An additively manufactured titanium tilting suture anchor: a biomechanical assessment on human and ovine bone specimens.

Introduction: A novel titanium tilting suture anchor was designed and fabricated using additive manufacturing. The anchor enjoyed a nonsymmetrical structure to facilitate its insertion procedure through a weight-induced tilt, a saw-teeth penetrating edge to provide a strong initial fixation into cancellous bones of various densities, and an appropriate surface texture to enhance the longterm fixation strength through bone ingrowth. Methods: Biomechanical tests were performed on 10 ovine and 10 human cadaveric humeri to examine the insertion procedure and assess the initial fixation strength of the anchor, in comparison with a standard screw-type anchor as control. Results: This study indicated a simple yet reliable insertion procedure for the tilting anchor. All anchors survived after 400 cycles of cyclic loadings and failed in the load-to-failure step. There were no significant differences between the displacements and fixation stiffnesses of the anchors in either group. The ultimate failure load was significantly smaller (p<0.05) for tilting anchors in ovine group (273.7 ± 129.72 N vs. 375.6 ± 106.36 N), but not different in human group (311.8 ± 82.55 N vs. 281.9 ± 88.35). Also, a larger number of tilting anchors were pulled out in ovine group (6 vs. 3) but a smaller number in human group (4 vs. 6). Conclusion: It was concluded that the biomechanical performance of the designed tilting anchor is comparable with that of the standard screw-type anchors.

Is a Complete Anatomical Fit of the Tomofix Plate Biomechanically Favorable? A Parametric Study Using the Finite Element Method.

Background: The opening wedge high tibial osteotomy (HTO) fixation using the Tomofix system is at the risk of mechanical failure due to unstable fixation, lateral hinge fracture, and hardware breakage. This study aimed to investigate the effect of the level of anatomical fit (LOF) of the plate on the failure mechanisms of fixation. Methods: A finite element model of the HTO with a correction angle of 12 degrees was developed. The LOF of the TomoFix plate was changed parametrically by altering the curvature of the plate in the sagittal plane. The effect of the LOF on the fixation performance was studied in terms of the factor of safety (FOS) against failure mechanisms. The FOSs were found by 1) dividing the actual stiffness of the plate-bone construct by the minimum allowable one for unstable fixation, 2) dividing the compressive strength of the cortical bone by the actual maximum pressure at the lateral hinge for the lateral hinge fracture, and 3) the Soderberg criterion for fatigue fracture of the plate and screws. Results: The increase of the LOF by applying a larger bent to the plate changed the fixation stiffness slightly. However, it reduced the lateral hinge pressure substantially (from 182 MPa to 71 MPa) and increased the maximum equivalent stresses in screws considerably (from 187 MPa to 258 MPa). Based on the FOS-LOF diagram, a gap smaller than 2.3 mm was safe, with the highest biomechanical performance associated with a 0.5 mm gap size. Conclusion: Although a high LOF is necessary for the Tomofix plate fixation to avoid mechanical failure, a gap size of 0.5mm is favored biomechanically over complete anatomical fit.

An extended algorithm for autonomous grasping of soft tissues during robotic surgery.

BACKGROUND: Autonomous grasping of soft tissues can facilitate the robotic surgery procedures. The previous attempts for implementing auto-grasping have been based on a simplistic representation of the actual surgery maneuvers. METHOD: A generalized three-zone grasp model was introduced to consider the effect of the pull force angulation on the grasp mode, that is, damage, slip, or safe grasp. Also, an extended auto-grasping algorithm was proposed in which the trigger force is automatically controlled against the pull force magnitude and direction, to achieve a safe and secure grasp. RESULTS: The autonomous grasping experiments against a varying pull force in a phantom study indicated a good agreement between the desired and actual pinch and trigger forces (root mean square errors lower than 0.168 N and 0.280 N, respectively) and no sign of tissue tear or slippage. CONCLUSIONS: The proposed auto-grasping algorithm can help manipulating the soft tissues safely and effectively during robotic surgery procedures.

Automatic classification of gait patterns in children with cerebral palsy using fuzzy clustering method.

