Biomechanics of the classic metaphyseal lesion: finite element analysis

Post-mortem skeletal survey (PMSS) versus post-mortem computed tomography (PMCT) for the detection of corner metaphyseal lesions (CML) in children

OBJECTIVES

Corner metaphyseal lesions (CMLs) are specific for child abuse but challenging to detect on radiographs. The accuracy of CT for CML detection is unknown. Our aim was to compare diagnostic accuracy for CML detection on post-mortem skeletal surveys (PMSS, plain radiography) versus post-mortem CT (PMCT).

METHODS

A 10-year retrospective review was performed at a children's hospital for patients having PMSS, PMCT and histopathological correlation (reference standard) for suspected CMLs. Twenty-four radiologists independently reported the presence or absence of CMLs in all cases in a blinded randomised cross-over design across two rounds. Logistic regression models were used to compare accuracy between modalities.

RESULTS

Twenty CMLs were reviewed for each of the 10 subjects (200 metaphyses in all). Among them, 20 CMLs were confirmed by bone histopathology. Sensitivity for these CMLs was significantly higher for PMSS (69.6%, 95% CI 61.7 to 76.7) than PMCT (60.5%, 95% CI 51.9 to 68.6). Using PMSS for detection of CMLs would yield one extra correct diagnosis for every 11.1 (95% CI 6.6 to 37.0) fractured bones. In contrast, specificity was higher on PMCT (92.7%, 95% CI 90.3 to 94.5) than PMSS (90.5%, 95% CI 87.6 to 92.8) with an absolute difference of 2.2% (95% CI 1.0 to 3.4, p < 0.001). More fractures were reported collectively by readers on PMSS (785) than on PMCT (640).

CONCLUSION

PMSS remains preferable to PMCT for CML evaluation. Any investigation of suspected abuse or unexplained deaths should include radiographs of the limbs to exclude CMLs.

CLINICAL RELEVANCE STATEMENT

In order to avoid missing evidence that could indicate child abuse as a contributory cause for death in children, radiographs of the limbs should be performed to exclude CMLs, even if a PMCT is being acquired.

KEY POINTS

• Corner metaphyseal lesions (CMLs) are indicative for abuse, but challenging to detect. Skeletal surveys (i.e. radiographs) are standard practice; however, accuracy of CT is unknown. • Sensitivity for CML detection on radiographs is significantly higher than CT. • Investigation of unexplained paediatric deaths should include radiographs to exclude CMLs even if CT is also being performed.

Comparison of different internal fixation models in ankle arthrodesis using 3D finite-element analysis

BACKGROUND

The purpose of this study is to use three-dimensional finite-element analysis to better understand the biomechanical features of various internal fixators for ankle arthrodesis.

METHODS

We used finite-element analysis to compare four different types of internal fixations in ankle arthrodesis: Group A had three crossed screws (Ø6.5 mm); Group B had two crossed screws (Ø6.5 mm) and an anterior plate (Ø2.7 mm); Group C only had an anterior anatomical plate (Ø3.5 mm); Group D had one anterior anatomical plate (Ø3.5 mm) and one posterior-lateral screw (Ø6.5 mm). We adopted Ansys 21.0 software to analyze and compare the four types in terms of the displacement of the arthrodesis surface and the stress peak and stress distribution of these models under intorsion, extorsion, dorsiflexion torque, and neutral vertical load.

RESULTS

① Displacement of the arthrodesis surface: In Group A, the maximum displacement was larger than Group D under neutral vertical load and dorsiflexion torque but less than it under intorsion and extorsion torque. In Group B, the maximum displacement against dorsiflexion, neutral vertical load, intorsion, and extorsion was less than that in the other three fixation models. In Group C, the maximum displacement against the above four loading patterns were significantly higher than that in another three fixation models. ② Stress peak and stress distribution: based on the stress distribution of the four models, the peak von Mises stress was concentrated in the central sections of the compression screws, plate joints, and bending parts of the plates.

