Evaluation of the efficacy of modal analysis in predicting the pullout strength of fixation bone screws

Abstract Background Pilot hole preparation has been shown to have an impact on the short and long‐term stability of the screw fixation constructs. Purpose Investigation and comparison of two nondestructive modal analysis methods with conventional insertion torque (IT) and pullout tests in optimum pilot hole diameter detection. Methods Twenty conical core titanium screws were embedded in high‐density polyethylene blocks with different pilot hole diameters. The maximum IT was recorded for each screw during implantation. Then, two modal analysis methods including accelerometer (classical modal analysis [CMA]) and acoustic modal analysis (AMA) were carried out to measure the natural frequency (NF) of the bone‐screw structure. Finally, stiffness (S), pullout force (Fult), displacement at Fult (dult) and energy dissipation (ED) were obtained from the destructive pullout test. Results The IT increased, as the pilot hole diameter decreased. The maximum value of IT was observed in the smallest pilot hole diameter. The same trend was found for the Fult and the first NF derived from both modal methods except for 5.5 mm pilot hole diameter. The natural NFs derived from CMA and AMA showed high correlations in different groups (R2 = 0.94) and did not deviate from y = x hypothesis in linear regression analysis. The Fult, dult, and ED were measured 4800 ± 172 N, 3.10 ± 0.08 mm and 14.23 ± 1.10 N.mm, respectively. Discussion No significant change was observed in “S” between the groups. The highest Fult and first NF were obtained for the 5.5 mm pilot hole diameter. Both CMA and AMA were found to be reliable methods and can promote the undesirable contradiction between Fult and IT

Biomechanical Evaluation of Lumbar Interbody Fixation Techniques: A Comparative Study of Standalone Cages vs. 360-Fixation Constructs

Low fusion rates and cage subsidence have been reported as the main drawbacks of lumbar fixation with static interbody cages [1]. Although several clinical and biomechanical studies have evaluated the efficacy of 360 interbody fixation constructs (Anterior cage plus posterior fixation) [2,3], no study has reported the biomechanical comparison between such constructs and more novel techniques which use standalone fixation implants [4]. A cadaver validated computational model of lumbar spine was used to compare the biomechanics of spine instrumented with 360 fixations versus standalone cage with screw and cage with lateral plate systems. To compare the mechanical stability of different interbody fixation techniques in lumbar spinal segments with standalone interbody versus static cage with posterior fixation or lateral plate system. <br/

A unique modular implant system enhances load sharing in anterior cervical interbody fusion: a finite element study

BACKGROUND: The efficacy of dynamic anterior cervical plates is somewhat controversial. Screws in static-plate designs have a smaller diameter and can cut through bone under load. While not ideal, this unintended loosening can help mitigate stress shielding. Stand-alone interbody devices with integral fixation have large endplate contact areas that may inhibit or prevent loosening of the fixation. This study investigates the load sharing ability of a novel dynamic plate design in preventing the stress shielding of the graft material compared to the non-dynamic devices. METHODS: An experimentally validated intact C5-C6 finite element model was modified to simulate discectomy and accommodate implant-graft assembly. Four implant iterations were modeled; InterPlate titanium device with dynamic surface features (springs), InterPlate titanium non-dynamic device, InterPlate titanium design having a fully enclosed graft chamber, and the InterPlate design in unfilled PEEK having a fully enclosed graft chamber. All the models were fixed at the inferior-most surface of C6 and the axial displacement required to completely embed the dynamic surface features was applied to the model. RESULTS: InterPlate device with dynamic surface features induced higher graft stresses compared to the other design iterations resulting in uniform load sharing. The distribution of these graft stresses were more uniform for the InterPlate dynamic design. CONCLUSIONS: These results indicate that the dynamic design decreases the stress shielding by increasing and more uniformly distributing the graft stress. Fully enclosed graft chambers increase stress shielding. Lower implant material modulus of elasticity does not reduce stress shielding significantly

Analysis, Interpretation, and Recognition of Facial Action Units and Expressions Using Neuro-Fuzzy Modeling

Abstract. In this paper an accurate real-time sequence-based system for representation, recognition, interpretation, and analysis of the facial action units (AUs) and expressions is presented. Our system has the following characteristics: 1) employing adaptive-network-based fuzzy inference systems (ANFIS) and temporal information, we developed a classification scheme based on neuro-fuzzy modeling of the AU intensity, which is robust to intensity variations, 2) using both geometric and appearance-based features, and applying efficient dimension reduction techniques, our system is robust to illumination changes and it can represent the subtle changes as well as temporal information involved in formation of the facial expressions, and 3) by continuous values of intensity and employing top-down hierarchical rule-based classifiers, we can develop accurate human-interpretable AU-to-expression converters. Extensive experiments on Cohn-Kanade database show the superiority of the proposed method, in comparison with support vector machines, hidden Markov models, and neural network classifiers