Uncemented Cup With Metal Augments or Structural Graft
David G. Lewallen
The goal of any uncemented acetabular revision procedure is to maximize stable implant contact against viable host bone to encourage bone ingrowth for long-term durability.
When faced with irregularly shaped acetabular bone defects, simply reaming larger and larger to try to fill up the void can remove excessive amounts of remaining host bone and may destroy key rim or column support for the cup.
Creation of an individualized irregularly shaped acetabular construct is possible by intraoperative assembly of a hemispherical acetabular component with one or more off-the-shelf highly porous acetabular augments.
Acetabular augments can serve as a prosthetic structural bone graft alternative without the risk of late resorption.
Sterile Instruments and Implants
Standard retractors and hip instruments.
High-speed burr to contour bone to fit defects.
Hemispherical acetabular component instruments and trials.
Acetabular augment trials in a variety of sizes and thicknesses to aid in intraoperative assessment, sizing, and planning of final construct.
Large plastic syringe to aid in placing cement precisely along the concave surfaces and edges of the augment where it contacts the revision cup.
Cancellous bone graft to fill the fenestrations of the augment and any small remaining gaps or defects.
Any of the standard potentially extensile surgical approaches can be used per surgeon preference similar to any revision total hip arthroplasty (THA).
Posterolateral and direct lateral approaches are the most commonly used at our institution either alone or in combination with an extended trochanteric osteotomy as needed to address the femoral side.
Careful assessment of the location and extent of acetabular bone defects is critical for the preoperative planning and preparation needed to ensure that the implants, instrumentation, and bone graft materials that might be needed are available for not only the planned procedure but also for potential alternative procedures or implant combinations, because intraoperative findings and events may require a change in plan.
Radiographic assessment begins with the 3 standard views of the hip (anteroposterior [AP] pelvis, AP of the hip, cross-table lateral).
In cases of major bone defects or suspected pelvic discontinuity, iliac and obturator oblique x-rays (Judet views) are extremely helpful and are recommended.
Occasionally, if uncertainty about defect character, size, and location still exists after obtaining the above-mentioned 5 standard radiographs, a computed tomography (CT) scan with 3D reconstructions can assist in bone defect assessment.
CT scans are used selectively as needed after careful study of the x-ray views because of the added cost and x-ray exposure to the patient.
Although a general idea of whether and where an augment may be needed can be gained from preoperative review and planning, final implant sizing, orientation, and placement is based on intraoperative assessment of the deficient acetabulum and provisional use of cup and augment trials.
Bone, Implant, and Soft Tissue Techniques
The initial goal of any acetabular reconstruction should be to achieve stable cup support on as large an area of host bone as possible.
In more than 90% of cases, this can be achieved using a hemispherical cup and multiple screws and is the preferred reconstruction when possible.
Maximal cup fixation is achieved with an array of screws across the dome of the acetabulum and down the posterior column into the base of the ischium (Figure 26.1).
Major acetabular bone loss encountered at the time of revision surgery can threaten cup support and fixation, especially when uncontained or segmental bone loss has occurred as seen in Paprosky 3A (“up and out”) or 3B (“up and in”) bone defects.
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