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

Should nails be locked dynamically or statically in atypical femoral fractures? - A radiological analysis of time to union and reoperations in 236 displaced fractures with 4 years average follow-up

INTRODUCTION

Atypical femoral fractures (AFFs) are associated with delayed union and higher reoperation rates. Axial dynamization of intramedullary nails is hypothesized to reduce time-to-union (TTU) and fixation failure as compared to static locking.

METHODS

Consecutive acutely displaced AFFs fixed with long intramedullary nails across five centres between 2006 and 2021 with a minimum postoperative follow-up of three months were retrospectively reviewed. The primary outcome was TTU, compared between AFFs treated with dynamically or statically locked intramedullary nails. Fracture union was defined as a modified Radiographic Union Score for Tibial fractures score of 13 or greater. Secondary outcomes involved revision surgery and treatment failure, defined as non-union beyond 18 months or revision internal fixation for mechanical reasons.

RESULTS

A total of 236 AFFs (127 dynamically locked and 109 statically locked) were analysed with good interobserver reliability of fracture union assessment (intraclass correlation coefficient = 0.89; 95% CI = 0.82-0.98). AFFs treated with dynamized nails had significantly shorter median TTU (10.1 months; 95% CI = 9.24-10.96 vs 13.0 months; 95% CI = 10.60-15.40) (log-rank test, p = 0.019). Multivariate Cox regression revealed that dynamic locking was independently associated with greater likelihood of fracture union within 24 months (p = 0.009). Reoperations were less frequent in the dynamic locking group (18.9% vs 28.4%), although the difference was not statistically significant (p = 0.084). Static locking was an independent risk factor for reoperation (p = 0.049), as were varus reduction and lack of teriparatide use within three months of surgery. Static locking also demonstrated a higher frequency of treatment failure (39.4% vs 22.8%, p = 0.006) and was an independent predictor of treatment failure in logistic regression (p = 0.018). Other factors associated with treatment failure included varus reduction and open reduction.

CONCLUSIONS

Dynamic locking of intramedullary nails in AFFs is associated with faster time to union, lower rate of non-union, and fewer treatment failures.

Associations between long-term exercise participation and lower limb joint and whole-bone geometry in young and older adults

Introduction: Features of lower limb bone geometry are associated with movement kinematics and clinical outcomes including fractures and osteoarthritis. Therefore, it is important to identify their determinants. Lower limb geometry changes dramatically during development, partly due to adaptation to the forces experienced during physical activity. However, the effects of adulthood physical activity on lower limb geometry, and subsequent associations with muscle function are relatively unexplored. Methods: 43 adult males were recruited; 10 young (20-35 years) trained i.e., regional to world-class athletes, 12 young sedentary, 10 older (60-75 years) trained and 11 older sedentary. Skeletal hip and lower limb geometry including acetabular coverage and version angle, total and regional femoral torsion, femoral and tibial lateral and frontal bowing, and frontal plane lower limb alignment were assessed using magnetic resonance imaging. Muscle function was assessed recording peak power and force of jumping and hopping using mechanography. Associations between age, training status and geometry were assessed using multiple linear regression, whilst associations between geometry and muscle function were assessed by linear mixed effects models with adjustment for age and training. Results: Trained individuals had 2° (95% CI:0.6°-3.8°; p = 0.009) higher femoral frontal bowing and older individuals had 2.2° (95% CI:0.8°-3.7°; p = 0.005) greater lateral bowing. An age-by-training interaction indicated 4° (95% CI:1.4°-7.1°; p = 0.005) greater acetabular version angle in younger trained individuals only. Lower limb geometry was not associated with muscle function (p > 0.05). Discussion: The ability to alter skeletal geometry via exercise in adulthood appears limited, especially in epiphyseal regions. Furthermore, lower limb geometry does not appear to be associated with muscle function.

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.

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.

Associations of alpha-actinin-3 genotype with thigh muscle volume and physical performance in older adults with sarcopenia or pre-sarcopenia

BACKGROUND

This cross-sectional study aimed to investigate the relationship of the ACTN3 genotype with thigh muscle volume and physical performance in older adults with sarcopenia or pre-sarcopenia.

METHODS

Data from 64 older Japanese adults (mean age 74.4 ± 6.9 years, women 71.9%) with sarcopenia or pre-sarcopenia were analyzed. Sarcopenia and pre-sarcopenia were defined using the Asian Working Group for Sarcopenia. We collected oral mucosa samples to determine the ACTN3 genotype. Thigh muscle volumes were measured using magnetic resonance imaging. Physical performance was assessed using the usual and maximum gait speed, timed up and go test, and five-repetition sit-to-stand test. Muscle strength was assessed using grip strength.

