Abstract
Purpose
This study assessed implant survival and dislocation following proximal femur tumor endoprosthetic replacement.
Methods
Thirty-eight procedures were performed between 2005 and 2019. The cumulative incidence of implant revision was calculated with death as a competing risk.
Results
The majority of endoprostheses were bipolar hemiarthroplasty (n = 33, 86.8%). The cumulative incidence of revision was 14.6% (95% CI, 3.2%–34.1%) at five years. Dislocation occurred in 7.9% (n = 3) of hips at a mean (SD) 44 ± 35.2 days.
Conclusions
Proximal femur tumor endoprosthetic replacement is a durable option that tends to outlive patients. Strict postoperative bracing may lower dislocation rates.
Level of evidence
III. Retrospective Study.
Keywords: Tumor endoprosthesis, Proximal femur, Metastatic bone disease, Hip dislocation
1. Introduction
The proximal femur is one of the most common anatomical locations for primary and non-primary tumors of bone.1 A variety of treatment options exist for tumors in this location, such as internal fixation, reconstruction with a modular endoprosthesis, and various bone graft options depending on the extent of disease and goals of surgery.2
In cases of significant bony loss, endoprosthetic reconstruction may be the treatment of choice due to its relative ease.3 Complications are high, however, and long-term survival remains an issue. The modes of failure for lower extremity endoprostheses were originally described by Henderson et al. and include soft tissue failure (Type 1), aseptic loosening (Type 2), structural failure (Type 3), infection (Type 4), and failure due to tumor progression (Type 5).4 Soft tissue failure, which is among the most common of these complications and is likely due to inadequate soft tissue reattachment, may cause dislocation and a need for revision surgery.5, 6, 7, 8, 9, 10
There are limited data that describe proximal femur implant survival using competing risks analysis, and there are few data to assess the incidence and prevention of hip dislocation in this setting. In our institution, patients undergoing oncologic proximal femur replacements adhere to a strict postoperative protocol which aims to minimize complications and maximize the functional outcome. Therefore, the purpose of this study is to provide the experience of our tertiary referral center in order to i) characterize postoperative complications and reasons for revision such as dislocation, ii) assess limb salvage rates, and iii) determine whether modular tumor endoprostheses of the proximal femur outlive patients.
2. Materials and methods
2.1. Clinical characteristics
Following Institutional Review Board approval, we retrospectively reviewed the medical records of 41 patients who underwent 42 proximal femur replacements between 2005 and 2019. Three of these patients were treated for non-oncologic conditions and were excluded from the study. The remaining group consisted of 37 patients (23 female and 14 male) who underwent 38 procedures, with one patient undergoing bilateral endoprosthetic reconstruction due to metastatic renal cell carcinoma. There was no minimum follow-up needed to meet inclusion due to the limited sample size. All procedures were performed by one of three fellowship-trained musculoskeletal oncologists through a posterolateral approach to the hip. We excluded cases of total femur replacements.
Among all procedures, 87.7% (n = 36) were a modular or global modular replacement system (Onkos Surgical, Parsippany, NJ; n = 14; Stryker Orthopedics, Kalamazoo, MI; n = 10; LINK®, Hamburg, Germany; n = 9; Zimmer/Biomet, Warsaw, IN; n = 3) and 2.6% (n = 1) were custom expandable prostheses (Stanmore, United Kingdom). Implant information was unavailable for one patient in the cohort. The articulating head segment was bipolar hemiarthroplasty (n = 33, 86.8%) or total hip arthroplasty (n = 5, 13.2%), and was chosen from preoperative degenerative changes on radiographs and intraoperative assessment of acetabular integrity and soft tissue.
All patients were fitted with a hip-knee-ankle-foot orthotic either preoperatively or immediately following surgery, to be utilized at all times out of bed post-operatively. Patients were made weight-bearing as tolerated with the brace immediately postoperatively with some limitations in hip range of motion. Namely, abduction was fixed at 15°, with no internal external rotation permitted, and flexion and extension were limited from 0° to 60° for six weeks. Additionally, full range of motion was permitted at the knee. This brace was strictly kept in place for six weeks following surgery, and for three months postoperatively in cases of a previous dislocation.