BACKGROUND: Subjective classification of gait pattern in children with cerebral palsy depends on the assessor's experience, while mathematical methods produce virtual groups with no clinical interpretation. METHODS: In a retrospective study, gait data from 66 children (132 limbs) with a mean age of 9.6 (SD 3.7) years with cerebral palsy and no history of surgery or botulinum toxin injection were reviewed. The gait pattern of each limb was classified in four groups according to Rodda using three methods: 1) a team of experts subjectively assigning a gait pattern, 2) using the plantarflexor-knee extension couple index introduced by Sangeux et al., and 3) employing a fuzzy algorithm to translate the experiences of experts into objective rules and execute a clustering tool. To define fuzzy repeated-measures, 75% of the members in each group were used, and the remaining were used for validation. Eight parameters were objectively extracted from kinematic data for each group and compared using repeated measure ANOVA and post-hoc analysis was performed. Finally, the results of the clustering of the latter two methods were compared to the subjective method. FINDINGS: The plantarflexor-knee extension couple index achieved 86% accuracy while the fuzzy system yielded a 98% accuracy. The most substantial errors occurred between jump and apparent in both methods. INTERPRETATION: The presented method is a fast, reliable, and objective fuzzy clustering system to classify gait patterns in cerebral palsy, which produces clinically-relevant results. It can provide a universal common language for researchers.

Pre-planning of intramedullary nailing procedures: A methodology for predicting the position of the distal hole.

Inserting the distal locking screws is a challenging step of the intramedullary nailing procedures due to the nail deformation that makes the proximally mounted targeting systems ineffective. A pre-planning methodology is proposed, based on an analytical model of the nail-bone construct, to predict the nail deformation during surgery using orthogonal preoperative radiographs. Each of the femoral shaft and the nail was modeled as a curved tubular Euler-Bernoulli beam. The unknown positions and forces of the nail-bone interaction were found using a systematic trial and error approach, which minimized the total strain energy of the system while satisfying the force and geometrical constraints. The predictions of the model for the nail deformation were compared with the experimental results of five cadaver specimens in 15 test conditions. Relatively large displacements (up to 13 mm) were found for the distal hole in sagittal plane only. The model predictions were in close agreement with the experimental results, with a root mean square error of 1.2 mm. It was concluded that the proposed pre-planning methodology is promising for practical clinical use in intramedullary nailing operations, in order to provide the compensatory information that is required for tuning of proximally mounted targeting systems.

A validation study of a virtual-based haptic system for endoscopic sinus surgery training.

BACKGROUND: The development of endoscopic sinus surgery (ESS) training simulators for clinical environment applications has reduced the existing shortcomings in conventional teaching methods, creating a standard environment for trainers and trainees in a more accurate and repeatable fashion. MATERIALS AND METHODS: In this research, the validation study of an ESS training simulator has been addressed. It is important to consider components that guide trainees to improve their hand movements control in the orbital floor removal in an ESS operation. Therefore, we defined three tasks to perform: pre-experiment learning, training, and evaluation. In these tasks, the critical regions introduced in the virtual training environment are forbidden to be touched. Recruiting 20 participants, divided into two groups, we investigated the performance metrics: quality (the percentage of the realism for the generated force for orbital floor removal and the usefulness of the proposed training system for the surgical educational curricula.), efficiency (time, path length), and safety (touching the goal and forbidden wall). RESULTS: All recruited participants answered a post-evaluation questionnaire regarding their perceptions of training system realism, potential educational benefits, and practiced skills. We investigate the differences between groups' performance metrics by utilizing the analysis of variance-Kruskal-Wallis test. Acquired results indicate that training before the actual process of the surgery has a significant effect on the accuracy and validity of the process for surgeons. CONCLUSIONS: Utilizing a standardized environment, trainers and trainees are able to carry out a process with regular features. In addition to traditional education methods, trainees can learn the risk of surgical operations. The training simulators can, also, provide a standard method for assessing the skills of surgical and medical students.

Phenomenological tissue fracture modeling for an Endoscopic Sinus and Skull Base Surgery training system based on experimental data.

