Options for Acetabular Revision
In 2000, a 72-year-old woman, who had a right, porous-coated anatomic prosthesis placed in 1986, presented to our institution with a limp and complaints about groin pain with weight bearing and activity. This disability had progressed slowly over the past year. She was able to walk with a cane and had a severely antalgic gait.
Anteroposterior radiographs of the pelvis and hip and a cross-table lateral radiograph of the hip showed acetabular component loosening and displacement with anterior and medial migration into the pelvis ( Fig. 59A.1 ). The stem did not show radiographic evidence of loosening. On the Johnson (cross-table) lateral view, the posterior column appeared to be intact. Results of the workup for infection, including the erythrocyte sedimentation rate (ESR), C-reactive protein (CRP) level, and hip aspirate culture, were all negative.
During revision surgery, the acetabular component was found to be loose and was easily extracted, exposing a large segmental defect of the medial acetabular wall. A massive ischial cavitary lesion and a large posterior column cavitary defect were identified. The dome was found to be intact at the periphery, and the posterior column was intact. The acetabular opening was reamed up to peripheral contact with a power reamer ( Fig. 59A.2 ).
A trial acetabular component was used to visually plan the reconstruction. The goal of reconstruction was to set the new hip center as close as possible to the native hip center. Placing a cup superiorly and medially to optimize bone contact in the large deficient cavity would result in significant hip center elevation and medialization, which would likely compromise hip stability considering the plan to retain the well-fixed stem. The large medial defect would leave a large area of cup unsupported by host bone, and the 20% cup coverage would be insufficient to prevent long-term medial migration of the acetabular shell into the pelvis ( Fig. 59A.3 ).
The porous tantalum augment trials and the shell trial guided the decision to use the augments as footings to support the acetabular component. This type of reconstruction produces sufficient primary stability to allow peripheral bone contact and ingrowth, and the primary failure mode of medial migration or protrusio is avoided. The optimal reconstruction of the defect was determined to be two 10-mm wedge augments with a 58-mm, porous tantalum revision shell. One augment was placed inferiorly into the ischial defect and posterior column, and one was placed superiorly into the medial defect and anterior column ( Fig. 59A.4 ).
Allograft cancellous bone was placed against the inner pelvic membrane, followed by the augments fitted into the defect from deep to superficial portions. More cancellous graft was then placed within the augment fenestrations, followed by the revision acetabular component. Native bone and augments were fashioned using a high-speed bur and helicoidal rasp to optimize stable contact with host bone. The posterior augment was impacted into place and provisionally fixed with one screw placed through a hole drilled through the augment and into the ischium ( Fig. 59A.5 ). Due to the inherent material properties of the augments and the ability to customize the shape using high-speed tools, excellent stability was achieved with the augments ( Fig. 59A.6 ).
Morcellized cancellous allograft was packed into the cavitary deficiencies and into the fenestrations within the augments. Final reaming was performed with the augments and allograft bone in place, taking care to obtain a peripheral rim fit. The shell trial was used to confirm the final size of the implant that would result in a reasonable rim fit when placed in optimal abduction and anteversion. This also restored the anatomic hip center. The final porous tantalum revision shell was opened, and antibiotic-laden cement used to unitize the augments to the shell. While the cement was hardening, five screws were placed through the cup (some through the prefabricated holes and others through newly made holes in the revision shell) and augments into host bone. Excellent stability of the overall construct was achieved, with cup–bone contact along the mouth of the acetabulum and secure fixation of the medial surface of the cup with the well-fixed deep augments.
At the 3-month follow-up evaluation, the patient reported minimal pain and no postoperative complications. She was walking with only a slight limp and without assistive devices. Radiographs showed excellent maintenance of position and contact of components with host bone. She returned for her 1-year, 2-year, 5-year, and 10-year postoperative visits walking without a limp and with minimal pain and smooth motion of her hip. She had an extension-flexion arc of 0 to 95 degrees, 30 degrees of abduction, and 30 degrees of adduction in full extension. She had external rotation of 60 degrees and internal rotation of 25 degrees with the hip flexed to 90 degrees. Radiographs at follow-up demonstrated no component loosening or lucency, with maintenance of the postoperative position. Her 10-year postoperative radiographs are shown in Figure 59A.7 .
The following algorithm is used to determine the need for acetabular revision and the manner of treatment.
Order studies to rule out infection, including erythrocyte sedimentation rate (ESR), C-reactive protein (CRP) level, and white blood cell count with a differential. A hip aspirate with cell count and culture should be performed.
If the patient is infected, remove hardware and stage with a cement spacer or resection arthroplasty, along with a period of appropriate antibiotic therapy.
If the patient has a metal-on-metal articulation, manual cell count of the hip aspirate is required, because debris may excessively elevate an automated count. Levels of serum metal ions (i.e., cobalt and chromium) should be determined.
Obtain anteroposterior radiographs of the pelvis and femur and a Johnson (cross-table) lateral view of the hip.
If the lateral radiograph suggests a discontinuity of the posterior column, consider ordering Judet views or a computed tomography scan.
Obtain reports about implants and tools used in previous operations, especially when considering retaining well-fixed components.
Order appropriate reconstruction equipment.
Porous tantalum revision shell, augments, and trials
Posterior column plates or cages (e.g., cup–cage construct) if discontinuity is a concern
Allograft (i.e., cancellous chips or structural grafts in some cases)
Dual-mobility head and liner for an abductor deficiency
Optimize the surgical approach for access and visualization.
Remove loose components and fibrous membrane.
Routinely send tissue for frozen section and culture.
Test for discontinuity of the posterior column by evaluating motion between the superior and inferior pelvis with a Cobb elevator or ball spike pusher.
