Treatment Planning and Fracture Prediction in Patients with Skeletal Metastasis with CT-Based Rigidity Analysis

Computed tomography-based structural rigidity analysis can assess tumor- and treatment-induced changes in rat bones with metastatic lesions

BACKGROUND

Breast cancer (BrCa) is a predominant malignancy, with metastasis occurring in one in eight patients, nearly half of which target the bone, leading to serious complications such as pain, fractures, and compromised mobility. Structural rigidity, crucial for bone strength, becomes compromised with osteolytic lesions, highlighting the vulnerability and increased fracture risk in affected areas. Historically, two-dimensional radiographs have been employed to predict these fracture risks; however, their limitations in capturing the three-dimensional structural and material changes in bone have raised concerns. Recent advances in CT-based Structural Rigidity Analysis (CTRA), offer a promising, more accurate non-invasive 3D approach. This study aims to assess the efficacy of CTRA in monitoring osteolytic lesions' progression and response to therapy, suggesting its potential superiority over existing methodologies in guiding treatment strategies.

METHODS

Twenty-seven female nude rats underwent femoral intra-medullary inoculation with MDA-MB-231 human breast cancer cells or saline control. They were divided into Control, Cancer Control, Ibandronate, and Paclitaxel groups. Osteolytic progression was monitored weekly using biplanar radiography, quantitative computed tomography (QCT), and dual-energy X-ray absorptiometry (DEXA). CTRA was employed to predict fracture risk, normalized using the contralateral femur. Statistical analyses, including Kruskal-Wallis and ANOVA, assessed differences in outcomes among groups and over time.

RESULTS

Biplanar radiographs showed treatment benefits over time; however, only certain time-specific differences between the Control and other treatment groups were discernible. Notably, observer subjectivity in X-ray scoring became evident, with significant inter-operator variations. DEXA measurements for metaphyseal Bone Mineral Content (BMC) did not exhibit notable differences between groups. Although diaphyseal BMC highlighted some variance, it did not reveal significant differences between treatments at specific time points, suggesting a limited ability for DEXA to differentiate between treatment effects. In contrast, the CTRA consistently demonstrated variations across different treatments, effectively capturing bone rigidity changes over time, and the axial- (EA), bending- (EI), and torsional rigidity (GJ) outcomes from the CTRA method successfully distinguished differences among treatments at specific time points.

CONCLUSION

Traditional approaches, such as biplanar radiographs and DEXA, have exhibited inherent limitations, notably observer bias and time-specific inefficacies. Our study accentuates the capability of CTRA in capturing real-time, progressive changes in bone structure, with the potential to predict fractures more accurately and provide a more objective analysis. Ultimately, this innovative approach may bridge the existing gap in clinical guidelines, ushering in enhanced Clinical Decision Support Tool (CDST) for both surgical and non-surgical treatments.

Computed tomography-derived structural analysis for the likelihood of pathologic fracture in canine antebrachial osteosarcoma

Determining the risk of pathologic fracture in dogs with a primary bone tumor would aid in case selection for in-situ treatment options. Prior research found strong relationships between in vitro strength of canine antebrachii with primary bone tumors and CT-derived metrics. This study assesses the prognosis for pathologic fracture in dogs with distal radial bone tumors using CT-derived structural analysis metrics. CT images of the antebrachium in dogs with aggressive osseous lesions of the radius were used to calculate structural rigidity and failure forces, including axial rigidity (AR), craniocaudal bending rigidity (BR), torsional rigidity (TR), and failure forces for a slightly-curved/asymmetric beam (Fs) or a curved beam (Fc). Metrics were compared with the clinical outcome of radial fracture. Eight of 19 dogs with CT-derived metrics developed a radial fracture. The prognostic potential of the metrics to discriminate fractured and nonfractured bones was analyzed using receiver operating characteristic curves (area under the curve), stepwise logistic regression, and classification regression (CART) analyses. Fc was the most sensitive and specific metric for prognosing fracture occurrence (AUC = 0.864). When dog body weight (BW) was included, all five metrics had AUC > 0.705. Fc was the best predictor of fracture using stepwise logistic regression and CART analysis, followed by BR. An indication of fracture probability can be determined by normalizing Fc or BR with dog BW or by using the logistic regression equation of either metric with dog BW. Results warrant further analysis of a larger cohort to evaluate fracture likelihood in dogs with antebrachial bone neoplasia.

Modification to Mirels scoring system location component improves fracture prediction for metastatic disease of the proximal femur

BACKGROUND

Correctly identifying patients at risk of femoral fracture due to metastatic bone disease remains a clinical challenge. Mirels criteria remains the most widely referenced method with the advantage of being easily calculated but it suffers from poor specificity. The purpose of this study was to develop and evaluate a modified Mirels scoring system through scoring modification of the original Mirels location component within the proximal femur.

METHODS

Computational (finite element) experiments were performed to quantify strength reduction in the proximal femur caused by simulated lytic lesions at defined locations. Virtual spherical defects representing lytic lesions were placed at 32 defined locations based on axial (4 axial positions: neck, intertrochanteric, subtrochanteric or diaphyseal) and circumferential (8 circumferential: 45-degree intervals) positions. Finite element meshes were created, material property assignment was based on CT mineral density, and femoral head/greater trochanter loading consistent with stair ascent was applied. The strength of each femur with a simulated lesion divided by the strength of the intact femur was used to calculate the Location-Based Strength Fraction (LBSF). A modified Mirels location score was next defined for each of the 32 lesion locations with an assignment of 1 (LBSF > 75%), 2 (LBSF: 51-75%), and 3 (LBSF: 0-50%). To test the new scoring system, data from 48 patients with metastatic disease to the femur, previously enrolled in a Musculoskeletal Tumor Society (MSTS) cross-sectional study was used. The lesion location was identified for each case based on axial and circumferential location from the CT images and assigned an original (2 or 3) and modified (1,2, or 3) Mirels location score. The total score for each was then calculated. Eight patients had a fracture of the femur and 40 did not over a 4-month follow-up period. Logistic regression and decision curve analysis were used to explore relationships between clinical outcome (Fracture/No Fracture) and the two Mirels scoring methods.

