Error Analysis: How Precise is Fused Deposition Modeling in Fabrication of Bone Models in Comparison to the Parent Bones?

BACKGROUND

Rapid prototyping (RP) is used widely in dental and faciomaxillary surgery with anecdotal uses in orthopedics. The purview of RP in orthopedics is vast. However, there is no error analysis reported in the literature on bone models generated using office-based RP. This study evaluates the accuracy of fused deposition modeling (FDM) using standard tessellation language (STL) files and errors generated during the fabrication of bone models.

MATERIALS AND METHODS

Nine dry bones were selected and were computed tomography (CT) scanned. STL files were procured from the CT scans and three-dimensional (3D) models of the bones were printed using our in-house FDM based 3D printer using Acrylonitrile Butadiene Styrene (ABS) filament. Measurements were made on the bone and 3D models according to data collection procedures for forensic skeletal material. Statistical analysis was performed to establish interobserver co-relation for measurements on dry bones and the 3D bone models. Statistical analysis was performed using SPSS version 13.0 software to analyze the collected data.

RESULTS

The inter-observer reliability was established using intra-class coefficient for both the dry bones and the 3D models. The mean of absolute difference is 0.4 that is very minimal. The 3D models are comparable to the dry bones.

CONCLUSIONS

STL file dependent FDM using ABS material produces near-anatomical 3D models. The high 3D accuracy hold a promise in the clinical scenario for preoperative planning, mock surgery, and choice of implants and prostheses, especially in complicated acetabular trauma and complex hip surgeries.

Complex Tibial Plateau Fractures Treated by Hybrid External Fixation System: A correlation of followup computed tomography derived quality of reduction with clinical results

BACKGROUND

Tibial plateau fractures are common due to high energy injuries. The principles of treatment include respect for the soft tissues, restoring the congruity of the articular surface and reduction of the anatomic alignment of the lower limb to enable early movement of the knee joint. There are various surgical fixation methods that can achieve these principles of treatment. Recognition of the particular fracture pattern is important, as this guides the surgical approach required in order to adequately stabilize the fracture. This study evaluates the results of the combined treatment of external fixator and limited internal fixation along with the advantages using postoperative computed tomography (CT) scan after implant removal. Materials and.

METHODS

55 patients with a mean age of 42 years (range 17-65 years) with tibial plateau fracture, were managed in our institution between October 2010 and September 2013., Twenty fractures were classified as Schatzker VI and 35 as Schatzker V. There were 8 open fractures (2 Gustilo Anderson 3A and 6 Gustilo Anderson 2). All fractures were treated with closed reduction and hybrid external fixation (n = 21/38.2%) or with minimal open reduction internal fixation and a hybrid system (n = 34/61.8%). After the removal of the fixators, CT-scan was programmed for all the cases, for correlation with the results. At final followup, the American Knee Society Score (AKSS) was administered.

RESULTS

All patients were evaluated with a minimum of 12 months (range 12-21 months) followup. Average time to union was 15.5 weeks (range 13-19 weeks). The postoperative joint congruity as evaluated in the postoperative CT-scan was <2 mm of articular step-off in 8 patients (14.5%), between 2 and 4 mm in 18 patients (32.7%) and over 4 mm in 29 (52.7%). The injured limb mechanical axis was restored within 5° compared to the contralateral limb in 36 cases (65%) and with an angulation >5° in 19 cases (35%). Patients with residual joint depression <3.5 mm had a 95% chance of having excellent AKSS knee score results and 80% chance of having excellent AKSS function scores. On the other hand, residual joint depression of >4.5 mm displayed a 100% chance of getting poor-fair scores both in AKSS knee and AKSS function score. The association of a postoperative mechanical axis within 5° of the contralateral limb and improved knee scores was statistically significant for the AKSS function and total scores but not for the AKSS knee score. The AKSS was negatively correlated with postoperative joint depression magnitude which was statistically significant. Only the amount of joint collapse was verified as a prognostic factor in a multivariate logistic regression analysis.

CONCLUSIONS

The postoperative CT-scan shows important information about bone healing, and an exact image of the reduction and the shaft alignment. Postoperative radiographs may have led to an underestimation of the degree of residual displacement. On the contrary, CT-scan demonstrates the exact grade of articular displacement and depending on CT-scan results one can better manage the postoperative rehabilitation.