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Something shiny, something new: the human body is still revealing new secrets to scientists, keeping implant manufacturers on their toes.

What's in a knee?

A lot. In fact, the knee is one of the largest and most complex joints in the body, not in the least because it carries much of the weight of the human body and is subject to the impact of walking, running and jumping. The anterior cruciate ligament prevents the femur from sliding backward on the tibia (or the tibia sliding forward on the femur). The posterior cruciate ligament prevents the femur from sliding forward on the tibia (or the tibia from sliding backward on the femur). The medial and lateral collateral ligaments prevent the femur from sliding side to side. Two C-shaped pieces of cartilage called the medial and lateral menisci act as shock absorbers between the femur and tibia. Numerous bursae, or fluid-filled sacs, help the knee move smoothly. And those are just the basics.

Although what we call modern science grew in the 19th century and rapidly advanced to the stage at which we find ourselves today, scientists have existed as long as civilization has existed. The study of human anatomy began as early as 1600 B.C., which is the date ascribed to the ancient Egyptian medical text the Edwin Smith Papyrus. This document describes 48 surgical case studies dealing with injuries, fractures, wounds, dislocations and tumors. And yet, despite more than 3,600 years of anatomical study, we are still discovering brand new parts of human anatomy that have never been identified before.

Just two years ago in 2013, scientists discovered a brand new ligament in the human knee that had never been named before. Steven Claes, M.D., of the Department of Orthopedic Surgery & Traumatology, University Hospitals Leuven, Leuven, Belgium, is the lead author of the simply titled paper "Anatomy of the anterolateral ligament of the knee" that made global news in 2013 by finally naming the elusive ligament. The Belgian researchers named it the anterolateral ligament (ALL), and it is found at the anterolateral aspect of the human knee--i.e., the outside of the knee. The ligament itself was first observed in 1879 by the French surgeon Paul Ferdinand Segond, who is considered the founder of obstetrics and also was an expert in the human knee. He described the ligament as a "pearly, resistant, fibrous band," and since then, that piece of our anatomy has been variously referred to as the"(mid-third) lateral capsular ligament," "capsuloosseous layer of the iliotibial band" or now, definitively, the "anterolateral ligament." And as if it isn't enough that the biological sciences are still discovering parts of the human body in the 21st century, consider this: The 2013 paper that unveiled the identification of the ALL proposed that "further studies are needed to investigate its biomechanical function." In other words, we still don't fully know what the ALL actually does.

Mirroring the grand journey of the discovery of human anatomy, specifically the knee, is the journey of knee replacements. However, while the study of the knee is possibly thousands of years old, the man-made version is only about 40 years old, the first total condylar knee replacement being completed in 1974 (the very first knee implant was performed in 1968, but those hinged implants did not work very well and had high infection rates). History shows us that the pace of scientific advancement only gets faster, and within just 40 years, we find ourselves at the doorstep of a new era of knee implants: namely, customized implants. Implants can be customized by shape, such as with unique implants manufactured via 3-D printing techniques, or by biological compatibility--i.e., a knee "implant" made from an allograft technique to regrow damaged bone or cartilage in the joint. Of course, these are oversimplifications, because the ways a knee can be injured (and repaired) are as numerous as the range of parts found in the human knee itself.

The same trends apply to implants in the other major joints, such as shoulders and hips, as well as the spine. Biomaterials play a central role in the development, advancement and manufacture of orthopedic implants. The rapid advancement of materials, chemical and engineering technologies contributes to the rapid advancement of medical, including surgical implant, technology. Biomaterials falls broadly under metals, polymers and ceramics, and their job is to mimic the load-bearing and biological function of bones and joints. Titanium and cobalt alloys are common, and nitinol, a nickel-titanium alloy, is becoming very popular due to its notable shape-memory properties--i.e., it can undergo deformation at a certain temperature, but will return to its original shape when heated above its "transformation temperature." An innovative plastic called PEEK (polyether ether ketone) also has become very popular due to its mechanical and chemical resistance properties.