RESULTS

The location-based strength fraction (LBSF) was lowest for lesions in the subtrochanteric and diaphyseal regions on the lateral side of the femur; lesions in these regions would be at greatest risk of fracture. Neck lesions located at the anterior and antero-medial positions were at the lowest risk of fracture. When grouped, neck lesions had the highest LBSF (83%), followed by intertrochanteric (72%), with subtrochanteric (50%) and diaphyseal lesions (49%) having the lowest LBSF. There was a significant difference (p < 0.0001) in LBSF between each axial location, except subtrochanteric and diaphyseal which were not different from each other (p = 0.96). The area under the receiver operator characteristic (ROC) curve using logistic regression was greatest for modified Mirels Score using site specific location of the lesion (Modified Mirels-ss, AUC = 0.950), followed by a modified Mirels Score using axial location of lesion (Modified Mirels-ax, AUC = 0.941). Both were an improvement over the original Mirels score (AUC = 0.853). Decision curve analysis was used to quantify the relative risks of identifying patients that would fracture (TP, true positives) and those erroneously predicted to fracture (FP, false positives) for the original and modified Mirels scoring systems. The net benefit of the scoring system weighed the benefits (TP) and harms (FP) on the same scale. At a threshold probability of fracture of 10%, use of the modified Mirels scoring reduced the number of false positives by 17-20% compared to Mirels scoring.

CONCLUSIONS

A modified Mirels scoring system, informed by detailed analysis of the influence of lesion location, improved the ability to predict impending pathological fractures of the proximal femur for patients with metastatic bone disease. Decision curve analysis is a useful tool to weigh costs and benefits concerning fracture risk and could be combined with other patient/clinical factors that contribute to clinical decision making.

Finite Element Model-Computed Mechanical Behavior of Femurs with Metastatic Disease Varies Between Physiologic and Idealized Loading Simulations

Background and objectives:

Femurs affected by metastatic bone disease (MBD) frequently undergo surgery to prevent impending pathologic fractures due to clinician-perceived increases in fracture risk. Finite element (FE) models can provide more objective assessments of fracture risk. However, FE models of femurs with MBD have implemented strain- and strength-based estimates of fracture risk under a wide variety of loading configurations, and “physiologic” loading models typically simulate a single abductor force. Due to these variations, it is currently difficult to interpret mechanical fracture risk results across studies of femoral MBD. Our aims were to evaluate (1) differences in mechanical behavior between idealized loading configurations and those incorporating physiologic muscle forces, and (2) differences in the rankings of mechanical behavior between different loading configurations, in FE simulations to predict fracture risk in femurs with MBD.

Methods:

We evaluated 9 different patient-specific FE loading simulations for a cohort of 54 MBD femurs: strain outcome simulations—physiologic (normal walking [NW], stair ascent [SA], stumbling), and joint contact only (NW contact force, excluding muscle forces); strength outcome simulations—physiologic (NW, SA), joint contact only, offset torsion, and sideways fall. Tensile principal strain and femur strength were compared between simulations using statistical analyses.

Results:

Tensile principal strain was 26% higher ( R2 = 0.719, P < .001) and femur strength was 4% lower ( R2 = 0.984, P < .001) in simulations excluding physiologic muscle forces. Rankings of the mechanical predictions were correlated between the strain outcome simulations (ρ = 0.723 to 0.990, P < .001), and between strength outcome simulations (ρ = 0.524 to 0.984, P < .001).

Conclusions:

Overall, simulations incorporating physiologic muscle forces affected local strain outcomes more than global strength outcomes. Absolute values of strain and strength computed using idealized (no muscle forces) and physiologic loading configurations should be used within the appropriate context when interpreting fracture risk in femurs with MBD.

Socioeconomic and insurance-related disparities in disease-specific survival among patients with metastatic bone disease

BACKGROUND

Approximately 5% of cancer patients in the United States presented with metastatic bone disease (MBD) at diagnosis. Current study explores the disparities in survival for patients with MBD.

METHODS

Patients with the diagnosis of MBD at presentation for the five most common primary anatomical sites were extracted from Surveillance, Epidemiology, and End Results Census tract-level dataset (2010-2016). Kaplan-Meier and Cox Proportional Hazard models were used to evaluate survival, and prognostic factors for each cohort. Prognostic significance of socioeconomic status (SES) and insurance status were ascertained.

RESULTS

The five most common anatomical-sites with MBD at presentation included "lung" (n = 59 739), "prostate" (n = 19 732), "breast" (n = 16 244), "renal and urothelium" (n = 7718) and "colon" (n= 3068). Lower SES was an independent risk factor for worse disease-specific survival (DSS) for patients with MBD originating from lung, prostate, breast and colon. Lack of insurance was an independent risk factor for worse DSS for MBD patients with primary tumors in lung and breast.

CONCLUSIONS

MBD patients from the five most common primary sites demonstrated SES and insurance-related disparities in disease-specific survival. This is the first and largest study to explore SES and insurance-related disparities among patients specifically afflicted with MBD. Our findings highlight vulnerability of patients with MBD across multiple primary sites to financial toxicity.

Finite element analysis potentially identifies nonessential prophylactic stabilization in femurs with metastatic disease

Metastatic bone disease (MBD) is often managed by non-specialized orthopedic surgeons who rely on Mirels’ criteria to predict pathologic fracture risk. However, low specificity of Mirels’ criteria implies many lesions are scored at high fracture risk when the actual mechanical fracture risk is minimal. Our goal was to retrospectively compare mechanical fracture risk in MBD patients to Mirels’ score and clinical treatment received. Using a CT-based finite element (FE) model of the proximal femur affected by MBD, femur strength and load-to-strength ratio (LSR) were determined for 52 femurs from 48 patients. Associations of femur strength with pain and Mirels’ scores (Pearson r/Spearman ρ correlations), and the decision to operate (percentile analysis), and associations of LSR with pain and Mirels’ scores (Spearman correlations) were determined. Nineteen of 52 femurs (37%) had a very low computed mechanical fracture risk (LSR < 0.4); 5 of those 19 underwent prophylactic stabilization, suggesting that clinical decision-making in MBD is substantially influenced by non-mechanical factors that likely overestimate pathologic fracture risk. Of the 30 femurs managed non-operatively, 24 had a low computed mechanical fracture risk (LSR ≤ 0.5), none of which (0%) experienced a fracture within 9 months. Patient-reported pain did not correlate with femur strength ( r = −0.05, p = 0.748) nor with LSR (ρ = 0.07, p = 0.632). Mirels’ score correlated weakly with femur strength (ρ = −0.32, p = 0.019) and with LSR (ρ = 0.29, p = 0.034). Computational mechanical tools like this FE model could be used as a clinical decision aid when considering non-surgical management in appropriate patients, potentially alleviating nonessential surgical treatment in some patients with femur MBD.