CONCLUSIONS

The fixation model consisting of two crossed screws and an anterior outperformed the other three fixation models in terms of biomedical advantages; thus, this model can be deemed a safe and reliable internal fixation approach for ankle arthrodesis.

Iatrogenic Flexion-Related Classic Metaphyseal Lesion of the Distal Tibia: Three Cases

BACKGROUND

Classic metaphyseal lesions (CMLs) should raise concern for nonaccidental trauma. However, iatrogenic causes for CMLs have increasingly been described and warrant close consideration. Increasing the clinical understanding of CML mechanics and their relation to often routine medical procedures will enhance provider awareness and expand the differential diagnosis when these otherwise highly concerning injuries are identified.

CASE REPORTS

We describe three clinical cases where suspected iatrogenic dorsiflexion or plantar flexion resulted in an isolated distal tibia CML. Respectively, we present heel-stick testing and i.v. line placement as clinical correlates of these two mechanisms. Although prior reports have aimed to describe iatrogenic CML etiologies, they have not focused on dorsiflexion or plantar flexion as predominant mechanisms of injury. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: Emergency physicians are critical to the surveillance and identification of nonaccidental trauma. Given that children oftentimes present to the emergency department with subtle yet concerning signs of maltreatment, an emergency physician must be aware of the potential causes of injury as well as the recommended response. Although avoiding missed cases of abuse and improving the detection of injuries is crucial for child health and well-being, failing to consider or recognize alternative explanations could also have serious implications for a child and their caregivers.

Debunking Fringe Beliefs in Child Abuse Imaging: AJR Expert Panel Narrative Review

Child abuse is a global public health concern. Injuries from physical abuse may be clinically occult and not appreciable on physical examination. Imaging is therefore critical in identifying and documenting such injuries. The radiologic approach for a child who has potentially been abused has received considerable attention and recommendations according to decades of experience and rigorous scientific study. Nonetheless, fringe beliefs describing alternative explanations for child abuse-related injuries have emerged and received mainstream attention. Subsequently, imaging findings identified in abused children have been attributed to poorly supported underlying medical conditions, clouding the evidence basis for radiologic findings indicative of nonaccidental trauma. Fringe beliefs that attribute findings seen in child abuse to alternate pathologies such as genetic disorders, birth trauma, metabolic imbalances, vitamin D deficiency, and short-distance falls typically have limited evidence basis and lack professional society support. Careful review of the scientific evidence and professional society consensus statements is important in differentiating findings attributable to child abuse from fringe beliefs used to discount the possibility that a child's constellation of injuries is consistent with abuse. This review refutes fringe beliefs used to provide alternative explanations in cases of suspected child abuse and reinforces the key literature and scientific consensus regarding child abuse imaging.

Fractures of child abuse

The objective of this paper is to review common challenges when evaluating fractures in the setting of possible child abuse and approaches to navigate them. This paper reviews the variety of imaging modalities available for evaluating child abuse and the advantages/disadvantages of each. Additionally, the authors discuss management of equivocal fractures, including the impact of double-reading skeletal surveys. The complexity of dating the acuity of fractures in young children is discussed. Utilizing the knowledge of fracture type, fracture patterns and patient history, as well as in the setting of cardiopulmonary resuscitation, the authors provide methods for determining the likelihood of abuse.

Revisiting the radiographic assessment of osteoporosis-Osteopenia in children 0-2 years of age. A systematic review

BACKGROUND

Imaging for osteoporosis has two major aims, first, to identify the presence of low bone mass (osteopenia), and second, to quantify bone mass using semiquantitative (conventional radiography) or quantitative (densitometry) methods. In young children, densitometry is hampered by the lack of reference values, and high-quality radiographs still play a role although the evaluation of osteopenia as a marker for osteoporosis is subjective and based on personal experience. Medical experts questioned in court over child abuse, often refer to the literature and state that 20-40% loss of bone mass is warranted before osteopenia becomes evident on radiographs. In our systematic review, we aimed at identifying evidence underpinning this statement. A secondary outcome was identifying normal references for cortical thickness of the skeleton in infants born term, < 2 years of age.

