Improving stability of atlantoaxial fusion: a biomechanical study.

PURPOSE: The incidence of atlanto-axial injuries is continuously increasing and often requires surgical treatment. Recently, Harati developed a new procedure combining polyaxial transarticular screws with polyaxial atlas massae lateralis screws via a rod system with promising clinical results, yet biomechanical data is lacking. This biomechanical study consequently aims to evaluate the properties of the Harati technique. METHODS: Two groups, each consisting of 7 cervical vertebral segments (C1/2), were formed and provided with a dens axis type 2 fracture according to Alonzo. One group was treated with the Harms and the other with the Harati technique. The specimen was loaded via a lever arm to simulate extension, flexion, lateral flexion and rotation. For statistical analysis, dislocation (°) was measured and compared. RESULTS: For extension and flexion, the Harati technique displayed a mean dislocation of 4.12° ± 2.36° and the Harms technique of 8.48° ± 1.49° (p < 0.01). For lateral flexion, the dislocation was 0.57° ± 0.30° for the Harati and 1.19° ± 0.25° for the Harms group (p < 0.01). The mean dislocation for rotation was 1.09° ± 0.48° for the Harati and 2.10° ± 0.31° for the Harms group (p < 0.01). No implant failure occurred. CONCLUSION: This study found a significant increase in biomechanical stability of the Harati technique when compared to the technique by Harms et al. Consequently, this novel technique can be regarded as a promising alternative for the treatment of atlanto-axial instabilities.

Novel minimally invasive tape suture osteosynthesis for instabilities of the pubic symphysis: a biomechanical study.

INTRODUCTION: Open book fractures are challenging injuries oftentimes requiring surgical treatment. The current treatment of choice is symphyseal plating, which requires extensive surgery and entirely limits physiological movement of the symphyseal joint, frequently resulting in implant failure. Therefore, we investigated the biomechanical properties of a semi-rigid implant (modified SpeedBridge™) as a minimally invasive tape suture construct for the treatment of open book fractures and evaluated the superiority of two techniques of implementation: criss-cross vs. triangle technique. MATERIALS AND METHODS: Nine synthetic symphyseal joints were dissected creating an open book fracture. The different osteosynthesis methods (plating, modified SpeedBridge™ in criss-cross/triangle technique) were then applied. All constructs underwent horizontal and vertical loading, simulating biomechanical forces while sitting, standing and walking. For statistical analysis, dislocation (mm) and stiffness (N/mm) were calculated. RESULTS: Symphyseal plating for the treatment of open book fractures proved to be a rigid osteosynthesis significantly limiting the physiological mobility of the symphyseal joint (dislocation: 0.08 ± 0.01 mm) compared to the tape sutures (dislocation: triangle technique 0.27 ± 0.07 mm, criss-cross technique 0.23 ± 0.05 mm) regarding horizontal tension (p < 0.01). Both modified SpeedBridge™ techniques showed sufficient biomechanical stability without one being superior to the other (p > 0.05 in all directions). Considering vertical loading, no statistical difference was found between all osteosynthesis methods (caudal: p = 0.41; cranial: p = 0.61). CONCLUSIONS: Symphyseal plating proved to be the osteosynthesis method with the highest rigidity. The modified SpeedBridge™ as a semi-rigid suture construct provided statistically sufficient biomechanical stability while maintaining a minimum of symphyseal movement, consequently allowing ligamental healing of the injured joint without iatrogenic arthrodesis. Furthermore, both the criss-cross and the triangle technique displayed significant biomechanical stability without one method being superior.

[Funnel Chest Corrective Surgery with the Aid of a 3D Reconstruction of the Bony Thorax for Preoperative Adjustment of the Metal Bar]. / Trichterbrust-Korrektur-OP unter Zuhilfenahme einer 3-D-Rekonstruktion des Thorax zur präoperativen Anpassung des Korrekturstabes.

