LINARES MEDICAL DEVICES (LMD)

 

 

            Linares Medical Devices (LMD) is an exciting medical company based in Auburn Hills, Michigan focused on the development of medical hardware made of specialized plastics.  The company has a long history of success in designing and manufacturing innovative solutions using plastics in various industries.   The company has long felt the light weight and excellent durability of plastics used to design high wear items would be ideal for artificial human joint applications. LMD has applied its engineering and design expertise to solving long-standing problems in orthopedic surgery. 

 

            Linares has teamed with highly regarded Beaumont orthopedic surgeons Perry Greene, M.D., a specialist in knee and hip replacement, and Richard Easton, M.D., a specialist in spine surgery, as well as Craig Ramsdell, M.D., a Beaumont anesthesiologist with a background in clinical research, to assist in the development process.  The result of this collaboration is over 40 patented products on a range of orthopedic hardware including prosthetic knee, hip, and shoulder joints, fracture fixation devices, hardware for use in spine surgery, process patents on new materials, as well as patents on several medical devices. 

 

            One of the most troublesome ongoing problems with artificial joints is they wear out and break, necessitating additional surgery following the initial replacement.  The Linares joints would last twice as long as conventional joints, which would save hundreds of thousands of patients the risk, pain, and inconvenience associated with joint revision surgery.

 

According to Dr. Greene, who has spent considerable time in studying the causes of total replacement joint failure, all artificial joints eventually produce small wear-related particles of plastic, metal, or ceramic from the repetitive rubbing of one surface against another.  These small particles are taken up by the surrounding bone and tissue, which leads to an inflammatory response in the body that eventually causes the surrounding bone to almost “melt away” or become reabsorbed, a condition called osteolysis.  This, in turn, leads to loosening of the joint, and increased wear, and in many cases fracture of the surrounding bone, which has become thinned and weakened.  Linares has solved this problem from two angles, first by developing new materials with better wear properties, and second, by changing the design to reduce friction and wear between joint components, and more closely mimic the natural human joint. 

 

            The new materials alone are something of a revolution; Linares’ proprietary materials are made from plastics that have been blended and alloyed with other elements.  This allows the best properties of both substances to be retained, while the undesirable properties are minimized.  This is similar in concept to the idea behind alloying steel with a small quantity of chromium and molybdenum to make a metal that is far stronger and more corrosion resistant than standard steel.  In metallurgy, small amounts of additives can have an enormously synergistic effect on the properties of the resulting metal.  These same concepts have now been applied to plastics Linares has developed, resulting in materials with the lightweight and elasticity of plastics, combined with the strength and durability found in metals and ceramics.  One further advantage with the use of plastic-based hardware for orthopedic surgery applications is that it is radiolucent, that is, it does not interfere with radiological imaging technologies such as Computed Tomography (CT), X-Rays, or Magnetic Resonance Imaging (MRI), important for better follow-up and evaluation after surgery. 

 

                        Linares’ ingenious new design concepts are just as innovative as the materials.  All modifications have been made with the goal of increasing the useful life of the joint.  To this end, the Linares team has carefully studied the three-dimensional curvature of the surfaces that contact each other (known as the articulating surfaces) and created a design that allows increased contact between the articulating surfaces to be maintained throughout the range of motion of the joint.  The result is that the wear of the joint is far more uniform because the load of each movement is spread over a much larger surface area.  This is in contrast to the situation in conventional joints where most of the load gets focused on fairly small, discrete points of the articulating surfaces, which in turn leads to the production of the wear particles responsible for causing osteolysis.

 

Another important innovation allows the normal lubricating fluid of the joint, called synovial fluid, to more completely cover the articulating surfaces, resulting in decreased friction and better wear characteristics.  And patients will love the new joints because they are designed to have the same range of motion as the normal human joint. 

 

The Linares team even has a design referred to as a “super knee”, which will allow for full-fledged athletic use and allows the athlete to return to action extremely quick.

 

The shoulder joint should prove to be very popular with patients based on its weight differential compared with conventional titanium joints, which cause patients to become fatigued when doing activities requiring them to reach above the level of their chest. 

 

            Normal bone is a living tissue, which is capable of remodeling and rebuilding itself continuously in response to the conditions it is experiencing.  Just as muscles become larger and stronger when subjected to the rigors of weightlifting, bone too becomes more dense, larger, and stronger in response to the stress of increased loading.  Thus, not only does a weightlifter develops large muscles, but also develops larger, thicker, denser bones.  The opposite occurs when bones are not stressed, that is, they become less dense, thinner, and weaker when they are not experiencing loads.  This is what happens to a limb that has been put in a cast for several months, or to astronauts who have spent several months on the space station.  The same effect also occurs in the long thighbone, or femur, following a hip replacement.  Commonly there is a loss of ten to forty-five percent of the bone mass in the bone surrounding the implant during the first years after total hip replacement.  This is thought to be due to the fact that the titanium implant that is cemented into the center of the femur is much harder and stronger than the surrounding bone.  Because this titanium rod is so hard and strong, the surrounding bone no longer has to work so hard to support the patient’s weight, and thus is unloaded.  This removal of stress from the bone by an implant is known as stress shielding, and leads to bone thinning and weakness, and can eventually cause the bone surrounding the titanium implant to break or significantly deteriorate.

 

            By better matching the strength and hardness of the implant with the natural bone, the loads will be more evenly borne between the implant and the host-bone.  The technical term for the strength and hardness of a substance is its modulus of elasticity.  A perfect match between the modulus of elasticity of the implanted joint material and that of the bone should act to decrease the amount of stress shielding on the bone, resulting in healthier, stronger bone, and greatly decreased complications from joint replacement surgery. 

