Assessment of femur geometrical parameters using EOS™ imaging technology in patients with atypical femur fractures; preliminary results

Cross-sectional geometry of the femoral diaphyseal cortical bones: analysis of central mass distribution

A detailed analysis of differences in skeletal shape among many individuals is expected to reveal the mechanical significance behind various morphological features. To confirm the distribution of the cortical bone region in cross sections, the relative position of the central mass distribution (CMD) of the cortical bone region to the CMD of the entire cross section was examined. A total of 90 right human femoral skeletons were examined using clinical multi-slice computed tomography. For nine cross sections of each femur, we determined the CMD of the whole area, including both cortical bone and medullary areas, as CMD-W, and that of the cortical bone region in the same cross section as CMD-C, and they were compared. The medial and anterior portion of the cortex was relatively thick just below the lesser trochanter. The posterior cortical bone tended to be relatively thick in the region from the center to the distal part of the diaphysis. Females had a significantly more medially deviated CMD than males throughout the entire diaphysis. These results suggest that femurs with advanced cortical bone thinning tend to have a concentration of cortical bone in their medial portion. CMD-C was located farther from the diaphysis axis as the degree of medial bending increased. Conversely, the greater the lateral bending of the diaphysis, the closer CMD-C was to the diaphysis axis. As the amount of bone decreases with age, self-adjustment could occur so that the cortical bone's critical area remains to prevent a decrease in mechanical strength.

Characteristics of bisphosphonate and non-bisphosphonate related atypical femoral fracture in a South East Asian population - Secondary analysis

INTRODUCTION

Studies have found that not all atypical femoral fractures (AFF) are associated with bisphosphonate (BP) use. There are limited data on AFF in non-BP patients. In this study, we characterise factors associated with BP and non-BP related AFF and its mortality in a single centre in Singapore.

METHODS

We conducted a cohort study of subjects above 50 years old admitted to Changi General Hospital (CGH), Singapore with fragility subtrochanteric and femoral fractures from 2009 to 2015. Using the ASBMR 2014 criteria fractures are classified into atypical and typical femoral fractures. CGH uses a nationalised electronic health record that allows review of information on patient's demographics, clinical history and previous investigations. Mortality was assessed as of 31st December 2019.

RESULTS

Between 2009 and 2015, there were 3097 hip fractures, of which 393 were subtrochanteric and femoral fractures and 69 were classified as AFF by ASBMR 2014 criteria. 35 of AFF occurred in BP exposed and 34 occurred in non-BP exposed patients. There were no significant demographic differences in patients with BP and non-BP related AFF. There were also similar incidences of type 2 diabetes, rheumatoid arthritis and glucocorticoid use. Notably, there were a higher percentage of previous fragility fractures (35.3 % vs 9.4 %) in BP related AFF. Time to healing of fracture was slightly longer in BP related AFF at median (3 months vs 2 month, p = 0.02), however there were no differences in incidence of delayed healing. Mortality between BP and non-BP related AFF were similar.

CONCLUSION

In a South East Asian population in Singapore, 47.8 % of AFF were found to be non-BP related. We found no major demographic and clinical differences between BP and non-BP related AFF. Mortality between BP and non-BP related AFF was similar. Further studies are needed to better understand the optimal treatment of osteoporosis in AFF prone patients in the Asian population.

Association of atypical femoral fracture location and lower limb mechanical axis: a computed tomography-based finite element analysis

Atypical femoral fractures (AFFs) are categorized as low-energy fractures of the femoral shaft or subtrochanteric region. The use of computed tomography-based finite element analysis demonstrated that the femoral weakest point against tensile stress coincided with AFF location, which was determined by the lower limb axis and femoral bowing.

INTRODUCTION

This study aimed to assess the relationship between the femoral weakest point against tensile stress and the lower limb axis and geometry, including femoral bowing, using a computed tomography (CT)-based finite element analysis (FEA) model.

METHODS

We retrospectively reviewed 19 patients with AFFs and analyzed their CT images of the contralateral intact femur. We performed FEA to find the maximum principal stress (MPS) and maximal tensile stress loading area (femoral weakest point, FWP) of each patient and matched the FWP with the real location of AFF. We applied mechanical axes differently, as neutral, varus, and valgus, in the FEA model, when we analyzed the change in MPS and FWP based on lower limb alignment. We compared the degree of agreement between the real fracture location and FWP before and after knee mechanical axis adjustment.

RESULTS

The average participant age was 75.9 (range, 61-87) years, and all participants were women. In the 19 patients included, we observed 20 and 7 shaft and subtrochanteric AFFs, respectively. The average mechanical axis at the knee joint level was 22.6 mm (range, 0-70 mm) of the varus. All the patients showed an increasing trend of MPS and a distal movement of FWP when the mechanical axis of the knee was applied from the valgus to varus alignment. The root mean square errors between the FWP and real fracture location were 14.58% and 10.87% before and after adjustment, respectively, implying that the degree of agreement was better in patients who underwent mechanical adjustment.