Prophylactic surgical treatment using CT-based rigidity analysis vs. after the fact fracture treatment of pathologic femoral lesions

Background

Accurate comparison of prophylactic surgical treatment (PST) to after fracture treatment (AF) of patients with femoral metastatic disease requires more accurately identifying patients for impending fracture, such as with CT-based structural rigidity analysis (CTRA). This study compares a more accurately defined PST group (of impending fractures defined by CTRA) to AF for metastatic femoral disease.

Methods

PST patients were enrolled and treated by the PI in a longitudinal multicenter study of impending pathologic fractures evaluated for accuracy by CTRA. The AF patients were also treated by the senior author and were identified by retrospective chart review. Fifty-five patients were treated surgically for metastatic femoral lesions and were divided into three groups for the purpose of this study: Group I (AF), Group II (PST-high), and Group III (PST-low). Demographic information, comorbidities, and clinical variables of interest were collected by retrospective chart review; cost data was collected by collaboration with our hospital financial personnel (office of the Chief Financial Officer).

Results

Survival showed statistically significant differences favoring Group II. Transfusions in Group I were nearly twice those of Groups II and III, but there was no statistically significant (NS) difference between groups. Estimated blood loss (EBL) was generally with NS difference. Similarly, there were NS differences in LOS between groups. Discharge disposition showed statistically significant differences between groups (P=0.012, global). Discharge to home was highest in Group II (76%) and lowest in Group I (27%). Discharge to rehab was lowest in Group II (24%) and highest in Group I (47%). There were no discharges to hospice or morgue in Group II, while both occurred in Group I. Mean direct and total costs were highest in Group I ($18,837 and $31,997, respectively) and lowest in Group II ($16,094 and $27,357) but the differences were NS.

Conclusions

This study shows benefits of PST over AF in a group of PST patients more accurately defined to have impending pathologic fractures by CTRA definition.

Breast Cancer Induced Bone Osteolysis Prediction Using Temporal Variational Autoencoders

Objective and Impact Statement. We adopt a deep learning model for bone osteolysis prediction on computed tomography (CT) images of murine breast cancer bone metastases. Given the bone CT scans at previous time steps, the model incorporates the bone-cancer interactions learned from the sequential images and generates future CT images. Its ability of predicting the development of bone lesions in cancer-invading bones can assist in assessing the risk of impending fractures and choosing proper treatments in breast cancer bone metastasis. Introduction. Breast cancer often metastasizes to bone, causes osteolytic lesions, and results in skeletal-related events (SREs) including severe pain and even fatal fractures. Although current imaging techniques can detect macroscopic bone lesions, predicting the occurrence and progression of bone lesions remains a challenge. Methods. We adopt a temporal variational autoencoder (T-VAE) model that utilizes a combination of variational autoencoders and long short-term memory networks to predict bone lesion emergence on our micro-CT dataset containing sequential images of murine tibiae. Given the CT scans of murine tibiae at early weeks, our model can learn the distribution of their future states from data. Results. We test our model against other deep learning-based prediction models on the bone lesion progression prediction task. Our model produces much more accurate predictions than existing models under various evaluation metrics. Conclusion. We develop a deep learning framework that can accurately predict and visualize the progression of osteolytic bone lesions. It will assist in planning and evaluating treatment strategies to prevent SREs in breast cancer patients.

Effectiveness of Rehabilitation for Cancer Patients with Bone Metastasis

Objectives:

Advances in cancer treatment have led to extended survival, and, as a result, the number of patients with bone metastases is increasing. Activities of daily living (ADL) decrease with bone metastasis and the need for rehabilitation is increasing. This study examined the effects of rehabilitation in patients with bone metastases.

Methods:

We retrospectively reviewed data of cancer patients with bone metastasis who received rehabilitation between 2016 and 2018. Efficacy of rehabilitation was evaluated in 92 patients as the change in the Functional Independence Measure (FIM) score divided by rehabilitation days (FIM change/day) and assessed by different metastatic sites.

Results:

Overall FIM scores significantly improved after rehabilitation. Moreover, FIM change/day improved in patients with pelvic metastases (n=44) more than in patients with other metastatic sites (n=48) (P=0.015). In FIM motor components, improvements in toilet, tub/shower, walk/wheelchair, and stairs were significantly greater in patients with pelvic metastasis than in those with other metastasis sites.

Conclusions:

Rehabilitation improved ADL status to a greater extent in patients with pelvic metastases than in those with other metastasis sites. Patients with pelvic metastases may fear fractures, limiting their ADL, but rehabilitation could eliminate this fear and improve FIM.

CT characteristics and proposed scoring scheme are predictive of pathologic fracture in dogs with appendicular osteosarcoma treated with stereotactic body radiation therapy

Stereotactic body radiation therapy (SBRT) is an established limb-sparing treatment for dogs with appendicular osteosarcoma (OSA) and pathologic fractures are a common sequela. The objectives of this retrospective, observational, and descriptive study were to develop and evaluate objective CT criteria for predicting pathologic fractures and assess impacts on survival time. Included dogs had confirmed or suspected appendicular OSA, available CT scans, available outcome data, and were treated with SBRT. For each study, the number of quartiles affected by lysis on the most severely affected transverse slice, longest measurable length of contiguous full cortical lysis, presence of subchondral bone lysis, and ratio of the length of the affected bone to normal bone were recorded. A scoring system was developed for assigning grades (summed score 1-4 = grade 1, 5-7 = grade 2, and 8 or greater = grade 3.) A total of 127 CT datasets were sampled (123 patients). The median summed score was 7. The grade was correlated with pathologic fracture development (23% of grade 1, 35% of grade 2, and 57% of grade 3 resulting in fracture, P = 0.028). Subchondral bone lysis was correlated with fracture (odds ratio, 2.2, P = 0.02). Percent affected bone ≥40% was associated with decreased survival (P = 0.002). Dogs with <40% of affected bone had a median survival of 256 days versus 178 days for dogs with ≥40% affected bone. Findings from the current study can be used to assist in determining prognosis and planning radiation therapy for future dogs affected by appendicular OSA.

