Keywords arthroplasty, replacement, hip - hip/surgery - printing, three-dimensional - models,
anatomic
Introduction
Briefly speaking, fast prototyping is a way to physically reproduce virtual three-dimensional
(3D) models using various techniques for the deposition of material layer by layer.[1 ] This physical deposition in layers enables the creation of a wide range of geometric
shapes that would be difficult or even impossible to obtain with conventional industrial
techniques, such as machining, which are based on material removal.[2 ] The technique has proven to be very useful to reproduce living organic structures,
including tissues and organs, which do not have perfect shapes (that is, they are
regular polyhedra), since their architecture is based on cell growth, an individual
process related to several genetic and environmental factors.[3 ] Because the phenotypic diversity in Homo sapiens is very high, competence regarding the medical praxis occurs by intervention/interaction
in countless patients who exhibit heterogeneous anatomical characteristics.
The growing search for excellence in the diagnosis and treatment of musculoskeletal
disorders has become a major challenge for orthopedists. As such, new technologies
in imaging diagnosis and in the planning of advanced therapies, including repair and
reconstructive surgery, must be implemented in the medical practice since the beginning
of orthopedic training.[3 ] Mothes et al.[4 ] used prototyping to study glenohumeral defects when planning shoulder arthroplasties.
In his master's dissertation, Marques[5 ] tested several prototyping models that could be applied in traumatology for implant
planning in osteosynthesis.
In the medical field, prototyping biomodels can be obtained from computed tomography
(CT) or magnetic resonance imaging (MRI) scans.[4 ] The technique is widespread in the medical practice and in orthopedic and traumatological
surgery, and it has been used to facilitate the understanding of bone deformities
and failures.[3 ] In addition, previous structural knowledge can reduce the surgical time and the
risks to the patients.[4 ]
Technique Description
The present technical note aims to demonstrate how fast prototyping (3D printing)
can be used as a tool to understand surgical techniques and improve staff training
in a medical residency service.
For the clinical cases herein presented, surgical training with fast prototyping models
was held. Two steps were required to build 3D models. Initially, CT scans of the patients
were requested, and their images were processed using the free software InVesalius
(CTI Renato Archer, Campinas, SP, Brazil) and MeshMixer (Autodesk, Inc., San Rafael,
CA, US). The biomodels were built with a 3D Cliever (Cliever Tecnologia, Belo Horizonte,
MG, Brazil) printer using polylactic acid (PLA) filament.
Both procedures were performed according to the recommended technique, and then, routinely
followed-up by the Orthopedics and Traumatology Service. The surgery was performed
using the technique planned during training.
The inclusion criteria were patients with major bone defects and deformities and CT
scans suitable for 3D measurements. A 3D printed model was made for each case and
then compared with the real situation in loco. The entire procedure was thoroughly
described.
In addition, the present study considered medical record data, including pre-, peri-
and postoperative parameters, along with an evaluation of the imaging findings and
of the printed model. The patients were coded to preserve their anonymity. The present
study was submitted and approved by the hospital ethics committee.
Case 1
A 77-year-old female patient with a right-sided cemented hip arthroplasty due to primary
coxarthrosis. This initial procedure had been performed 17 years ago at our service.
The patient complained of pain in the operated hip for 3 years. The outpatient radiological
follow-up revealed periacetabular osteolysis, and failure of the acetabular component
with loosening and rotation. The femoral component showed no significant changes in
comparison to previous imaging studies ([Figure 1A, B ]).
Fig. 1 Preoperative radiographs of the pelvis (A ) and lateral view of the right hip (B ) at the time of the review, revealing an important acetabular bone failure with loosening
of the components. (C ) View of the printed prototyping model; (D ) residents training with prototyping models; (E ) cavity and (F ) acetabulum preparation with visualization of the bone defect and its filling with
chopped, impacted bone; (G ) planning of the size and position of the implant; (H ) postoperative radiograph of the revision of the right total hip arthroplasty.
[Figure 1C ] shows a printed hemipelvis for a better evaluation of the bone defect and for the
training of the residents. The diagnostic hypothesis of acetabular failure, probably
of aseptic origin, was supported because the patient had no clinical and laboratory
signs of infection. As such, revision of the acetabular component was indicated ([Figures 1D, E, F, G ]), using chopped bone graft impacted on the acetabular roof and bottom. [Figure 1H ] shows a postoperative pelvic radiograph.