BACKGROUND: Funnel chest is a congenital deformity of the thorax in which the sternum and the adjacent ribs form a funnel towards the spine. As the pathogenesis has not yet been clearly clarified, there are different therapeutic approaches. These range from conservative measures and minimally invasive surgery to open corrective surgery. The patients suffer from aesthetic impairment, as well as cardiopulmonary restrictions due to the narrowing of the mediastinal space. The indication for funnel chest correction surgery is therefore justified by functional and aesthetic reasons. PATIENTS: We report a 23-year-old male patient who presented with subjectively impairing and objectively moderate funnel chest. A chest CT scan was performed preoperatively. The sternovertebral distance was 8 cm, the transverse thoracic diameter 28,9 cm (Haller's index 3.6). The preoperative pulmonary function test showed a slight restriction, the otherwise healthy patient described shortness of breath with greater exertion. The indication for funnel chest correction surgery was made. The operation was performed using a combined surgical technique: sternotomy and cartilage wedge resection according to Brunner/Grob and implantation of a metal bar without lateral antirotation plate. The most time-consuming step of the operation is the intraoperative adjustment of the metal bar. Therefore, in advance of the operation, we used a 3D printer to prepare a 3D reconstruction of the bony thorax with the help of the thorax CT scan. The metal bar was then bent and fitted to the thorax print and implanted during surgery. This allowed us to shorten the operation time by at least 15 min. RESULTS: The postoperative follow-up examinations showed a clearly erect funnel and a satisfactory aesthetic result. The metal bar explantation took place, as planned, 7 months after implantation. The postoperative CT scan now showed a Haller's index of 3.25, the pulmonary function test showed improved results. Subjectively, the patient was always symptom-free. CONCLUSION: The preparation of medical implants with 3D patient models as templates helps to save operation time. The practicability has not yet been established, as the creation of a 3D model of the bony thorax is associated with a different approach. With the increasing digitisation of the medical world, however, it is conceivable that the creation of digital and real 3D models will become easier and cheaper in the future.

[3D printing in orthopedic and trauma surgery education and training : Possibilities and fields of application]. / 3D-Druck in der unfallchirurgischen Fort- und Weiterbildung : Möglichkeiten und Anwendungsbereiche.

The 3D printing technology enables precise fracture models to be generated from volumetric digital imaging and communications in medicine (DICOM) computed tomography (CT) data. Apart from patient treatment, in the future this technology could potentially play a significant role in education and training in the field of orthopedic and trauma surgery. Preliminary results show that the understanding and classification of fractures can be improved when teaching medical students. The use of life-size and haptic models of real fractures for education is particularly interesting. Even experienced surgeons show an improved classification and treatment planning with the help of 3D printed models when compared to plain CT data. Especially for complex articular fractures, such as those of the acetabulum and tibial plateau, initial evidence shows patient benefits in terms of reduced surgery time and blood loss with the help of 3D models. The use of 3D printing on-site at the hospital is of particular interest in orthopedic and trauma surgery as it promises to provide products within a short time. The low investment and running costs and the increasing availability of convenient software solutions will spur increasing dissemination of this technology in the coming years.

A method for finding high accuracy surface zones on 3D printed bone models.

The use of three-dimensional (3D) printing for surgical applications is steadily increasing. Errors in the printed models can lead to complications, especially when the model is used for surgery planning or diagnostics. In patient care, the validation of printed models should therefore be performed routinely. However, there currently is no standard method to determine whether the printed model meets the necessary quality requirements. In this work, we present a method that not only finds surface deviations of a printed model, but also shows high accuracy zones of a potentially corrupted model, that are safe to be used for surgery planning. Our method was tested on printed patient bone models with acetabular fractures and was compared to two common methods in orthopedics, simple landmark registration as well as landmark plus subsequent iterative closest point registration. In order to find suitable parameters and to evaluate the performance of our method, 15 digital acetabular bone models were artificially deformed, imitating four typical 3D printing errors. A sensitivity of over 95% and a specificity of over 99% was observed in finding these surface deformations. Then, the method was applied to 32 printed models that had been re-digitized using a computed tomography scanner. It was found that only 25% of these printed models were free of significant deformations. However, focussing on two common implant locations, our method revealed that 72% of the models were within the acceptable error tolerance. In comparison, simple landmark registration resulted in a 9% acceptance rate and landmark registration followed by iterative closest point registration resulted in a 41% acceptance rate. This outcome shows that our method, named Similarity Subgroups Registration, allows clinicians to safely use partially corrupted 3D printed models for surgery planning. This improves efficiency and reduces time to treatment by avoiding reprints. The similarity subgroups registration is applicable in further clinical domains as well as non-medical applications that share the requirement of local high accuracy zones on the surface of a 3D model.

3D printing method for next-day acetabular fracture surgery using a surface filtering pipeline: feasibility and 1-year clinical results.