2.2. Outcomes
Follow-up included routine radiographs and surveillance as well as adjuvant therapy depending on the diagnosis. The majority of patients received chemotherapy (73.7%, n = 28) and/or radiation (52.6%, n = 20) throughout the course of their treatment. Final radiographs were screened for periprosthetic fracture and stress shielding, which was defined as bony resorption near the bone-implant interface. Failure was defined according to Henderson criteria and included partial or total component revisions, prosthesis removal, and/or amputation.4 Complications following surgery such as dislocation, fracture, and infection were also recorded.
2.3. Statistical analysis
Continuous and categorical data were analyzed using descriptive statistics. Risk of implant revision was calculated using cumulative incidence function curves with death as a competing risk. Statistical significance was defined as a p value of less than 0.05. All analyses were performed on SPSS version 26.0 (IBM Corp, Armonk, NY, USA) and R version 4.0.3 (R Foundation for Statistical Computing, Vienna, Austria).
3. Results
3.1. Clinical characteristics
Indications for surgery included metastatic bone disease or metastatic sarcoma (n = 24, 63.2%), primary sarcoma (n = 13, 34.2%), and hematologic malignancy (n = 1, 2.6%) (Table 1). With respect to femoral stem fixation, 86.8% (n = 33) were cemented, 7.9% (n = 3) were uncemented, and 5.3% (n = 2) utilized compressive osteointegration fixation.
Table 1.
Study characteristics.
| Variable | n (%) |
|---|---|
| Age (years)a | 59.3 (19.8) |
| Body mass index (kg/m2)a | 29.9 (6.8) |
| Female | 23 (60.5) |
| Male | 15 (39.5) |
| Preoperative diagnosis | |
| Metastatic bone disease | 24 (63.2) |
| Chondrosarcoma | 8 (21.1) |
| Osteosarcoma | 4 (10.5) |
| Ewing sarcoma | 1 (2.6) |
| Lymphoma | 1 (2.6) |
| Acetabular component | |
| Bipolar hemiarthroplasty | 33 (86.8) |
| Total arthroplasty | 2 (5.3) |
| Constrained arthroplasty | 2 (5.3) |
| Dual mobility | 1 (2.6) |
| Fixation | |
| Cemented | 33 (86.8) |
| Uncemented | 3 (7.9) |
| Compress | 2 (5.3) |
| Endoprosthetic system | |
| Modular | 33 (86.8) |
| Segmental | 3 (7.9) |
| Custom expandable | 1 (2.6) |
| Missing | 1 (2.6) |
| Femoral resection (cm)a | 15.2 (4.7) |
| Femoral stem diameter (mm)a | 12.6 (2.2) |
| Revision | |
| Yes | 3 (7.9) |
| No | 35 (92.1) |
| Instability (dislocation) | |
| Yes | 3 (7.9) |
| No | 35 (92.1) |
| Follow-up (months)a | 23.5 (26.6) |
Mean (standard deviation).
The mean follow-up was 23.5 ± 26.6 months (range, 0–60 months). At maximum recorded follow-up, 21.1% (n = 8) of patients were deceased with a mean time to death of 45 ± 39.1 months (range, 3–123 months). The all-cause revision rate was 7.9% (n = 3) at a mean 18.3 ± 10.7 months following surgery, and the cumulative risk of implant revision was 14.6% (95% confidence interval [CI], 3.2%–34.1%) at both five and ten years (Fig. 1).
Fig. 1.
Cumulative incidence function using a competing risk analysis with death of the patient as the competing risk. The risk of implant revision (left) was 14.6% (95% CI, 3.2%–34.1%) at both five- and ten-years following surgery. However, the cumulative mortality risk at both five- and ten-years (right) was 28.4% (95% CI, 7.1%–54.9%), which was higher than the revision risk for any cause and suggests implants tend to outlive patients. PFR, proximal femur replacement.