Fracture Risk of Long Bone Metastases: A Review of Current and New Decision-Making Tools for Prophylactic Surgery

Simple Summary

Long bone metastases are frequently a pivotal point in the oncological history of patients. Weakening of the bone results in pathologic fractures that not only compromise patient function but also their survival. Therefore, the main issue for tumor boards remains timely assessment of the risk of fracture, as this is a key consideration in providing preventive surgery while also avoiding overtreatment. As the Mirels scoring system takes into account both the radiological and the clinical criteria, it has been used worldwide since the 1990s. However, due to increasing concern regarding the lack of accuracy, new thresholds have been defined for the identification of impending fractures that require prophylactic surgery, on the basis of axial cortical involvement and biomechanical models involving quantitative computed tomography. The aim of this review is to establish a state-of-the-art of the risk assessment of long bone metastases fractures, from simple radiologic scores to more complex multidimensional bone models, in order to define new decision-making tools.

Abstract

Long bone pathological fractures very much reflect bone metastases morbidity in many types of cancer. Bearing in mind that they not only compromise patient function but also survival, identifying impending fractures before the actual event is one of the main concerns for tumor boards. Indeed, timely prophylactic surgery has been demonstrated to increase patient quality of life as well as survival. However, early surgery for long bone metastases remains controversial as the current fracture risk assessment tools lack accuracy. This review first focuses on the gold standard Mirels rating system. It then explores other unique imaging thresholds such as axial or circumferential cortical involvement and the merits of nuclear imaging tools. To overcome the lack of specificity, other fracture prediction strategies have focused on biomechanical models based on quantitative computed tomography (CT): computed tomography rigidity analysis (CT-RA) and finite element analysis (CT-FEA). Despite their higher specificities in impending fracture assessment, their limited availability, along with a need for standardization, have limited their use in everyday practice. Currently, the prediction of long bone pathologic fractures is a multifactorial process. In this regard, machine learning could potentially be of value by taking into account clinical survival prediction as well as clinical and improved CT-RA/FEA data.

Predicting Fracture Risk in Patients with Metastatic Bone Disease of the Femur: A Pictorial Review Using Three Different Techniques

One of the key roles of an orthopedic surgeon treating metastatic bone disease (MBD) is fracture risk prediction. Current widely used impending fracture risk tools such as Mirels scoring lack specificity. Two newer methods of fracture risk prediction, CT-based structural rigidity analysis (CTRA) and finite element analysis (FEA), have each been shown to be more accurate than Mirels. This case series illustrates comparative Mirels, CTRA, and FEA for 8 femurs in 7 subjects. These cases were selected from a much larger data set to portray examples of true positives, true negatives, false positives, and false negatives as defined by CTRA relative to the fracture outcome. Case illustrations demonstrate comparative Mirels and FEA. This series illustrates the use, efficacy, and limitations of these tools. As all current tools have limitations, further work is needed in refining and developing fracture risk prediction.

High rate of fracture in long-bone metastasis: Proposal for an improved Mirels predictive score

INTRODUCTION

Pathologic fracture is the most feared complication in long-bone metastasis. Various radiographic tools are available for identifying at-risk patients and guide preventive treatment. The Mirels score is the most frequently studied and widely used, but has been criticized, many patients not being operated on until the actual fracture stage. We therefore conducted a French national multicenter prospective study: (1) to determine the proportion of patients operated on at fracture stage versus preventively; (2) to compare Mirels score between the two; and (3) to identify factors for operation at fracture stage according to Mirels score and other epidemiological, clinical and biological criteria.

HYPOTHESIS

Simple discriminatory items can be identified to as to complete the Mirels score and enhance its predictive capacity.

MATERIAL AND METHODS

A non-controlled multicenter prospective study included 245 patients operated on for non-revelatory long-bone metastasis, comparing patients operated on for fracture versus preventively according to body-mass index (BMI), ASA score, Katagiri score items and the 4 Mirels items.

RESULTS

One hundred and twenty-six patients (51.4%) were operated on at fracture stage: 106 (84.1%) showed high risk on Mirels score (score>8), and 15 (11.9%) moderate risk (score=8). On multivariate analysis, 4 independent factors emerged: in increasing order, advanced age (OR=1.03; 95%CI 1.01-1.06), VAS pain score>6 (OR=1.47; 95%CI 1.02-2.11), WHO grade>2 (OR=2.74; 95%CI 1.22-6.15), and upper-limb location (OR=5.26; 95%CI 2.13-12.84).

DISCUSSION

The present study confirmed that more than half of patients with long-bone metastasis are operated on at actual fracture stage, in agreement with the literature. Several studies highlighted the weakness of the Mirels score as a predictive instrument. Comparison between preventive and fracture-stage surgery showed that upper-limb location, intense pain, advanced age and impaired functional status were associated with fracture-stage surgery, and should be taken into account alongside the original Mirels criteria. This improved scoring instrument remains to be validated in a prospective study.

LEVEL OF EVIDENCE

IV, prospective cohort study without control group.

