Acetabular Reconstruction

Algorithm

The following algorithm is used to determine the need for acetabular revision and the manner of treatment.

• 1.

  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.

• 2.

  Obtain anteroposterior radiographs of the pelvis and femur and a Johnson (cross-table) lateral view of the hip.

• 3.

  If the lateral radiograph suggests a discontinuity of the posterior column, consider ordering Judet views or a computed tomography scan.

• 4.

  Obtain reports about implants and tools used in previous operations, especially when considering retaining well-fixed components.

• 5.

  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

• 6.

  Optimize the surgical approach for access and visualization.

• 7.

  Remove loose components and fibrous membrane.

• 8.

  Routinely send tissue for frozen section and culture.

• 9.

  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.

• 10.

  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.

• 11.

  Place final augments, and secure them to bone with multiple screws.

• 12.

  Pack cancellous graft in the fenestrations of augments and around the construct.

• 13.

  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.

• 14.

  Cement the liner in the revision shell using antibiotic-loaded cement.

• 15.

  Continue reconstruction with the femoral component.

Introduction

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.

Surgical Techniques

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.

Anterolateral Approach

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 ).

An incision is made in the vastus lateralis fascia laterally that is in line with the long axis of the femur, below the vastus ridge, and it is brought down to bone. A straight osteotome is used to mobilize this anterior wafer of the greater trochanter, which includes attachment of the anterior gluteus medius and vastus lateralis. The wafer is retracted anteriorly, the femur is retracted posteriorly, and the approach is continued down the femoral neck, releasing the gluteus minimus and capsule directly from their attachments to bone ( Fig. 59A.9 ).

Acetabular Exposure

Capsular scar should be removed to facilitate visualization and exposure. The hip is dislocated, and the femoral shaft is retracted posteriorly, protecting the sciatic nerve. We have found it easiest for the surgeon to stand on the abdominal side of the patient when performing the acetabular reconstruction, regardless of the preferred surgical exposure.

Circumferential retractors are placed to expose the acetabulum. We use a short, spiked cobra retractor superiorly and anteriorly; blunt-tipped, curved retractors anteriorly and posteriorly; and a large-diameter bone hook with the assistant pulling downfield and posteriorly with the Charnley retractor still in place. Placing the leg with the knee in extension just at the opening of the anterior pocket and in maximal external rotation with an assistant holding the foot externally rotated keeps the femur out of the way of reamers. Scar is then removed circumferentially from around the rim of the acetabulum ( Figs. 59A.10 ).

If the cup is well fixed and has no screws in place through the shell, a concentric cup-removing osteotome is used to separate the cup from host bone. We have found that this results in minimal bone loss. If screws are in place through a well-fixed shell, the modular liner is removed using a drill hole and screw technique. The acetabular screws are removed, the liner is replaced, and the concentric cup-removing osteotome is used, keeping in mind that the hardest bone is usually located in previous screw tracts. For metal-on-metal shells, a bipolar trial can be used to center the curved-blade cup-removal osteotome. A cemented polyethylene liner can be removed with a power reamer to expose screw heads for removal ( Figs. 59A.11 to 59A.13 ).

After the components are removed, fibrous tissue is excised from bone inside the acetabulum and around the periphery, and an assessment is made of defects and pelvic bone left to support a reconstruction. A high-speed 9 × 12.3 mm acorn bur is useful for this, as are progressively larger acetabular reamers. At this point, it is important to determine the spatial orientation of the patient and to correct it if the patient has shifted by adjusting the table inclination or yaw. Anatomic landmarks such as the transverse acetabular ligament, acetabular rim, and sciatic notch are also useful in acetabular component positioning. Acetabular reconstruction is discussed further in Chapter 59B .