CONCLUSION

The use of CT/FEA demonstrated that the FWP against tensile stress coincided with AFF location, which was determined by the lower limb axis and femoral bowing.

Biomechanical analysis of the correlation between mid-shaft atypical femoral fracture (AFF) and axial varus deformation

Background

Atypical femoral fractures (AFF) are diaphyseal fractures of the elderly that occur at the end of a minor trauma. The objective of this biomechanical study, using finite element modelling, was to evaluate the variations of the femoral diaphysis fracture indicator according to the variations of the mechanical axis of the lower limb, which can explain all the different atypical fracture types identified in the literature.

Methods

In order to measure variations in stress and risk factors for fracture of the femoral diaphysis, the distal end of the femur was constrained in all degrees of freedom. An axial compression load was applied to the femoral head to digitally simulate the bipodal support configuration in neutral position as well as in different axial positions in varus/valgus (− 10°/10°).

Results

The maximum stress value of Von Mises was twice as high (17.96 ± 4.87 MPa) at a varus angle of − 10^° as in the neutral position. The fracture risk indicator of the femoral diaphysis varies proportionally with the absolute value of the steering angle. However, the largest simulated varus deformation (− 10°) found a higher risk of diaphysis fracture indicator than in valgus (10°).

Conclusions

Variations in the mechanical axis of the lower limb influence the stress distribution at the femur diaphysis and consequently increase the risk of AFF. The axial deformation in varus is particularly at risk of AFF. The combination of axial deformation stresses and bone fragility consequently contribute to the creation of an environment favorable to the development of AFF.

Trial registration: ‘retrospectively registered’.

Differences in femur geometry and bone markers in atypical femur fractures and the general population

This study aimed to identify differences in femur geometry between patients with subtrochanteric/shaft atypical femur fractures (AFFs) and the general population, and to evaluate the biomechanical factors related to femoral bowing in AFFs. We retrospectively reviewed 46 patients. Data on age, and history and duration of bisphosphonate use were evaluated. Femur computed tomography images were reconstructed into a 3D model, which was analyzed with a geometry analysis program to obtain the femur length, femur width and length, and femoral bowing. Patients were divided into two groups according to fracture location: the subtrochanteric and shaft AFF groups. We compared all parameters between groups, and also between each group and a general population of 300 women ≥ 60 years. Thirty-five patients had a history of bisphosphonate use (average duration, 6.1 years; range, 0.8–20 years). There was no statistical difference in bone turnover markers between the two groups. The shaft AFF group had a lower radius of curvature (ROC) (P = 0.001), lower bone mineral density (BMD, T score) (P = 0.020), and lower calcium (P = 0.016). However, other parameters and rate of bisphosphonate use were not significantly different. There were no significant differences in the parameters of the subtrochanter AFF group and the general population, but the shaft AFF group demonstrated a wider femur width (P < 0.001), longer anteroposterior length (P = 0.001), and lower ROC (P < 0.001) than the general population. Femoral bowing and width increased in shaft AFFs, but similar to subtrochanter AFFs compared to the general population. Our results highlight the biomechanical factors of femur geometry in AFFs.

Biomechanical mechanisms of atypical femoral fracture

Antiresorptives such as bisphosphonates (BP) and denosumab are commonly used osteoporosis treatments that are effective in preventing osteoporotic fractures by suppressing bone turnover. Although these treatments reduce fracture risk, their long-term use has been associated with atypical femoral fracture (AFF), a rare potential side effect. Despite its rare occurrence, AFF has had a disproportionately significant adverse impact on society due to its severe outcomes such as loss of function and delayed healing. These severe outcomes have led to the decrease in the use and prescription of osteoporosis treatment drugs due to patient anxiety and clinician reluctance. This creates the risk for increasing osteoporotic fracture rates in the population. The existing information on the pathogenesis of AFF primarily relies on retrospective observational studies. However, these studies do not explain the underlying mechanisms that contribute to AFF, and therefore the mechanistic origins of AFF are still poorly understood. The purpose of this review is to outline the current state of knowledge of the mechanical mechanisms of AFF. The review focuses on three major potential mechanical mechanisms of AFF based on the current literature which are (1) macroscale femoral geometry which influences the stress/strain distribution in the femur under loading; (2) bone matrix composition, potentially altered by long-term remodeling suppression by BPs, which directly influences the material properties of bone and its mechanical behavior; and (3) microstructure, potentially altered by long-term remodeling suppression by BPs, which impacts fracture resistance through interaction with crack propagation. In addition, this review presents the critical knowledge gaps in understanding AFF and also discusses approaches to closing the knowledge gap in understanding the underlying mechanisms of AFF.