The effects of metastatic lesion on the structural determinants of bone: Current clinical and experimental approaches

Metastatic bone disease is incurable with an associated increase in skeletal-related events, particularly a 17-50% risk of pathologic fractures. Current surgical and oncological treatments are palliative, do not reduce overall mortality, and therefore optimal management of adults at risk of pathologic fractures presents an unmet medical need. Plain radiography lacks specificity and may result in unnecessary prophylactic fixation. Radionuclide imaging techniques primarily supply information on the metabolic activity of the tumor or the bone itself. Magnetic resonance imaging and computed tomography provide excellent anatomical and structural information but do not quantitatively assess bone matrix. Research has now shifted to developing unbiased data-driven tools that can predict risk of impending fractures and guide individualized treatment decisions. This review discusses the state-of-the-art in clinical and experimental approaches for prediction of pathologic fractures with bone metastases. Alterations in bone matrix quality are associated with an age-related increase in skeletal fragility but the impact of metastases on the intrinsic material properties of bone is unclear. Engineering-based analyses are non-invasive with the capability to evaluate oncological treatments and predict failure due to the progression of metastasis. The combination of these approaches may improve our understanding of the underlying deterioration in mechanical performance.

Bone Metastases: Mechanisms of the Metastatic Process, Imaging and Therapy

The mechanisms by which tumors metastasize to bone are complex. Upon the successful establishment of metastatic deposits in the skeleton, detection of the disease becomes essential for therapeutic planning. The roles of CT, skeletal scintigraphy, SPECT/CT, MRI, PET/CT and PET/MRI will be reviewed. Therapeutic response criteria specifically designed to evaluate bone metastases (MD Anderson/MDA criteria) can guide image interpretation. Knowledge of therapeutic strategies such as systemic therapy with bisphosphonates or radiopharmaceuticals, radiation therapy, surgery, and percutaneous interventions such as vertebroplasty and radiofrequency ablation can help the radiologist produce reports that will provide maximum benefit to clinicians and patients.

Fracture risk assessment and clinical decision making for patients with metastatic bone disease

Metastatic breast, prostate, lung, and other cancers often affect bone, causing pain, increasing fracture risk, and decreasing function. Management of metastatic bone disease (MBD) is clinically challenging when there is potential but uncertain risk of pathological fracture. Management of MBD has become a major focus within orthopedic oncology with respect to fracture and impending fracture care. If impending skeletal-related events (SREs), particularly pathologic fracture, could be predicted, increasing evidence suggests that prophylactic surgical treatment improves patient outcomes. However, current fracture risk assessment and radiographic metrics do not have high accuracy and have not been combined with relevant patient survival tools. This review first explores the prevalence, incidence, and morbidity of MBD and associated SREs for different cancer types. Strengths and limitations of current fracture risk scoring systems for spinal stability and long bone fracture are highlighted. More recent computed tomography (CT)-based structural rigidity analysis (CTRA) and finite element (FE) analysis methods offer advantages of increased specificity (true negative rate), but are limited in availability. Other fracture prediction approaches including parametric response mapping and positron emission tomography/computed tomography measures show early promise. Substantial new information to inform clinical decision-making includes measures of survival, clinical benefits, and economic analysis of prophylactic treatment compared to after-fracture stabilization. Areas of future research include use of big data and machine learning to predict SREs, greater access and refinement of CTRA/FE approaches, combination of clinical survival prediction tools with radiographically based fracture risk assessment, and net benefit analysis for fracture risk assessment and prophylactic treatment.

When and where do patients with bone metastases actually break their femurs?

AIMS

Accurate estimations of the risk of fracture due to metastatic bone disease in the femur is essential in order to avoid both under-treatment and over-treatment of patients with an impending pathological fracture. The purpose of the current retrospective in vivo study was to use CT-based finite element analyses (CTFEA) to identify a clear quantitative differentiating factor between patients who are at imminent risk of fracturing their femur and those who are not, and to identify the exact location of maximal weakness where the fracture is most likely to occur.

METHODS

Data were collected on 82 patients with femoral metastatic bone disease, 41 of whom did not undergo prophylactic fixation. A total of 15 had a pathological fracture within six months following the CT scan, and 26 were fracture-free during the five months following the scan. The Mirels score and strain fold ratio (SFR) based on CTFEA was computed for all patients. A SFR value of 1.48 was used as the threshold for a pathological fracture. The sensitivity, specificity, positive, and negative predicted values for Mirels score and SFR predictions were computed for nine patients who fractured and 24 who did not, as well as a comparison of areas under the receiver operating characteristic curves (AUC of the ROC curves).

RESULTS

The sensitivity of SFR was 100% compared with 88% for the Mirels score, and the specificity of SFR was 67% compared with 38% for the Mirels score. The AUC was 0.905 for SFR compared with 0.578 for the Mirels score (p = 0.008).

CONCLUSION

All the patients who sustained a pathological fracture of the femur had an SFR of > 1.48. CTFEA was far better at predicting the risk of fracture and its location accurately compared with the Mirels score. CTFEA is quick and automated and can be incorporated into the protocol of CT scanners. Cite this article: Bone Joint J 2020;102-B(5):638-645.

Simulated lesions representative of metastatic disease predict proximal femur failure strength more accurately than idealized lesions

Metastatic disease in bone is characterized by highly amorphous and variable lesion geometry, with increased fracture risk. Assumptions of idealized lesion geometry made in previous finite element (FE) studies of metastatic disease in the proximal femur may not sufficiently capture effects of local stress/strain concentrations on predicted failure strength. The goal of this study was to develop and validate a FE failure model of the proximal femur incorporating artificial defects representative of physiologic metastatic disease. Data from 11 cadaveric femur specimens were randomly divided into either a training set (n = 5) or a test set (n = 6). Clinically representative artificial defects were created, and the femurs were loaded to failure under offset torsion. Voxel-based FE models replicating the experimental setup were created from the training set pre-fracture computed tomography data. Failure loads from the linear model with maximum principal strain failure criterion correlated best with the experimental data (R² = 0.86, p = 0.024). The developed model was found to be reliable when applied to the test dataset with a relatively low RMSE of 46.9 N, mean absolute percent error of 12.7 ± 17.1%, and cross-validation R² = 0.88 (p < 0.001). Models simulating realistic lesion geometry explained an additional 26% of the variance in experimental failure load compared to idealized lesion models (R² = 0.62, p = 0.062). Our validated automated FE model representative of physiologic metastatic disease may improve clinical fracture risk prediction and facilitate research studies of fracture risk during functional activities and with treatment interventions.

