Using Symmetry and 3D-Printed Medical Models to Repair Bone Fractures

In a new study, a team of researchers from China compared the clinical outcomes of treating isolated acetabular (concave surface of the pelvis) fractures with traditional 3D-printed planning models and using an approach that mirrors the affected area following the bilaterally symmetric nature of human anatomy. Their hypothesis is that, while 3D-printed models can definitely help when fixing hip fractures, mirroring hip bone models to gain a more accurate reconstruction of the pre-damaged bone might be more effective in its ultimate repair. This is important news in China, as the amount of “acetabular fractures and associated mortality” has been on the rise there for several years.

What Are Acetabular Fractures?

The acetabulum is the concave socket in the pelvis where the femoral head (the ball of the hip joint) fits. Acetabular fractures are serious injuries that can lead to long-term hip dysfunction, arthritis, and disability if not properly treated [2]. These fractures typically result from high-energy trauma such as car accidents, falls from heights, or severe sports injuries.

Traditional treatment involves open reduction and internal fixation (ORIF), where surgeons realign the fractured bone fragments and secure them with plates and screws. However, achieving perfect anatomical reduction—restoring the bone to its original pre-injury state—is challenging, especially with complex, comminuted fractures where the bone shatters into multiple pieces.

“Our findings are consistent with previous reports 1,5,7 and suggested that mirror model technology tends to improve the clinical outcomes for patients with acetabular fractures,” the researchers wrote.

The Mirror Model Approach

They explained that for the most part, a human skeleton is “bilaterally symmetric; this is known as a mirror relationship.”

“This mirror relationship is the theoretical basis for using the contralateral acetabular mirror model as a template for the affected side. The mirror imaging model of the contralateral acetabulum replaces the post-reduction state of the affected acetabulum, which can greatly simplify the process of fracture assembly and reduction, improve the accuracy of reduction, and provide an excellent template for pre-bending of the pelvic reconstruction plate and determination of the screw length.”

This innovative approach creates a digital and physical replica of the patient’s healthy acetabulum, mirrors it horizontally, and uses it as a perfect template for reconstructing the damaged side. Essentially, if your left hip is fractured, surgeons can create a mirror image of your healthy right hip to know exactly what the left hip should look like after repair.

3D Printing in Orthopedic Surgery

Over the last few years, we’ve seen 3D printing grow more useful in the operating room and for custom fracture management. To complete a successful acetabular fracture surgery, strong internal fixation is necessary. The femoral head and acetabulum need to match, and the articular surface must have high integrity. 3D images are obviously better than CT data, but they’re still read on a 2D plane. This is why 3D-printed models can help.

“With the 3D model, we can accurately measure the degree of collapse of the articular surface, determine the number and shape of the fracture fragments, perform segmentation of each fragment model, separately print and assemble the fracture fragments, simulate reduction, and determine the position, length, and number of implants,” they stated.

3D printing technology has revolutionized preoperative planning in orthopedic surgery. Surgeons can now hold accurate, patient-specific models of complex fractures in their hands before entering the operating room [3]. This allows for:

• Enhanced visualization: Understanding complex fracture patterns that are difficult to interpret on 2D CT scans
• Surgical rehearsal: Practicing reduction techniques and plate placement before the actual surgery
• Patient communication: Explaining the injury and proposed treatment to patients and their families
• Custom implant selection: Choosing the right plates and screws based on the physical model
• Reduced operating time: Less time spent intraoperatively figuring out how to approach the fracture

Study Methodology

The researchers used CT medical imaging data to print models of the contralateral acetabulum, then used the new 3D-printed mirror model “as a benchmark for surgical predrilling and determined the position and pre-bending properties of the pelvic reconstruction plate and the length of the screws.”

“We conducted a retrospective review of prospectively gathered data from our medical center from June 2011 to December 2017, in which consecutive patients who underwent traditional 3D printing technology or 3D printing mirror model technology following an isolated acetabular fracture were identified by the International Classification of Diseases (10th revision). Follow-up was initiated at the onset of the first day after primary acetabular fracture surgery,” they explained.

A total of 62 men and 84 women participated in the study. The patients treated with traditional 3D printing were in Group T, while those treated with 3D printing mirror model technology were in Group M.

“In total, 146 advanced-age patients (146 hips) with an isolated acetabular fracture (Group T, n = 72; Group M, n = 74) were assessed for a mean follow-up period of 29 months (range, 24–34 months),” the team wrote. “The primary endpoint was the postoperative Harris hip score (HHS). The secondary endpoints were the operation time, intraoperative blood loss, fluoroscopy screening time, fracture reduction quality, and incidence of postoperative complications at the final follow-up.”

Inclusion Criteria

All patients needed certain criteria to be included:

• a unilateral isolated acetabular fracture
• fresh acetabular fracture with a 2-week duration from injury to operation
• no hip joint dysfunction or deformity pre-fracture
• able to understand instructions and follow rehab program

Technical Workflow

Materialise Mimics software was used for data processing, and the researchers directly generated 3D images of the affected acetabulum for Group T, while with Group M, “a 3D image of the affected acetabulum as well as a new 3D image of the contralateral acetabulum” were both generated. See also: Best 3D Printer Upgrades That Actually Improve Pri…. The STL files were sliced using Cura software and 3D printed on a Stratasys Objet 3D printer.

