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Purpose Stabilization of C1-2 using a Harms–Goel construct with 3.5 mm titanium (Ti) rods has been established as a standard of reference (SOR). A reduction in craniocervical deformities can indicate increased construct stiffness at C1-2. A reduction in C1-2 can result in C1-2 joint gapping. Therefore, the authors sought to study the biomechanical consequences of C1-2 gapping on construct stiffness using different instrumentations, including a novel 6-screw/3-rod (6S3R) construct, to compare the results to the SOR. We hypothesized that different instrument pattern will reveal significant differences in reduction in ROM among constructs tested. Methods The range of motion (ROM) of instrumented C1-2 polyamide models was analyzed in a six-degree-of-freedom spine tester. The models were loaded with pure moments (2.0 Nm) in axial rotation (AR), flexion extension (FE), and lateral bending (LB). Comparisons of C1-2 construct stiffness among the constructs included variations in rod diameter (3.5 mm vs. 4.0 mm), rod material (Ti. vs. CoCr) and a cross-link (CLX). Construct stiffness was tested with C1-2 facets in contact (Contact Group) and in a 2 mm distracted position (Gapping Group). The ROM (°) was recorded and reported as a percentage of ROM (%ROM) normalized to the SOR. A difference > 30% between the SOR and the %ROM among the constructs was defined as significant. Results Among all constructs, an increase in construct stiffness up to 50% was achieved with the addition of CLX, particularly with a 6S3R construct. These differences showed the greatest effect for the CLX in AR testing and for the 6S3R construct in FE and AR testing. Among all constructs, C1-2 gapping resulted in a significant loss of construct stiffness. A protective effect was shown for the CLX, particularly using a 6S3R construct in AR and FE testing. The selection of rod diameter (3.5 mm vs. 4.0 mm) and rod material (Ti vs. CoCr) did show a constant trend but did not yield significance. Conclusion This study is the first to show the loss of construct stiffness at C1-2 with gapping and increased restoration of stability using CLX and 6S3R constructs. In the correction of a craniocervical deformity, nuances in the surgical technique and advanced instrumentation may positively impact construct stability.

Für Privatpersonen war dies vor einigen Jahren nicht vorstellbar, dass dreidimensionale Objekte entworfen werden können und diese dann schnell und preisgünstig in Kunststoff gefertigt werden können. Einige Mitarbeiter der Firma plasoft GmbH diskutierten wesentliche Heraus-forderungen sowohl im Spritzguss als auch im 3D Druck und welches Verarbeitungsverfahren für das jeweilige Einsatzgebiet zum Zuge kommen kann. Die Bachelorarbeit wurde in Kooperation mit der Firma plasoft GmbH erarbeitet, welche im Bereich Spritzgussfertigung und Softwareentwicklung für den Bereich Kunststoffmaschinen tätig ist. In weiterer Folge wurde eine Spritzgussproduktion aufgebaut, in der Bauteile für unterschiedlichste Branchen gefertigt werden. Derzeit stehen einige Firmen immer wieder vor der selben Entscheidung, ob ihre Produkte im 3D Druck oder mit dem Spritzgussverfahren gefertigt werden sollen. Somit soll in der folgenden Arbeit anhand von Beispielen gezeigt wer-den, ob durch die Erstellung eines Entscheidungsleitfadens das optimale Fertigungsverfahren gewählt werden kann. Die Bedeutung eines Entscheidungsleitfaden wird in weiterer Folge immer wichtiger, da geschäftlich eine schnelle Entscheidung getroffen werden muss um Zeit und Kosten einsparen zu können. A few years ago, it was inconceivable to private individuals that three-dimensional objects could be designed and then quickly and inexpensively manufactured in plastic. Some employees of the company plasoft GmbH discussed essential challenges in injection molding as well as in 3D printing and which processing method can be used for the respective field of application. The bachelor thesis was developed in cooperation with the company plasoft GmbH, which is active in the field of injection molding production and software development for the plastics machinery sector. Subsequently, an injection molding production facility was set up in which components for a wide variety of industries are manufactured. Currently, some companies are faced with the same decision again and again, whether their products should be manufactured in 3D printing or with the injection molding process. Therefore, the following work will show by means of examples, whether the optimal manufacturing process can be selected by the creation of a decision guideline. The importance of a decision guideline will become increasingly important in the future because business decisions have to be made quickly in order to save time and money. Verfasser: Raphael Gmeiner Abweichender Titel laut Übersetzung der Verfasserin/des Verfassers Bachelorarbeit FH JOANNEUM 2022