Patient-specific finite element computer models improve fracture risk assessments in cancer patients with femoral bone metastases compared to clinical guidelines

PURPOSE

To determine whether patient-specific finite element (FE) computer models are better at assessing fracture risk for femoral bone metastases compared to clinical assessments based on axial cortical involvement on conventional radiographs, as described in current clinical guidelines.

METHODS

Forty-five patients with 50 femoral bone metastases, who were treated with palliative radiotherapy for pain, were included (64% single fraction (8Gy), 36% multiple fractions (5 or 6x4Gy)) and were followed for six months to determine whether they developed a pathological femoral fracture. All plain radiographs available within a two month period prior to radiotherapy were obtained. Patient-specific FE models were constructed based on the geometry and bone density obtained from the baseline quantitative CT scans used for radiotherapy planning. Femoral failure loads normalized for body weight (BW) were calculated. Patients with a failure load of 7.5 x BW or lower were identified as having high fracture risk, whereas patients with a failure load higher than 7.5 x BW were classified as low fracture risk. Experienced assessors measured axial cortical involvement on conventional radiographs. Following clinical guidelines, patients with lesions larger than 30mm were identified as having a high fracture risk. FE predictions were compared to clinical assessments by means of diagnostic accuracy values (sensitivity, specificity and positive (PPV) and negative predictive values (NPV)).

RESULTS

Seven femurs (14%) fractured during follow-up. Median time to fracture was 8 weeks. FE models were better at assessing fracture risk in comparison to axial cortical involvement (sensitivity 100% vs. 86%, specificity 74% vs. 42%, PPV 39% vs. 19%, and NPV 100% vs. 95%, for the FE computer model vs. axial cortical involvement, respectively).

CONCLUSIONS

Patient-specific FE computer models improve fracture risk assessments of femoral bone metastases in advanced cancer patients compared to clinical assessments based on axial cortical involvement, which is currently used in clinical guidelines.

Prophylactic Versus Postfracture Stabilization for Metastatic Lesions of the Long Bones: A Comparison of 30-day Postoperative Outcomes

INTRODUCTION

The goals of orthopaedic treatment for most patients with osseous metastases are to control pain, maintain function, and maximize quality of life and time at home. The aim of this study was to determine differences in 30-day postoperative morbidity and mortality between patients who underwent prophylactic versus postfracture stabilization for metastatic lesions of long bones.

METHODS

The American College of Surgeons National Surgical Quality Improvement Program database was queried for patients who underwent prophylactic fixation (n = 461) or postfracture stabilization (n = 856) for pathologic fractures because of metastatic lesions of long bones from 2006 to 2016. The groups were compared with respect to several potential confounders using Student t, Kruskal-Wallis, and χ tests. Logistic and Poisson regression models (inclusion threshold of P < 0.1) were used to assess the associations of functional status with outcomes. The alpha level was set at 0.05.

RESULTS

Prophylactic fixation was associated with a lower risk of major medical complications (odds ratio = 0.64; 95% confidence interval [CI], 0.45 to 0.93; P = 0.02), discharge to a care facility rather than home (odds ratio = 0.48; 95% CI, 0.36 to 0.63; P < 0.01), and lower risk of a longer hospital stay (incidence risk ratio = 0.86; 95% CI, 0.74 to 0.96; P = 0.01) compared with postfracture stabilization. No significant difference was found in the risk of unplanned revision surgery or 30-day postoperative mortality between the two groups.

CONCLUSION

Although prevention of pathologic fractures caused by metastatic disease may not always be possible, patients who underwent prophylactic stabilization had a lower risk of major complications within 30 days postoperatively and shorter hospital stays compared with patients who underwent postfracture stabilization.

LEVEL OF EVIDENCE

Level IV, retrospective cohort.

An Automatic Personalized Internal Fixation Plate Modeling Framework for Minimally Invasive Curved Bone Fracture Surgery Based on Preregistration With Capsule Projection Model

OBJECTIVE

In this paper, a framework to visualize and model internal fixation plates is presented for computer-aided personalized and minimally invasive curved bone fracture surgery.

METHODS

We focus on personalized reverse reconstruction of the bone fracture plate based on three-dimensional (3-D) mesh models obtained from a 3-D optical scanner. The steps of the method are as follows. First, principal component analysis and the K-means method are used to reconstruct a Bezier curve (ridge line) of broken bones. Second, based on the geometric shape of the curved broken bones, a capsule projection model of the broken bones is proposed to obtain the feature information of the broken bone sections. Third, the ordering points to identify the clustering structure (OPTICS) method is utilized for preregistration (rough registration). Fourth, a regional self-growth strategy is designed to extract the cross-section points. Fifth, the iterative closest point method is applied for the accurate registration of the fracture surface models. Finally, a personalized internal fixation plate model is reconstructed based on several user points.

RESULTS

The internal fixation plate model can be reconstructed according to the patient's bone parameters.

CONCLUSION

Clinicians can use this framework to obtain personalized and accurate internal fixation plate models that effectively represent the broken bones of patients. Via X-ray navigation, the personalized forged plate can be fixed on the target area through a small incision.

SIGNIFICANCE

This framework provides a reasonable and practicable technical approach for computer-aided minimally invasive curved bone fracture surgery.

Contemporary Management of Appendicular Skeletal Metastasis by Primary Tumor Type

Skeletal metastases exert a profound effect on patients and society, and will be encountered by most orthopedic surgeons. Once a primary malignancy is diagnosed, multidisciplinary management should focus on maximizing the quality of life while minimizing disease- and treatment-related morbidity. This may be best achieved with discerning attention to the unique characteristics of primary cancer types, including pathologic fracture healing rates, longevity, and efficacy of adjuvant therapies. Some lesions may respond well to nonsurgical measures, whereas others may require surgery. A single surgical intervention should allow immediate unrestricted activity and outlive the patient. In certain scenarios, a therapeutic benefit may be provided by excision with a curative intent. In these scenarios, or when endoprosthetic reconstruction is necessary, patients may be best referred to an orthopedic oncologist.