"The advancements in biomaterials and development of integrated orthopedic implants have been significant in terms of recent technological gains," John Ducaji, director of sales and business development for Ivyland, Pa.-based Vistek Medical Inc., told Orthopedic Design & Technology. "We are seeing a trend toward single piece implants that may combine materials like PEEK and titanium and we are also still seeing growth in coated implants."

Manufacturing Advancements

Advancements in materials and science that enable orthopedic implants to service a wider range of patients better must be accompanied by advancements in the manufacturing technologies used to create those implants. In explaining how complexly composed implants are becoming consolidated into easier-to-handle pieces, Ducaji noted that 3-D printing is playing an important part in this story.

"Design for manufacturability (DFM) collaboration with the OEM early in the process is critical to identify best manufacturing practices. The [recent] advancements in 3-D printing technology are interesting and we have been able to utilize some 3-D printed parts to help in early project planning for implants we are going to machine," Ducaji said. "Technology like that could really impact our industry and it will be interesting to see what happens with this technology within the next 5 years in the United States. While we [at Vistek] do machining right now, we often have some 3-D printed parts made early on in a development cycle. If an OEM comes to us with a project that they want to launch, we can get some 3-D printed parts made and get a head start on planning in advance of us having a part off the mill or Swiss machine. It allows us to get a head start on the quality side as well by, for instance, setting up whatever type of optics equipment we're going to use to measure those parts. It allows us to establish some kind of an early baseline because we have a physical part in our hand already before any machining begins."

One of the key considerations in orthopedic implants is customization. While allografts and autografts provide their own advantages in terms of very closely (or exactly) matching patient tissue, large implants like total knees or total hips shape and size and important. Many knee and hip implants come in standard, off-the shelf sizes that may or not be able to be shaved down to fit a particular patient. The ideal would be an exact match to a patient's joint, of which there are as many shapes and sizes as there are patients. 3-D printing, a.k.a. additive manufacturing, offers the possibility of creating individualized implants for each and every patient. This year, the first 3-D printed knee was implanted in a patient in Indiana. William Berghoff, M.D., a joint reconstructive surgeon at Ortho NorthEast in Fort Wayne, performed the surgery on a 70-year-old woman. The patient's first implant was an off-the-shelf model. Her second surgery resulted in an almost pain free recovery, much unlike her first. The 3-D printed, customized knee was the key, shaped to her anatomy so perfectly that her body adjusted to the new joint easily.

"It's crazy stuff," Berghoff said to "Inside Indiana Business" of the new capabilities of additive manufacturing. "It's taken us into that sort of space-age technology. This is the leading edge of something that's going to be the mainstay. If we have this conversation in five years, everyone will be getting this type of knee."

The manufacture of this 3-D printed knee started with a CT (computed tomography) scan through the patient's hip, knee and ankle. Software developed by Bedford, Mass.-based orthopedic device company ConforMIS Inc. then converted the two-dimensional CT data into a 3-D wax model of the knee before the degenerative disease set in. The implant then was built with 3-D printing from the ground up to be an exact fit to the patient's unique anatomical bone geometry.

"Advancements in additive manufacturing is something we are keeping an extremely close eye on as there are many benefits to construction geometry that would not otherwise be able to be fabricated by conventional manufacturing methods," said Andrew Thomas, Ph.D., director of operations for Triangle Manufacturing Company Inc.

The company's view of this miracle manufacturing technology, however, remains cautiously grounded.

"Although we are seeing huge strides in the accuracy and build platform, we feel that to be competitively priced, this method is still in its infancy for manufacturing purposes," Thomas said. "Additive manufacturing capabilities do align well with the needs of the orthopedic medical device community, enhancing product customization and enabling efficient, cost-effective production and delivery solutions."