INTRODUCTION: In orthopedic surgery, 3D printing is a technology with promising medical applications. Publications show promising results in acetabular fracture surgery over the last years using 3D printing. However, only little information about the workflow and circumstances of how to properly derive the 3D printed fracture model out of a CT scan is published. MATERIALS AND METHODS: We conducted a retrospective analysis of patients with acetabular fractures in a level 1 trauma center. DICOM data were preoperatively used in a series of patients with acetabular fractures. The 3D mesh models were created using 3D Slicer (https://www.slicer.org) with a newly introduced surface filtering method. The models were printed using PLA material with FDM printer. After reduction in the printed model, the acetabular reconstruction plate was bent preoperatively and sterilized. A clinical follow-up after 12 months in average was conducted with the patients. RESULTS: In total, 12 patients included. Mean printing time was 8:40 h. The calculated mean printing time without applying the surface filter was 25:26 h. This concludes an average printing time reduction of 65%. Mean operation time was 3:16 h, and mean blood loss was 853 ml. Model creation time was about 11 min, and mean printing time of the 3D model was 8:40 h, preoperative model reduction time was 5 min on average, and preoperative bending of the plate took about 10 min. After 12 months, patients underwent a structured follow-up. Harris Hip Score was 75.7 points, the Modified Harris Hip Score 71.6 points and the Merle d'Aubigne Score 11.1 points on average. CONCLUSIONS: We presented the first clinical practical technique to use 3D printing in acetabular fracture surgery. By introducing a new surface filtering pipeline, we reduced printing time and cost compared to the current literature and the state of the art. Low costs and easy handling of the 3D printing workflow make it usable in nearly every hospital setting for acetabular fracture surgery.

On-the-fly augmented reality for orthopedic surgery using a multimodal fiducial.

Fluoroscopic x-ray guidance is a cornerstone for percutaneous orthopedic surgical procedures. However, two-dimensional (2-D) observations of the three-dimensional (3-D) anatomy suffer from the effects of projective simplification. Consequently, many x-ray images from various orientations need to be acquired for the surgeon to accurately assess the spatial relations between the patient's anatomy and the surgical tools. We present an on-the-fly surgical support system that provides guidance using augmented reality and can be used in quasiunprepared operating rooms. The proposed system builds upon a multimodality marker and simultaneous localization and mapping technique to cocalibrate an optical see-through head mounted display to a C-arm fluoroscopy system. Then, annotations on the 2-D x-ray images can be rendered as virtual objects in 3-D providing surgical guidance. We quantitatively evaluate the components of the proposed system and, finally, design a feasibility study on a semianthropomorphic phantom. The accuracy of our system was comparable to the traditional image-guided technique while substantially reducing the number of acquired x-ray images as well as procedure time. Our promising results encourage further research on the interaction between virtual and real objects that we believe will directly benefit the proposed method. Further, we would like to explore the capabilities of our on-the-fly augmented reality support system in a larger study directed toward common orthopedic interventions.

Image guided percutaneous spine procedures using an optical see-through head mounted display: proof of concept and rationale.

BACKGROUND AND PURPOSE: Optical see-through head mounted displays (OST-HMDs) offer a mixed reality (MixR) experience with unhindered procedural site visualization during procedures using high resolution radiographic imaging. This technical note describes our preliminary experience with percutaneous spine procedures utilizing OST-HMD as an alternative to traditional angiography suite monitors. METHODS: MixR visualization was achieved using the Microsoft HoloLens system. Various spine procedures (vertebroplasty, kyphoplasty, and percutaneous discectomy) were performed on a lumbar spine phantom with commercially available devices. The HMD created a real time MixR environment by superimposing virtual posteroanterior and lateral views onto the interventionalist's field of view. The procedures were filmed from the operator's perspective. Videos were reviewed to assess whether key anatomic landmarks and materials were reliably visualized. Dosimetry and procedural times were recorded. The operator completed a questionnaire following each procedure, detailing benefits, limitations, and visualization mode preferences. RESULTS: Percutaneous vertebroplasty, kyphoplasty, and discectomy procedures were successfully performed using OST-HMD image guidance on a lumbar spine phantom. Dosimetry and procedural time compared favorably with typical procedural times. Conventional and MixR visualization modes were equally effective in providing image guidance, with key anatomic landmarks and materials reliably visualized. CONCLUSION: This preliminary study demonstrates the feasibility of utilizing OST-HMDs for image guidance in interventional spine procedures. This novel visualization approach may serve as a valuable adjunct tool during minimally invasive percutaneous spine treatment.