On Measuring Implant Fixation Stability in ACL Reconstruction

Numerous methods and devices are available for implant fixation in anterior cruciate ligament (ACL) reconstruction. Biomechanical data indicate high variability in fixation stability across different devices. This study aims to provide a better insight into measuring the structural characteristics and mechanical behavior of ACL implant fixations. Fourteen human tibial specimens with reconstructed ACLs were subjected to progressively increasing dynamic loading until failure. The motions of the tibia, the proximal and distal graft ends, as well as the testing frame and actuator, were continuously recorded via a motion tracking system. Significantly higher displacements of the machine actuator (1.0 mm at graft slippage onset, and 12.2 mm at ultimate load) were measured compared to the displacements of the proximal (0.8 and 4.3 mm, respectively) and distal graft (0.1 and 3.4 mm, respectively) ends. The displacements measured at different sites showed significant correlations. The provided data suggest significant and systematic inaccuracies in the stiffness and slippage of the fixation when using machine displacement, as commonly reported in the literature. The assessment of the distal graft displacement excludes the artifactual graft elongation, and most accurately reflects the graft slippage onset indicating clinical failure. Considering the high displacement at the ultimate load, the ultimate load could be used as a standardized variable to compare different fixation methods. However, the ultimate load alone is not sufficient to qualitatively describe fixation stability

Fracture load prediction in patients with metastatic lesions in the femur using finite element analysis

