3D model-assisted instrumentation of the pediatric spine: a technical note.

BACKGROUND: Instrumentation of the pediatric spine is challenging due to anatomical constraints and the absence of specific instrumentation, which may result in iatrogenic injury and implant failure, especially in occipito-cervical constructs. Therefore, preoperative planning and in vitro testing of instrumentation may be necessary. METHODS: In this paper, we present a technical note on the use of 1:1 scale patient-specific 3D printed spinal models for preoperative assessment of feasibility of spinal instrumentation with conventional spinal implants in pediatric spinal pathologies. RESULTS: The printed 3D models fully matched the intraoperative anatomy and allowed a preoperative confirmation of the feasibility of the planned instrumentation with conventional screws for adult patients. In addition, the possibility of intraoperative model assessment resulted in better intraoperative sense of spinal anatomy and easier freehand screw insertion, thereby reducing the potential for iatrogenic injury. All 3D models were printed at the surgical department at a very low cost, and the direct communication between the surgeon and the dedicated specialist allowed for multiple models or special spinal segments to be printed for more detailed consideration. CONCLUSIONS: Our technical note highlights the critical steps for preoperative virtual planning and in vitro testing of spinal instrumentation on patient-specific 3D printed models at 1:1 scale. The simple and affordable method helps to better visualize pediatric spinal anatomy and confirm the suitability of preplanned conventional spinal instrumentation, thereby reducing X-ray exposure and intraoperative complications in freehand screw insertion without navigation.

3D printing of implants for patient-specific acetabular fracture fixation: an experimental study.

PURPOSE: To test the effect of 3D printed implants, designed according to surgeon's individual plan, on the accuracy of reduction of an acetabular fracture model. METHODS: Seven identical standardized plastic bone models of an anterior column/posterior hemi-transverse acetabular fracture were used. A CT of one plastic fracture model was made. Using preoperative planning software, three surgeons independently planned the reduction and fixation procedure and designed implants and drill guides. The designed implants and guides were then 3D printed. Each surgeon first executed his plan using his 3D printed plates and guides on one fracture model and then performed another procedure on an identical model with standard implants and instrumentation. Displacement of the fragments at the weight-bearing fracture lines in the acetabulum was measured after fixation. Linear mixed effect models were used to evaluate the effect of different solutions to the same fracture pattern. RESULTS: Mean (SD) displacement of the fracture line between the ischium and stable fragment was 1.1 (0.9) mm for the standard implant and 0.8 (0.6) mm for the 3D printed implant, while the displacements of the fracture line between the stable fragment and anterior column were 0.6 (0.6) and 0.3 (0.3) for the standard and 3D printed methods, respectively (p < 0.001). Mean (SD) fracture line step-off at any fracture line for the standard implant was 1.2 (0.9) mm and 0.4 (0.4) mm for the 3D printed implant (p = 0.022). CONCLUSIONS: Patient-specific 3D printed plates and drill guides may facilitate retaining accurate reduction and fixation of select acetabular fracture patterns.

Fractures of the acetabulum: from yesterday to tomorrow.

PURPOSE: The aim of this article is to present history, state of the art, and future trends in the treatment of acetabular fractures. METHODS: Review of recent and historical literature. RESULTS: Acetabular fractures are difficult to treat. The first descriptions of this injury already appeared in ancient Greek history, but intensive development started in the second half of the twentieth century after Judet and Letournel's seminal work. Their classification is still the gold standard today. It is actually a pre-operative planning system and is used to determine the most appropriate surgical approach. The therapy of choice for dislocated fractures is open reduction and internal fixation. Recent modern techniques based on high-tech computerized planning systems and 3D printing have been successfully integrated into orthopaedic trauma practice. CONCLUSION: There is no ideal surgical approach for acetabulum fracture treatment, so new approaches have been developed in recent decades. The best outcome series have shown good or excellent results, between 70 and 80%.

Hip stress distribution - Predictor of dislocation in hip arthroplasties. A retrospective study of 149 arthroplasties.

Dislocation after hip arthroplasty is still a major concern. Recent study of the volumetric wear of the cup has suggested that stresses studied in a one-legged stance model could predispose arthroplasty dislocation. The aim of this work was to study whether biomechanical parameters of contact stress distribution in total hip arthroplasty during a neutral hip position can predict a higher possibility of the arthroplasty dislocating. Biomechanical parameters were determined using 3-dimensional mathematical models of the one-legged stance within the HIPSTRESS method. Geometrical parameters were measured from standard anteroposterior X-ray images of the pelvis and proximal femora. Fifty-five patients subjected to total hip arthroplasty that later suffered dislocation of the head and, for comparison, ninety-four total hip arthroplasties that were functional at least 10 years after the implantation, were included in the study. Arthroplasties that suffered dislocation had on average a 6% higher resultant hip force than the control group (p = 0.004), 11% higher peak stress on the load-bearing area (p = 0.001) and a 50% more laterally positioned stress pole (p = 0.026), all parameters being less favorable in the group of unstable arthroplasties. There was no statistically significant difference in the gradient index or in the functional angle of the weight bearing. Our study showed that arthroplasties that show a tendency to push the head out of the cup in the representative body position-the one-legged stance-are prone to dislocation. An unfavorable resultant hip force, peak stress on the load bearing and laterally positioned stress pole are predictors of arthroplasty dislocation.