The ideal simulator for Endoscopic Sinus and Skull Base Surgery (ESSS) training must be supported by a physical model and provide repetitive behavior in a controlled environment. Development of realistic tissue models is a key part of ESSS virtual reality (VR)-based surgical simulation. Considerable research has been conducted to address haptic or force feedback and propose a phenomenological tissue fracture model for sino-nasal tissue during surgical tool indentation. Mechanical properties of specific sino-nasal regions of the sheep head have been studied in various indentation and relaxation experiments. Tool insertion at different indentation rates into coronal orbital floor (COF) tissue is modeled as a sequence of three events: deformation, fracture, and cutting. The behavior in the deformation phase can be characterized using a non-linear, rate-dependent modified Kelvin-Voigt model. A non-linear model for tissue behavior prior to the fracture point is presented. The overall model shows a non-positive dependency of maximum force on tool indentation rate, which indicates faster tool insertion velocity decreases the maximum final fracture force. The tissue cutting phase has been modeled to characterize the force necessary to slice through the COF. The proposed model in this study can help develop VR-based ESSS base simulators in otolaryngology and ophthalmology surgeries. Such simulators are useful in preoperative planning, accurate surgical simulation, intelligent robotic assistance, and treatment applications.

A minimally invasive robotic surgery approach to perform totally endoscopic coronary artery bypass on beating hearts.

The currently available robotic systems rely on rigid heart stabilizers to perform totally endoscopic coronary artery bypass (TECAB) surgery on beating hearts. Although such stabilizers facilitate the anastomosis procedure by immobilizing the heart and holding the surgery site steady, they can cause damage to the heart tissue and rupture of the capillary vessels, due to applying relatively large pressures on the epicardium. In this paper, we propose an advanced robotic approach to perform TECAB on a beating heart with minimal invasiveness. The idea comes from the fact that the main pulsations of the heart occur as excursions in normal direction, i.e., perpendicular to the heart surface. We devise a 1-DOF flexible heart stabilizer which eliminates the lateral movements of the heart, and a 1-DOF compensator mechanism which follows the heart trajectory in the normal direction, thus canceling the relative motion between the surgical tool and the heart surface. In fact, we bring a compromise between two radical approaches of operating on a completely immobilized beating heart with no heart motion compensation, and operating on a freely beating heart with full compensation of heart motion, considering the invasiveness of the first and the technical challenges of the second approach. We propose operating on a partially stabilized beating heart with unidirectional compensation of the heart motion; the flexible stabilizer would exert much less holding force to the heart tissue and the robotic system with unidirectional compensator would be technically feasible. In the proposed approach, a motion sensor mounted on the stabilizer measures the heart excursion data and sends it into a control unit. A predictive controller uses this data to generate an automated trajectory. The slave robots follow this trajectory, which is superimposed on the surgeon's tele-operation commands received from a master console. Finally, the tool-activation units in the slave robots actuate the articulated laparoscopic tools to perform the anastomosis procedure. The evaluation of the hypothesis showed that our solution for the robotic TECAB on beating heart is both practical and cost effective. We showed in an in-vivo study that the flexible stabilizer can effectively restrict the heart lateral movements, while allowing for its normal excursion. We found readily available linear motors which could afford the high forces, speeds and accelerations required for following the heart trajectory. Finally, we showed that the tool-activation unit is capable of providing the maneuverability and workspace required for the most challenging task of CABG procedure, i.e., anastomosis suturing.

A comprehensive multimodality heart motion prediction algorithm for robotic-assisted beating heart surgery.

BACKGROUND: An essential requirement for performing robotic-assisted surgery on a freely beating heart is a prediction algorithm that can estimate the future heart trajectory. METHOD: Heart motion, respiratory volume (RV) and electrocardiogram (ECG) signal were measured from two dogs during thoracotomy surgery. A comprehensive multimodality prediction algorithm was developed based on the multivariate autoregressive model to incorporate the heart trajectory and cardiorespiratory data with multiple inherent measurement rates explicitly. RESULTS: Experimental results indicated strong relationships between the dominant frequencies of heart motion with RV and ECG. The prediction algorithm revealed a high steady state accuracy, with the root mean square (RMS) errors in the range of 82 to 162 µm for a 300-second interval, less than half of that of the best competitor. CONCLUSION: The proposed multimodality prediction algorithm is promising for practical use in robotic assisted beating heart surgery, considering its capability of providing highly accurate predictions in long horizons.