Pathologic femoral fractures in patients with metastatic cancer are associated with high morbidity and mortality. Clinical predictions of impending fractures are inaccurate and often lead to overtreatment or underestimation. If the specific fracture risk could be assessed, patients with an impendingfracture could be saved from a traumatic event, while others with a non-impending fracture could be spared from unnecessary prophylactic treatment. This study was aiming to investigate the effect of metastatic lesions on the biomechanical behaviour of the proximal femur. In more detail, a quantitative computed tomography (QCT)-based homogenized voxel finite element (hvFE) model was developed allowing a patient-specific pathologicfracture prediction. First, regions in the femur, most affected by metastatic lesions, were identified by reviewing clinical data of patients, who suffered a pathologic fracture. Sixteen pairs human femora were used for data collection of the study. One femur of each pair remained intact while a defined lesion, based on clinical findings, was milled out in either the superolateral or inferomedial portion of theneck of the contralateral femur. Prior to the biomechanical experiment, the femora were scanned with QCT. All femora were loaded in a mechanical setup mimicking one-legged stance. Stiffness, ultimate load, and fracture location were evaluated. In parallel, nonlinear hvFE models were generated from QCT images of the specimens and loaded in the same way as in the experiments. Data from the experiments and simulations were compared statistically to validate the hvFE model. A first finding was that the most affected region in reviewed patients was the superolateral- and inferomedial femoral neck, causing a higher stiffness reduction in specimens with the inferomediallesion. The mean ultimate load in experiments was 40% and 75% lower for specimen with the superolateral and inferomedial lesions, respectively, compared to intact specimens. The hvFEmodel predicted both stiffness and ultimate load for tested specimens in high correlation with experimental data and with higher accuracy than clinical guidelines. In addition, the model predicted qualitatively well the failure location. Lesions in the femoral neck lead to a reduction of structural integrity, whereby their site has a predominant effect on the magnitude of the reduction, underlining the inaccuracy of current predictive clinical guidelines. The automated subject-specific QCT-based hvFE model could predict the effectof metastatic lesions in the proximal femur better than clinical guidelines. Furthermore, it provided qualitative information about stiffness, ultimate load, and failure location in pathologic femora.Pathologische Frakturen bei Patienten mit metastasierendem Krebs führen zu einer erhöhten Morbidität und Mortalität. Aktuelle Vorhersagemethoden bevorstehender Frakturen sind ungenau und führen oft zum Übertherapieren oder zur Unterschätzung. Die Bestimmung des individuellen Frakturrisikos könnte Patienten mit einer drohenden Fraktur vor einem Trauma bewahren, während anderen Patienten eine unnötiger prophylaktische operative Behandlung erspart werden könnte. Das Ziel dieser Arbeit war es den Einfluss von metastatischen Läsionen auf das biomechanischeVerhalten des proximalen Femurs zu untersuchen. Des Weiteren wurde ein auf quantitativer Computertomographie(QCT) basierendes homogenisiertes nichtlineares Voxel-Finite-Elemente-Modell(hvFE) erstellt um die patientenindividuelle pathologische Frakturabschätzung zu ermöglichen. Als Erstes wurden klinische Daten von Patienten mit metastatischen Läsionen am Femur, welcheproximal eine pathologische Fraktur erlitten haben, ausgewertet um die Lagen, welche am häufigsten von den Läsionen betroffen sind zu bestimmen. Insgesamt wurden für die Datengewinnungder Studie 16 Paare humane Femora verwendet. Ein Femur jeden Paares wurde intaktbelassen, während am Femur der kontralateralen Seite eine definierte Läsion, basierend auf klinischer Verteilung, im superolateralen- bzw. inferomedialen Schenkelhalsbereich aufgebracht wurde. Vor dem biomechanischen Experiment wurden die Femora mit QCT gescannt. Alle Femora wurdenin einem Standlastfall belastet und die Steifigkeit, Festigkeit, sowie Bruchstelle evaluiert. Paralleldazu wurden nichtlineare hvFE Modelle aus QCT-Daten der Präparate generiert und den gleichen Belastungsbedingungen wie im biomechanischen Experiment unterzogen. Experimentelle Simulationsdatenwurden statistisch korreliert um das hvFE Modell zu validieren. Der superolaterale und inferomediale Schenkelhals waren die von Metastasen am meisten betroffenen Regionen mit einer höheren Steifigkeitsreduktion bei inferomedialen Läsionen. Die mittlereexperimentelle Festigkeit war um 40% bzw. 75% niedriger bei Präparaten mit superolateraler bzw. inferomedialer Läsion im Vergleich zu gesunden Präparaten. Die QCT-basierende hvFE Modellekonnten die Steifigkeit und Festigkeit in hoher Korrelation mit experimentellen Daten vorhersagen und mit höherer Genauigkeit, als klinische Methoden und zusätzlich die Bruchstelle qualitativ gutbestimmen. Läsionen am femoralen Schenkelhals führten zur Reduktion der strukturellen Integrität, wobei ihreLage einen großen Einfluss auf das Ausmaß dieser Reduktion hat. Präsentierte Daten zeigten einehohe Ungenauigkeit von aktuellen klinischen Methoden zur Frakturrisikoabschätzung. Patientenspezifische hoch-automatisierte hvFE Modelle konnten den Effekt von metastatischen Läsionen auf das biomechanische Verhalten des proximalen Femur besser als klinische Methoden voraussagen und liefern eine qualitative Information über die Steifigkeit, Festigkeit, sowie die Bruchstellein den pathologischen Knochen.submitted by Emir BencaZusammenfassung in deutscher SpracheAbweichender Titel laut Übersetzung der Verfasserin/des VerfassersMedizinische Universität, Dissertation, 2017OeB

The insufficiencies of risk analysis of impending pathological fractures in patients with femoral metastases: A literature review

Purpose: Pathologic fractures in patients with bone metastases are a common problem in clinical orthopaedic routine. On one hand recognition of metastatic lesions, which are at a high risk of fracture, is essential for timely prophylactic fixation, while on the other hand patients with a low risk of pathologic fractures should be spared from overtreatment.The purpose of this review is to identify all methods for fracture risk evaluation in patients with femoral metastases in the literature and to evaluate their predictive values in clinical applications. Methods: A MEDLINE database literature research was conducted in order to identify clinical scoring systems, conclusions from prospective and retrospective radiologic and/or clinical studies, as well as data from biomechanical experiments, numerical computational methods, and computer simulations. Results: The search identified 441 articles of which 18 articles met the inclusion criteria; 4 more articles were identified from citations of the primarily found studies. In principle there are two distinct methodologies, namely fracture risk prediction factors based on clinical and radiological data such as the most deployed the Mirels' score and fracture risk prediction based on engineering methods. Fracture risk prediction using Mirels' score, based on pure clinical data, shows a negative predictive value between 86 and 100%, but moderate to poor results in predicting non-impending fractures with a positive predictive value between 23 and 70%. Engineering methods provide a high accuracy (correlation coefficient between ex vivo and results from numerical calculations: 0.68 < r2 < 0.96) in biomechanical lab experiments, but have not been applied to clinical routine yet. Conclusion: This review clearly points out a lack of adequate clinical methods for fracture risk prediction in patients with femoral metastases. Today's golden standard, the Mirels' score leads to an overtreatment. Whereas, engineering methods showed high potential but require a clinical validation. In future definition of patient-specific, quantitative risk factor based modelling methods could serve as useful decision support for individualized treatment strategies in patients with a metastatic lesion. Keywords: Pathologic fracture, Femur, Metastatic lesion, Risk prediction, Mirels' scor