 

Plastic based orthopedic hardware has just that advantage that is the modulus of elasticity can be adjusted so it matches the bone.  Furthermore, Linares has developed a method of transitioning the modulus of elasticity smoothly and continuously within a section of implant.   The articulating surface can be made softer and more elastic to mimic cartilage, while the bone segment can be made the same hardness as natural bone.  Again, by making the implant in the image of the natural joint, the Linares team has created a longer lasting and better performing product.

           

Although millions of patients have undergone joint replacement surgery, this number pales in comparison to the numbers of people who are affected by chronic back pain.  According to the National Institute of Health’s National Institute of Neurological Disorders and Stroke, Americans spend at least fifty billion dollars each year on low back pain, the most common cause of job-related disability and a leading contributor to missed work. 

 

Dr. Richard Easton, the Division Director of Spine Surgery at William Beaumont Hospital in Troy, Michigan and on the Linares Medical Devices team, compares the state of surgery on the spine to the state of joint replacement surgery forty years ago: “What we’re doing in spine surgery is, frankly, primitive, compared to what has been done in joint surgery”, says Easton.  He goes on to explain that most surgery on the spine is done to simply either remove pieces of disc material or bone to reduce compression of spinal nerve roots, or actually fuse vertebrae together to reduce motion and pain at one or more spine segments.  This is similar to the state-of-the-art in joint surgery decades ago, when fusing severely arthritic joints was one of the only options available to surgeons. 

 

            Unfortunately, spinal fusion surgery results in a loss of mobility in the fused section of spine.  Normally the spine is very mobile, allowing a high degree of bending and rotation.  Fusing vertebrae together causes extreme wear and tear on the vertebrae and discs above and below the area that was fused, as these segments must compensate for the immobile segment.  This, in turn, can lead to a new disc herniation, bone spurs, and narrowing of the spine (spinal stenosis).  Since a spinal fusion cannot be reversed, patients may be subjected to years of problems afterward.  Furthermore, spinal fusion recovery is long and painful, and ultimately close to a quarter of spinal fusion grafts do not successfully form, necessitating further surgery.  Worse, these operations will not alleviate pain and symptoms fifty percent of the time. 

 

            With that in mind, the Linares team has designed a device that will provide for decompression of spinal nerve roots and increased stability to a segment of spine, but will also allow motion of the spine to be preserved.  The best part is this is a dynamic device which may be adjusted even years after the initial placement, requiring only a small skin incision, and can be done in a few minutes the doctor’s office under only local anesthesia.  Because the modulus of elasticity can be matched to the vertebrae, and because segmental motion is preserved, vertebrae and discs above and below the operative level should not be adversely affected.  Also in the works is a disc replacement system that will be far less invasive and more effective than the limited and imperfect options available to surgeons today. 

 

Another large area of orthopedic surgery where Linares seeks to have an impact is in fracture repair.  When surgery is required to fix a broken bone, the current widespread practice is to screw titanium plates into the bone on either side of the fracture line to stabilize the bone for healing.  In long bone fractures, another technique is to drive a titanium rod down the length of the bone in order to stabilize the fracture from within.  It is not at all uncommon for these titanium plates to break, as well as cause considerable pain to the patient, necessitating their subsequent surgical removal.  Linares has patented an entirely new type of fracture stabilization system incorporating extremely thin, high-strength, lightweight, and low profile plates made entirely of plastic.  These will be fixed to the bone in a novel way, not employing traditional screws, and in such a way they can be easily removed if necessary.  Because of their thin, streamlined design, they should cause far less discomfort to patients as tendons, muscles, and nerves slide over them when compared to the bulkier titanium plates and screws in use today.  In addition, they can be placed through minimally invasive small incisions in the skin above and below the fracture, and slid along the length of the bone.  Furthermore, because they are made of plastic, they will not interfere with imaging by CT or MRI scanners. 

 

Perhaps one of the most important Linares innovations will prove to be the incorporation of antimicrobial substances into the matrix of the plastic implants.  Infected hardware, both in joint replacement and spine surgery, is one of the leading and most devastating operative complications.  Early tests of plastics with antimicrobial substances incorporated into them have been very promising, suggesting that they may provide a high degree of resistance to bacterial infections.  Because the only remedy for infected hardware is surgical removal and eventual replacement, hardware that is infection-resistant could prevent hundreds of thousands of operations annually, as well as save many lives, and billions of dollars.

 

Evidence of LMD genius for seeing solutions to mechanical problems in three dimensions is remarkable and very much in evidence all around the Linares development center in Auburn Hills.  The company demonstrates a complex looking apparatus for wear testing samples of their newly created materials.  When it came time to test the new materials, Linares was not happy with any of the available equipment on the market, so they constructed their own testing apparatus, machining its parts out of raw steel and aluminum.  The finished product resembles equipment from a German scientific instrument manufacturer.  Commercially available machines to do this type of testing could only test one sample at a time, and could only apply a ten pound load.  This one can test a dozen samples at a time, running them through a quarter million cycles over forty-eight hours, and apply a 600-pound load. This patented test machine is equipped with a microscope and digitization system to make minute measurements of the surface, to quantify wear. 

 

This testing apparatus is another indication of what is yet to come from this company; it is apparent that LMD is in for some stunning developments in the years to come. 

 

 

 

More information about Linares Medical Devices can be found by contacting Tom Bolz at tmb@gtco.us.