3.2. Revision rates
One of three revisions occurred in a patient who was reconstructed with a global modular system (Stryker Orthopedics) and bipolar head segment. This patient developed an infected dislocation at six months (Type 4) necessitating closed reduction in the emergency department with subsequent operative irrigation and debridement with exchange of the modular femoral head component. The patient then suffered a recurrent atraumatic dislocation two months later, requiring a second extensive irrigation and debridement with partial component exchange in addition to antibiotic cement coating and placement of a constrained liner. The remaining two revisions occurred in the setting metastatic sarcoma within the distal femur (Type 5), in patients who had previously undergone a negative margin surgical resection with proximal femur replacement performed. Each patient subsequently underwent resection of the distal femur with conversion to a total femur replacement (Fig. 2).
Fig. 2.
Henderson Type 5 failure refers to failure of a lower extremity endoprosthesis secondary to tumor progression requiring revision. A-C. One Type 5 failure occurred in a patient with recurrent osteosarcoma of the distal femur who was converted to a total femur. D-F. The other Type 5 failure occurred in a patient with recurrent dedifferentiated chondrosarcoma who required conversion to a total femur as well though died shortly after.
3.3. Adverse events
The overall incidence of dislocation was 7.9% (n = 3) at a mean 44 ± 35.2 days following surgery. Two dislocations occurred with bipolar hemiarthroplasty articulation and the third was in the setting of a constrained liner articulation. Of the three dislocations, two underwent open reduction while the remaining case was infected and required revision as mentioned above (Type 4). No patients required resurfacing or revision for acetabular wear by maximum recorded follow-up, which included acetabular liner wear or degenerative changes of the native acetabulum requiring revision. Stress shielding at the bone-implant junction was observed in one case 22 months after surgery (Fig. 3), and there were no instances of amputation (local control rate: 100%).
Fig. 3.
Stress shielding refers to bony resorption at the junctional interface between bone and implant due to the loss of natural stress and may be common in cemented and uncemented systems. A-B. A patient with metastatic bone disease underwent proximal femur replacement with a cemented femoral stem shown at one-year post-operative. C-D. Stress shielding (arrow) at the anterior junction was noted on postoperative standing radiographs at 22 months, with some posterolateral bridging osteosynthesis. This patient did not progress to structural failure.
4. Discussion
Endoprosthetic reconstruction for tumors in proximal femur is often the treatment of choice given its relative ease. The findings of this study support the role of endoprosthetic reconstruction for oncologic indications as a durable option with low dislocation rates when following brace protocols. At five years, the estimated cumulative incidence of implant revision was 14.6%, which although high, is comparable to the literature and among some of the better reported outcomes.
Limb salvage for tumors in the proximal femur is typically accomplished by resection and reconstruction either with a custom or modular endoprosthesis or allograft-prosthetic composite. For palliative procedures, internal fixation may be performed, though most patients who undergo local control surgery are offered limb salvage. While the functional outcomes between modular endoprostheses and allograft-prosthetic composites are similar according to recent data, the latter tend to be associated with higher rates of infection and non-union.11 Therefore, endoprostheses may permit a more ideal reconstruction and are typically the preferred choice for limb salvage in the proximal femur.
The overall revision rate following endoprosthetic reconstruction for proximal femur tumors ranges from 0% to 70%, with an overall cumulative estimate of about 10% according to a recent systematic review.12 Two of the largest cohorts by Houdek et al. (n = 204) and Unwin et al. (n = 263) describe rates of 11% and 13%, respectively.9,13 However, there is significant variation among smaller cohorts, which range from 3% in studies by Harvey et al. and Stevenson et al., to 47% and 69% in case series by Zehr et al. and Hobusch et al., respectively.8,14, 15, 16 Some smaller studies have also recorded a 0% revision rate.17, 18, 19, 20, 21 Thus, there exists variation among the literature, and our results seem to align with the overall cumulative estimates with lower rates than other similar cohorts. We also had zero patients who required a subsequent amputation procedure, which appears to coincide with the cumulative limb-salvage rate among proximal femur tumor prostheses according to the literature (overall: 97%; range, 76%–100%).12 Therefore, our results support the assertion that endoprosthetic replacement of the proximal femur is a durable option and affords a high rate of local disease control.