Scandinavian Journal of Medicine & Science in Sports / Biomechanical evaluation of different ankle orthoses in a simulated lateral ankle sprain in two different modes

Ankle orthoses are commonly used for prevention of recurrent ankle sprains. While there are some data on their functional performance or restriction of range of motion, there is little knowledge on the quantifiable passive mechanical effectiveness of various devices. This study aimed to determine the prophylactic stabilization effect for commonly prescribed ankle orthoses in a simulated recurrent ankle sprain. Eleven anatomic lower leg specimens were tested in plantar flexion and hindfoot inversion in a simulated ankle sprain in a quasistatic and dynamic test mode at 0.5/s and 50/s internal rotation, respectively. Tests included intact specimens, same specimens with the ruptured anterior talofibular ligament (ATFL), followed by stabilization with five different semirigid orthoses: AirGo Ankle Brace, Air Stirrup Ankle Brace, Dyna Ankle 50S1, MalleoLoc, and Aequi. Compared to the injured and unprotected state, two orthoses (AirGo and Air Stirrup) significantly reinforced the ankle. The Aequi ankle brace restored stability comparable to an intact joint. Dyna Ankle 50S1 and MalleoLoc provided insufficient resistance to applied internal rotation compared to the ankle with ruptured ATFL. Ankle orthoses varied significantly in their ability to stabilize the unstable ankle during an ankle sprain in both testing modes. Presented objective data on passive stabilization reveal a lack of supporting evidence for clinical application of ankle orthoses.(VLID)489320

International Orthopaedics / Measurement considerations on examiner-dependent factors in the ultrasound assessment of developmental dysplasia of the hip

Purpose The standardized sonographic hip screening according to Graf has increased reliability and comparability of measurements in the screening of developmental dysplasia of the hip (DDH). However, examiner dependent factors have been discussed to influence sonographic measurements. The objectives of this study were to examine the tolerance of the transducer positioning and to analyse the impact of transducer inclinations on Grafs hip grading system. Materials and methods Twenty-four hips in consecutive newborns were screened sonographically in combination with an optoelectronic motion capture system to trace transducer positions in space. Subsequently five defined inclinations of the transducer relative to Grafs neutral transducer position were analysed, giving a total of 144 sonographic images. Results We found a permissible transducer inclination in the axial plane of 8.8 to anterior and 8.1 to posterior. In the frontal plane we found a permissible inclination of 15.4 to caudal and 7.2 to cranial. The impact on the -angle was significant for posterior-cranial (p < 0.001), cranial (p = 0.009), and caudal (p < 0.001) inclined transducer positions. The effect on the results according to Grafs grading system was significant for the caudal inclination of the transducer position (p < 0.001). Conclusion Our findings show that the standardized plane defined by Grafs criteria allows notable inclinations of the transducer positions. Transducer inclinations show an impact on measurement results, which are clinically relevant. Those effects cannot be ruled out using Grafs ultrasound criteria alone. The examiner should pay attention to avoid transducer inclinations in the frontal plane and a combination of posterior and cranial inclination.(VLID)354443

Sensors / Evaluation of Aerosol Electrospray Analysis of Metal-on-Metal Wear Particles from Simulated Total Joint Replacement