Duration-Dependent Increase of Human Bone Matrix Mineralization in Long-Term Bisphosphonate Users with Atypical Femur Fracture

Bisphosphonates (BPs) are the most widely used drugs for the treatment of osteoporosis but prolonged use of BPs might increase the risk of atypical femur fracture (AFF). There are only a few studies that address the bone material quality in patients on long-term BP treatment with or without AFFs. We analyzed 52 trans-iliac bone biopsies from patients on long-term BP therapy with (n = 26) and without (n = 26) AFF. At the microscopic level, the degree of mineralization of bone (DMB) was assessed on whole bone by X-ray digitized microradiography while microhardness by Vickers microindentation, and bone matrix characteristics by Fourier transform infrared microspectroscopy (FTIRM) (mineral/organic ratio, mineral maturity and crystallinity, and collagen maturity) were measured at random focal areas. The AFF patients were treated longer than non-AFF patients (9.7 ± 3.3 years versus 7.9 ± 2.7 years). As expected, bone remodeling was low in both groups, without difference between them. The AFF group had significantly higher DMB in cortical bone (+2.9%, p = .001), which remained so after adjusting for treatment duration (p = .007), and showed a trend in cancellous bone (+1.6%, p = .05). Consistent with higher DMB, heterogeneity index (HI) was lower in the AFF than in the non-AFF group, illustrating lower heterogeneity of mineralization in the AFF group. A significant positive correlation between the duration of treatment and DMB in cortical bone was found in AFF, and not in the non-AFF group. Microhardness and bone matrix characteristics were similar between groups. We conclude that the AFF group had a duration-dependent increase in DMB leading to a significantly higher DMB than the non-AFF. Because BPs have high affinity to bone mineral and lining the walls of the osteocyte lacunae, the accumulation of matrix-bound BPs in AFF could lead to inhibition of the osteocyte cytoskeleton blunting their response to mechanical strains, a hypothesis to be further investigated. © 2021 American Society for Bone and Mineral Research (ASBMR).

The Sydney AFF Score: A Simple Tool to Distinguish Females Presenting With Atypical Femur Fractures Versus Typical Femur Fractures

Atypical femur fractures (AFF) are a rare but serious complication of long-term bisphosphonate use. Although clearly defined by ASBMR criteria, a proportion of patients with AFFs may go unrecognized and the use of qualitative fracture criteria may lead to uncertainty in AFF diagnosis, with significant therapeutic implications. A score that rapidly and accurately identifies AFFs among subtrochanteric femur fractures using quantitative, measurable parameters is needed. In a retrospective cohort of 110 female patients presenting with AFFs or typical femur fractures (TFFs), multiple logistic regression and decision tree analysis were used to develop the Sydney AFF score. This score, based on demographic and femoral geometry variables, uses three dichotomized independent predictors and adds one point for each: (age ≤80 years) + (femoral neck width <37 mm) + (lateral cortical width at lesser trochanter ≥5 mm), (score, 0 to 3). In an independent validation set of 53 female patients at a different centre in Sydney, a score ≥2 demonstrated 73.3% sensitivity and 69.6% specificity for AFF (area under the receiver-operating characteristic curve [AUC] 0.775, SE 0.063) and remained independently associated with AFF after adjustment for bisphosphonate use. The Sydney AFF score provides a quantitative means of flagging female patients with atraumatic femur fractures who have sustained an AFF as opposed to a TFF. This distinction has clear management implications and may augment current ASBMR diagnostic criteria. © 2021 American Society for Bone and Mineral Research (ASBMR).

Evaluation and management of atypical femoral fractures: an update of current knowledge

Atypical femoral fractures are often attributed to the use of anti-resorptive medications such as bisphosphonates (BP). Whilst they have proven effects on fragility fracture prevention, clinical and laboratory evidence is evolving linking BP-related suppression of bone remodelling to the development of atypical stress-related sub-trochanteric fractures (Shane et al. in JBMR 29:1-23, 2014; Odvina et al. in JCEM 90:1294-301, 2005; Durchschlag et al. in JBMR 21(10):1581-1590, 2006; Donnelly et al. in JBMR 27:672-678, 2012; Mashiba et al. in Bone 28(5):524-531, 2001; Dell et al. in JBMR 27(12):2544-2550, 2012; Black et al. in Lancet 348:1535-1541, 1996; Black et al. in NEJM 356:1809-1822, 2007; Black et al. in JAMA 296:2927-2938, 2006; Schwartz et al. in JBMR 25:976-82, 2010). Injuries may present asymptomatically or with prodromal thigh pain and most can be successfully managed with cephalomedullary nailing and discontinuation of BP therapy. Such injuries exhibit a prolonged time to fracture union with high rates of non-union and metal-work failure when compared to typical subtrochanteric osteoporotic femoral fractures. Despite emerging literature on AFFs, their management continues to pose a challenge to the orthopaedic and extended multi-disciplinary team. The purpose of this review includes evaluation of the current evidence supporting the management of AFFs, clinical and radiological features associated with their presentation and a review of reported surgical strategies to treat and prevent these devastating injures.