Based in Upper Saddle River, N.J., Triangle is an engineering and contract manufacturing partner to the medical device industry and a provider of surgical implants and instruments, with an expertise in powered hand tools.

As Andreas Wenger, director of operations for manufacturer Precipart's mechanical components and assemblies product line in Farmingdale, N.Y., told ODT, manufacturing processes that recently were used only for simple, prototyping applications (such as certain 3-D printing techniques) have now advanced enough to be used appropriately in medical device manufacturing. And as much as additive manufacturing is advancing the medical device market in exciting ways today, other manufacturing processes are proving just as capable of offering important solutions to the questions posed by complex bone implant problems. Molding, for instance, is capable of producing very tiny, complex parts, with much greater load bearing capacities (important for orthopedic implants, as the entire skeleton is load-bearing by definition) than some 3-D printed devices.

"Precipart is usually involved in products that are just about market in exciting ways today, other manufacturing processes are proving just as capable of offering important solutions to the questions posed by complex bone implant problems. Molding, for instance, is capable of producing very tiny, complex parts, with much greater load bearing capacities (important for orthopedic implants, as the entire skeleton is load-bearing by definition) than some 3-D printed devices.

"Precipart is usually involved in products that are just about to be released to the market or already are available on the market and therefore new materials get to us a few years after you first hear about them in journals," explained Wenger. "But on the manufacturing side we see a lot of advancements. Techniques and processes that only two or three years ago were used for prototyping have reached a quality level that makes them viable for the production of medical products. One example would be the adaptive manufacturing technology laser sintering that is now used for patient-specific cranial implants. On the other hand, we see manufacturing technologies that are mainly used for other industries now making their way into the medical field. For example metal injection molding which has been used for small complex parts in high quantities for industrial applications for many years is now being used for tips of endoscopic instruments."

Driving Rapid Innovation

The force behind the storyline of advancement is, of course, people. The first discovery and identification of the various ligaments in the knee was done by a surgeon; fast forward thousands of years, and the first knee implant was constructed by an engineer. Today, any implant manufacturer will say the same thing--human resources are the ultimate key to driving innovation in design. Yes, technology is important, but all the ideas originate from creative minds and creative collaboration. Maumee, Ohio-based Hammill Medical Company has kept that notion at the center of its operations over the last 60 years it has been in business. A common practice in Germany, American manufacturing companies have slowly dropped apprenticeship programs over the decades since World War II due to a brain drain of workers who leave their home company after training. Hammill is proud of its tradition that was started by the current president John Hammill Jr.'s grandfather, however, and it has allowed the company to cultivate a strong pool of manufacturing professionals who remain faithful to the company.

Hammill explained to ODT that the company started with basic operations on implants such as grinding a knee or milling a particular feature onto the implant. Today, the company aims to be close to a one-stop-shop for implant OEMs, providing finishing, laser marking, laser welding and other full-spectrum services.

"Our customers' requirements are constantly expanding, and that requires us to have highly skilled people capable of implementing and managing new processes and technologies," Hammill said. "One of the things we've always done that's really paying off for us is our four-year apprenticeship program that's both state and nationally accredited. In that program our employees will take classes at a local community college, and then in conjunction with their machine time they get a nationally recognized journeyman's card. Without developing that kind of talent, we wouldn't have the ability to employ these new practices or to absorb the new technologies we have integrated into our manufacturing processes."

"It's not as much part innovation, which is what you usually think of when you talk about innovation, but manufacturing innovation," added Stan Pearson, vice president of sales and marketing for Hammill. "We're constantly looking at new ways to do things faster, more accurately, with less cost. There are a lot of new options out there in the future such as 3-D printing, and we evaluate those as well, looking for when they will become a cost effective solution. One thing about Hammill management is that they don't hesitate to invest in new capital when they find it can be productive. Sometimes you can't justify it just yet, but it may be a technology we want to learn about and move forward on. You have to stay current because the market moves quick."