Wear is a common cause for aseptic loosening in artificial joints. The purpose of this study was to develop an automated diagnostical method for identification of the number and size distribution of wear debris. For this purpose, metal debris samples were extracted from a hip simulator and then analyzed by the electrospray method combined with a differential mobility analyzer, allowing particle detection ranging from several nanometers up to 1 m. Wear particles were identified with a characteristic peak at 15 nm. The electrospray setup was successfully used and validated for the first time to characterize wear debris from simulated total joint replacement. The advantages of this diagnostic method are its time- and financial efficiency and its suitability for testing of different materials.(VLID)491881

Relative lateral wall thickness is an improved predictor for postoperative lateral wall fracture after trochanteric femoral fracture osteosynthesis

Abstract Lateral wall thickness is a known predictor for postoperative stability of trochanteric femoral fractures and occurrence of secondary lateral wall fractures. Currently, the AO/OTA classification relies on the absolute lateral wall thickness (aLWT) to distinguish between stable A1.3 and unstable A2.1 fractures that does not take interpersonal patient differences into account. Thus, a more individualized and accurate measure would be favorable. Therefore, we proposed and validated a new patient-specific measure—the relative lateral wall thickness (rLWT)—to consider individualized measures and hypothesized its higher sensitivity and specificity compared with aLWT. First, in 146 pelvic radiographs of patients without a trochanteric femoral fracture, the symmetry of both caput-collum-diaphyseal angle (CCD) and total trochanteric thickness (TTT) was assessed to determine whether the contralateral side can be used for rLWT determination. Then, data of 202 patients were re-evaluated to compare rLWT versus previously published aLWT. Bilateral symmetry was found for both CCD and TTT (p ≥ 0.827), implying that bone morphology and geometry of the contralateral intact side could be used to calculate rLWT. Validation revealed increased accuracy of the rLWT compared with the gold standard aLWT, with increased specificity by 3.5% (Number Needed to Treat = 64 patients) and sensitivity by 1% (Number Needed to Treat = 75 patients). The novel rLWT is a more accurate and individualized predictor of secondary lateral wall fractures compared with the standard aLWT. This study established the threshold of 50.5% rLWT as a reference value for predicting fracture stability in trochanteric femoral fractures

Dimensional accuracy and precision and surgeon perception of additively manufactured bone models: effect of manufacturing technology and part orientation

Abstract Background Additively manufactured (AM) anatomical bone models are primarily utilized for training and preoperative planning purposes. As such, they must meet stringent requirements, with dimensional accuracy being of utmost importance. This study aimed to evaluate the precision and accuracy of anatomical bone models manufactured using three different AM technologies: digital light processing (DLP), fused deposition modeling (FDM), and PolyJetting (PJ), built in three different part orientations. Additionally, the study sought to assess surgeons’ perceptions of how well these models mimic real bones in simulated osteosynthesis. Methods Computer-aided design (CAD) models of six human radii were generated from computed tomography (CT) imaging data. Anatomical models were then manufactured using the three aforementioned technologies and in three different part orientations. The surfaces of all models were 3D-scanned and compared with the original CAD models. Furthermore, an anatomical model of a proximal femur including a metastatic lesion was manufactured using the three technologies, followed by (mock) osteosynthesis performed by six surgeons on each type of model. The surgeons’ perceptions of the quality and haptic properties of each model were assessed using a questionnaire. Results The mean dimensional deviations from the original CAD model ranged between 0.00 and 0.13 mm with maximal inaccuracies < 1 mm for all models. In surgical simulation, PJ models achieved the highest total score on a 5-point Likert scale ranging from 1 to 5 (with 1 and 5 representing the lowest and highest level of agreement, respectively), (3.74 ± 0.99) in the surgeons’ perception assessment, followed by DLP (3.41 ± 0.99) and FDM (2.43 ± 1.02). Notably, FDM was perceived as unsuitable for surgical simulation, as the material melted during drilling and sawing. Conclusions In conclusion, the choice of technology and part orientation significantly influenced the accuracy and precision of additively manufactured bone models. However, all anatomical models showed satisfying accuracies and precisions, independent of the AM technology or part orientation. The anatomical and functional performance of FDM models was rated by surgeons as poor