METHODS

We undertook systematic searches in Medline, Embase and Svemed+, covering 1946-2020. Unpublished material was searched in Clinical trials and International Clinical Trials Registry Platform (ICTRP). Both relevant subject headings and free text words were used for the following concepts: osteoporosis or osteopenia, radiography, children up to 6 years.

RESULTS

A total 5592 publications were identified, of which none met the inclusion criteria for the primary outcome; the degree of bone loss warranted before osteopenia becomes visible radiographically. As for the secondary outcome, 21 studies were identified. None of the studies was true population based and none covered the pre-defined age range from 0-2 years. However, four studies of which three having a crossectional and one a longitudinal design, included newborns while one study included children 0-2 years.

CONCLUSIONS

Despite an extensive literature search, we did not find any studies supporting the assumption that a 20-40% bone loss is required before osteopenia becomes visible on radiographs. Reference values for cortical thickness were sparse. Further studies addressing this important topic are warranted.

Are classic metaphyseal lesions pathognomonic for child abuse? Two cases of motor vehicle collision-related extremity CML and a review of the literature

Long bone fractures at the infant growth plate, known as classic metaphyseal lesions (CMLs), raise a strong suspicion for abusive injury. CMLs persist as a hallmark for inflicted injury although a handful of documented cases of CMLs created by other, non-abusive mechanisms within various healthcare settings are scattered throughout the past few decades of medical literature. The forces required to sustain a CML are typically defined as a combination of tensile, compressive, or rotational energy applied to the metaphyseal regions of an infant's long bones. Recently, two separate child protection teams each encountered a case of CML discovered after reported motor vehicle collisions (MVC). This provoked a critical appraisal of the medical literature to inform clinical practice regarding MVCs as a potential mechanism for this fracture type and to remind clinicians that there is no single injury pathognomonic for abuse.

Investigating rolling as mechanism for humeral fractures in non-ambulant infants: a preliminary finite element study

AIM

To use personalised computed tomography (CT)-based finite element models to quantitatively investigate the likelihood of self-inflicted humeral fracture in non-ambulant infants secondary to rolling.

MATERIALS AND METHODS

Three whole-body post-mortem CT examinations of children at the age of rolling (two 4-month-old and one 6-month-old) were used. The mechanical moment needed by each infant to perform a rolling manoeuvre was calculated and applied to the finite element model in order to simulate spontaneous rolling from the prone to the supine position.

RESULTS

The maximum predicted strains were found to be substantially lower (with a difference of >80%) than the elastic limit of the bone.

CONCLUSION

Results of this study challenge the plausibility of self-inflicted humeral fracture caused by rolling in non-ambulant infants and indicate that it is unlikely for a humeral fracture to result from this mechanism without the assistance of an external force.

Buckle fracture of the proximal tibia in children and frequency of association with trampoline and inflatable bouncer use

BACKGROUND

Proximal tibial buckle fractures are often called "trampoline fractures," but mechanisms are more varied.

OBJECTIVE

To assess the frequency of trampoline or bouncer etiology among children with buckle fracture of the proximal tibia, characterizing demographics, alternative etiologies, and fracture patterns.

MATERIALS AND METHODS

We performed retrospective chart review of mechanisms, age and gender of children with radiographs interpreted as proximal tibial buckle fracture between 2010 and 2016. Two pediatric radiologists assessed presence of cortical impaction, cortical break, increased anterior scoop deformity, and oblique extension of fracture toward the physis. We studied the associations among demographics, etiology and fracture appearance using analysis of variance and chi-square/Fisher exact tests.

RESULTS

We identified 145 exams interpreted as proximal tibial buckle fracture (median age 34 months, 64% girls). Bouncing surface was the most common mechanism (44%), and 80% of those cases reported multiple people on the bouncing surface. Falls were the second most common mechanism (30%). Children injured while bouncing were older (median 41 months) than others (median 21 months, P<0.005) and more likely to have oblique extension of fracture toward the physis (P<0.05). Buckle deformity was associated with a younger age (F=8.67; P<0.01), while oblique extension to the physis and concurrent fibula fracture were associated with older age (F=18.62, P<0.001; and F=8.02, P<0.01, respectively).

