1 Introduction

About 1.7 million people are diagnosed with cancer each year.¹ Approximately 5% of these patients are affected by metastatic disease to the bone, with an estimated cost of nearly 13 billion dollars to the healthcare system.^1,2 Pathologic fractures are an increasing concern in the field of musculoskeletal oncology, largely due to the improved diagnosis and treatment of metastatic disease with prolonged survival.³ A primary goal in the management of metastatic disease to bone is providing stability before fracture via prophylactic fixation, which has been shown to reduce morbidity and maintain ambulatory status in these at-risk patients.^4,5

The tip-apex distance (TAD) is the cumulative distance between the tip of the proximal lag screw to the center of the femoral head taken on anteroposterior (AP) and lateral radiographs.⁶ Prior orthopaedic trauma literature has demonstrated TAD is related to the frequency of lag-screw cutout, and thus implant failure in the treatment of intertrochanteric femur fractures.^6–10 A TAD index >25 mm has been shown to correlate with a significantly greater risk of failure compared with a TAD index of <25 mm.^6,7,11,12 However, there are currently no guidelines for the prognostic value of TAD index in patients undergoing prophylactic fixation of impending pathologic peritrochanteric fractures.¹³

Given the importance of durable postoperative stability in metastatic bone disease, it is necessary to determine an appropriate guideline for TAD index in this patient population. The primary purpose of the present study is to examine the prognostic significance of TAD index in predicting failure of prophylactic fixation of impending pathologic peritrochanteric femur fractures treated with cephalomedullary nails (CMNs). We hypothesized that in patients undergoing prophylactic fixation of pathologic peritrochanteric fractures, a tip-to-apex distance (TAD) index >25 mm will not have any prognostic significance in predicting failure of fixation. This baseline study will provide evidence and information regarding TAD index values in metastatic bone disease, with the ultimate long-term goal of developing standardized treatment guidelines for cancer patients undergoing prophylactic fixation for impending peritrochanteric fractures.

2 Methods

Patient demographic and surgical data were retrieved from retrospective chart review of all individuals with impending pathologic peritrochanteric fractures who were treated by two fellowship trained orthopaedic oncologists with cephalomedullary nail (CMN) fixation at a single institution between January 1, 2010, and January 1, 2020, with the billed Current Procedural Terminology (CPT) codes 27495 or 27187. This study was approved by the Institutional Review Board at the respective institution. All cases were reviewed to confirm they were performed in individuals greater than 18 years old for metastatic disease with prophylactic fixation in the basicervical, intertrochanteric and subtrochanteric regions. Patients who were less than 18 years old, had a completed pathologic fracture, had a lesion located in the femoral head, neck, or an isolated distal metastasis in the femoral shaft, or had inadequate imaging to make measurements including intraoperative fluoroscopy, post-operative films, or computed tomography (CT) were excluded from the study (Table 1). Data collected included patient age, sex, tip-to-apex distance (TAD) index, implant type, primary malignancy diagnosis, revision surgery, presence of cut-out or failure of fixation, implant survival, patient status, date of last follow up, post-operative radiation therapy, post-operative chemotherapy, and post-operative weight bearing status.

The tip-apex distance was measured using the equation: TAD = (Xap*DtrueDap)+(Xlat*DtrueDlat), where X represents the distance from the tip of the proximal lag screw to the center of the femoral head and D represents the true and measured diameter of the lag screw on anteroposterior (AP) and lateral post-operative radiographs. In order to adjust for magnification, the measured distances of both AP and lateral radiographs were multiplied by the ratio of the true to measured lag screw diameter (Fig. 1). The study group was divided into two cohorts (patients with TAD 0-25 mm, and TAD>25 mm). Pearson-chi square tests were used to compare for differences in baseline demographics, clinical characteristics, and study outcomes. Multi-variate logistic regression analyses were used to assess whether a TAD>25 mm was associated with differences in rates of failure of fixation and cut-out. Cut-out was defined as the presence of screw back out from its original position not due to tumor progression, ultimately leading to extrusion of the cephalic nail from the superior femoral head (Fig. 3).

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Fig. 1 Tip-apex distance (TAD) measurement, where X represents the distance from the tip of the proximal lag screw to the center of the femoral head and D represents the true and measured diameter of the lag screw on anteroposterior and lateral radiographs.