Multimodal Treatment of Bone Metastasis-A Surgical Perspective

Over the past decades there has been an increase in the incidence of cancer worldwide. With the advancement in treatment, patient survival has improved in tandem with the increasing incidence. This, together with the availability of advanced modern diagnostic modalities, has resulted in more cases of metastatic bone disease being identified. Bone metastasis is an ongoing problem and has significant morbidity implications for patients affected. Multimodal treatment strategies are required in dealing with metastatic bone disease, which include both surgical and non-surgical treatment options. In the multidisciplinary team, orthopedic surgeons play an important role in improving the quality of life of cancer patients. Surgical intervention in this setting is aimed at pain relief, restoration of function and improvement in functional independence. In selected cases with resectable solitary metastasis, surgical treatment may be curative. With the advancement of surgical technique and improvement in implant design and manufacture, a vast array of surgical options are available in the modern orthopedic arena. In the majority of cases, limb salvage procedures have become the standard of care in the treatment of metastatic bone disease. Non-surgical adjuvant treatment also contributes significantly to the improvement of cancer patient care. A multidisciplinary approach in this setting is of paramount importance.

Predicting pathological fracture in femoral metastases using a clinical CT scan based algorithm: A case-control study

BACKGROUND

We assessed whether there was a difference in attenuation measurements (in Hounsfield units - HU) and geometric distribution of HU between femora with metastatic lesions that fracture, and metastatic lesions that did not fracture nor underwent prophylactic fixation.

METHODS

Nine patients with femoral metastases who underwent CT and developed a pathological fracture were matched to controls. All femora were delineated in axial CT slices using a region of interest (ROI) tool; the HU within these ROIs were used to calculate: (1) the cumulative HU of the affected over the nonaffected side per slice and presented as a percentage, and (2) the cumulative HU accounting for geometric distribution (polar moment of HU). We repeated the analyses including cortical bone only (HU of 600 and above).

RESULTS

CT-based calculations did not differ between patients with a lesion that fractured and those that did not fracture nor underwent prophylactic fixation when analyzing all tissue. However, when including cortical bone only, the pathological fracture group had a lower cumulative HU value compared to the no fracture and no fixation group for the weakest cross-sectional CT image (pathological fracture group, mean: 71, SD: 23 and no fracture and no prophylactic fixation group, mean: 85, SD: 18, p = 0.042) and the complete lesion analysis (pathological fracture group, mean: 78, SD: 21 and no fracture and no prophylactic fixation group, mean: 92, SD: 15, p = 0.032).

CONCLUSION

The demonstrated CT-based algorithms can be useful for predicting pathological fractures in metastatic lesions.

Has the Level of Evidence of Podium Presentations at the Musculoskeletal Tumor Society Annual Meeting Changed Over Time?

BACKGROUND

Level of evidence (LOE) framework is a tool with which to categorize clinical studies based on their likelihood to be influenced by bias. Improvements in LOE have been demonstrated throughout orthopaedics, prompting our evaluation of orthopaedic oncology research LOE to determine if it has changed in kind.

QUESTIONS/PURPOSES

(1) Has the LOE presented at the Musculoskeletal Tumor Society (MSTS) annual meeting improved over time? (2) Over the past decade, how do the MSTS and Orthopaedic Trauma Association (OTA) annual meetings compare regarding LOE overall and for the subset of therapeutic studies?

METHODS

We reviewed abstracts from MSTS and OTA annual meeting podium presentations from 2005 to 2014. Three independent reviewers evaluated a total of 1222 abstracts for study type and LOE; there were 577 abstracts from MSTS and 645 from OTA. Changes in the distributions of study type and LOE over time were evaluated by Pearson chi-square test.

RESULTS

There was no change over time in MSTS LOE for all study types (p = 0.13) and therapeutic (p = 0.36) study types during the reviewed decade. In contrast, OTA LOE increased over this time for all study types (p < 0.01). The proportion of Level I therapeutic studies was higher at the OTA than the MSTS (3% [14 of 413] versus 0.5% [two of 387], respectively), whereas the proportion of Level IV studies was lower at the OTA than the MSTS (32% [134 of 413] versus 75% [292 of 387], respectively) during the reviewed decade. The proportion of controlled therapeutic studies (LOE I through III) versus uncontrolled studies (LOE IV) increased over time at OTA (p < 0.021), but not at MSTS (p = 0.10).

CONCLUSIONS

Uncontrolled case series continue to dominate the MSTS scientific program, limiting progress in evidence-based clinical care. Techniques used by the OTA to improve LOE may be emulated by the MSTS. These techniques focus on broad participation in multicenter collaborations that are designed in a comprehensive manner and answer a pragmatic clinical question.

Current orthopaedic management of bony metastases in the proximal third of the femur

Patients presenting with skeletal metastatic lesions requiring surgery are increasing, this is due to an ageing population and improved oncological survival following advances in medical management. Furthermore, patients are living longer with skeletal metastatic disease. The majority of bone metastases occur in the proximal femur. Robust diagnosis (Biopsy) and treatment is required to ensure that patients can mobilise fully weight bearing immediately post-surgery and that the construct should outlive the patients expected survival. We review the changing management of metastatic disease in the proximal femur.

Thromboembolic Disease in Patients with Metastatic Femoral Lesions: A Comparison Between Prophylactic Fixation and Fracture Fixation

BACKGROUND

We are not aware of any previous studies that have compared the rate of venous thromboembolic events in patients who underwent prophylactic intramedullary nailing because of an impending fracture with the rate in patients who underwent intramedullary nailing after a pathological fracture. The objective of the present study was to determine if the rate of venous thromboembolic events varies between patients who are managed with prophylactic fixation and those who are managed with fixation after a pathological fracture.

METHODS

We performed a retrospective comparative study in which the Nationwide Inpatient Sample database was used to identify all patients who had undergone femoral stabilization, either for a pathological femoral fracture or for prophylactic fixation of femoral metastatic lesion, over a period of 10 consecutive years (between 2002 and 2011) in the United States. Demographic data, comorbidities, venous thromboembolic event rates, and other common postoperative complications were compared between the 2 groups.