RESULT

The ACTN3 genotype proportions were 20.3% for RR, 51.6% for RX, and 28.1% for XX. Participants with the RR genotype showed greater thigh muscle volume/ht² compared to those with the RX and XX ACTN3 genotypes (p < 0.05). The multiple linear regression analysis revealed that RX (p < 0.01) and XX (p < 0.01) ACTN3 genotypes, compared to RR, were associated with lower thigh muscle volume/ht² and with age, sex (reference; men), weight and maximum walking speed. There was no significant difference between physical performance and muscle strength between the ACTN3 genotypes.

CONCLUSION

The ACTN3 genotype of the X allele was associated with decreased thigh muscle volume compared to the ACTN3 genotype of RR in older adults with sarcopenia or pre-sarcopenia.

Functional Analyses of Four CYP1A1 Missense Mutations Present in Patients with Atypical Femoral Fractures

Osteoporosis is the most common metabolic bone disorder and nitrogen-containing bisphosphonates (BP) are a first line treatment for it. Yet, atypical femoral fractures (AFF), a rare adverse effect, may appear after prolonged BP administration. Given the low incidence of AFF, an underlying genetic cause that increases the susceptibility to these fractures is suspected. Previous studies uncovered rare CYP1A1 mutations in osteoporosis patients who suffered AFF after long-term BP treatment. CYP1A1 is involved in drug metabolism and steroid catabolism, making it an interesting candidate. However, a functional validation for the AFF-associated CYP1A1 mutations was lacking. Here we tested the enzymatic activity of four such CYP1A1 variants, by transfecting them into Saos-2 cells. We also tested the effect of commonly used BPs on the enzymatic activity of the CYP1A1 forms. We demonstrated that the p.Arg98Trp and p.Arg136His CYP1A1 variants have a significant negative effect on enzymatic activity. Moreover, all the BP treatments decreased CYP1A1 activity, although no specific interaction with CYP1A1 variants was found. Our results provide functional support to the hypothesis that an additive effect between CYP1A1 heterozygous mutations p.Arg98Trp and p.Arg136His, other rare mutations and long-term BP exposure might generate susceptibility to AFF.

The Genetics of Atypical Femur Fractures-a Systematic Review

PURPOSE OF REVIEW

Atypical femur fractures (AFFs) are rare subtrochanteric or diaphyseal fractures regarded as side effects of bisphosphonates (BPs), possibly with a genetic background. Here, we summarize the most recent knowledge about genetics of AFFs.

RECENT FINDINGS

AFF has been reported in 57 patients with seven different monogenic bone disorders including hypophosphatasia and osteogenesis imperfecta; 56.1% had never used BPs, while 17.5% were diagnosed with the disorder only after the AFF. Gene mutation finding in familial and sporadic cases identified possible AFF-related variants in the GGPS1 and ATRAID genes respectively. Functional follow-up studies of mutant proteins showed possible roles in AFF. A recent small genome-wide association study on 51 AFF cases did not identify significant hits associated with AFF. Recent findings have strengthened the hypothesis that AFFs have underlying genetic components but more studies are needed in AFF families and larger cohorts of sporadic cases to confirm previous results and/or find novel gene variants involved in the pathogenesis of AFFs.

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.

Factors related to femoral bowing among Korean female farmers: a cross-sectional study

Background

Female farmers have a high prevalence of knee osteoarthritis (KOA) in South Korea. Femoral bowing has been reported to be related to KOA by increasing load on the mechanical axis. This study aimed to investigate factors related to femoral bowing in Korean female farmers.

Methods

We analyzed the legs of 264 female farmers registered with the Korea farmers' knee cohort of Jeonnam Center for Farmers' Safety and Health. A structured questionnaire was used to determine sociodemographic variables, agricultural career, cumulative squatting working time (CSWT), and cumulative heavy lifting working time. Femoral bone density was measured and Kellgren-Lawrence (KL) grades were obtained from the knee radiographs. Mechanical axis angle (MAA), femoral bowing angle (FBA), anatomical lateral distal femoral angle (aLDFA), anatomical medial proximal tibial angle (aMPTA), and condylar-plateau angle (CPA) were measured. We examined the relationship between the FBA and related factors by using multiple linear regression.

Results

The proportion of individuals with radiographic KOA (≥ KL grade 2) in this study was 37.9%. As KL grades increased, MAA, FBA, and CPA increased, whereas aLDFA and aMPTA decreased. FBA increased with age. Multiple linear regression analyses using FBA as a dependent variable showed relationship with higher age, lower height, higher BMI, lower bone mineral density, longer CSWT, and longer agricultural careers.

Conclusions

The results of this study suggest that external factors related to agricultural work in female farmers was associated with femoral bowing, in addition to internal factors such as age, bone density, height, and obesity.

