The DC2: Safer, Faster, Less Invasive
Type II odontoid fractures of the second cervical vertebra are the most common spinal column injury in patients over the age of 70. Despite this, treatment of these injuries remains controversial with only half of the patient population being treated surgically. The remaining patient population is left with conservative bracing techniques that lead to poor patient outcomes.
The controversy around treatment stems from the invasiveness of current surgical procedures. These procedures promote boney fusion via an implant construct to stabilize the first and second cervical vertebrae. The Harms procedure is the most common implant construct and is shown in Figure 1. However, the Harms procedure requires screws to be placed in high-risk areas of the first cervical vertebra, resulting in long operating times and significant blood loss.
A-Line Orthopaedics has developed the DC2, an implant designed to clamp on safe parts of the first cervical vertebra, eliminating the need for dangerously placed screws. Using rods, the DC2 can be connected to the fixation method of choice in the second cervical vertebra, completing the full construct. The DC2 allows more patients to benefit from the surgical treatment of odontoid fractures by enabling a safer, faster, and less invasive procedure.
Why Use Additive Manufacturing for the DC2?
Additive manufacturing offers several benefits for medical devices including optimal surface texture for bone ongrowth, the ability to make porous structures for bone ingrowth, and the unique ability to print a complete assembly in one manufacturing operation. The latter is key to reducing part count and avoiding the need for assembly operations with small complex-shaped components. The DC2 incorporates a ball and socket joint to hinge each jaw, which is printed in a single manufacturing operation.
A-Line has partnered with The Additive Design in Surgical Solutions (ADEISS) Center in London, ON to develop the additive manufacturing process needed to produce the DC2. ADEISS specializes in the development of surgical instruments, implants, and external prosthetics and was a natural partner for developing the DC2 implant
Manufacturing Challenge Encountered
The printed ball and socket joints must move freely and provide the required range of motion for proper implant positioning. However, early prototype builds produced ball and socket joints that had little to no motion after depowdering and removal from the build plate. Three different design changes were printed and evaluated, however, a root cause for the lack of motion could not be identified. The DC2 is a small device (25 mm x 20 mm x 12 mm) and is therefore difficult to study visually. The ability to determine the root cause was impeded by the inability to inspect the ball and socket joint in the as-printed state.
How Using X-ray CT Scanning Saved Time and Money
After three unsuccessful attempts to correct the limited motion of the ball in the socket, Expanse was contacted to perform diagnostic scans to identify the root cause of the binding. An X-ray CT scan showed regions where the ball and socket were fused, as shown in red in Figure 2. These fused regions occurred at unsupported regions (overhangs > 45°) of the part within the laser powder bed fusion build chamber. Armed with this information, design changes were made to minimize unsupported regions by adjusting both the orientation of the part during printing and the ball geometry. Printing the modified design resulted in free movement of the ball and socket joint with the required range of motion in the as-printed condition.
The primary advantages of using X-ray CT for qualitative investigative analysis include:
- 3D image allows 3D inspection. Problem areas can be found anywhere within the part and are not limited to a ‘lucky’ 2D cross section as with metallographic methods.
- Scan duration can often be less than 2 hours with no destructive sample preparation required. High quality diagnostic information is therefore available quickly.
Expanse Microtechnologies Inc. offers a full range of X-ray imaging solutions to support additive manufacturing, including metal powders, process parameter mapping, and part inspection. For more information about bringing X-ray CT into your development efforts, contact Craig Metcalfe at firstname.lastname@example.org.
A-line Orthopedics is a med-tech start-up developing new innovative products for applications in minimally-invasive orthopedic surgery. For more information about the DC2 contact Tim Lasswell at email@example.com.
The Additive Design in Surgical Solutions (ADEISS) Centre is a new development platform that makes it possible for researchers, clinicians and industry to design and fabricate working versions of medical devices, implants, surgical tools and intra-operative guides at a much faster pace, in a much more interactive and adaptive environment. For more information contact Matt Parkes at firstname.lastname@example.org.