Morphological divergence in the curvature of human femoral diaphyses: Tracing the central mass distributions of cross-sections

The diaphysis of the human femoral bone has a physiological anterior curvature; additionally, there is a curvature to the medial side or lateral side. In addition to compression stress from gravity during standing, walking, and running, these bones are continuously exposed to complex stresses from the traction forces of the various strong muscles attached to them. The femoral diaphysis is subjected to these mechanical stresses, and the direction and size of its curvature are defined according to Wolff's law and the mechanostat theory of Frost. The purpose of this study was to quantitatively evaluate the curvature of the femoral diaphysis in Japanese skeletons by determining the curve connecting the central mass distributions (CMD) of cross-sectional images. A total of 90 right femora (46 males and 44 females) were randomly selected from modern Japanese skeletal specimens. Full-length images of these bones were acquired using a clinical computed tomography scanner. The range between the lower end of the lesser trochanter and the adductor tubercle of each femur was divided at regular intervals to obtain ten planes, and nine levels were analyzed. The CMD curve was determined by connecting the CMDs of each of the nine cross-sections. First, the CMD of a cross-section in each of the nine slices was calculated, and the nine trajectories were superimposed from above. Then, by converting the shape of the entire CMD curve to superimpose the coordinates of the endpoint on the starting point, a closed arc representing the curvature of the femur was determined. For both males and females, the patterns varied from mostly medial to largely lateral curvature. The size of the curvature also varied for individuals. By analyzing only the coordinates of the vertex of the CMD curve of each femoral bone, the outlines of the diaphyseal curvatures could be recognized. The femora were thereby divided into two groups: medial bending and lateral bending. Considering males and females together, the number in the lateral-curvature group (n = 51) was larger than that in the medial-curvature group (n = 39). Moreover, the average age of the lateral-curvature group was significantly higher than that of the medial-curvature group (p < 0.05). In males, with an increase in the cortical bone proportion of the cross-sectional area, the anterior vertex of diaphyseal bending tended to be more prominent. This cortical proportion was significantly higher in the medial-curvature groups than in the lateral-curvature group (p < 0.01). The phenomena observed in this study may be related to pathophysiologies such as atypical fractures of the femur and osteoarthritis of the knee joints.

Atypical femur fractures: current understanding and approach to management

Osteoporosis and resulting osteoporotic fractures are responsible for significant morbidity, excess mortality, and health care costs in the developed world. Medical therapy for osteoporosis has been shown in multiple randomized controlled trials to reduce the risk of vertebral and non-vertebral fractures and hip fractures, and in some studies bisphosphonate medications have been associated with improved survival. Although the overall benefit to risk ratio of osteoporosis medications remains favorable, there have been concerns raised about the long-term safety of these treatments. Atypical femur fracture, which is a rare type of fracture that has been associated with the long-term use of potent antiresorptive bone medications, is a potentially devastating consequence of osteoporosis treatment. This paper reviews our current understanding of atypical femur fractures, their relationship to antiresorptive osteoporosis medications, and proposed strategies for management, in order to inform clinical decision making about the optimal use and duration of medical therapy for the treatment of patients with osteoporosis or at high risk for osteoporotic fractures.

Reliability of measuring lateral bowing angle of the femur in patients with atypical femur fractures

BACKGROUND

Lateral femoral bowing causes a higher tensile mechanical load on the lateral side of the femur, which plays a critical role in the pathogenesis of atypical femoral fractures (AFFs). There are many ways to measure lateral femoral bowing on plain radiographs, and there are difficulties in finding a correspondence point between measurements among multiple measurers. The purpose of this study is to prove the best method of correspondence between the investigators by analyzing the reliability of various methods for measuring lateral femoral bowing.

MATERIALS AND METHODS

We retrospectively collected data from 85 patients (87 femurs) diagnosed with AFF who had plain radiographs of entire femur from October 2013 to March 2018. The femoral bowing was measured in coronal view of femur plain radiographs using five methods (Sasaki, Morin, Jang, Kim, and Yau) by three examiners, respectively. The intra- and interobserver reliability of each method was assessed using intraclass correlation coefficient (ICC) for continuous variables.

RESULTS

All methods showed excellent intra- and interobserver reliability with ICC of >0.8. Among five methods, the Yau's method was the highest reliable method (ICC = 0.980, 95% confidence interval = 0.971-0.986).

