CORR Insights®: What are the Complications of Three-dimensionally Printed, Custom-made, Integrative Hemipelvic Endoprostheses in Patients with Primary Malignancies Involving the Acetabulum, and What is the Function of These Patients?

Where Are We Now?

Surgical management of malignancies involving the acetabulum is a controversial and difficult problem. Metastatic tumors have a different set of treatment goals than those associated with curative surgery for primary lesions do. Even in curative surgery for primary lesions, there are important variations between patients in the extent of anatomic resection, tumor biology, and the use of adjuvant therapy [2].

Tumor margins are a prognostic factor worthy of careful analysis, especially if the reconstruction method affects the planning of resection. As one recent study reported, a surgical margin of even 4 mm is considered acceptable for chondrosarcoma [7]. However, the influence of margins in dedifferentiated chondrosarcoma and many other aggressive sarcomas is less clear. The use of cutting guides has been shown to improve tumor margins [4].

In pelvic reconstructions, complications are a major concern [1, 2, 6]. As noted by Wang et al. [8] in this issue of Clinical Orthopaedics and Related Research®, infection and instability because of hip dislocation and fixation failure are the most-frequently reported complications. The risk of infection is an essential factor in decision-making, especially when adjuvant therapy is contemplated. The absence of reported infections in this paper [8] is at odds with the findings of a recent systematic review (10% to 45% rate of complications) [2], although very low rates of infection have occasionally been reported [5]. The authors’ strategy includes minimizing dissection of uninvolved tissue, reducing dead space by suturing muscles to the implant, and performing serial irrigation and soaks in 10% povidone-iodine solution. They described a streamlined procedure including preoperative simulation for 4 hours. As a result, the duration of surgery and blood loss may have been lower than might be expected. These factors are important risk factors to consider for decreasing the risk of infection. Soft-tissue transfers might be performed for this reason as well.

Newer constrained implants might decrease the risk of hip dislocation in the short-term but might also be associated with other long-term complications, such as implant failure through loosening or failure. The absence of hip instability reported by Wang et al. [8], which is associated with a careful acetabular orientation and constrained cup design, merits longer term follow-up, but is certainly encouraging.

Based on this study, it is reasonable to consider patient-specific cutting guides and implants as an option for this clinical problem. The authors have developed a streamlined approach that includes many strategies to prevent infection, including preoperative simulation, that can be considered state of the art.

Where Do We Need To Go?

Questions that remain to be answered when considering the options for acetabular reconstruction after resection include: how are soft-tissue margins affected by the use of cutting guides? How can we decrease the high rate of infection associated with these procedures? How can we improve implant stability in this setting? What is the best functional assessment strategy? How do we predict the effect of soft-tissue resection on function? Can we decrease the cost of these complex reconstructions, especially in patients with metastatic disease?

A protocol-based approach has improved the complication risks for the revision of infected joint implants and other complex reconstructive procedures. The approach by Wang et al. [8] is promising and deserves to be applied in a rigorous, prospective fashion for validation in a larger study.

The application of recent technology in arthroplasty and fracture care, including locking screws and the use of porous metal implants with a precise geometrical fit, offers promise in solving the difficult problem of implant stability. Three-dimensional imaging software to design cutting guides and matched implants is an increasingly attractive technology that may not only improve margins, but also streamline the entire procedure and decrease complications. The study by Wang et al. [8] is particularly interesting from this point of view. Although many musculoskeletal oncology centers worldwide do not have access to this technology, the cost is likely to decrease with wider use.

Preoperative planning and simulation are of interest in avoiding technical errors and decreasing surgical time and blood loss, both of which are associated with infection. The software used for simulation can be used for 3D virtual reality simulation of surgical procedures in education at various levels of professional development. Surgeons and their patients must be able to compare the purported benefits of the various types of reconstruction and their inherent risks, including the option of no reconstruction. Many young adults today lead vigorous physical and professional lives decades after radical hemipelvectomy for a primary malignancy of the pelvis without any significant reconstruction. We should aim to perform large-scale global studies that can offer better comparative data. Functional results at 5, 10, and 15 years are, arguably, the most pertinent data to weigh the short-term risk against any long-term benefit. Comparing different forms of reconstructions will remain difficult unless large cooperative groups can reach a consensus on how to measure complications, function, and resection margins. Cost is also an issue, given the global variation in available resources for these patients.

A similar effort is even more pertinent for managing patients with metastatic disease. The treatment goals for these patients are different than they were two decades ago, because these patients are more active and live longer, often with targeted therapy. Acetabular lesions are not rare in this population and are a source of significant disability. For some of these patients, regaining mobility means receiving more-aggressive medical treatment, with benefits to the oncologic outcome. They are more likely to receive adjuvant therapy than most patients with primary malignancies of the acetabulum. These issues merit treating this paradigm as a separate one.

How Do We Get There?

Cutting guides are gaining acceptance as aids in achieving predictable margins, as is navigation. However, dissecting soft tissue of bone to apply guides may compromise the tumor’s margins. A well-designed, prospective cohort study could offer useful data on how the use of cutting guides affect soft tissue and bone margins.

Given the number of variables inherent in tumor biology and those related to the use of adjuvant therapy, an ideal cohort study to determine the benefits and risks of any surgical strategy for primary tumors involving the acetabulum would have the following parameters:

1. It would study only tumors for which no adjuvant therapy is used.

2. It would prospectively accrue data for which a wide (global) consensus has been reached. These studies would have to define the methodology to measure the quality of surgical margins, complications (infection, loss of fixation, and hip instability), and the short-term and long-term functional outcomes.

3. It would attempt to standardize and validate protocols designed to decrease complications.

4. It would have a cooperative group involving multiple centers worldwide that could generate data of sufficient quality and quantity to address these questions.

Although this seems to be a daunting proposition, we have just completed a global-scale, randomized prospective study (Prophylactic Antibiotic Regimens in Tumor Surgery study) to study an equally complex research question (regarding antibioprophylaxis in limb salvage surgery). The details regarding the organization and challenges of this study have been published [3].

The manufacture of customized implants is generally a costly and time-consuming process, which in some cases will cause a delay in treatment. Wang et al. [8] described a combination of management strategies including local manufacture of cutting guides and implants, which would be difficult to reproduce in most tertiary care centers globally. This technology has evolved to a point where it is more accessible, and the data published by these authors [8] support its adoption on a wider scale.

Lesions involving the acetabulum for which surgery is not curative (including metastatic disease, multiple myeloma, and lymphoma) are not rare. These patients are increasingly being treated with targeted therapy for their disease and surviving for many years. A distinct, prospective study aligned with the therapeutic goals of this population would allow surgeons to choose wisely and make the most of the resources available to health delivery systems. A first step would involve validating the prognostic tools used by oncologists to ascertain how these tools predict the benefit of such a major surgery. The validity of such an analysis would be stronger if we study one disease, or a group of similar biologies, at a time.