A Hybrid Algorithm for Prediction of Varying Heart Rate Motion in Computer-Assisted Beating Heart Surgery.

An essential requirement for performing robotic assisted surgery on a freely beating heart is a prediction algorithm which can estimate the future trajectory of the heart in the varying heart rate (HR) conditions of real surgery with a high accuracy. In this study, a hybrid amplitude modulation- (AM) and autoregressive- (AR) based algorithm was developed to enable estimating the global and local oscillations of the beating heart, raised from its major and minor physiological activities. The AM model was equipped with an estimator of the heartbeat frequency to compensate for the HR variations. The RMS of the prediction errors of the hybrid algorithm was in the range of 165-361 µm for the varying HR motion, 21% less than that of the single AM model. With the capability of providing highly accurate predictions in a wide range of HR variation, the hybrid model is promising for practical use in robotic assisted beating heart surgery.

Micromechanics of brain white matter tissue: A fiber-reinforced hyperelastic model using embedded element technique.

A transverse-plane hyperelastic micromechanical model of brain white matter tissue was developed using the embedded element technique (EET). The model consisted of a histology-informed probabilistic distribution of axonal fibers embedded within an extracellular matrix, both described using the generalized Ogden hyperelastic material model. A correcting method, based on the strain energy density function, was formulated to resolve the stiffness redundancy problem of the EET in large deformation regime. The model was then used to predict the homogenized tissue behavior and the associated localized responses of the axonal fibers under quasi-static, transverse, large deformations. Results indicated that with a sufficiently large representative volume element (RVE) and fine mesh, the statistically randomized microstructure implemented in the RVE exhibits directional independency in transverse plane, and the model predictions for the overall and local tissue responses, characterized by the normalized strain energy density and Cauchy and von Mises stresses, are independent from the modeling parameters. Comparison of the responses of the probabilistic model with that of a simple uniform RVE revealed that only the first one is capable of representing the localized behavior of the tissue constituents. The validity test of the model predictions for the corona radiata against experimental data from the literature indicated a very close agreement. In comparison with the conventional direct meshing method, the model provided almost the same results after correcting the stiffness redundancy, however, with much less computational cost and facilitated geometrical modeling, meshing, and boundary conditions imposing. It was concluded that the EET can be used effectively for detailed probabilistic micromechanical modeling of the white matter in order to provide more accurate predictions for the axonal responses, which are of great importance when simulating the brain trauma or tumor growth.

Feasibility of infrared tracking of beating heart motion for robotic assisted beating heart surgery.

BACKGROUND: Accurate tracking of the heart surface motion is a major requirement for robot assisted beating heart surgery. METHOD: The feasibility of a stereo infrared tracking system for measuring the free beating heart motion was investigated by experiments on a heart motion simulator, as well as model surgery on a dog. RESULTS: Simulator experiments revealed a high tracking accuracy (81 µm root mean square error) when the capturing times were synchronized and the tracker pointed at the target from a 100 cm distance. The animal experiment revealed the applicability of the infrared tracker with passive markers in practical heart surgery conditions. CONCLUSION: With the current technology, infrared tracking with passive markers might be the optimal solution for accurate, fast, and reliable tracking of heart motion during robot assisted beating heart surgery.

A novel laparoscopic grasper with two parallel jaws capable of extracting the mechanical behaviour of soft tissues.

Data related to force-deformation behaviour of soft tissue plays an important role in medical/surgical applications such as realistically modelling mechanical behaviour of soft tissue as well as minimally invasive surgery (MIS) and medical diagnosis. While the mechanical behaviour of soft tissue is very complex due to its different constitutive components, some issues increase its complexity like behavioural changes between the live and dead tissues. Indeed, an adequate quantitative description of mechanical behaviour of soft tissues requires high quality in vivo experimental data to be obtained and analysed. This paper describes a novel laparoscopic grasper with two parallel jaws capable of obtaining compressive force-deformation data related to mechanical behaviour of soft tissues. This new laparoscopic grasper includes four sections as mechanical hardware, sensory part, electrical/electronical part and data storage part. By considering a unique design for mechanical hardware, data recording conditions will be close to unconfined-compression-test conditions; so obtained data can be properly used in extracting the mechanical behaviour of soft tissues. Also, the other distinguishing feature of this new system is its applicability during different laparoscopic surgeries and subsequently obtaining in vivo data. However, more preclinical examinations are needed to evaluate the practicality of the novel laparoscopic grasper with two parallel jaws.