CONCLUSIONS

All methods of measuring lateral femoral bowing in the coronal plane of plain radiographs are reliable. And, we recommend Yau's method, which has a clear reference point for measuring femoral bowing and is highest reproducible.

Assessment of the multifactorial causes of atypical femoral fractures using a novel multiscale finite element approach

Atypical femoral fracture (AFF), which is a low energy fracture in the subtrochanteric or diaphysis region of the femur, has multifactorial causes that span macro- to microscale mechanisms including femoral geometry, cortical bone composition and structure. However, the extent of individual and combined influence of these factors on AFF is still not well understood. As a result, the aim of this study is to develop a multiscale fracture mechanics-based finite element modeling framework that is capable of quantifying the individual and combined influence of macroscale femoral geometrical properties as well as cortical bone microscale material properties and structure on AFF. In this study, three different femoral geometries with two different cortical bone microstructures, and two different material property distributions were investigated by first determining the critical AFF locations in the femur using macroscale stress analysis and then performing coupled macro-microscale fracture simulations. The simulation results showed that femoral geometry led to substantial differences in crack growth independent of cortical microstructure and tissue level material properties. The results suggest that multiple femoral geometrical properties, including neck-shaft angle and curvature, may contribute to the fracture behavior at AFF sites rather than a single macroscale geometrical feature. Osteonal area had a significant effect on microcrack propagation at AFF sites independent of microscale material property distribution and femoral geometry. In addition, cortical bone tissue level material heterogeneity improved the fracture resistance independent of femoral geometry and cortical microstructure. In summary, the computational approach developed in this study identified the individual, combined, and relative influence of multiscale factors on AFF risk. The new framework developed in this study could help identify the governing multiscale mechanisms of AFF and bring additional insight into the possible association of long-term bisphosphate treatment with AFF.

The Role of Lower-Limb Geometry in the Pathophysiology of Atypical Femoral Fracture

PURPOSEOF REVIEW

The etiology of atypical femoral fracture (AFF) is likely multifactorial. In this review, we examined the recent literature investigating the role of lower-limb geometry in the pathophysiology of AFF.

RECENT FINDINGS

Increased femoral bowing was associated with prevalent AFF and a greater likelihood of a diaphyseal versus a subtrochanteric AFF location. Femoral neck geometry or hip alignment may also be related to AFF, but findings remain equivocal. Differences in femoral geometry may, in part, be responsible for the high rate of AFF in Asian compared with Caucasian populations. Finally, simulation studies suggest that lower-limb geometry influences AFF risk via its effects on mechanical strain of the lateral femoral cortex. Femoral geometry, and bowing in particular, is related to prevalent AFF, but more prospective investigation is needed to determine whether measurements of geometry can be used for clinical risk stratification.

Medialized Trochanteric Starting Point and Focused Lateral Endosteal Beak Reaming to Optimize Success of Intramedullary Nailing in Atypical Femur Fractures: A Technical Trick and Case Series

Optimal intramedullary treatment of atypical femur fractures associated with bisphosphonate use requires avoidance of postoperative malreduction, particularly varus. This can be difficult to achieve, given the fracture location, errors with nail entry point, endosteal beaking, and underlying patient osteology, all of which can contribute to postoperative varus and predispose the patient to treatment failure. We present a surgical technique and clinical series of 10 patients emphasizing a medialized trochanteric nail entry point and preferential lateral endosteal reaming to secure a biologically and biomechanically favorable reduction and fixation.

Atypical Femur Fractures: Review of Epidemiology, Relationship to Bisphosphonates, Prevention, and Clinical Management

Bisphosphonates (BPs) are highly effective in treating osteoporosis and reducing hip, vertebral, and other fractures by as much as 50% to 70%. However, since 2006, atypical femur fractures (AFFs) emerged as potential side effects of BPs and other treatments. These fractures have unusual radiologic features and occur with little trauma. Public concern has led to a >50% decrease in BP usage. AFFs are rare: for each AFF, >1200 fractures, including 135 hip fractures, are prevented. Case definition criteria were updated by the American Society of Bone and Mineral Research in 2014. Many epidemiologic studies have been reported, and although methodologically challenging, generally support a BP-AFF association. However, the magnitude of the association between BPs and AFFs is uncertain: estimates of relative risk for AFFs among BP users vs nonusers range from 1 to 65 with a meta-analysis estimate of 1.7. Although mechanistic studies have proposed several hypotheses explaining how BPs might decrease bone strength, AFF pathogenesis remains uncertain and cannot explain the paradox of efficacy of reduction of common fractures while increasing risk for rare fractures at one site. There are several consistent risk factors, including Asian race (in North America), femoral bowing, and glucocorticoid use, whereas others remain unclear. Consensus is emerging about strategies to prevent AFFs in BP users (including drug holidays after 5 years' use in some patients). In conclusion, AFFs can be devastating, but even under the most pessimistic assumptions, the benefit/risk ratio is highly positive for BPs, particularly during 3 to 5 years of use. As understanding of AFFs increases, it is becoming increasingly possible to maximize BP benefits while minimizing AFF risk.

