the acetabular rim from 9 a.m. to 5 p.m. (“up and in”).