Hammill, like its peers, is having to produce smaller, more complex parts with traditional manufacturing processes such as turning, milling, electrical discharge machining (edm), grinding polishing and more. Certainly, additive manufacturing can handle complex geometries, but as orthopedic implants advance and become more complex, so too must the manufacturing processes that make those implants have to advance alongside them. Hammill has close to a hundred machines that perform a variety of differentiated functions, including several types of CNC (computer numerical control) grinders, screw machines, machines that can turn and mill simultaneously and dozens more

"The biggest factor affecting Hammill is that the complexity of the parts is increasing whether its materials, or part-specific features and tolerance," said Hammill. "We are seeing manufacturing applications with requirements for higher spindle RPM (revolutions per minute), smaller part features, and tighter tolerances work which requires us to employ technology that can start and finish the part in one operation. When you move a part between machines, both processes have to be validated. To consolidate handling you need to have equipment and technologies in place that can do extremely high accuracy work in multiple orientations. We employ equipment with machining spindles as high as 60,000 RPM so we have the capability to machine the small and complex part geometries in a single validated process."

Ligament Legacies

"Given its anatomical location at the anterolateral edge of the knee, we hypothesize that the ALL functions as a stabilizer for internal rotation," wrote Claes et al in their aforementioned mapper on the anterolateral ligament. However, they continued in the conclusion, "Given its suggested role in common knee instability patterns such as the pivot-shift, the precise anatomical knowledge of this enigmatic structure delivered by this study could be highly relevant for clinical practice. However, further research is needed to establish the function of the ALL and to determine its role in clinical knee injuries."

We are currently bearing witness to the birth of new possibility for orthopedic implant innovation and manufacture. Allentown, Pa.-based Good Shepherd Rehabilitation reported that during knee replacement procedures, surgical exposure while inserting the knee prosthesis also may damage the ligament. Following surgery, the rehabilitation center reports, many patients describe their knee "giving way" while walking, running or stair climbing, which is speculated to be caused by an ALL injury. Another study led by Claes in 2014 found that almost 80 percent of patients with ACL (anterior cruciate ligament) injuries showed ALL damage as well. And very soon after Claes' original publication, other articles were quickly published that examined the effect of surgeries including implant procedures on the newly discovered ligament. Camilo Partezani Helito, M.D., and colleagues' December 2013 Orthopaedic Journal of Sports Medicine article, for example, found in a study of 20 cadavers that ALL is consistently present in the anterolateral region of the knee, leading to complications in surgeries and procedures including implant placements. Despite advancements in surgical techniques, some patients still have residual anterolateral rotatory laxity after reconstruction, the paper observed.

Currently, the National Institutes of Health names posttraumatic arthritis as one of the causes for the need for a knee replacement. Post-traumatic arthritis is a form of osteoarthritis that may occur after a knee injury such as a fracture or ligament tear. These kinds of injuries can cause inflammation and affect the alignment of the knee, leading to cartilage damage over time. Because of this, a ligament injury suffered earlier in life can cause arthritis at middle age or later. As such, a new, previously misunderstood or ignored ligament's appearance in the knee presents a new path to understanding why an injury happens and how a patient can best be served by an implant.

Further study into the newly discovered ALL has the potential for providing a better understanding of injuries that sometimes lead to the need for knee replacements, or whether the injury of the ALL itself could have major implications leading to the need for an implant. For instance, Robert F. LaPrade, M.D., Ph.D, complex knee and sports medicine specialist of The Steadman Clinic of Vail, Colo., predicts that it is only over the next five to 10 years that studies will show reliable information on whether reconstruction of the ALL will benefit the 10 to 15 percent of patients who experience unsatisfactory results following an ACL reconstruction. Certainly, these things take time. But not as much time as they used to.

Ranica Arrowsmith * Associate Editor
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Author:Arrowsmith, Ranica
Publication:Orthopedic Design & Technology
Date:May 1, 2015
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