If the discontinuity has the potential of healing (i.e., reasonably intact bone of the posterior column), consider plating the posterior column and placing the acetabular component with multiple screws on both sides of the dissociation.
The porous tantalum revision shell should not be used alone for fixation of discontinuity, even with screws placed in DeLee and Charnley zones 1 and 3.
If the discontinuity and bone defect are in the posterior column, consider alternative methods such as a Paprosky distracting technique with a large-diameter trabecular metal revision cup, a cup–cage construct, or combined anterior and posterior column plates.
Begin the reconstruction process.
Visually and manually assess bone deficiencies.
Use trial augments and a trial acetabular component to optimize fixation, achieve stability, restore the hip center and limb alignment, maximize host bone contact anterosuperiorly and posteroinferiorly, and fill defects.
Use high-speed tools to modify final augments and host bone for a customized fit.
Consider making new screw holes in components to direct fixation to the best remaining bone.
Place final augments, and secure them to bone with multiple screws.
Pack cancellous graft in the fenestrations of augments and around the construct.
Place the revision cup in appropriate anteversion and abduction, unitize to the augments with antibiotic-loaded cement between porous tantalum surfaces, and fix with screws traversing the cup, augments, and host bone.
Cement the liner in the revision shell using antibiotic-loaded cement.
Continue reconstruction with the femoral component.
Strategies for acetabular reconstruction of bone deficiencies during revision total hip arthroplasty have included antiprotrusio cages, rings and allografts, and custom triflange devices. Potential drawbacks of these treatment modalities range from failure due to loosening and graft resorption (e.g., cages, rings, allografts) to cost, required imaging studies, extensile soft tissue exposure, and wait time for custom prosthesis fabrication (e.g., triflange implants). For more than a decade, off-the-shelf, hemispherical, porous tantalum acetabular shells have provided a reliable ingrowth surface, offering the possibility of more permanent results at the time of revision surgery without the cost or wait time associated with custom implant fabrication.
Many acetabular deficiency classifications have been proposed. In our experience, modern acetabular components that fail and require significant reconstruction do so in two fundamental ways. They rock vertically and then roll out posteriorly, or they roll up and in, creating a superior-medial defect. Components that roll up and out seem to be associated more often with pelvic dissociation and posterior column defects. Components that roll up and in tend to be less associated with posterior column defects and dissociation. In both cases, acetabular component failure commonly occurs in a predictable radiographic sequence, beginning with a gap or separation in zone 3. The component then rocks on a superior pivot point and rolls anteriorly or posteriorly, resulting in one of the failure modalities described previously. The key to preventing these failures is fixation and ingrowth in zone 3 inferiorly. After failure has occurred, reconstruction of both types of defects can be facilitated by using the porous tantalum revision shell in conjunction with porous tantalum augments when indicated.
Examination and Imaging
The preoperative examination should include evaluation of gait mechanics, including assessment of abductor strength. Hip range of motion, distal motor power, sensation, and vascular status should be evaluated and documented. Skin should be examined for scar locations, keloids, and draining sinuses.
We rely mainly on radiographs for the diagnosis and operative planning. Essential views include anteroposterior radiographs of the pelvis and femur and a Johnson (cross-table) lateral view of the hip. The anteroposterior views are used to evaluate the ilioischial line to determine the integrity of the medial wall and anterior column. We next determine the extent of ischial radiolucency and attempt to judge the integrity of the posterior wall and column. A teardrop can suggest integrity of the medial wall and inferior portion of the anterior and posterior columns. Vertical cup migration can be an indicator of superior dome bone loss.
If pelvic dissociation is suspected on the Johnson lateral view, Judet views can be obtained to further inspect the radiographic continuity of the posterior column. Advanced imaging such as magnetic resonance imaging (MRI) or computed tomography (CT) can be useful adjuncts in selected cases. Lumbar spine radiographs may be useful for patients who have concomitant spine disease or a fixed deformity resulting in pelvic obliquity.
Anatomy and Approaches
Many approaches can be used to access the acetabulum in revision surgery. The preferred approach is the one with which the operating surgeon is the most comfortable and that provides the best and safest exposure in his or her hands. Familiarity with extensile versions of the preferred approach is important in case added exposure is needed during surgery. In all situations, it is essential to spare as much hip abductor muscle as possible.
We prefer an anterolateral approach using an anterior trochanteric wafer osteotomy. If a more extensile approach is required, the exposure can be extended distally into the vastus lateralis and superiorly with elevation and splitting of the gluteus medius along the superior rim of the acetabulum. Abductor splitting greater than 5 cm superiorly may endanger the superior gluteal nerve.
We prefer general anesthesia with a psoas nerve catheter for postoperative pain control in our hip revisions. After careful lateral decubitus positioning, padded hip clamps are used to secure the patient. Standardized patient positioning by a trained individual can facilitate later acetabular component placement.
After standard surgical preparation and draping, the most optimal previous incision is used, and scar is excised if it is hypertrophic. The preferred skin incision is located directly lateral to the greater trochanter when the hip is abducted 30 degrees and in neutral rotation, centered on the most prominent point of the greater trochanter. With the leg held in this position, the incision is sharply brought down to and through the iliotibial band. A Charnley retractor is helpful at this point.
The anatomy of the gluteus medius is then inspected, and the soft spot between the superior and anterior heads of this muscle identified. There exists an intermuscular interval between the lateral (abductor) portion of the medius and the anterior (internal rotator) portion of the medius. During this approach, the surgeon releases the anterior portion of the medius with its attachment to a wafer of bone from the anterior greater trochanter. Bovie cautery is used to demarcate an anterior wafer osteotomy fragment to include attachment of the anterior head of gluteus medius and the anterior vastus lateralis ( Fig. 59A.8 ).