3d modeling

3D modeling and 3D printing can improve THA diagnosis, classification and surgical planning – 3DPrint.com

The Electronic Online Presentation System, or EPOS, is the European Society of Radiology’s electronic database for scientific exhibitions. A group of researchers published in EPOS their work on the use of 3D modeling and printing tools to diagnose, classify and perform surgical planning for the fixation of periprosthetic acetabular fractures, which are a difficult but common complication. total hip arthroplasty (THA).

“Periprosthetic acetabular fractures are linked to traumatic events and underlying pathological conditions that reduce the structural integrity of the supporting bone[1] and are often associated with aseptic loosening, periprosthetic osteolysis and severe bone loss[2]“, wrote the researchers.

“Analysis based on plain radiographs alone is not suitable for reliably detecting residual implant stability and measuring fracture extent and pelvic bone loss [3].”

Fig. 1: (a) Anterior-posterior (AP) radiographs of the pelvis and (b) lateral view radiographs of the right hip showed mild signs of periacetabular osteolysis with no evidence of implant loosening or acetabular fracture.

They state that when it comes to defining a fracture model, CT is the “gold standard”, which is certainly the case when a 3D virtual rendering is needed to help with pre-surgical planning.

3D modeling software based on CT scans allows clinicians to obtain accurate images of “three-dimensional reconstructions of the bone surface” by virtually removing metal implants with segmentation. Other analytical tools include measurement of remaining bone stock, assessment of implant stability, and fracture characterization, and 3D images can also be used to 3D print anatomical models for planning purposes. and surgical simulation.

The researchers said their paper will show that the assessment of bone quality and fracture morphology can be improved with 3D modeling software, and reveal how useful 3D modeling and 3D printing are for the process. diagnosis of periprosthetic acetabular fracture around the ATH, as well as the manufacture of life-size models for modelling, simulation and sizing of preoperative implants.

Fig. 2: CT scan of the pelvis. (a) The coronal view shows a slightly medial protruding acetabular cup; (b) A sagittal view of the hip revealed a fracture of the posterior wall of the acetabulum. The three-dimensional reconstruction of the fracture is visible (c), but its extension is obscured by image artifacts.

They used the case of a 75-year-old woman who came to the emergency room after a domestic trauma incident. The patient had a history of severe coxarthrosis of the right hip, which had been treated a decade before the use of cementless THA. Doctors took AP X-rays of her pelvis and a cross-sectional view of her hip, and saw no signs of fracture or loosening around the acetabulum or shaft. However, a “MAR pelvic scan” showed that the posterior wall of the acetabulum had a fracture, although the acetabular cup had not been displaced.

Materialize Mimics software was used to create a 3D digital model of the pelvis based on CT scan data. The bone was differentiated from the surrounding soft tissues and the patient’s prosthetic implants by segmentation.

Fig. 3: Three-dimensional images created with 3D modeling software. (a,b) Entire pelvis with retained acetabular cup. The femurs and femoral stem were removed during segmentation. (c,d) The bone quality map shows regions with normal bone quality (green) and regions with poor bone quality and thickness (red). (e,f) Measurements of bone defect area and fracture extension.

“The first phase is thresholding, which includes all voxels whose density falls within a specified range of Hounsfield Unit (HU) values. We used a mask with a HU range of 130 to 1750 to exclude metal and ceramic implants and to include both cancellous and cortical bone,” the researchers explained.

“Final segmentation, with removal of soft tissue and artifacts, was performed manually using additional software tools (Fig. 3 a, b). Finally, the femurs and metal implants were digitally removed from the corresponding pelvis and a 3D image of the isolated region of interest (ROI) was created.

A bone quality map with a color gradient was used for the acetabulum, according to the cortical and global bone thickness of the different regions. Measurements of fracture area, shape, and spatial location were analyzed later, along with “acetabular bone loss and center of rotation, relative to the contralateral acetabulum.”

Finally, a life-size model of the patient’s entire pelvis was 3D printed on a Form 3L system.

Fig. 4: (a) 3D printed life-size plastic model of the entire pelvis. (b,c) Detail of the medial wall and posterior column fracture.

After analyzing the 3D images and the 3D printed model, they reclassified the posterior wall fracture as an incomplete posterior column and a medial wall acetabular fracture. Furthermore, the fracture was found to be “spontaneous”, with less than 50% loss of bone stock. Finally, the bone quality map determined the overall bone loss, showing poor quality of the posterior and medial walls. The 3D printed model was also used to make preoperative models.

“The treatment strategy was chosen according to the algorithm proposed by Simon et al. [14, 15, 16]which suggest that acetabular revision surgery either bridges or distracts the fracture, without fixing the fracture,” the researchers explained.

Fig. 5: (a) Postoperative AP radiograph of the pelvis and (b,c) CT of the pelvis 3 months postoperatively showing good positioning of the implant and complete healing of the fracture.

AP X-rays taken of the pelvis and the right hip after the operation showed that the implant was “well positioned and fixed”. Three months later, a CT scan was taken of the patient’s pelvis, which showed “bony integration of the trabecular cup” and complete healing of the fracture “with callus formation”. A 3D digital model built from DICOM images confirmed this.

Fig. 6: Digital reconstruction by 3D modeling. The posterior column and the medial wall of the acetabulum were restored.

“The use of 3D modeling software has shown that periprosthetic acetabular fractures can be treated better, compared to plain X-rays and CT scans,” the researchers concluded.

“3D modeling software provides additional measurement tools that enable volumetric analysis of bone defects and assessment of bone quality.”

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