Krzysztof J. Rechowicz

Development of an Average Chest Shape for Objective Evaluation of the Aesthetic Outcome in the Nuss Procedure Planning Process

The Nuss procedure is a minimally invasive surgery for correcting pectus excavatum. Pectus excavatum (PE), also called sunken or funnel chest, is a congenital chest wall deformity which is characterized by a deep depression of the sternum. This condition affects primarily children and young adults and is responsible for about 90% of congenital chest wall abnormalities.

A strategy for simulating and validating the Nuss procedure for the minimally invasive correction of pectus excavatum

Surgical planners are used to achieve the optimal outcome for surgery. They are especially desired in procedures where a positive aesthetic outcome is the primary goal, such as the Nuss procedure which is a minimally invasive surgery for correcting pectus excavatum (PE) — a congenital chest wall deformity. Although this procedure is routinely performed, the outcome depends mostly on the correct placement of the bar. It would be beneficial if a surgeon had a chance to practice and review possible strategies for placement of the corrective bar and the associated appearance of the chest. Therefore, we propose a strategy for the development of a Nuss procedure surgical trainer and planner, taking into account the biomechanical properties of the PE ribcage, emerging trends in surgical planners, deformable models, and visualization techniques. Additionally, we present the initial results of before and after surgery surface scans analysis as a means to validate results, comparison of an average chest shape with post-operative to quantify the outcome of the surgery, and the hardware setup of the simulator.

Patient Specific Modeling of Pectus Excavatum for the Nuss Procedure Simulation

Patient specific models are crucial for both simulation and surgical planning. It is not different for the Nuss procedure, which is a minimally invasive surgery for correcting pectus excavatum (PE)—a congenital chest wall deformity. Typically, patients differ not only in size but also severity of the chest depression and type of the deformity, making the simulation process challenging. In this paper, we approach the problem of a patient specific model creation resulting in the development of a parameterized model of the human torso including the ribcage. All the parameters are obtainable from pre-surgical CT. In order to validate our model, we compared the simulated shape of the chest with surface scans obtained from PE patients for both pre- and post-surgery. Results showed that both shapes are in agreement in the area of the deformity, making this method valid for the need of simulating the Nuss procedure.

Development and validation methodology of the Nuss procedure surgical planner

Surgical planners are used to achieve the optimal outcome for surgery. They are especially desired in procedures where a positive aesthetic outcome is the primary goal, such as the Nuss procedure which is a minimally invasive surgery for correcting pectus excavatum (PE) – a congenital chest wall deformity which is characterized by a deep depression of the sternum. The Nuss procedure consists of placement of a metal bar(s) underneath the sternum, thereby forcibly changing the geometry of the ribcage. Because of the prevalence of PE and the popularity of the Nuss procedure, the demand to perform this surgery is greater than ever. Therefore, a Nuss procedure surgical planner is an invaluable planning tool ensuring an optimal physiological and aesthetic outcome. We propose the development and validation of the Nuss procedure planner. First, a generic model of the ribcage is developed. Then, the computed tomography (CT) data collected from actual patients with PE is used to create a set of patient-specific finite element models (FEM). Based on finite element analyses (FEA) a force–displacement data set is created. This data is used to train an artificial neural network (ANN) to generalize the data set. In order to evaluate the planning process, a methodology which uses an average shape of the chest for comparison with results of the Nuss procedure planner is developed. Haptic feedback and inertial tracking is also implemented. The results show that it is possible to utilize this approximation of the force–displacement model for a Nuss procedure planner and trainer.

Optimized surgical tool for pectus bar extraction

Surgeons on a daily basis improve or rescue human lives. Therefore, they should be provided with the most optimal tools so their skills are fully utilized. In this paper, we present such an optimized tool for surgeons who employ the Nuss procedure to correct pectus excavatum - a congenital chest wall deformity. The Nuss procedure is a minimally invasive procedure that results in the placement of a metal bar inside the chest cavity. The bar is removed after approximately two years. Surgeons have been reporting that the currently available tools for the bar extraction do not provide the most optimal functionality. Therefore, we have proposed an optimized and improved design of the tool for the bar extraction. The improved design tool is further analyzed using finite element techniques. Additionally, we have built a physical prototype to ensure that the new tool to seamlessly integrate with the bar and to further evaluate by the surgeons who routinely practice the Nuss procedure. In order to validate in the future the final design, we have manufactured wax models that will serve as the patterns in the casting process of metal prototypes. They should provide enough strength to withstand stresses present in the bar straightening process.