RESULTS

Patients who were managed with prophylactic fixation had significantly higher rates of pulmonary embolism (p < 0.001; adjusted odds ratio, 2.1) and deep-vein thrombosis (p = 0.03; adjusted odds ratio, 1.5). Patients who were managed with fixation after a pathological fracture had a significantly greater need for blood transfusion, higher rates of postoperative urinary tract infection, and a decreased likelihood of being discharged to home (p < 0.001 for all).

CONCLUSIONS

Patients with metastatic disease who undergo prophylactic intramedullary nailing have higher observed rates of venous thromboembolic events than those who undergo nailing for the treatment of a pathological fracture and should be actively and vigilantly managed in the postoperative period.

LEVEL OF EVIDENCE

Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

The current status of prophylactic femoral intramedullary nailing for metastatic cancer

The most common site for cancer to spread is bone. At post-mortem, bony metastases have been found in 70% of patients dying from breast and prostate cancer. Due to the prevalence of cancer, bone metastasis and the associated management represents a huge burden on NHS resources. In patients with metastasis, around 56% of these involve the lower limb long bones. Due to the huge forces placed upon long bones during weight bearing, there is a high risk of fracture through areas of metastasis. It is reported that 23% of pathological fractures occur in the femoral subtrochanteric region. This area is subjected to forces up to four times the body weight, resulting in poor union rate for these fractures, and significant morbidity associated with difficulty in mobilising, and in patient nursing. As cancer treatments improve, the life expectancy in this subgroup of patients is likely to increase. Therefore medium-to-long-term management of these fractures, beyond the palliative, will become essential. We aim to evaluate the current management for metastatic malignant femoral disease, with particular focus on the prophylactic augmentation of diseased femorii using intramedullary nails.

Does CT-based Rigidity Analysis Influence Clinical Decision-making in Simulations of Metastatic Bone Disease?

BACKGROUND

There is a need to improve the prediction of fracture risk for patients with metastatic bone disease. CT-based rigidity analysis (CTRA) is a sensitive and specific method, yet its influence on clinical decision-making has never been quantified.

QUESTIONS/PURPOSES

What is the influence of CTRA on providers' perceived risk of fracture? (2) What is the influence of CTRA on providers' treatment recommendations in simulated clinical scenarios of metastatic bone disease of the femur? (3) Does CTRA improve interobserver agreement regarding treatment recommendations?

METHODS

We conducted a survey among 80 academic physicians (orthopaedic oncologists, musculoskeletal radiologists, and radiation oncologists) using simulated vignettes of femoral lesions presented as three separate scenarios: (1) no CTRA input (baseline); (2) CTRA input suggesting increased risk of fracture (CTRA+); and (3) CTRA input suggesting decreased risk of fracture (CTRA-). Participants were asked to rate the patient's risk of fracture on a scale of 0% to 100% and to provide a treatment recommendation. Overall response rate was 62.5% (50 of 80).

RESULTS

When CTRA suggested an increased risk of fracture, physicians perceived the fracture risk to be slightly greater (37% ± 3% versus 42% ± 3%, p < 0.001; mean difference [95% confidence interval {CI}] = 5% [4.7%-5.2%]) and were more prone to recommend surgical stabilization (46% ± 9% versus 54% ± 9%, p < 0.001; mean difference [95% CI] = 9% [7.9-10.1]). When CTRA suggested a decreased risk of fracture, physicians perceived the risk to be slightly decreased (37% ± 25% versus 35% ± 25%, p = 0.04; mean difference [95% CI] = 2% [2.74%-2.26%]) and were less prone to recommend surgical stabilization (46% ± 9% versus 42% ± 9%, p < 0.03; mean difference [95% CI] = 4% [3.9-5.1]). The effect size of the influence of CTRA on physicians' perception of fracture risk and treatment planning varied with lesion severity and specialty of the responders. CTRA did not increase interobserver agreement regarding treatment recommendations when compared with the baseline scenario (κ = 0.41 versus κ = 0.43, respectively).

CONCLUSIONS

Based on this survey study, CTRA had a small influence on perceived fracture risk and treatment recommendations and did not increase interobserver agreement. Further work is required to properly introduce this technique to physicians involved in the care of patients with metastatic lesions. Given the number of preclinical and clinical studies outlining the efficacy of this technique, better education through presentations at seminars/webinars and symposia will be the first step. This should be followed by clinical trials to establish CTRA-based clinical guidelines based on evidence-based medicine. Increased exposure of clinicians to CTRA, including its underlying methodology to study bone structural characteristics, may establish CTRA as a uniform guideline to assess fracture risk.

LEVEL OF EVIDENCE

Level III, economic and decision analyses.

Computed tomography-based rigidity analysis: a review of the approach in preclinical and clinical studies

The assessment of fracture risk in patients afflicted with osseous neoplasms has long presented a problem for orthopedic oncologists. These patients are at risk for developing pathologic fractures through lytic defects in the appendicular and axial skeleton with devastating consequences on their quality of life. Lesions with a high risk of fracture may require prophylactic surgical stabilization, whereas low-risk lesions can be treated conservatively. Therefore, effective prevention of pathologic fractures depends on accurate assessment of fracture risk and is a critical step to avoid debilitating complications. Given the complex nature of osseous neoplasms, treatment requires a multidisciplinary approach; yet, little consensus regarding fracture risk assessment exists among physicians involved in the care of these patients. In order to improve the overall standard of care, specific criteria must be adopted to formulate consistent and accurate fracture risk predictions. However, clinicians make subjective assessments about fracture risk on plain radiographs using guidelines now recognized to be inaccurate. Osseous neoplasms alter both the material and geometric properties of bone; failure to account for changes in both of these parameters limits the accuracy of current fracture risk assessments. Rigidity, the capacity to resist deformation upon loading, is a structural property that integrates both the material and geometric properties of bone. Therefore, rigidity can be used as a mechanical assay of the changes induced by lytic lesions to the structural competency of bone. Using this principle, computed tomography (CT)-based structural rigidity analysis (CTRA) was developed and validated in a series of preclinical and clinical studies.