Abstract
Acetabular osteolysis not infrequently presents the hip surgeon with the daunting and conflicting challenges of bone stock restoration and implant stability. Recognition of the size, position, and extent of the defect preoperatively is necessary for safe navigation of these difficult seas!
Routine radiographic examination is the single most useful preoperative test, as techniques such as CAT scans or MRI examination will be frustrated in the presence of metal-backed devices because of metal artefact. A careful review of the preoperative x-rays will allow the surgeon to properly and accurately anticipate the type of bone defect.
Revision of the failed acetabulum when the peripheral rim is intact, with small (< 2 cm) medial defects, and in the absence of large cavitary defects may be reliably managed with simple hemispheric porous ingrowth prostheses, with adjunctive cancellous allograft. However, at least 50% of the prosthesis should be in contact with viable and stable host bone for reliable outcomes. In the absence of this, a revision ring is indicated.
The presence of medial wall defects, as indicated by the protrusion of the implant beyond the iliopectineal line on the AP radiograph, indicates the probability of an uncontained central defect. Consideration should be given to the use of a protrusio ring with allograft in these cases, particularly when the defect is larger than 2 cm in diameter. If significant rim defects also exist, the use of a revision cage with allograft in indicated.
Rim defects should be suspected in cases of implant “breakout”, or in the presence of implants significantly larger than the apparent diameter of the contralateral acetabulum. Rim defects may contraindicate the use of an oversized porous socket, particularly when more than 2 cm of implant is exposed posterosuperiorly, because of the difficulty in establishing a stable implant-bone interface. In these situations, use of a revision ring is advised.
The presence of large “blowout” lesions in the ileum or ischium will indicate the need for substantial quantities of cancellous allograft, which may make the use of a simple porous acetabular shell questionable. Frequently, these lesions will lead to severe peripheral rim defects, requiring the use of a reconstruction ring.
Acetabular defects can be recognised reliably with routine radiographs. However, the revision surgeon is advised to be prepared for unanticipated defects by having available reconstruction rings, allograft, and a variety of revision acetabular implants.
The abstracts were prepared by Mrs Dorothy L. Granchi, Course Coordinator. Correspondence should be addressed to her at PMB 295, 8000 Plaza Boulevard, Mentor, Ohio 44060, USA.