Simulation of the critical steps of the Nuss procedure

Simulation can be a critical component in the surgical training, planning and rehearsal process of difficult or new procedures. This is true for the Nuss procedure, which is a minimally invasive surgery for correcting pectus excavatum (PE) – a congenital chest wall deformity. Surgeons who routinely perform this surgery identified the most critical steps during the procedure. We chose to simulate these components which involve the process of creating a pathway anterior to the pericardium underneath the sternum as this step can, if incorrectly performed, lead to the death of a patient or, at least, serious complications. In this paper, we describe the hardware setup of the Nuss procedure surgical simulator, the constructed virtual environment, modelling of anatomical structures, surgical instrument and its insertion point without the aid of physical components, reproducing PE deformity, and eventually physics of the tunnelling process.

Poster: Modeling insertion point for general purpose haptic device simulations for minimally invasive surgeries

Minimally invasive surgery has revolutionized surgical procedures over the last decades. This trend has impacted the surgical simulation field and promoted a wide use of haptic devices. The majority of minimally invasive surgery simulators follow a visuo-haptic setup where ports are mounted stationary and physical constraints are used to simulate the pivot of surgical tools. This setup may add limitations to certain procedures and result in negative training, as those assumptions may not hold true during surgery. In this work, we investigate challenges in modeling general purpose haptic device simulations for minimally invasive surgeries, namely accurate pivoting around the insertion point, collisions with surrounding objects during procedure, and system scalability for various devices. The system behavior is evaluated on a Nuss procedure surgical simulator and tested by experienced surgeons on the field. The findings are promising and may benefit other surgical simulators in which the kinematics and dynamics of the surgical tool are utilized within the context of minimally invasive surgeries.

Improvement of a Virtual Pivot for Minimally Invasive Surgery Simulators Using Haptic Augmentation

With rapid development of minimally invasive surgery, proficiency with intricate skills is becoming a greater concern. Consequently, the use of out-of-operating room training has increased significantly through employing high-fidelity and anatomically-correct graphics and haptic interfaces in virtual reality simulations. The effort in developing surgical simulators for generic minimally invasive procedures is still, however, suboptimal for many haptic implementations. A main aspect of such simulations is the pivoting behavior of the surgical tool realized using the haptic device. This paper investigates the limitation of a fully-virtual implementation of the pivot and the ability to augment haptic interfaces to achieve a natural representation of forces. The design and implementation of two surgical tool pivoting techniques are introduced. Furthermore, a phantom is constructed from synthesized components to be used to measure and reproduce realistic mechanical properties of the anatomical model and pivot behavior.

Investigating an approach to identifying the biomechanical differences between intercostal cartilage in subjects with pectus excavatum and normals in vivo: preliminary assessment of normal subjects

The cause of pectus excavatum (PE) is unknown and little research has been done to assess the material properties of the PE costal cartilage. One source reported, after studying ex vivo various properties of the costal cartilage in cases of PE that the biomechanical stability of PE cartilage is decreased when compared to that of normals. Building on this idea, it would be beneficial to measure the biomechanical properties of the costal cartilages in vivo to further determine the differences between PE subjects and normals. An approach to doing this would be to use a modified FARO arm, which can read applied loads and resulting deflections. These values can be used to establish a finite element model of the chest area of a person with PE. So far, a validated technique for the registration between a CT based 3D model of the ribcage and a skin surface scan in case of PE has been addressed. On the basis of the data gathered from 10 subjects with normal chests using a robot arm, stylus and 3D laser scanner, we tried to evaluate the influence of inter-measurement respiration of a subject on results accuracy and the possibility of using the stylus for deflection measurement. In addition, we established the best strategy for taking measurements.