Modes of failure for endoprosthetic systems are historically described according to Henderson et al.4 These include soft-tissue failure (Type 1), aseptic loosening (Type 2), structural failure (Type 3), infection (Type 4), and tumor progression (Type 5). The current study recorded a 2.6% rate of Type 4 failure (n = 1) with a 5.3% rate of Type 5 failure due to tumor progression (n = 2). According to the literature, the most common reasons for failure of a lower extremity tumor endoprosthesis are soft tissue compromise which occurs in about 5%–38% of patients.4 However, when selecting for proximal femur tumor endoprostheses only, the cumulative estimates are slightly lower. For example, pooled estimates from a recent systematic review demonstrate an overall soft tissue failure rate of 1.2% (range, 0%–31%) and an overall structural failure rate of 2.2% (range, 0%–19%).12 For failure due to tumor progression, which is relatively uncommon among all lower extremity endoprostheses, the rates in proximal femur replacements range from 0% to 11% with a cumulative estimate of 2.0%. Thus, the results of the current study align with these reported trends and contribute to the literature describing potential reasons for failure.
Generally speaking, implant survival of proximal femur tumor endoprostheses is relatively high. However, given the heterogeneity of studies that record survival data, it is often unclear whether implants outlive patients. Furthermore, most data record survival as a Kaplan-Meier estimate, which calculates survival with death as a censored event rather than a competing risk. Some recent data suggest cumulative incidence functions are more precise especially for tumor endoprostheses, and this study estimated the cumulative incidence of long-term revision with death as a competing risk. We found a 14.6% incidence of implant revision at both five- and ten-years, which was less than the incidence of death and implies these reconstructions tend to outlive patients. Among other studies, five-year Kaplan-Meier estimates for proximal femur tumor endoprostheses range from 63% to 100%, and at ten-years, these estimates drop to between 55% and 86% with only two studies describe twenty-year estimates at 56% and 57%.22,23 Therefore, along with these studies our findings also support the conclusion that proximal femur tumor endoprostheses are reliable for use in the oncologic setting and afford favorable short to midterm implant survival.
We sought to determine our institutional dislocation rate, and if applicable, what factors would contribute to greater stability following proximal femur replacement. The noteworthy adverse events in this series included a 7.9% rate of hip dislocation that occurred at a mean 44 days following surgery, which is lower than historical controls. We considered soft tissue reattachment as a way to improve the dislocation rate, though the degree and quality of the reconstruction was surgeon-dependent which precluded an accurate comparison of this technique. While advances in prosthesis design, specifically the quality of abductor reattachment, may have also been protective against dislocation, this effect was likely insignificant in our cohort as the majority of patients received the same endoprostheses. Further research is needed to identify whether innovation or reattachment techniques improve soft tissue reconstruction.
In the setting of endoprosthetic reconstruction of the proximal femur, there are limited data that attempt to address ways to improve the overall rate of dislocation. Among studies that do assess dislocation following proximal femur replacement, the rates are as high as 20% which indicates a closer look into various ways to mitigate this common adverse event is needed.2,6,15,23, 24, 25, 26 In our institution, patients are made weightbearing as tolerated following proximal femur replacement and are placed in a brace with strict precautions to prevent dislocation as mentioned above. Given that we observed a relatively low dislocation rate compared to the literature, we believe strict adherence to the brace may contribute to improved stability by limiting range of motion while improving overall function. Given these promising results, future research with larger samples might compare brace use to no bracing in an attempt to validate this finding.
