The importance of patient outcomes is the highest priority for surgeons when selecting the best course of action, and the best implant suitability for their patients. In complex cases such as tumor surgery where large bone mass needs to be removed, or for trauma cases where there is significant damage to the bone, the decision of what will best suit the patient can be a difficult one, as off the shelf implants do not always offer the best solution.

So what alternatives are there for surgeons and their patients? One of the few options available for these difficult cases is the development of patient-specific or personalized implants, and New Zealand based medical device design and manufacturing company Enztec, has been providing this alternative to off the shelf implants for over a decade.

“We have developed many personalized implants which have produced great outcomes for patients”, says Mr Paul Morrison, Co-founder of Enztec Ltd. “Major pelvic reconstruction, knee revision, cervical spine and cranial maxilla facial implants are just some of the areas we have been involved with.”

While Enztec has been developing custom implants for more than a decade, advances in technology have meant the company has recently partnered with Colorado based Medical Modeling to contract out the manufacturing of some of the more complex implants which cannot be achieved through traditional machining.

Medical Modeling uses the revolutionary electron beam melting (EBM) process which is well-suited to one-off manufacturing for personalized implants.

So what is EBM?

EBM is a manufacturing technique that has been used for a number of years but with advances in computer software has become a powerful tool for creating implants. The process can create extremely strong pure titanium, titanium alloy and cobalt chrome parts with extremely complex geometries.

An EBM machine works by importing data from a 3D CAD computer model and puts down successive layers of powdered material to build up the model. These layers are fused together using a computer controlled electron beam.
In addition to supporting extremely complex, organic shapes, EBM is cheaper and faster than traditional methods such as forging or machining which are better suited for larger volume runs.

How does the personalized implant process work?

The process for getting a personalized, or patient specific implant developed is relatively simple for the customer. While each project depends on the complexity of the case the process typically follows a simple all-digital process.

CT scan and modeling
The patient’s CT scan data is converted into a file compatible with the FreeForm 3D modeling system. The files are cleaned to remove scatter artifacts present due to any existing metallic implants in place.

3D Modeling
The personalized implant development team at Enztec works extensively with the surgeon to establish the surgical objectives and issues affecting the design of the implant such as age, weight, and bone condition. The team also discus other requirements such as the surgical approach, associated implants that may be used in conjunction with the personalized implant, expected outcomes, and any special devices that may be required.

Design
The design of the 3D model requires anywhere between 1-3 weeks depending on the complexity of the case, and the number of reviews needed by surgeon.
The design work requires extreme precision, a highly skilled technician and a deep understanding of anatomy as well as fluency with the software systems used.

Review
In most cases the team at Enztec email or FTP images of the 3D model of the implant to the surgical team as this speeds up the process. In some cases, the dialogue takes place via conference call or web-based review. This way, changes can be made immediately and the physical distance of the team in New Zealand does not affect the project.
A bio-model can be created if the surgeon requires a physical model of the proposed implant prior moving forward with manufacturing.

Manufacture
The implant is manufactured using traditional machining or in the case of more complex implants Enztec use the services of Colorado based Medical Modeling’s Electron Beam Melting technology.

Finishing
The custom implant is finished using machining and additional work such as threading fixed-angle screw holes to accommodate locking screw fixation are also completed. Being an ISO 13475 company, Enztec is also able to clean and package the implant for delivery to the hospital for sterilization and use in surgery.

Case Study

A 70 year old female’s (Patient A) quality of life was being significantly compromised by increasing levels of pain from a major pelvic failure.

Patient A had a portion of her hip intact, but the acetabulum had been previously revised. While the stem was her original bone structure, it showed some sign of osteolysis.

Orthopaedic Surgeon Dr Paul Armour said she was grossly disabled as a result of the dislocation of her old hip replacement into the pelvic area and it was potentially dangerous, particularly in terms of salvaging the situation.

Patient A could no longer weight bear was confined to crutches. The basic objective was to get the woman who was in considerable discomfort and largely house-bound, mobile again.

The Process

CT data was taken and fed into the development process, along with Dr Armour’s assessment and surgical objectives. A computer model of the implant was developed and a solid bio-model of the patient’s pelvis was produced for the surgeon’s approval.

From these specifications Enztec worked with Medical Modeling in Colorado, USA to grow the personalized implant using Electron Beam Melting.

The result is a very specific implant that can only fit the patient in question, and is likely to fit more neatly with the anatomy than a traditional implant.

The Outcome

The personalized implant allowed the surgery to be completed in half the anticipated time. Having something that conformed to the patient’s anatomy made a potentially technically difficult procedure into something much easier.
The scheduled six hour surgery was completed in three. Dr Armour said he believed the alternative trying to use an off the shelf would have been much harder. All the difficultly has been taken away because the implant had been carefully engineered.

“Surgery involves a lot of careful preparation, skilled staff, and the correct equipment,” Dr Armour said. “We staked our plan with Enztec in this case, and it worked.”

The positive outcome for Patient A was achieved. She is walking around, she has no pain, and she’s over the moon.
As this case illustrates, personalized implants can offer surgeons and patients a better alternative to off the shelf implants for those difficult cases. With the use of the EBM technology and the ability to work within short timeframes customized implants also offer a cost competitive option.

“Custom implants have always been an extremely emotional and demanding component of our business. Our partnership with Medical Modeling has enabled us to consistently increase the complexity, reduce the lead time, and positively influence the overall cost of implants,” Morrison said.

“Orthopaedic surgery is complex, challenging and not always predictable. Initiatives like our personalized implant service can make some contribution to making that process a little smoother.”