This chapter describes the appropriate treatment of cavitary defects.
Cavitary defects are contained defects.
The defects may be successfully treated with a hemispherical or elliptical acetabular component and supplemental bone grafting.
Structural integrity should be carefully assessed to ensure that there is no violation of the posterior column or a pelvic discontinuity.
The location of the true hip center should be identified.
All excess soft tissue should be curetted.
Reaming must be done carefully to avoid structural compromise.
Careful inspection is necessary to identify a pelvic discontinuity.
The initial fixation should be firm.
The projected increase in demand for total hip arthroplasty by the year 2030 will be accompanied by an increased need for revision surgery. As with any revision arthroplasty procedure, restoring function while preserving bone stock is crucial. Acetabular cavitary defects have several causes, including overzealous reaming, inadvertent bone removal during cup extraction, and osteolysis. These defects may also be seen in cases of advanced arthritis, infection, trauma, or tumor. Assessment of bone loss can determine the appropriate treatment from among the various surgical options available. We describe the procedures for treating cavitary defects in selected cases.
The classification of acetabular defects is outlined in Chapter 43 . We prefer the classification of Paprosky because it enables a thorough evaluation of the acetabular defect and directs management.
By definition, cavitary defects involve a volumetric loss of bone with preservation of the acetabular rim. Most cavitary defects can be managed with a hemispherical or elliptical acetabular component ( Fig. 54.1 ). The reconstruction is often combined with bone grafting or substitute material to fill the void. This allows the restoration of bone stock in case another revision is required, but it does not add to the initial stability of the construct.
Indications and Contraindications
Reconstruction is indicated if there is pain, obvious loosening of the acetabular component, or significant wear of the polyethylene. The patient must be screened for all medical comorbidities and should be medically stable for what is most commonly an elective procedure. The appropriate steps to rule out infection are necessary because management of a cavitary defect includes the possible use of larger acetabular components, augments, and allograft, whose success is jeopardized by underlying infection.
Anatomy and Approaches
Isolated cavitary defects can be addressed from an anterior or a posterior approach to the hip. Most commonly, we use the approach that was employed for the primary arthroplasty. If an extended trochanteric osteotomy is anticipated, we use a posterior approach.
Examination and Imaging
For simple defects, standard anteroposterior pelvic and lateral hip radiographs are sufficient. Oblique radiographic views of the pelvis and a computed tomography (CT) scan occasionally may be used to further assess extensive lesions.
Step 1. Acetabular Exposure and Evaluation
Acetabular exposure is performed from an anterior or posterior approach, depending on the surgeon’s comfort and extent of the lesion. For well-fixed acetabular components with isolated, small, retroacetabular cavitary defects from osteolysis, attempts should be made to retain the component. Screw holes or a small cortical window can be used to pack bone graft or bone graft substitute into the defect ( Fig. 54.2 ).