Acetabular revision with impaction grafting for severe acetabular bone loss without pelvic discontinuity

Background

Acetabular reconstruction in the presence of significant or severe acetabular bone loss can be achieved in different ways. Classification of the expected bone loss is important. Similarly, patient characteristics and clinical experience should be considered when determining how best to manage each individual patient.

Numerous techniques exist in acetabular revision. With regard to the use of cemented components in acetabular revision, results have been varied secondary to the poor environment for cement integration into host bone found in acetabular revision. ^, The concept of using impaction bone grafting (IBG) to manage bone defects facilitates bone stock restoration while also recreating an excellent surface for more reliable cemented fixation. Bone stock restoration is a specific potential benefit in a younger patient population. Simultaneously, successful use of this technique provides versatility for the surgeon to reconstruct the mechanics of the hip on the acetabular side, managing irregular bone defects, yet still able to restore the hip center of rotation accurately, with the acetabular component then subsequently orientated optimally and secured against restored bone stock in a reconstructed acetabulum. The technique, developed initially and popularized in Europe, provides a versatile and reliable option in the management of these complex problems, perhaps more specifically in a younger patient group, with excellent medium- and longer-term outcomes reported from Nijmegen and Exeter, among others.

Premise: In this chapter, we will discuss and illustrate the management of this complex problem in the absence of pelvic discontinuity, utilizing IBG with both uncemented and cemented acetabular components.

Patient positioning and surgical approach

While the technique can be performed using any of the exposures and approaches through which revision surgery is performed, it is the author’s preference to use the posterior approach. Whichever approach is chosen, it is critical that the patient is stable and well-supported on the table, with the surgeon confident of pelvic orientation to ensure reliably accurate eventual component orientation. Support positioning and draping are important. It should be appreciated that frequently, a more extensive exposure will be required around the acetabulum. Specifically, proximal access beneath the abductors and more distal posterior exposure down to and including the ischium may be required when managing severe acetabular defects. Planning should identify that adequate mobilization of the hip and surrounding soft tissue envelope is required. Exposure and soft tissue release should allow the femur to be translated away from the acetabulum and secured in that position to facilitate circumferential visualization of the acetabulum. Careful positioning of retractors around the acetabulum allows the surgeon the required visualization while ensuring a reliable appreciation of acetabular orientation. Exposure can be a specific challenge if the femoral component is to remain in situ during the procedure. While there is no prescribed surgical approach through which this technique can be utilized, a number of factors should be borne in mind as the surgeon plans the surgical approach and exposure.

Required equipment

Ensuring the correct instrumentation is available in the operating theater requires careful preoperative planning. The equipment required to extract the existing component safely, with iatrogenic bone loss, should be determined within that process. The IBG technique is used specifically in circumstances where there is bone loss around the component. Additional equipment, such as sharp-edged straight and angled curettes, can be helpful to scrape lytic debris away from residual host bone. A high-speed burr can be useful at the time of debridement. Large rongeurs are used to prepare the graft. Bone reamers are helpful to regularize residual bone and to prepare a healthy bleeding bed into which impaction grafting is performed. Additional specific instrumentation required includes medial and peripheral metal rim mesh, used to contain defects, within which suitably prepared bone graft can be impacted using specific impactors. These are available in various shapes and sizes to allow the graft to be impacted into the various areas where bone stock restoration is required ( Fig. 9.1 ). Small fragment screws are required to gain secure fixation of the mesh required to contain rim defects. Flanged hemispherical impaction devices are also helpful to regularize the graft. The technique typically involves gentle ‘reverse reaming’ with standard reamers as the process proceeds, facilitating the development of a solid bone graft layer. A cemented acetabular component, typically with a trimmable flange, with the required cement mixing system is used. On some occasions, and typically with less significant bone loss and smaller areas of grafting, porous metal-backed uncemented acetabular components can be used in association with an IBG technique.

Surgical technique

A full, safe circumferential exposure of the acetabulum in the management of severe bone loss cases is essential. Careful positioning and retraction of the femur with or without a retained component is critical. Care to avoid further damage to the compromised acetabulum both when explanting the existing component and when positioning the femur should be taken - this may require additional release and a wider exposure. With the acetabulum exposed and the existing acetabular component removed carefully, attention can be turned to reconstruction. Much is gained from a thorough preoperative plan and classification of the acetabular defect likely to be encountered. In the presence of severe bone loss, particularly with type 3 defects, the surgeon should be clear that there is no discontinuity that could compromise the existing plan for reconstruction. Very careful use of a sharp-edged curette to remove acetabular debris should be followed by gentle circumferential exploration of the residual bone stock, identifying the extent of contained and areas of uncontained bone loss.

A successful outcome with this technique requires the bone graft introduced to be contained and subsequently impacted to create a structurally robust neoacetabulum. Subsequent incorporation is facilitated by circumferential loading with mobilization. As the bone graft material is introduced, it is impacted and gently ‘reverse reamed,’ sequentially building structural integrity and restoring acetabular bone stock and anatomy. It is important that the surgeon is mindful of the planned location of the hip center of rotation. As the impaction process proceeds, the center of impaction grafting approaches that planned position. Occasionally, the impaction reverse reaming process will be eccentric within the irregular bone loss and acetabular defect.