The same group of orthopedic surgeons operated on all of the patients.

“For Group M, we selected the appropriate reconstruction plate, pre-bent it to fit the bone surface, and adjusted it to the appropriate position; we then determined the specification and model of the pelvic reconstruction plate, the direction and length of the fixing screw, and the relationship of the acetabular joints,” they wrote.

The same intraoperative management was completed with the Group T patients, except before the reconstruction plate was chosen, the team removed the supports from between the bones in the 3D-printed model, and “dissociated each fragment to intuitively and accurately understand the fracture situation,” before resetting the fracture model.

“According to the preoperative plan, we completed the reduction as soon as possible, placed the pre-bent pelvic reconstruction plate in the position that had been established during the rehearsal, ensured that the plate and bone surface fit well, temporarily fixed the position, and inserted the appropriate screw into the predesigned screw trajectory on the 3D model to provide absolute stability of fracture reduction,” the team explained. “C-arm images were viewed in multiple planes to certify anatomic reduction.”

Postoperative Care

The patients all followed the same postoperative and rehabilitation instructions, such as wearing compression stockings for at least 21 days, completing continuous passive motion one day post-op, and touch-down weight-bearing with a walker between 2-30 days, and crutches between 30-90 days, post-op. Full weight-bearing was allowed after 90 days, based on clinical and radiography results.

“The patients were reviewed clinically and radiographically at 1, 3, 6, 9, and 12 months postoperatively and yearly thereafter,” the team stated. “The HHS, operation time, intraoperative blood loss, fluoroscopy screening time, and incidence of postoperative complications were significantly different between the groups, with Group M showing superior clinical outcomes.”

Comparison: Traditional vs. Mirror Model 3D Printing

You can see the results of both the primary and secondary endpoints in the tables below.

Primary Endpoint Results	Group T (Traditional)	Group M (Mirror)	P Value
Harris Hip Score (HHS)	78.5 ± 8.2	86.3 ± 6.7	< 0.001
Excellent/Good HHS Rating	65.3%	89.2%	< 0.001

Secondary Endpoint Results	Group T (Traditional)	Group M (Mirror)	P Value
Operation Time (minutes)	185 ± 42	142 ± 35	< 0.001
Intraoperative Blood Loss (mL)	685 ± 215	412 ± 178	< 0.001
Fluoroscopy Time (seconds)	45.2 ± 12.8	28.6 ± 9.4	< 0.001
Fracture Reduction Quality (Excellent)	68.1%	87.8%	< 0.01
Postoperative Complications	12.5%	4.1%	< 0.05

Clinical Implications

The results demonstrate a clear advantage for mirror model technology across all measured parameters. Patients in Group M achieved significantly higher Harris Hip Scores, with nearly 90% achieving excellent or good outcomes compared to 65% in the traditional group. The functional improvement is clinically meaningful and likely translates to better quality of life for patients [4].

From a surgical perspective, the reduction in operation time by approximately 43 minutes per case represents significant operating room efficiency. In busy trauma centers, this time savings could allow for additional cases to be performed, improving access to care. Reduced blood loss of nearly 300 mL is also clinically relevant, as it decreases the risk of transfusion-related complications [5].

The lower fluoroscopy time is important for reducing radiation exposure to both patients and surgical staff. Occupational radiation exposure is a known concern in orthopedic surgery, and any technique that reduces cumulative dose is beneficial [6].

Limitations and Future Directions

“In conclusion, 3D printing mirror model technology in the treatment of acetabular fractures is associated with superior clinical outcomes compared with traditional 3D printing technology,” the researchers wrote. “The number of patients in this study was relatively limited, and it was not a prospective study; therefore, analysis of larger samples is needed for more accurate conclusions. Nevertheless, this study revealed accurate treatment of acetabular fractures through 3D printing mirror model technology, providing a new direction for the surgical treatment of acetabular fractures.”

Several limitations should be noted. See also: Best Budget 3D Printer Upgrades That Actually Impr…. The study was retrospective, which introduces potential bias in patient selection and data collection. Additionally, the study was conducted at a single center with a relatively small sample size. Multi-center, prospective, randomized controlled trials would provide stronger evidence and better generalizability [7].

Future research could explore the application of mirror model technology to other bilateral anatomical structures, such as the distal radius, calcaneus, or proximal femur. Additionally, integration with virtual reality and augmented reality platforms could further enhance surgical planning and training [8].

Cost Considerations

While 3D printing adds cost to the preoperative phase, the reduction in operating time and complications may offset these expenses. A cost-benefit analysis would be valuable to determine the economic impact of this technology in different healthcare systems. As 3D printing technology becomes more affordable and accessible, these techniques may become standard of care for complex orthopedic trauma [9].

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