Case 2
A 61-year-old male patient with a history of left-hip arthroplasty performed 18 years
ago due to acetabular fracture, with subsequent revision 6 years ago. The patient
had reported progressive pain in the left hip associated with significant functional
loss for at least 5 years. During this period, the patient consulted with several
colleagues who advised on expectant behavior or implant removal, claiming there were
no more therapeutic options. Preoperative radiographs revealed that the patient had
a total cementless hip prosthesis with a loose acetabular component, extensive acetabular
erosion, steel mesh ruptures, and screw fractures ([Figure 2A, B ]). There were no significant changes in the femoral component, and the patient did
not show clinical or laboratory signs of infection. A CT scan was requested to better
assess the bone defect, followed by hip prototyping ([Figures 2C, D, E ]). Considering the extensive bone lesion, we initially considered using bone from
the Bone Bank, but this service is not available in our city. Next, residents and
staff were trained using assemblies with trabecular metal and interspace bone grafting
([Figures 2F, G, H, I ]). Given the severity of the injury, we initially considered the two acetabula option
proposed by Paprosky, but the circumferences of the cups did not fit properly. Then
we thought about a new structural option with two cages and an anchoring system with
divergent screws, filled with bone graft, on which the new acetabulum was placed and
cemented in the appropriate inclination and anteversion. The surgical procedure occurred
exactly as planned, saving a lot of time in a major procedure and with little bleeding
([Figures 2J, K, L, M, N ]). The postoperative radiograph was satisfactory ([Figure 2O ]), with perfect graft integration and excellent function at a 3-year follow-up ([Figure 2P ]). Currently, the patient is asymptomatic and satisfied with the procedure.
Fig. 2 (A, B ) Preoperative radiographs of the pelvis and lateral view of the left hip; (C, D ) computed tomography scans; (E ) visualization of the extensive acetabular lesion; (F ) study of the situation; (G ) assembly of a new arrangement with trabeculated metal and study of its anchoring;
(H ) placement of the new acetabulum; (I ) positioning the cemented polyethylene; (J ) visualization of the intraoperative lesion (note the virtual absence of the acetabular
roof and of the anterior and posterior walls); (K ) assembly of the trabeculated metal structure; (L ) placement of divergent screws and chopped, impacted bone graft; (M ) placement of the trabeculated metal cup after deposition of a thin layer of cement
between the metal components to avoid metallic contact; (N ) acetabulum cementation at the proper position; (O ) immediate postoperative radiograph; and (P ) radiograph three years after the procedure (note the graft integration).
Discussion
The present research evaluated different cases of revision of total hip arthroplasty
involving 3D printing in the surgical planning and training of orthopedics and traumatology
residents. Several authors have endorsed the importance of such technology in preoperative
planning. Mothes et al.[4 ] report the role of prototyping for preoperative planning to treat bone deformities
in the shoulder and believe that it minimizes the risk of intraoperative complications
while attempting to improve outcomes.
The treatment of a CT scan image takes approximately one shift, since it requires
correction and removal of potential artifacts, implants, and volume failures. Printing
takes about 16 hours depending on the filling (the density of the material). The average
cost of printing each biomodel is 56 reais (around 10 US dollars). It is worth mentioning
that the hips are sectioned in the software to print only from the pubic symphysis
to the near sacroiliac area.
The use of prototyped models can simplify the 3D visualization of different conditions,
facilitate the understanding and planning of complex surgical procedures, and expand
anatomical, radiological, and surgical knowledge.
Final Considerations
In the present work, we observed the need to modify the surgical technique by training
in a prototype, using a new trabeculated metal arrangement. The inclusion of these
technologies in the preceptor's repertoire is critical for the differentiation of
future specialists in the job market, since medical education must adapt to train
professionals able to meet societal demands. Therefore, fast prototyping combines
the convenience of preoperative training with the use of technology in orthopedic
surgeries, and it must become widespread in the medical teaching environment. We emphasize
that the present study is not only applicable to orthopedics and traumatology, but
to all medical areas.