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Fig. 2 Flowchart demonstrating patient selection criteria.

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Fig. 3 Demonstration of lag screw cut out from proximal femoral head.

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3 Results

Overall, 330 patients were identified from initial query search, of which 127 (38%) met final inclusion criteria (Fig. 2). Factors that excluded patients from the study included absence of metastatic disease, inadequate imaging, revision or alternative procedures, and completed fractures.¹⁴ A total of 66 patients (52%) were male, with the most common types of metastatic disease including lung cancer, myeloma, and breast cancer (Table 2). From the 127 patients included in the study, 45 (35.4%) had a TAD>25 mm (Table 3). Pearson chi-square tests demonstrated patients with a TAD>25 mm had a slightly higher, but insignificant rate of cut-out or fixation failure (8.9% vs. 6.1%; p = 0.558), need for revision surgery (13.3% vs. 7.3%; p = 0.268), and implant failure (11.1% vs. 6.1%; p = 0.316) compared to patients with a TAD<25 mm. A majority of the implants used were Synthes TFNA IMN (West Chester, PA, USA) followed by Styker Gamma IMN (Kalamazoo, MI, USA) (Table 4). The rate of fixation failure or screw cut out was insignificant between implant types (p = 0.123). Partial weight bearing was associated with a lower odds of screw cut-out or fixation failure when compared to weight bearing as tolerated postoperatively (OR 0.04 [0.004-0.36]; p = 0.004) (Table 5). Multi-variate analysis showed that higher TAD was not associated with greater odds of failure to fixation (OR 1.92 [95% CI 0.18-20.24]; p = 0.587).

4 Discussion

Metastatic bone disease can lead to profound osseous disruption, increasing its susceptibility to fracture.^4,5,15,16 When occurring in long bones such as the femur, this can have a catastrophic effect on patient function and overall health secondary to limitations in supporting and transferring weight during ambulation. Intramedullary prophylactic fixation is a primary goal in the management of metastatic disease to bone in order to provide stability prior to fracture and allow for early postoperative mobilization, thereby improving quality of life in patients with metastatic disease.¹⁷ Limiting weight bearing following intramedullary fixation in femur fractures has been shown to delay radiographic healing, further supporting the need to advance weight-bearing status.¹⁸ Compared with delayed weight bearing, immediate weight bearing has also been shown to improve early functional outcomes without increasing the complication or mortality rates in geriatric intertrochanteric femur fracture patients.¹⁹ However, impending pathologic fractures warrant special consideration given the osseus disruption and risk for osteolysis progression, which can lead to implant failure.^4,5,15,16,20 Limited literature regarding weight bearing status exists specifically in patients undergoing fixation for impending pathologic peritrochanteric femur fractures, but early postoperative mobilization is important to facilitate rehabilitation and improved quality of life.²¹ Our study demonstrated that patients with partial weight bearing status had slightly lower odds of screw cut-out or fixation failure when compared to weight bearing as tolerated patients postoperatively. However, the overall effect size was low given that only 23 patients were in the partial weight bearing group postoperatively. Further studies with larger patient cohorts will be necessary to further delineate these outcomes.

Potential complications of cephalomedullary fixation include post-operative failure of fixation at the distal or proximal ends of the implant. This may occur secondary to disease progression, insufficient bone stock at the time of the index procedure, or implant malpositioning. Furthermore, prior trauma literature has demonstrated a tip-to-apex distance (TAD) index >25 mm is related to the frequency of lag-screw cutout and ultimately implant failure.^6–10 Our goal was to determine the prognostic value of TAD in predicting failure of prophylactic fixation for pathologic peritrochanteric femur fractures due to limited existing literature. In order to answer this question, our study group was divided into two cohorts in order to analyze baseline demographics, clinical characteristics, and TAD values to evaluate for differences in rates of failure of fixation and cut-out. In contrast to prior literature, we anticipated TAD index would not have any prognostic significance in predicting failure following prophylactic peritrochanteric fixation. Notably, without a fracture, the lag screw in cephalomedullary nails (CMN) would simply serve to protect the femoral neck. Despite the fact the previous literature has demonstrated a TAD>25 mm leads to higher rates of screw cutout and implant failure, these studies included patients with completed fractures.^6,7,11,12 In the case of patients with metastatic disease, the goal is stabilization of their impending pathologic fracture before completion. Therefore, in the absence of completed fracture, the risk of lag screw cutout or fixation failure would be seemingly low.

