INDICATIONS AND CONTRAINDICATIONS

The main indications for lesional treatment of periprosthetic osteolysis of the acetabulum include progressive osteolysis or a major lytic lesion around a well-fixed shell ( Fig. 52-1 ). Femoral head and acetabular liner exchange may also be indicated for accelerated polyethylene wear or catastrophic acetabular liner failure in the absence of major osteolysis. In these clinical situations the surgeon can contemplate grafting around the acetabular shell (if osteolysis is present) with retention of the shell and exchanging the articulating surfaces including the acetabular liner and femoral head. Lesional treatment of acetabular osteolysis has specific indications that should be met before this type of reconstruction is performed. Most important, in order for the acetabular component to be retained, it must be rigidly osseointegrated with the host bone and must be in an adequate position to provide a stable hip reconstruction. The lesion itself should be accessible to surgical curettage and grafting around the acetabular shell.

A, Anteroposterior (AP) radiograph of the left hip in an active 62-year-old man with mild hip pain demonstrates supra-acetabular osteolysis. B, Preoperative CT scan delineates the extent and specific location of the lesion. The patient was treated with an acetabular liner and femoral head exchange. The femoral head size was increased to a 36 diameter, and a highly cross-linked polyethylene liner was placed. C, The superacetabular region was grafted with morcelized allograft. D, At 2-year follow-up the patient had no symptoms and no complaints. He was involved in unrestricted activities. The anteroposterior radiograph of the hip shows partial resolution of the osteolytic defect. White arrows indicate osteolytic lesion on the anteroposterior hip radiograph and the CT scan images.

There are several relative contraindications to this revision technique. If the shell is not osseointegrated, if the shell is malpositioned, if a liner is not available, or if the shell is damaged to the point at which a liner cannot be inserted or cemented, the acetabular component should be revised. If the osteolytic lesion is large and is not accessible or if the osteolytic lesion is massive, the surgeon should contemplate complete revision of the acetabular component. This will allow improved access to and grafting of the defect as long as the pelvic bone stock is not significantly compromised by explantation of the shell. If the acetabular component has a poor track record or a suboptimal “ongrowth” fixation surface rather than a three-dimensional “ingrowth” surface, the stability must be carefully assessed and then complete revision of the implant should be contemplated, especially in a young patient. Specific examples of suboptimal fixation surfaces include titanium plasma spray and hydroxyapatite-coated macrotexture shells. Other contraindications include minor, asymptomatic osteolytic lesions or small osteolytic lesions that have not progressed over time. Major medical comorbidities that put the patient at unacceptable risk for surgical complications and concurrent implant infection are less common contraindications to lesional treatment of acetabular defects.

PREOPERATIVE PLANNING

Preoperative planning is an extremely important aspect of the surgical treatment of patients who have periprosthetic osteolysis. The surgeon should devise a specific preoperative plan and should be prepared for alternative reconstructive strategies. For optimization of surgical treatment, the appropriate equipment, hip implants, extraction instruments, and bone graft materials should be available. Even if lesional treatment is planned, the surgeon should have alternative options for complete revision. Equipment may include instruments to extract a well-fixed socket, acetabular reconstructive devices, and grafting materials.

As part of the preoperative plan, the patient’s history and physical examination should be reviewed. The number of previous surgeries, the position of previous incisions, the abductor function of the hip, and leg length discrepancies should all be noted. For hips with abductor deficiency, a constrained acetabular liner or large-diameter femoral head may be implanted to optimize hip stability. Periprosthetic infections should be ruled out before one proceeds with hip revision surgery. We routinely screen for implant infection with an erythrocyte sedimentation rate and C-reactive protein. If one or both of these are elevated, a hip aspiration sample for joint fluid cell count and culture is obtained.

Preoperative radiographic examination determines implant fixation status, the degree of polyethylene wear, and the size and location of the osteolytic lesion. We routinely obtain anteroposterior (AP) pelvic and cross-table lateral films of the involved hip to assess the acetabular component. The AP pelvic view gives us a sense of the eccentricity of the femoral head, which is an indicator of the linear wear of the polyethylene liner. The acetabular component position is assessed to determine if implant retention is an option. The presence or absence, size, and location of periprosthetic osteolytic lesions are noted. The cross-table lateral view reveals the relative version of the acetabular component, the bone stock and integrity of the posterior column, and the size and location of osteolytic lesions. If there is concern about the presence or extent of an osteolytic lesion in the anterior or posterior column, an obturator oblique or iliac oblique view can be obtained. The obturator oblique view of the pelvis demonstrates the integrity of the anterior column, and the iliac oblique view provides visualization of the posterior column. This combination of radiographs can be used to accurately assess the integrity of the host bone and usually to detect periprosthetic osteolytic lesions. Radiographic analysis can also identify the type of implants present and the fixation status. If the surgeon is not familiar with the particular implant, then the hospital and surgical records from the original surgery should be obtained to ensure that the appropriate prosthetic options are available at the time of revision surgery.

To supplement plain radiographs, a CT scan with artifact reduction is more sensitive in detecting questionable lesions and is better for localizing and estimating the size of documented osteolytic areas (see Fig. 52-1 ). CT scans can also more accurately delineate the integrity of the anterior column, posterior column, and medial wall, thereby contributing valuable information about the available host bone for acetabular reconstruction if shell removal is being considered.

If preoperative radiographs suggest the acetabular component is well fixed, is well positioned, and is associated with a progressive or major osteolytic lesion that can be treated locally, then our primary treatment plan would include retention of the acetabular component. The osseointegration of the component should be assessed radiographically but should also be confirmed at the time of surgery. The size of the acetabular component should be determined, and the possible liner size options should be investigated. Offset, oblique, or elevated lip liners may provide enhanced stability. Increasing femoral head size at the time of revision will enhance hip stability, but the acetabular shell must accommodate a liner with adequate polyethylene thickness and a larger inner diameter. The track record of the liner locking mechanism should be factored into the preoperative plan. The size of the liner should be estimated. The relative size of the femoral head that can be accommodated by the liner should also be determined so that all implant options are present at the time of surgery. We presently prefer to use a larger femoral head owing to the known higher risk of dislocation with head and liner exchanges. In general, 32- and 36-mm–diameter heads are used at the time of lesional treatment, and we prefer to avoid smaller and skirted femoral heads. We routinely use highly cross-linked polyethylene liners, and we have a low threshold for cementing the liner into the existing shell rather than depending on a questionable liner locking mechanism. The surgeon should always be prepared for a full acetabular revision with bone grafting if needed. In addition to templating of the acetabular side, the femoral implant needs to be identified, and an appropriate selection of femoral heads needs to be available. Bone graft options may include morcelized allograft chips, bulk allograft, or a variety of commercially available bone substitute products. Implant augments may be preferred for providing structural support. Instruments for lesional treatment of the periprosthetic osteolysis can also be helpful in accessing, débriding, and adequately grafting these lesions. A high-speed bur should be available to “texture” the surface of the liner as well as the acetabular shell. Texturing enhances the mechanical stability of the shell-cement and liner-cement interfaces. Hip explant instruments and an acetabular component for revision should be available.

The described aspects of preoperative planning will give the surgeon a specific strategy for surgical treatment and should ensure the availability of appropriate hip implants, extraction instruments, and bone grafting and augment options for the case.