Asian ethnicity is associated with atypical femur fractures in an Australian population study

Asian race, younger age, higher body mass index (BMI) and antiresorptive drugs have all been associated with atypical femur fractures (AFFs). This increased risk of AFF in Asians is important as by 2050, >50% of hip fractures globally will occur in Asia, with an increased demand for antiresorptive drugs being likely. It is also currently unclear whether AFF risk is increased in all Asian subgroups. We therefore aimed to identify the incidence of AFFs in an Australian tertiary hospital, the contribution of ethnic origin to AFF risk, and determine other clinical risk factors for AFF. From January 1, 2009 to December 31, 2017, 97 AFFs (82 complete and 15 incomplete) occurred in 71 individuals in the overall study population of 204,358. Patients with AFF were more likely to be female (88.7% vs 69.1%, p < 0.001) and younger [median (IQR): 74(52-92) years vs 83(75-88) years, p < 0.001] than the "typical" femur fracture group (n = 3330). The cumulative incidence rate of AFF was 4.2 per 100,000 person-years, far lower than for any ICD-10 AM coded "typical" femur fracture (202.9 per 100,000 person-years). Asians were 3.4 (95%CI, 2.1-5.6) times more likely to sustain an AFF than non-Asians, the highest incidence being in those from South East Asian countries (16.6 per 100,000 person years), suggesting differences in risk between Asian countries. In the nested case-control study, bisphosphonate use was an independent association with AFF development. We conclude Asian ethnicity is an important association with AFF in this large Australian cohort.

Morphological profile of atypical femoral fractures: age-related changes to the cross-sectional geometry of the diaphysis

The use of bisphosphonates for osteoporosis patients has markedly decreased the incidence of femoral neck or trochanteric fractures. However, anti-osteoporosis drugs have been reported to increase the incidence of atypical femoral fractures, which involve stress fractures in the subtrochanteric region or the proximal diaphysis. In this study, the morphological characteristics of the cortical bone in human femoral diaphysis samples were analyzed from individuals who lived before bisphosphonate drugs were available in Japan. A total of 90 right femoral bones were arbitrarily selected (46 males and 44 females) from modern Japanese skeletal specimens. Full-length images of these femurs were acquired using a computed tomography scanner. An image processing method for binarization was used to calculate the threshold values of individual bones for determining their contours. The range between the lower end of the lesser trochanter and the adductor tubercle of each femur was divided at regular intervals to obtain 10 planes. The mean value of cortical bone thickness, periosteal border length, and the cortical cross-sectional area was evaluated for all planes. Moreover, the ratio of the area of the cortical bone to the total area of cross-section at the mid-diaphysis was calculated. A comparison between males and females demonstrated that most females had lower cortical bone area ratios at the mid-diaphysis. The femoral outer shape did not differ markedly according to age or sex; however, substantial individual differences were observed in the shape of the inner surface of the cortical bone. The cortical bone thickness and the cross-sectional area decreased with age in the femoral diaphysis; furthermore, in females, the decrease was higher for the former than for the latter. This may be due to a compensatory increase in the circumference of the femoral diaphysis. In addition, in about half of the subjects there was a discrepancy between the region with maximal value of the cortical bone thickness and that of the total cross-sectional area. Biological responses to mechanical stresses to the femoral diaphysis are thought not to be uniform. Bisphosphonates inhibit bone resorption and may promote non-physiological bone remodeling. Thus, a nonhomogeneous decrease in cortical thickness may be related to the fracture occurrence in the femoral diaphysis in some cases. Thus, long-term administration of bisphosphonates in patients with morphological vulnerability in the femoral cortical bones may increase the occurrence of atypical femoral fractures.

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.

The enigma of atypical femoral fractures: A summary of current knowledge

Atypical femoral fractures (AFF) are stress or ‘insufficiency’ fractures, often complicated by the use of bisphosphonates or other bone turnover inhibitors. While these drugs are beneficial for the intact osteoporotic bone, they probably prevent a stress fracture from healing which thus progresses to a complete fracture.

Key features of atypical femoral fractures, essential for the diagnosis, are: location in the subtrochanteric region and diaphysis; lack of trauma history and comminution; and a transverse or short oblique configuration.

The relative risk of patients developing an atypical femoral fracture when taking bisphosphonates is high; however, the absolute risk of these fractures in patients on bisphosphonates is low, ranging from 3.2 to 50 cases per 100,000 person-years.

Treatment strategy in patients with AFF involves: radiograph of the contralateral side (computed tomography and magnetic resonance imaging should also be considered); dietary calcium and vitamin D supplementation should be prescribed following assessment; bisphosphonates or other potent antiresorptive agents should be discontinued; prophylactic surgical treatment of incomplete AFF with cephalomedullary nail, unless pain free; cephalomedullary nailing for surgical fixation of complete fractures; avoidance of gaps in the lateral and anterior cortex; avoidance of varus malreduction.

Cite this article: EFORT Open Rev 2018;3:494-500. DOI: 10.1302/2058-5241.3.170070.