A retrospective study by Moon et al. identified 141 patients with metastatic bone disease, myeloma, or lymphoma who underwent intramedullary nailing between 2001 and 2011 with the purpose to determine the incidence of femoral neck metastases in patients with symptomatic, isolated femoral diaphyseal lesions treated with surgical fixation.²² They found 0 patients with femoral neck metastases at mean follow-up of 13 months, ultimately concluding their results did not support the use of cephalomedullary implants for the sole purpose of prophylactic femoral neck stabilization.²² However, these results must be taken in context due to specifically analyzing patients with isolated femoral diaphyseal lesions. The study also highlighted the relatively small sample size and need for similar studies at additional orthopaedic oncology centers. Ultimately, this study may also provide further evidence that TAD would not be applicable in the prophylactic fixation of peritrochanteric lesions. However, our study trend suggests that when utilizing intramedullary fixation to protect the femoral neck, we should attempt to keep the TAD <25 mm in patients with impending pathologic peritrochanteric fractures in concordance with prior orthopaedic trauma literature.

The goal of this study was to provide baseline information regarding the prognostic evidence of TAD index values in metastatic bone disease. However, there are several limitations present in our study. First, not all patients were accounted for in the final analysis. Out of 330 patients identified from initial query, only 127 patients were included in final analysis due to factors such as absence of metastatic disease, prior surgical procedures, and inadequate imaging. Additionally, the presence of multiple types of malignancy and differing nature, location, and aggressiveness of lesions could impact outcomes that were observed. Furthermore, due to our study inclusion criteria isolated to femoral peritrochanteric lesions as well as our limited sample size, our findings could be the result of selection bias. It is also possible a type II error is present given the small sample size. Further studies are likely required with a larger study population to confirm these findings. Additionally, we do not address the prophylactic fixation of femoral neck lesions with the Femoral Recon Nailing (FRN) system, another common alternative to lag screw fixation. Although this study evaluated failure of fixation secondary to implant cut out, disease progression could have contributed to these failures which was not analyzed. This study also does not take differing IMN lengths (i.e. short, intermediate, long) and alternative technologies into account that could impact our conclusions, such as evaluating helical blades versus lag screws and the presence or absence of cement augmentation.

Overall, there is a trend towards a higher rate of fixation failure, revision surgery and low implant survival with a TAD >25 mm among patients undergoing fixation for pathologic proximal peritrochanteric femur fractures. Although the findings do not reach significance, our baseline study suggests providers should still strive to adhere to orthopedic trauma principles when treating impending pathologic peritrochanteric femur fractures. Although partial weight bearing was associated with a lower odds of screw cut-out or fixation failure when compared to weight bearing as tolerated postoperatively, future studies are needed and it is important to maximize functional status and quality of life for these patients postoperatively. Ultimately, ongoing studies will help further assess these findings with increased sample size in order to provide standardized treatment guidelines and operative recommendations for eligible orthopaedic oncologic patients.

IRB approval

This study was approved by the Institutional Review Board of The Ohio State University, Columbus, OH. Study performed at The Ohio State University Wexner Medical Center, Columbus, OH.

Previous communication

This article is not based on a previous communication to a society or meeting.

Ethical statement

This study was approved by the Institutional Review Board of The Ohio State University, Columbus, OH. Study performed at The Ohio State University Wexner Medical Center, Columbus, OH.

Guardian/patient statement

Informed Consent has been obtained from patient or guardian for the study's participation and publication.

Credit author statement

CDQ, BWJ, TJS conceptualized the study. LMG, DPP, and ATM developed the methodology and conducted the formal analysis. ATM and CDQ curated the data. CDQ, BWJ and TJS provided resources and supervision. LMG and DPP wrote the original draft of the manuscript. DPP, BWJ, and TJS reviewed and edited the manuscript. All authors read and approved the final manuscript.

Funding

No funding, grants or in-kind support were received for the purposes of this research. None of the authors received financial support for this study.

Funding statement

None.