Prevalence and Characteristics of Atypical Periprosthetic Femoral Fractures

Bisphosphonate use has been associated with atypical femoral fractures (AFFs), defined by the American Society of Bone and Mineral Research (ASBMR) Task Force criteria, which currently exclude periprosthetic fractures. The objectives of this study were to establish the prevalence of atypical periprosthetic femoral fractures (APFFs) in patients with hip and knee arthroplasties and to determine the clinical and radiological risk factors associated with these fractures. We performed a retrospective radiological review of all femoral fractures between January 1, 2006, and March 31, 2015, in Quebec City, Canada. Patients who sustained a periprosthetic femoral fracture (PFF) were identified and included in this study. We used the ASBMR Task Force criteria to identify atypical fractures and establish their prevalence. Data from medical records and radiological assessments of the femoral anatomy, the characteristics of the fracture, and the positioning of the prosthesis were collected. The prevalence of APFFs among PFFs was 8.3% (11/133). A strong association with bisphosphonates (p = 0.007) was observed, as well as an increased risk of APFFs among alendronate users compared to risedronate users (p = 0.04). A transverse fracture (p < 0.0001), a periosteal thickening of the lateral cortex at the fracture (p < 0.0001), a unicortical fracture (p = 0.02), and prodromal symptoms (p = 0.03) were associated with APFFs. The type of implant, its positioning, and the femoral geometry did not appear to be risk factors for APFFs compared to PFFs. © 2018 American Society for Bone and Mineral Research.

Current Understanding of Epidemiology, Pathophysiology, and Management of Atypical Femur Fractures

PURPOSE OF REVIEW

To summarize reports published since the 2013 American Society of Bone and Mineral Research Task Force Report on atypical femoral fractures (AFF).

RECENT FINDINGS

The absolute incidence of AFFs remains low. AFFs are primarily associated with prolonged bisphosphonate (BP) exposure, but have also been reported in unexposed patients and those receiving denosumab for osteoporosis and metastatic bone disease. Asians may be more susceptible to AFFs. Lateral femoral bowing and varus hip geometry, which increase loading forces on the lateral femoral cortex, may increase AFF risk. Altered bone material properties associated with BP therapy may predispose to AFFs by permitting initiation and increasing propagation of micro-cracks. Relevant genetic mutations have been reported in patients with AFFs. Single X-ray absorptiometry femur scans permit early detection of incomplete and/or asymptomatic AFFs. Orthopedists recommend intramedullary rods for complete AFFs and for incomplete, radiologically advanced AFFs associated with pain and/or marrow edema on MRI. Teriparatide may advance AFF healing but few data support its efficacy. Greater understanding of biological and genetic predisposition to AFF may allow characterization of individual risk prior to initiating osteoporosis therapy and help allay fear in those at low risk for this complication, which remains rare in comparison to the osteoporotic fractures prevented by antiresorptive therapy.

Critical differences between subtrochanteric and diaphyseal atypical femoral fractures: analyses of 51 cases at a single institution in Korean population

There still remains controversy on the pathomechanism of atypical femoral fracture (AFF). The angle of lateral bowing and bone mineral density showed significant differences between subtrochanteric and diaphyseal atypical fracture groups. In addition to the use of bisphosphonate, mechanical factors might play important roles in the occurrence of AFFs.

INTRODUCTION

Although AFF could be divided into subtrochanteric and diaphyseal fracture according to the location of fractures, there is a lack of evidence regarding differences between two fractures and etiology of the occurrence. The aim of study is to determine differences between atypical subtrochanteric and diaphyseal fracture in Korean population.

METHODS

Between February 2010 and March 2015, 51 AFFs in 40 patients were included in this study. Their medical records were retrospectively reviewed. The AFF patients satisfied all the diagnostic criteria of the 2014 revised edition of the ASMBR. To analyze the differences according to the location of fracture, the AFFs were divided into subtrochanteric (n = 16) and diaphyseal (n = 35) fracture groups. The following factors were compared between two groups: patients' demographics, underlying diseases, laboratory findings (serum-25(OH) VitD3, osteocalcin, c-telopeptide, ALP, Ca, and P), bone mineral density (BMD), duration of bisphosphonate (BP) usage, and lateral bowing of the femur at time of the fracture.

