Life on the Edge: CAD Design at the Musculoskeletal Transplant Foundation

ENGINEERING.com speaks with the Musculoskeletal Transplant Foundation to learn how the organization uses Solid Edge to design and optimize spinal spacers made from donated human tissue for spinal surgeries.

As sensitive as it is surprising, the work of the Musculoskeletal Transplant Foundation (MTF) is an inspiring demonstration of the good that engineering can do on a very personal, human level.

MTF is a not-for-profit organization with a mission to save and heal lives. The organization collects musculoskeletal tissue (typically bone, soft tissue, tendons and skin) from donors—an incredible gift from recently deceased patients and their bereaved families and one that MTF is determined to put to best use, not only for the benefit of patients but also out of respect to the donors and their families.

MTF began 30 years ago when access to donated human tissues used in orthopedic surgery was extremely limited.  At that time, spine surgeons typically used a patient’s own hip bone for spine fusion surgery —the procedure used to remedy degenerative disc disease. The problem was that the patient’s hip was often more painful than the spine surgery itself.

Tissue banks like MTF offered an alternative – donated human tissue that could be used to treat a patient without affecting another part of the patient’s body. In the 30 years of MTF’s existence, they have received tissues from more than 115,000 donors, resulting in the provision of over 7 million tissue grafts to patients throughout the US and abroad.  More than 50% of the tissues provided by MTF are used in spinal surgery; many are machined to fit specific anatomic needs of each patient.

Ray Ferrara is Director of Engineering at MTF and is accustomed to fielding questions about where engineering fits into a tissue bank. “The product development cycle starts with the conceptual phase—a call from a surgeon perhaps,” explained Ferrara. “That’s where our engineering begins.”

And that engineering is done in Solid Edge, the 3D CAD platform that has allowed MTF to use the precious donated tissue it receives only when the final design of the allograft has been agreed upon. Ferrara continued, “The visualization side is where Solid Edge has really helped us. We’ve been able to send over solid models to the surgeon, and we’ve even been able to do some 3D printing as well, which has been great.” Having a solid model helps the surgeon to make sense of the designed part and to judge its suitability.

The design side includes the development of tools and fixtures needed on MTF’s CNC equipment, as well as the design of the product itself. Simulation tools within Solid Edge are important, even when it comes to moving the CAD into CAM in preparation for the machining and necessary tooling. “We need to get the process to a good 90 percent plus of exactly what we want it to do before we bring the tissue into the room—that is very important for us. Only when we are at that stage do we finally go through and machine the bone.”

A further complication in this process is that no two donors are alike. Everyone has different sized bones, and this affects the size of the grafts that can be prepared. Creating a larger shape from a smaller bone doesn’t work, so MTF has developed a bone assembly method.

“It’s just like woodworking,” claimed Ferrara. “We’ve got patents on these assembly techniques of bone. We’ll actually take multiple pieces of bone and slide those together through dovetails.”

On top of that they make pins or dowels to fit through drilled holes to stop the dovetail pieces from moving apart once implanted in the spine. These parts are made on 30 custom-made CNC machines in cleanrooms. Regulations stipulate that only one donor can be processed at one time to avoid cross-contamination.

An exploded view of an allograft spacer used in spinal surgery showing how the separate parts fit together. (Image courtesy of MTF.)

An exploded view of an allograft spacer used in spinal surgery showing how the separate parts fit together. (Image courtesy of MTF.)

Creating assemblies maximizes the resource offered by a donor, as it minimizes waste and allows as much of the bone to be used as possible. An example is spinal spacers used in spinal fusion surgery, and MTF makes eight sizes of them ranging from 5 mm to 12 mm. Sometimes it is impossible to make a complete bone graft from one piece of bone, but we can stack two or three pieces to achieve the required size. “It’s a unique process of assembling bone to truly meet the surgery needs at the end,” said Ferrara.

Beyond its use to design these parts, Solid Edge gives surgeons the freedom to customize the bone graft—perhaps, for example, they want a special configuration or a larger hole through the middle. Doing this up front in the CAD environment both saves time and prevents potential waste of donated tissue.

During design of the bone graft and the migration to processing, Solid Edge has the interesting feature of assembling the processing tool kits that the processing technicians use. These kits include the tools and fixtures that mount onto the CNC equipment that machines the bone. These components all need to be steam sterilized and taken into the cleanroom by the technicians, who are not allowed to lift more than 40 lb. Thus, by adding physical properties to the CAD, a virtual weight can be determined to ensure that the kit meets its ergonomic requirements.

The metal tools are illustrated in KeyShot to speed up the CNC setup process until the actual metal parts are made. (Image courtesy of MTF.)

The metal tools are illustrated in KeyShot to speed up the CNC setup process until the actual metal parts are made. (Image courtesy of MTF.)

A further capability is the ability to create photo-quality renderings. MTF uses the KeyShot plug-in for Solid Edge to illustrate all of the mechanical (metal) tools and fixtures for CNC setup and insert them into Work Instructions to keep the process moving, while the actual metal parts are out for fabrication.

Setup instructions make it possible to prep the CNC while the metal parts are in the process of being made. (Image courtesy of MTF.)

Setup instructions make it possible to prep the CNC while the metal parts are in the process of being made. (Image courtesy of MTF.)

In the past, MTF had to wait eight weeks for the metal tools and fixtures to be fabricated, then take pictures of them and insert them in Work Instructions. Creating the Work Instructions in parallel with actual tooling/fixturing fabrication has saved two months on projects. MTF also uses KeyShot to send an illustration of its bone concept to a surgeon for review, so they can ‘see’ realistic interpretations of the design.

The same allograft spacer assembled and rendered in KeyShot. (Image courtesy of MTF.)

The same allograft spacer assembled and rendered in KeyShot. (Image courtesy of MTF.)

It is further evidence of the importance of Solid Edge, not just for the efficiency it provides to MTF as an operation, but also because of the sensitivities involved in dealing with tissue from over 400 donors each month. “You really have to think about it at the end of the day,” added Ferrara. “It’s not stainless steel; it’s not aluminium; it’s not titanium. Someone has decided to be a donor in order to help other people. We’re helping 400,000 patients every year, but we never want to go back to one family and say, ‘Hey, we were not able to use your loved one’s gift  because we had a problem prototyping.’ By using all the design tools and capabilities up front, we really try to fulfil a family’s wish to make a difference.”

Using all of the capabilities within Solid Edge to do the design, the simulations, the setup and analysis, MTF has been able to achieve this goal of making the most use of that donated gift. “Each donor has the capability of helping more than 75 people,” concluded Ferrara. “It really is amazing. I’ve been honored to meet donor families who lost a spouse, a brother, a sister, a child. They say it’s so rewarding that their loved one has been able to help other people.  It doesn’t lessen their loss, but they’re proud of their loved one’s legacy.”

Learn more about organ, eye and tissue donation and register today at DonateLife.net.

Siemens PLM has sponsored this post. They have no editorial input to this post. All opinions are mine. —Tim Fryer