Review Question - QID 219977

The AP pelvis of this failed total hip arthroplasty (THA) demonstrates severe hip center migration in the superomedial direction, disruption of the Kohler line, and possible pelvic discontinuity, indicating a Paprosky Type IIIB defect. The correct treatment of this bone loss in the revision setting is utilizing a cup-cage construct with structural bone allograft (Answer choice 5).

Acetabular bone loss in the setting of revision THA is a challenging issue with increasing prevalence. Bone loss can result from osteolysis, implant loosening, fracture, or infection. The workup for acetabular bone loss before revision should be exhaustive. Along with a standard AP pelvis, Judet views can be used to evaluate the anterior and posterior columns and assess for pelvic discontinuity. CT scans with or without 3D reconstruction can be helpful to better evaluate the extent of bone loss, amount and quality of remaining bone, and to plan for surgical reconstruction. The American Academy of Orthopaedic Surgeons (AAOS) proposed an acetabular bone loss classification (Illustration A) based on the presence of segmental, cavitary, or combined defects. The Paprosky classification (Illustration B) is more commonly used and provides treatment recommendations based on the degree and location of bone loss. In general, the Paprosky classification divides bone loss into three types with Type I being an undistorted hemispherical acetabulum, Type II being a distorted acetabulum with intact columns, and Type III represents a distorted acetabulum without supportive columns. Type I defects are often managed with cementless revision cups with or without grafting. Type II defects may require jumbo revision acetabular implants with structural grafts, augments, or cages. Type III defects require at minimum structural allografts or augments, and may require reconstruction cages or custom triflange cups. The key to acetabular reconstruction in the setting of bone loss is to optimize host bone contact and minimize further bone loss while maintaining an adequate hip center.

Sculco et al. published the outcomes of a consensus symposium regarding acetabular bone loss in revision THA. The symposium featured panels of experts meeting to establish recommendations for the diagnosis, classification, and management of THA acetabular bone loss. Regarding the classification system, the authors note the universal utility of the Paprosky classification to standardize bone defects. The symposium provides algorithms to guide surgeons through reconstruction techniques based on the defect severity. The authors provide this comprehensive resource as a useful tool when planning and addressing complex acetabular bone loss cases.

Telleria et al. published an overview of the Paprosky classification of acetabular bone loss. The classification, again, divides bone loss into three major types. Type I represents minimal bone loss with intact columns. Type II (IIA, IIB, IIC) represents moderate bone loss with partial structural compromise. Type III (IIIA, IIIB) represents severe bone loss with significant structural instability. Type IIIB, in particular, features superior migration with or without pelvic discontinuity that may require a custom triflange cup. Although the intraobserver and interobserver reliability is limited, the Paprosky classification tends to outperform other common classification systems. The authors conclude that the Paprosky classification remains a useful system for consistent communication and dictating management of acetabular bone loss.

Sheth et al. provide another review of acetabular bone loss in revision THA. The authors highlight the importance of the Paprosky classification and emphasize the importance of radiographic parameters in classifying bone loss. The authors explain radiographically evaluating the acetabulum including the teardrop, the superior obturator line, the Kohler line, and the presence or absence of ischial lysis. Using this information, the Paprosky classification can be successfully applied and subsequently guide treatment during reconstruction. The review continues to discuss the different treatment modalities available and the biomechanical principles involved in the reconstruction of the acetabulum. The authors provide a valuable resource for surgeons addressing acetabular bone loss in revision THA.

Figure A demonstrates a failed left total hip arthroplasty with significant superomedial migration of the acetabular and femoral head components and significant destruction of the anterior column, anterior wall, medial wall, and superior acetabulum. Illustration A is a table summary of the AAOS acetabular bone loss classification. Illustration B is a table summary of the Paprosky acetabular bone loss classification.

Incorrect Answers:
Answer 1: The bone loss in Figure A would be better classified as a Type IIIB defect and treated with either a cup-cage construct or a custom triflange construct. A non-cemented multi-hole revision cup would require more bone stock to support the cup.
Answer 2: Although a custom triflange would be an acceptable treatment option in this scenario, the defect is more correctly classified as a Paprosky IIIB defect. IIB defects have moderate (<3 cm) hip center migration and an intact Kohler line, unlike the radiograph shown in Figure A.
Answer 3: The bone loss in Figure A is better classified as a Type IIIB defect due to superomedial migration and Kohler line disruption.
Answer 4: The bone loss in Figure A is better classified as a Type IIIB defect due to superomedial migration and Kohler line disruption. Furthermore, Type III defects require some form of augmentation due to the lack of a supportive rim. A jumbo cup would not suffice for stability in this scenario.