RESULTS

All AFFs happened in female patients (mean age, 73.8 years) who have received bisphosphonate treatments except three patients. The mean duration of bisphosphonate usage was 95.3 months. Between the two groups, demographic data (age, height, weight, and BMI), underlying diseases, laboratory findings, hip BMD, and duration of BP treatment were comparable to each other (p > 0.05). However, the subtrochanteric fracture group showed higher FNSBA (femoral neck shaft bowing angle, p < 0.001) and spine BMD (p = 0.014) compared to the diaphyseal fracture group.

CONCLUSIONS

Angle of lateral bowing (FNSBA) and spine BMD showed significant differences between subtrochanteric and diaphyseal atypical fracture groups. According to our results, femoral bowing and spine BMD may play important roles in the AFF locations.

Influence of geometry on proximal femoral shaft strains: Implications for atypical femoral fracture

INTRODUCTION

Atypical femoral fractures (AFF) are characterized as low-energy fractures of the femoral shaft or subtrochanteric region. Femoral geometry is known to play a role in AFF risk; it is hypothesized that high-risk geometries are associated with elevated femoral shaft strain. However, it is not well known which geometric parameters have the greatest effect on strain, or whether interaction between parameters is significant. The purpose of this study was to thoroughly quantify the relationship between femoral geometry and diaphyseal strain, using patient specific finite element (FE) modelling in concert with parametric mesh morphing.

METHODS

Ten FE models were generated from computed tomography (CT) images of cadaveric femora. Heterogeneous material properties were assigned based on average CT intensities at element locations and models were subject to loads and boundary conditions representing the stance phase of gait. Mesh morphing was used to manipulate 8 geometric parameters: neck shaft angle (NSA), neck version angle (NV), neck length (NL), femoral length (FL), lateral bowing angle (L.Bow), anterior bowing angle (A.Bow), shaft diameter (S.Dia), and cortical bone thickness (C·Th). A 2-Level full factorial analysis was used to explore the effect of different combinations of physiologically realistic minimum and maximum values for each parameter. Statistical analysis (Generalized Estimating Equations) was used to assess main effects and first order interactions of each parameter.

RESULTS

Six independent parameters and seven interaction terms had statistically significant (p<0.05) effects on peak strain and strained volume. For both measures, the greatest changes were caused by S.Dia, L.Bow, and A.Bow, and/or first order interactions involving two of these variables.

CONCLUSIONS

As hypothesized, a large number of geometric measures (six) and first order interactions (seven) are associated with changes in femoral shaft strain. These measures can be evaluated radiographically, which may have important implications for future studies investigating AFF risk in clinical populations.

Atypical femur fractures: a survey of current practices in orthopedic surgery

The results of a self-administered online survey demonstrate that orthopedic surgeons' management practices for AFF are variable. These data will inform the development of clinical practice guidelines.

INTRODUCTION

We aimed to determine current AFF treatment practices of orthopedic surgeons to inform clinical practice guideline development.

METHODS

A self-administered online survey was developed and sequentially posted on the Orthopaedic Trauma Association (OTA) website from July to August 2015 and the Canadian Orthopaedic Association (COA) website from December 2015 to January 2016. Level of confidence in diagnosis and treatment as well as treatment preferences between respondents who self-identified as trauma surgeons vs. non-trauma surgeons were compared.

RESULTS

A total of 172 completed surveys were obtained (OTA, N = 100, 58%; COA, N = 72, 8%). Seventy-eight percent of respondents had treated ≥1 AFF in the previous 6 months. Seventy-six percent reported feeling extremely or very confident in diagnosing AFF (trauma 84% vs. non-trauma surgeons 70%, p = 0.04), and 63% reported feeling extremely or very confident in treating AFF (trauma 82%, non-trauma surgeons 50%, p < 0.01). Preferred management for complete and symptomatic incomplete AFFs was surgical fixation with a cephalomedullary nail (CMN) by 88 and 79%, respectively, while close follow-up was preferred for asymptomatic incomplete AFFs in 72% of respondents. Trauma surgeons used the CMN more frequently than non-trauma surgeons (90 vs. 76% p = 0.03). In patients with bilateral AFFs, with one side surgically treated, 56% were extremely likely to surgically treat the contralateral side, if symptomatic. Most felt guidelines (81%) and educational resources (73%) would be valuable.

CONCLUSIONS

Current orthopedic treatment practices for AFFs are variable. The results of this survey will inform the development of practice guidelines and educational resources.