CONCLUSION

Trampoline use was the most common single mechanism of injury in children with proximal tibial fracture interpreted as buckle deformity. However, non-bouncing mechanisms were overall more common and occurred in a younger age group at risk for "toddler fractures."

Prevalence of metaphyseal injury and its mimickers in otherwise healthy children under two years of age

BACKGROUND

Metaphyseal lesions in infants and toddlers are believed to have a high specificity for inflicted injury.

OBJECTIVES

To examine the prevalence of metaphyseal injury and its mimickers in otherwise healthy children younger than 2 years of age.

MATERIALS AND METHODS

During 2010-2015, all children 2 years old and younger seen at the Accident and Emergency (A&E) Department due to an injury who had radiographs taken were included. Information on mechanism and clinical findings were drawn from the medical notes. All radiographs were reviewed by two of five researchers together with an experienced paediatric radiologist, registering fracture site and type, and metaphyseal appearances.

RESULTS

Four hundred and eight children (212 boys) (mean age: 17.7 months, range: 3-24 months) were included, of whom 149 (77 boys) had a total of 162 fractures (incidence of 5.4 per 1,000 children). Only one metaphyseal lesion, without a history of trauma, was seen. Of the 860 metaphyses analysed, 140 (16.3%) were defined as either irregular (74/860, 8.6%) or as having a metaphyseal collar (66/860, 7.7%). Sixty-four of the 66 collars (97.0%) and 54/104 irregularities (60.8%) were located around the wrist and the ankle, while 25/74 irregularities (33.8%) were found around the knee joint.

CONCLUSION

Metaphyseal lesions with a history of trauma did not occur in otherwise healthy neonates and infants younger than 2 years of age, indicating that this type of fracture has a particular trauma mechanism. Metaphyseal irregularities/collars are frequently seen and should not be mistaken for a classic metaphyseal lesion.

Finite element modelling of the developing infant femur using paired CT and MRI scans

Bone finite element (FE) studies based on infant post-mortem computed tomography (CT) examinations are being developed to provide quantitative information to assist the differentiation between accidental and inflicted injury, and unsuspected underlying disease. As the growing skeleton contains non-ossified cartilaginous regions at the epiphyses, which are not well characterised on CT examinations, it is difficult to evaluate the mechanical behaviour of the developing whole bone. This study made use of paired paediatric post mortem femoral CT and magnetic resonance imaging (MRI) examinations at two different stages of development (4 and 7 months) to provide anatomical and constitutive information for both hard and soft tissues. The work aimed to evaluate the effect of epiphyseal ossification on the propensity to shaft fractures in infants. The outcomes suggest that the failure load of the femoral diaphysis in the models incorporating the non-ossified epiphysis is within the range of bone-only FE models. There may however be an effect on the metaphysis. Confirmation of these findings is required in a larger cohort of children.

Classic Metaphyseal Lesions among Victims of Abuse

OBJECTIVE

To use legal statements by perpetrators to gain new insights into the causative mechanism of classic metaphyseal lesion (CML). The CML, so called "corner fracture," is considered a highly specific marker for abuse in infants. However, the precise correlation between CMLs and abusive head trauma is still unknown.

STUDY DESIGN

In this retrospective observational study, we selected 67 cases with at least 1 CML from a 15-year cohort of legally prosecuted child abuse cases. Their clinical, radiologic, and forensic records were analyzed. In 27 cases, the perpetrator confessed to abusing the child and described the events. Potential associations with subdural hematoma and with confession were evaluated using 2 separate binary logistic regression models.

RESULTS

All 67 infants showed other signs of abuse. Median age was 3.4 months. Over 65% had multiple CMLs. Knees and ankles were predominantly involved (64%). Only CMLs of the shoulder were significantly associated with subdural hematoma (P = .03). Different-age fractures were more common in the nonsubdural hematoma group (P = .01). In the group with confessions, perpetrators admitted inflicting violent indirect skeletal forces (torsion, traction, compression, and forced movements). The most common circumstance was diapering (44%), reported by male perpetrators only (P = .03) followed by dressing/undressing (30%). The violence was habitual in 67% of cases.