4.1. Limitations
The primary limitation of this study is its retrospective nature and small sample size. We attempted to identify all patients in the abovementioned time frame who underwent proximal femur replacement for oncologic disease, though inevitably some patients may be missed during the initial screen. This may also be due to incomplete datasets dating back to five years and longer. This study is also significantly limited with respect to follow-up, and we were not able to assess whether survival trends extended to the long-term. It is also possible that patients received treatment in our institution and were revised elsewhere, which would affect our revision rates. A third limitation is the inherent lack of control with respect to soft tissue repair and evolving surgical techniques over the 14-year study period. While much of the operative techniques and selection of implants are surgeon-specific, it is possible that variations in the rates of instability and dislocation may be due to changes in surgical technique and implant design over time. Last, another important limitation is the lack of data assessing the functional outcomes of these patients. For endoprosthetic replacement of the proximal femur, various scoring systems and functional assessments have shown consistent improvement from the pre-to post-operative period.9,27,28 Without these data, it was impossible to know whether there was an increased quality of life in these patients from either a patient or clinician perspective.
5. Conclusions
Our results support the role of endoprosthetic reconstruction for tumors in the proximal femur as a durable option that tends to outlive patients. We found a comparable and slightly improved rate of implant revision as well as dislocation compared to that of the literature. While we explored a possible explanation for improving instability such as implant innovation, soft tissue reconstruction, or postoperative brace use, future research is ultimately needed to address these factors and identify a way to improve dislocation in the postoperative setting.
Ethics approval and consent to participate
Rush University Medical Center obtained individual Institutional Review Board approval with an approved waiver of consent prior to beginning any research efforts.
Availability of data
The data that support the findings of this study are available from the corresponding author upon reasonable request.
Funding
No funding sources were required for this study.
Disclosures
ATB: (BMJ Case Reports: Editorial or governing board; Clinical Orthopaedics and Related Research: Editorial or governing board; exparel/pacira: Stock or stock Options; Journal of Oncology Practice: Editorial or governing board; Journal of Surgical Oncology: ad hoc reviewer; Lancet - Oncology: Editorial or governing board; Musculoskeletal Tumor Society: Board or committee member; Onkos Surgical: Paid consultant; Pediatric Blood and Cancer: Editorial or governing board; Rare Tumors: Editorial or governing board; Rush Orthopedic Journal: Editorial or governing board; Swim Across America Cancer Research Grant: Research support); SG: (Onkos Surgical: Paid consultant; Stock or stock Options; USMI: Stock or stock Options); MWC: (Alphatec Spine: IP royalties; Paid consultant; AO Spine North America: Board or committee member; Research support; Cervical Spine Research Society: Board or committee member; CSRS: Research support; DePuy, A Johnson & Johnson Company: Paid presenter or speaker; K2M: Paid presenter or speaker; Musculoskeletal Tumor Society: Board or committee member; North American Spine Society: Board or committee member; Orthofix, Inc.: Paid presenter or speaker; Spinal Elements: Paid consultant). All other authors have no pertinent financial disclosures or pertinent conflicts of interest.
CRediT authorship contribution statement
Charles A. Gusho: Data curation, Formal analysis, Writing – original draft, Writing – review & editing. Bishir Clayton: Data curation, Formal analysis, Writing – original draft, Writing – review & editing. Nabil Mehta: Writing – original draft, Writing – review & editing. Matthew W. Colman: Investigation, Supervision. Steven Gitelis: Investigation, Supervision. Alan T. Blank: Conceptualization, Investigation, Methodology, Supervision, Writing – review & editing.
Declaration of competing interest
The authors declare that they have no competing interests.
Contributor Information
Charles A. Gusho, Email: charles_gusho@rush.edu.
Bishir Clayton, Email: bishir_clayton@rush.edu.
Nabil Mehta, Email: nabil_mehta@rush.edu.
Matthew W. Colman, Email: matthew_w_colman@rush.edu.
Steven Gitelis, Email: steven_gitelis@rush.edu.
Alan T. Blank, Email: alan_blank@rush.edu.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
The data that support the findings of this study are available from the corresponding author upon reasonable request.