3D Planning and Printing of Patient Specific Implants for Reconstruction of Bony Defects

This protocol allows the virtual treatment of patients with bony defects and the creation of novel surgical guide and fixation plates. Using this protocol allows implants to be virtually created and designed according to what is feasible for use in the operating room with superior accuracy and shortened operation duration. Patient-specific implants planned with our protocol are based on accurate 3D imaging resulting in perfectly fitting implants and enabling the restoration of proper tissue anatomy, symmetry, and function.

This protocol allows users to design and print complex models or structures from different materials and to examine different parameters such as their strength or ability to allow bone regeneration. Although these programs are very user friendly, it does take time to master the computer-assisted design process. Patience and practice will help the user get better and quicker.

As this protocol contains many steps of virtual planning, observing the stages will be extremely helpful. For segmentation of the 3D reconstructed model, in the appropriate segmentation software under the Bone Segmentation menu, select General and use the plus tool to indicate the segment of interest and the minus tool to indicate the unwanted segments while scrolling and moving through the scan. Use the Set button that initiates the segmentation and click Apply to create the new segment.

To perform a good bone segmentation, a large number of positive and negative markings should be used in the 3D reconstructed model. and all of the other views. When the segmentation is complete, correct the markings and add new ones for better accuracy as necessary.

Export the files as STL 3D files. To design the 3D reconstruction implant, import the STL files into the 3D design software and use the Shave tool to separate the bone into two parts. From the Select Move Clay menu, select the Clay tool and mark the region of interest.

Copy the marked region and create a new identical object in the object list to manipulate the position of the region. To make sure that the axis of rotation is set on the part of the bone that will stay in the same position, select Reposition and set the rotation axis as planned. As the human skull is mostly symmetrical, use the Mirror Clay tool for guidance to obtain the correct positioning or placement of the missing or malpositioned segment and set the plane at the center of the skull.

Based on the mirrored half, perform segment rotation as needed and use the Add Clay tool from the Construct Clay menu to reconstruct the avulsed bony part. In the Curves menu, select the Draw Curve option to create a continuous outer shape of the desired implant. Right-click the segment and select Duplicate to duplicate the bony segment.

Working in the new duplicated segment, in the Detail Clay menu select Emboss with Curve to create the volume of the reconstruction implant. Select the outer form of the sketched implant and place the circle-shaped cursor inside the sketched implant on the surface of the bone. Select the desired parameters, most importantly the distance to control the thickness of the implant and right-click on the duplicated segment to select Boolean and Remove From, then select the object containing the created implant.

In cases for which holes for screw fixation or angiogenesis are required, use the Create Plane function to create a parallel plane in which the holes for the plate are designed. When the planes are positioned in maximum parallelism to the implant, select a circle in the Sketch menu and create circles of the desired size and position within the segment. In the Curves menu, use the Project Sketch option to designate the sketches to be transferred from the plane to the implant.

To generate the countersink for the screws, in the Detail Clay menu, select Emboss with Curve and place the circle-shaped cursor inside the marked circular area on the segment surface. To complete the holes in the SubD Surfaces Menu use the Wire Cut SubD option to create rods perpendicular to the implant. To create the holes using the rods, select Boolean and Remove From and select each rod in succession, right-clicking Boolean, Remove From, and Create An Implant in the object list.

To create a mesh in the implant, use Draw Curve to generate a sketch of the planned mesh as demonstrated. In the Detail Clay menu use Emboss with Wrapped Image to select a template image after which the mesh will be designed. The white regions of the image will be subtracted and the black areas will remain.

Manually adjust the direction and size of the design and set the thickness of the generated, then click Apply. The patient-specific implant will then be ready for production. These images were obtained from a 40-year old female patient with a broken stock-supplied reconstruction fixation plate from a previous injury and a nonunion fracture in the left body of her lower jaw.

Segmentation of the lower jaw was performed as demonstrated to separate the broken fixation plate. Using 3D design software, the left segment of the mandible was repositioned to the correct anatomical position. Mirroring of the right healthy side was performed to allow proper reconstruction of the missing bone.

The patient-specific implant could then be designed, including holes for fixation screws. A mesh was designed to allow additional bone graft placement, according to the proper contour of the jaw based on the healthy side and to enable superior angiogenesis through the holes in the mesh. The implant printed from titanium using selective laser sintering technology and postoperative results can be observed in these images.

Note the continuity of the lower jaw, the correct vertical position of the left lower jaw segment and the symmetry in the body contour that was reconstructed using the patient-specific implant as the outer contour and an iliac crest bone graft for filling the voids. When designing the patient-specific implant, consider the planning of a minimally sized plate that is strong enough to allow load-bearing forces while withstanding shear and torque forces. Patient-specific implants can also be designed for cranioplasty, orthopedic procedures and may be potentially used for the design of soft tissue in all organs.

This protocol currently allows the planning of novel implants for surgeries and research studies and may eventually facilitate implant bioprinting and foreign material regeneration.