CONCLUSIONS

This unique forensic case series shows that CMLs are caused by violent acts inflicted most during physical care of infants. The frequency of habitual violence responsible for CMLs deserves greater attention.

Ultrasound findings in classic metaphyseal lesions: emphasis on the metaphyseal bone collar and zone of provisional calcification

BACKGROUND

The classic metaphyseal lesion (CML) is highly specific for non-accidental trauma in infants. While the radiographic findings are well documented, there is little literature on the ultrasound (US) appearance.

OBJECTIVE

To evaluate US findings in CMLs identified on radiographs.

MATERIAL AND METHODS

This institutional review board-approved, retrospective evaluation of targeted US of CMLs was performed in selected groups of children from 2014 to 2017. Only CMLs confidently identified on radiography by a consensus of two radiologists were included. US images were obtained with a linear transducer, including longitudinal images at lateral, anterior, medial and posterior aspects. Two pediatric radiologists evaluated the US appearance, specifically the metaphyseal bone collar for thickness, deformity and fracture, as well as the sonographic zone of provisional calcification for irregularity and appearance of multiple lines. Radiography was the reference standard.

RESULTS

Twenty-two patients (13 female; mean age: 4.2 months) were identified, with 39 CMLs in the tibia (n=22), femur (n=11), humerus (n=3), radius (n=2) and fibula (n=1). Thirty-three of the 39 CMLs (85%) were identified on US, while 6 (15%) were not seen (false negatives). Thirty of the 39 (77%) had metaphyseal bone collar thickening, 29 (74%) had collar deformity and 12 (31%) had visible fracture of the collar. At the sonographic zone of provisional calcification, 16/39 (41%) had irregularity and 5 (13%) had multiple lines visible.

CONCLUSION

Identifying metaphyseal bone collar and zone of provisional calcification abnormalities is key to recognizing CMLs on US. While additional studies are necessary to evaluate the accuracy of US in the diagnosis of CMLs, our findings suggest US may have a potential role in either confirming or evaluating radiographically equivocal/occult CMLs.

The distal tibial classic metaphyseal lesion: medial versus lateral cortical injury

BACKGROUND

The distal tibia is a common location for the classic metaphyseal lesion (CML). Prior radiologic-pathologic studies have suggested a tendency for medial, as opposed to lateral, cortical injury with the CML, but there has been no formal study of the geographic distribution of this strong indicator of abuse.

OBJECTIVE

This study compares medial versus lateral cortical involvement of distal tibial CMLs in a clinical cohort of infants with suspected abuse.

MATERIALS AND METHODS

Reports of 1,020 skeletal surveys performed for suspected abuse (July 2005-June 2016) were reviewed. Twenty-six distal tibial CMLs (14 unilateral, 6 bilateral) with anteroposterior (AP) and lateral projections on the initial skeletal survey and at least an AP view on the follow-up survey were identified in 20 infants. Two blinded pediatric radiologists determined if the medial and/or lateral margins of the distal tibial metaphysis were involved by the CML.

RESULTS

Average interreader absolute agreement and kappa scores were 0.69-0.90 and 0.45-0.72, respectively. Average intrareader absolute agreement and kappa scores were 0.65-0.88 and 0.44-0.57, respectively. Analyses showed that the distal tibial CML almost always involved the medial cortical margin (reader 1=89%, reader 2=88%, pooled=89%) and the fracture infrequently involved the lateral cortical margin (reader 1=12%, reader 2=38%, pooled=26%). The percentage point difference between fracture involvement in medial and lateral margins was statistically significant from zero (P<0.001).

CONCLUSION

The distal tibial CML is most often encountered medially; lateral involvement is uncommon. This observation should help guide the radiologic diagnosis and could have implications for understanding the biomechanics of this distinctive injury.