Antiresorptives: Safety Concerns-Clinical Perspective

Antiresorptive drugs, such as amino-bisphosphonates and denosumab (Dmab), have dominated osteoporosis therapies for over 20 years. Since osteoporosis is a chronic disease, antifracture therapy could continue for the rest of a patient's life. Phase III clinical trials for antiresorptive drugs assessed relatively small patient populations for short durations and excluded up to 80% of patients who might seek osteoporosis therapy in clinical practice. Postmarketing reports based upon millions of patient-years and long-term (>5 years) clinical administration have associated some previously unknown, rare adverse events with antiresorptive use including osteonecrosis of the jaw (ONJ) and atypical femur fractures (AFFs). In the osteoporosis patient population, who receive much lower doses of bisphosphonate (BP) or Dmab, the incidence of ONJ is estimated at 0.001% to 0.01%, which is only slightly higher than that seen in the general population. AFFs are insufficiency or fissure transverse fractures originating on the lateral cortex of the subtrochanteric or diaphyseal region of the femur becoming oblique as they progress medially when complete. Incidence rates of AFF range from 1.8/100,000 per year with a 2-year BP exposure to 113/100,000 per year with BP exposure from 8 to 9.9 years. Most recent pathogenic hypotheses of these rare events will be discussed.

Lateral fixation: an alternative surgical approach in the prevention of complete atypical femoral fractures

Little evidence is available on how to treat incomplete atypical fractures of the femur. When surgery is chosen, intramedullary nailing is the most common invasive technique. However, this approach is adopted from the treatment of other types of ordinary femoral fracture and does not aim to prevent the impending complete fracture by interrupting the mechanism underlying the pathology. We suggest a different surgical approach that intends to counteract the underlying biomechanical conditions leading to a complete atypical fracture and thus could be better suited in selected cases. Here, we share an alternative surgical approach and present two cases treated accordingly.

Atypical Femoral Shaft Fractures in Female Bisphosphonate Users Were Associated with an Increased Anterolateral Femoral Bow and a Thicker Lateral Cortex: A Case-Control Study

The purpose of our study was to investigate the radiographic characteristics of atypical femoral shaft fractures (AFSFs) in females with a particular focus on femoral bow and cortical thickness. We performed a fracture location-, age-, gender-, and ethnicity-matched case-control study. Forty-two AFSFs in 29 patients and 22 typical osteoporotic femoral shaft fractures in 22 patients were enrolled in AFSF group and control group, respectively. With comparing demographics between two groups, radiographically measured femoral bow and cortical thicknesses of AFSF group were compared with control group. All AFSF patients were females with a mean age of 74.4 years (range, 58–85 years). All had a history of bisphosphonate (BP) use with a mean duration of 7.3 years (range 1–17 years). Femoral bow of AFSF group was significantly higher than control group on both anteroposterior (AP) and lateral radiographs after age correction. Mean femoral bow on an AP radiograph was 12.39° ± 5.38° in AFSF group and 3.97 ± 3.62° in control group (P < 0.0001). Mean femoral bow on the lateral radiograph was 15.71° ± 5.62° in AFSF group and 10.72° ± 4.61° in control group (after age correction P = 0.003). And cortical thicknesses of AFSF group demonstrated marked disparity between tensile and compressive side of bowed femurs in this study. An adjusted lateral cortical thickness was 10.5 ± 1.4 mm in AFSF group and 8.1 ± 1.3 mm in control group (after age correction P < 0.0001) while medial cortical thickness of AFSF group was not statistically different from control group. Correlation analysis showed that the lateral femoral bow on the AP radiograph was solely related to lateral CTI (R = 0.378, P = 0.002). AFSFs in female BP users were associated with an increased anterolateral femoral bow and a thicker lateral cortex of femurs.

Anterolateral femoral bowing and loss of thigh muscle are associated with occurrence of atypical femoral fracture: Effect of failed tension band mechanism in mid-thigh

BACKGROUND

The purpose of this study was to characterize anterolateral bowing of the femur using X-rays and muscular atrophy in the mid-thigh using computed tomography (CT) in patients with atypical femoral fractures (AFFs). We then compared the results with those of an intertrochanteric fracture to understand whether these measures act as causative factors of AFFs.

METHODS

From January 2009 to December 2015, 37 patients with complete AFF and 12 patients with incomplete AFF were enrolled in this study. Lateral femoral bowing, anterior femoral bowing, cross-sectional area (CSA), and attenuation coefficient of thigh muscles in the AFF group are measured and compare with those in the intertrochanteric fracture group.

RESULTS

Lateral and anterior femoral bowing in the AFF group were significantly higher than those in the intertrochanteric fracture group. The level of fracture was found to be significantly associated with lateral and anterior femoral bowing (r = 0.569, r² = 0.324, p < 0.001; r = -0.530, r² = 0.281, p < 0.001, respectively). Total CSA and CSA of anterior and medial compartments were significantly lower in the AFF group (p < 0.05). The attenuation coefficient of the total thigh muscle and all three compartments in the AFF group were significantly lower than those in the intertrochanteric fracture group (p < 0.05).

CONCLUSIONS

This study demonstrated that anterolateral femoral bowing and loss of thigh muscle were highly associated with the occurrence of AFFs.