CORR Insights®: What Is the 10-year Survivorship of Cemented Distal Femoral Endoprostheses for Tumor Reconstructions and What Radiographic Features Are Associated with Survival?

Where Are We Now?

Aseptic loosening has long been identified as one of the causes of revision following reconstruction with an oncologic distal femur endoprosthesis [5]. Identifying the potential causes of loosening is important because it allows for counseling of patients in terms of expected outcomes, loosening rates, activity levels, as well as setting long-term expectations. Informed patients can help guide their medical treatment using shared decision-making.

Other studies have reported similar rates of aseptic loosening. A recent systematic review by Haijie and colleagues [3] of 4748 distal femoral replacements from 40 studies found that the mean 5-, 10-, 15-, and 20-year implant survival rates were 78.3%, 70.1%, 61.6%, and 38.3%, respectively, and the overall aseptic loosening rate was 8.8% [3]. Although the population in their systematic review was heterogenous (including multiple implant companies, different designs, and different techniques), the authors provided a comprehensive review of the long-term performance and outcomes of this surgery. Interestingly, their findings included both cemented and press-fit fixation and did not show a difference in aseptic loosening between the two fixation techniques. Several studies [2, 6] have shown that aseptic loosening rates overall range from 4% to 9% over multiple time periods.

In the current study, Piakong and colleagues [11] report on the 10-year survivorship of cemented stems (from five centers) for oncologic distal femur resections. All-cause survivorship of their cemented stems at 5 and 10 years was 74% and 64%, respectively with a 10% rate of infection and 7.2% rate of aseptic loosening. The authors also provide radiographic characteristics that suggest aseptic loosening and durable fixation of the prosthesis. Among the nine implants that loosened (out of 195 patients), all nine had a radiolucent area more than 20% of the total length of the stem without cortical expansion remodeling at the stem tip [11]. The findings of this study add to the existing literature by providing long-term follow-up on cemented stems and suggesting radiograph findings to predict loosening. Piakong and colleagues [11] define the worrisome radiographic findings for surgeons to monitor, potentially allowing for earlier intervention since these characteristics could lead to loosening of the prosthesis.

Where Do We Need To Go?

It is important that we continue to collect long-term information on the performance of modern modular replacement systems, although the clinical utility of these findings still needs to be defined. Overall, the two main questions surrounding this issue are: (1) What is the incidence of aseptic loosening using modern implants, and (2) what can we do about it?

Indications for modular endoprostheses are increasing. Patients with metastatic disease are living longer than ever before, and we are now seeing increasing use in both revision arthroplasty and fracture care for complex distal femur fractures [4, 12]. Although improving overall survivorship of these implants is the ultimate goal, outperforming the infection (10%) and aseptic loosening rates (7.2%) from the current study will require examining several additional factors.

Patient factors

There are several patient factors that may impact the survivorship of a prosthesis. Pertinent to this population, many patients with oncologic diagnosis will be treated with systemic chemotherapy and/or radiation therapy to the site. Both of these factors impede healing and decrease overall bone quality, predisposing the patient to both infection and aseptic loosening. Although neither of these adjuvant therapies may be modifiable factors, each patient should have a clear understanding that he or she may be at a higher risk to develop complications, which could ultimately lead to revision surgery and/or amputation.

Other patient factors include obesity, smoking, and diabetes. All of these factors have been linked both to infection and aseptic loosening in primary joint arthroplasty, so they likely have the same effect on larger endoprosthetic reconstructions, such as the ones we use in patients with tumors [7]. Because many of the oncologic procedures are both time-sensitive and not elective, modifying these factors may not be feasible, but we could still counsel the patient on potential lifestyle changes in the postoperative setting.

Surgeon factors

What can we as surgeons do to improve long-term survivorship of these implants? We need to understand better the type of stems we choose for this procedure. Size, shape, and fixation method are all considerations with no clear-cut best choices. These decisions are primarily made by surgeon preference or patterns learned during training and not based on clinical evidence. Studies comparing cemented and cementless fixation have not shown a difference in the risk of aseptic loosening [9, 10], so the indications remain unclear based on current evidence. Most authors have recommended cemented fixation in older patients, radiated bone, and patients with an overall poor prognosis. Cementless fixation often is recommended for younger patients with primary bone tumors. But again, these recommendations are not based on clinical evidence, but rather anecdotal experiences deriving from what seems to make intuitive sense. Size and shape of the stem are other considerations.

How Do We Get There?

Compared to primary THAs and TKAs, few patients receive distal femoral endoprostheses, and as mentioned, our decision-making is driven primarily by retrospective reviews, training preferences, and anecdotal evidence. Our adult reconstruction colleagues have demonstrated the value of joint registries to identify risk factors and implant complications earlier than retrospective reviews from single institutions or pooled data allow [8]. For example, and pertinent to this discussion, Bunyoz and colleagues [1] recently suggested that, based on registry data, femoral stem fixation may be the most important revision risk factor in older patients. The Musculoskeletal Tumor Society is in the process of establishing a registry for sarcoma surgeries; thus, there is a tremendous opportunity to include information regarding implant use. A large cohort of patients could be followed through the use of this registry and meaningful data (such as stem type, fixation methods, and patient comorbidities).

The authors of the current study [11] suggest that larger diameter, curved stems may be protective against aseptic loosening, but larger numbers are needed. In addition, different collar options to create a “hybrid” type fixation, side-plate or cross-screw fixation, or Compress® technology (Compress Device, Biomet Orthopedics, Warsaw, IN, USA) are all avenues to evaluate. We can achieve better stem designs through long-term registry follow-up to allow adequate analysis on performance. Finally, I believe that computer modeling studies—such as finite element analyses—can provide guidance as to which stems provide the best initial stability.