CORR Insights®: Does a Competing Risk Analysis Show Differences in the Cumulative Incidence of Revision Surgery Between Patients with Oncologic and Nononcologic Conditions After Distal Femur Replacement?

Where Are We Now?

In the current study, Staats and colleagues [7] analyzed how preoperative diagnoses of either oncologic or nononcologic conditions affected the overall cumulative incidence of revision surgery for those who underwent distal femur replacement. Generally reserved for managing primary bone tumors and bone metastasis to salvage the limb, more surgeons are using distal femur replacement for patients with revised TKA with severe femoral bone loss. Although previous studies have examined the efficacy of this procedure in both oncologic and nononcologic settings [4, 5], the majority of authors have not separately analyzed the outcomes of distal femur replacement for those with revised TKA or oncologic conditions. Staats and colleagues [7] concluded that patients treated with distal femoral replacements for oncologic or nononcologic conditions did not differ in terms of their eventual cumulative incidence of revision surgery after distal femur replacement, but survivorship was better among of cemented compared to cementless implants in the oncologic group in a competing-risk analyses.

Their study is important because we are still starting to tease apart the differences in implant survival and risk of revision surgery after distal femur replacement between patients with oncologic and nononcologic conditions. For example, after controlling for confounding variables in the current study, patients with oncologic diagnoses showed a lower risk of revision surgery as compared to nononcologic ones. But in a previous analysis [8], the authors did not find any difference in implant survival between these groups at a mean follow-up of 80 months in a Kaplan Meier survival analyses. The dissimilarities between these two studies might be explained by differences in the surgical techniques and implant designs, core statistical approaches, and patient cohorts. As such, concrete arguments on the comparative success of distal femur replacement in patients with oncologic and nononcologic conditions cannot be made at this point.

Where Do We Need to Go?

Although Staats and colleagues noted few differences between patients with oncologic and nononcologic conditions on competing-risk analyses, they found lower risk of revision surgery in oncologic patients on multivariate analyses [7]. This is because multivariate analyses tried to look at additional parameters such as age and fixation type, which can affect the risk of revision and potentially confound the results. Future studies should aim to characterize all the variables that can play a role in the success of distal femur replacement in both oncologic and nononcologic settings, as well as obtain patient-reported functional outcome scores (like knee functional scores and musculoskeletal tumor society scores, for example) and other variables such as time to functional/pain recovery after the surgery.

Those who undergo distal femur replacement do so because their alternative options are limited to either amputation or palliative care. We need to establish robust survivorship estimates, and expected quality of life for this cohort of patients. In oncology, there have been tremendous advances in systemic chemotherapy [2, 3, 6], increasing patient survival. Although it was not included in the current study, chemotherapy has been shown to adversely affect osseointegration, which can directly impact the implant fixation in patients undergoing distal femur replacement [1]. This should be investigated further in this patient population.

How Do We Get There?

Going further, we need to evaluate the indications for distal femur replacement independently using separate multivariate predictive models. The goal of that study should aim to obtain better data collection, and then develop comprehensive revision surgery risk and implant survivorship models that may lead to improved patient selection and set clear expectations after distal femur replacement.

Most patients who undergo distal femur replacements for oncologic conditions have normal knee functional scores prior to getting such conditions. However, that might not be the case with patients undergoing distal femur replacement for revision TKA. Unfortunately, there is no existing standard definition of “success” in terms of target knee pain and function scores or postoperative improvement in such scores which should be sought after distal femur replacement. We need further large-scale studies with heterogeneous cohorts to establish the threshold target knee score or change in score, predictive of long-term surgical success, such as revision risk and survivorship, for patients with oncologic and nononcologic conditions.

Future studies, preferably with a matched-case control design, should compare patients undergoing distal femur replacement for oncologic reasons who previously received or are on chemotherapy (cases), with those who did not receive or are not on chemotherapy (control) for revision surgery risk, implant survivorship, and knee functional scores.

Although distal femur replacement has been around for a long time, the risk of revision in these patients remains high. As such, biomechanical research must investigate ways to improve prosthetic design including enhanced force-bearing capacity, durability, and methods of bone fixation. Furthermore, the development of sophisticated implant survival predictive models for distal femur replacement (similar to that of PATHFx—a tool already in use to predict patient survival in orthopaedic oncology) would prove to be invaluable for the formulation of custom surgical plans and informed decision making in clinical practice.