Review on different experimental techniques developed for recording force-deformation behaviour of soft tissues; with a view to surgery simulation applications.

Different experimental techniques which have been developed to obtain data related to force-deformation behaviour of soft tissues play an important role in realistically simulating surgery processes as well as medical diagnoses and minimally invasive procedures. Indeed, an adequate quantitative description of soft-tissue-mechanical-behaviour requires high-quality experimental data to be obtained and analysed. In this review article we will first scan the motivations and basic technical issues on surgery simulation. Then, we will concentrate on different experimental techniques developed for recording force-deformation (stress-strain) behaviour of soft tissues with focussing on the in-vivo experimental setups. We will thoroughly review the available techniques by classifying them to four groups; elastography, indentation, aspiration and grasping techniques. The evolutions, advantages and limitations of each technique will be presented by a historical review. At the end, a discussion is given with the aim of summarising the proposed points and predicting the future of techniques utilised in extracting data related to force-deformation behaviour.

Automatic tracking of laparoscopic instruments for autonomous control of a cameraman robot.

BACKGROUND: An automated instrument tracking procedure was designed and developed for autonomous control of a cameraman robot during laparoscopic surgery. MATERIAL AND METHODS: The procedure was based on an innovative marker-free segmentation algorithm for detecting the tip of the surgical instruments in laparoscopic images. A compound measure of Saturation and Value components of HSV color space was incorporated that was enhanced further using the Hue component and some essential characteristics of the instrument segment, e.g., crossing the image boundaries. The procedure was then integrated into the controlling system of the RoboLens cameraman robot, within a triple-thread parallel processing scheme, such that the tip is always kept at the center of the image. RESULTS: Assessment of the performance of the system on prerecorded real surgery movies revealed an accuracy rate of 97% for high quality images and about 80% for those suffering from poor lighting and/or blood, water and smoke noises. A reasonably satisfying performance was also observed when employing the system for autonomous control of the robot in a laparoscopic surgery phantom, with a mean time delay of 200ms. CONCLUSION: It was concluded that with further developments, the proposed procedure can provide a practical solution for autonomous control of cameraman robots during laparoscopic surgery operations.

A modular force-controlled robotic instrument for minimally invasive surgery - efficacy for being used in autonomous grasping against a variable pull force.

BACKGROUND: Many deficiencies of minimally invasive robotic surgery systems can be eliminated by using automated laparoscopic tools with force measurement and control capability. METHOD: A fully modular, automated laparoscopic instrument with a proximal force sensory system was designed and fabricated. The efficacy of the instrument was evaluated experimentally when functioning in an autonomous force-controlled grasping scheme. RESULTS: The designed instrument was shown to work easily with standard laparoscopic tools, with the whole distal part detachable for autoclave sterilization. The root mean squared error (RMSE) of the actual pinch force from the target ramp was 0.318 N; it was 0.402 N for a sinusoidal pull force, which dropped by 21% using a static friction compensation. A secure grasping condition was achieved, in spite of this error, by applying a sufficiently large margin from the slip boundary. CONCLUSIONS: With a simple and practical design, the instrument enjoys affordability, versatility and autoclave sterilizability for clinical usage, with an acceptable performance for being used in an auto-grasping control scheme. Copyright © 2016 John Wiley & Sons, Ltd.

Cross-sectional area of human trunk paraspinal muscles before and after posterior lumbar surgery using magnetic resonance imaging.

