Acetabular bone defects: classification and diagnosis

Failure of the acetabular component of a total hip arthroplasty (THA) is frequently associated with bone loss as a result of loosening and osteolysis; it is likely that bone defects will be extended during implant removal. The amount and location of acetabular bone loss greatly influence the degree of technical difficulty of revision THA (rTHA) [1]. An accurate preoperative assessment of the bone defect is therefore extremely important for surgical planning and successful outcomes, with the ultimate goal to conserve bone stock and reconstruct bone defects to ensure the longevity of the revision. In the first part of this series of articles, Thomas Kostakos from the Henry Dunant Medical Center, Athens, Hellenic Republic (Greece), will explain the importance of acetabular bone loss estimation along with the existing classification systems and the methods employed for a diagnosis.

Several classification systems have been published: the American Academy of Orthopaedic Surgeons (AAOS) [2], Paprosky [1], Gustilo [3], Engh [4], Gross [5], Saleh [6], and Parry [7] systems. The AAOS and Paprosky systems have been most widely used in the orthopedic community; these two systems are explained in the following sections.

AAOS classification

The AAOS classification (Table 1) divides acetabular deficiencies into two basic categories: segmental and cavitary defects [2]. The cavitary defects represent a loss in volume of the acetabular bone without compromising the acetabular rim, while segmental defects involve the complete loss of acetabular bony structural support for the prosthesis [2].

The AAOS classification is widely used. Despite that, it does not address the magnitude of the defects, nor does it shed light on the specific management options of the defects [8–10]. In addition, this classification system was deemed to have low to moderate reliability and its validity has not been well established [9, 11].