PURPOSE: Iatrogenic injuries to paraspinal muscles during the posterior lumbar surgery (PLS) cause a reduction in their cross-sectional areas (CSAs) and contractile densities over time post-surgery. This study aims to quantify such alterations. METHOD: Pre- and postoperative CSAs (~6 months interval) of all paraspinal muscles were measured in six patients undergoing PLS using a 3-T magnetic resonance (MR) scanner to quantify the alterations in geometrical and tissue effective contractile (non-fatty) CSAs of these muscles at all lumbar levels. To examine the presence of any confounding effects on recorded changes within ~7-month period, measurements were also carried out on ten healthy volunteers. RESULTS: In the healthy population, an important (~22%) portion of CSA of the erector spinae (ES) was noncontractile at the lower lumbar levels. Negligible variations over time in both the total geometrical (<1.7% in average) and contractile (<1.2%) CSAs of muscles were observed in the healthy group (i.e., no confounding effect). Following PLS, significant reductions were observed in the geometrical CSA of only multifidus (MF) muscle by ~14 and 11% as well as in its contractile CSA by ~26 and 14% at the L5-S1 and L4-L5 levels, respectively. CONCLUSION: The total CSA of ES at lower lumbar levels shows substantial noncontractile contents in both healthy and patient populations. Biomechanical models of the spine should hence account for the noncontractile contents using only the effective contractile muscle CSAs. Postoperative variations in CSAs of paraspinal muscles may have profound effects on patterns of muscle activities, spinal loading, and stability.

Biomechanical Comparison Between Bashti Bone Plug Technique and Biodegradable Screw for Fixation of Grafts in Ligament surgery.

BACKGROUND: Ligament reconstruction is a common procedure in orthopedic surgery. Although several popular techniques are currently in use, new methods are proposed for secure fixation of the tendon graft into the bone tunnel. PURPOSES: We sought to introduce our new technique of Bashti bone plug for fixation of soft tissue graft in anterior cruciate ligament (ACL) reconstruction and to compare its biomechanical features with conventional absorbable interference screw technique in a bovine model. METHODS: Twenty pairs of bovine knees were harvested after death. Soft tissue was removed and the Achilles tendon was harvested to be used as an ACL graft. It was secured into the bone tunnel on the tibial side via two different methods: Bashti Bone Plug technique and conventional screw method. Biomechanical strength was measured using 200 N and 300 N cyclic loading on the graft. Pull out strength was also tested until the graft fails. RESULTS: No graft failure was observed after 200 N and 300 N cyclic loading in either fixation methods. When testing for pull out failure, 21 tendons (53%) were torn and 19 tendons (48%) slipped out. No fixation failure occurred, which did not reveal a significant difference between the bone plug or interference screw group (P=0.11). The mean pull out force until failure of the graft was 496±66 N in the screw group and 503±67 N in the bone plug group (P=0.76). CONCLUSIONS: Our suggested fixation technique of Bashti bone plug is a native, cheap, and feasible method that provides comparable biomechanical strength with interference screw when soft tissue fixation was attempted in bovine model.

A novel remote center of motion mechanism for the force-reflective master robot of haptic tele-surgery systems.

BACKGROUND: An effective master robot for haptic tele-surgery applications needs to provide a solution for the inversed movements of the surgical tool, in addition to sufficient workspace and manipulability, with minimal moving inertia. METHOD: A novel 4 + 1-DOF mechanism was proposed, based on a triple parallelogram linkage, which provided a Remote Center of Motion (RCM) at the back of the user's hand. The kinematics of the robot was analyzed and a prototype was fabricated and evaluated by experimental tests. RESULTS: With a RCM at the back of the user's hand the actuators far from the end effector, the robot could produce the sensation of hand-inside surgery with minimal moving inertia. The target workspace was achieved with an acceptable manipulability. The trajectory tracking experiments revealed small errors, due to backlash at the joints. CONCLUSIONS: The proposed mechanism meets the basic requirements of an effective master robot for haptic tele-surgery applications.

Tool-tissue force estimation in laparoscopic surgery using geometric features.

This paper introduces three geometric features, from deformed shape of a soft tissue, which demonstrate good correlation with probing force and maximum local stress. Using FEM simulation, 2D and 3D model of an in vivo porcine liver was built for different probing tasks. Maximum deformation angle, maximum deformation depth and width of displacement constraint of the reconstructed shape of the deformed body were calculated. Two neural networks were trained from these features and the calculated interaction forces. The features are shown to have high potential to provide force estimation either for haptic devices or to assess the damage to the tissue in large deformations of up to 40%.