Excelen has a long history of research to improve the treatment of bone fractures. At Hennepin County Medical Center in Minneapolis, Dr. Ramon Gustilo was founding chairman of the Department of Orthopaedic Surgery. Currently, Drs. Richard Kyle, David Templeman, Andrew Schmidt, Thomas Varecka, Patrick Yoon, and Jonathan Haas treat patients at HCMC with complex orthopaedic trauma. This relationship with patients and physicians creates a close, productive, and crucial connection between our laboratory work, development of improved devices and techniques, clinical outcome studies, and patient care. Our research and development is well grounded clinically.

Much of the laboratory’s trauma research is based on the use of segmental bone defect and closed fracture models for studying the efficacy of osteogenic agents in the presence of factors—infection, diabetes, steroids, and nicotine—that are known to clinically impair fracture healing. An ongoing clinical study of the use of platelet concentrates with autologous growth factors is exploring this method of providing growth factors to a site of injury.

The Orthopaedic Biomechanics Laboratory partners with surgeons and start up funding in the development and evaluation of a novel method of monitoring, preventing, and treating compartment syndrome using tissue ultrafiltration. This is currently in clinical trials and has received significant funding from the USA Army as a way to improve treatment of wounded soldiers. The treatment of hip fractures has been addressed by laboratory studies that determined the sliding characteristics of second-generation intramedullary nails and the usefulness of calcium phosphate cement in helping stabilize comminuted intertrochanteric fractures. In an attempt to reduce radiation exposure, surgical time and morbidity the laboratory collaborated on the design and development of an innovative intramedullary nail and flexible shape memory alloy drill that drills interlocking screw holes from within the nail rather than through the overlying skin and muscles.

A prospective randomized clinical outcome study on intramedullary nails inserted with and without reaming for open and closed tibial fractures was complemented by a laboratory study on the relative stability provided by these two competing treatments. Patient care was directly, efficiently, and positively affected.

Excelen’s involvement with total joint replacement began with Dr. Ramon Gustilo and Dr. Richard Kyle’s development of the BIAS hip replacement system. They conducted a controlled FDA study, resulting in the first FDA approved hip implant system for non-cemented use. Dr. Ramon Gustilo’s development of the Genesis I total knee system in the early 1980s resulted in one of the most popularly implanted knees for the last decade. The Reflection acetabular cup was the first on the market to tackle the problem of “backside wear” by polishing the inner surface of the metal cup, a practice that is now widely implemented. Development and evaluation work with a variety of implants and instruments continues unabated, in, association with the Excelen Orthopaedic Biomechanics Laboratory.

Most patients experience excellent results with hip and knee replacement surgery, and have one of the highest quality of life improvements per health care dollar spent for a major surgery. Unfortunately, if the implants do fail, their revisions have been much less successful. Due to the large number of patients having implants, and their longer life expectancies, the number of complex revision procedures is increasing. The ideal locations for revisions to be performed are specialty referral centers like HCMC. To meet the large and growing need for improved surgical technique and implant options, Excelen is investing in research in this area, much of it with NIH support.

We have used finite element modeling and statistical design of experiments to study the effect of design features of hip replacement acetabular components on articulating wear. A three-dimensional radiographic technique was used to measure wear between total hip arthroplasty components as function of the design and type of fixation (i.e., all-polyethylene or metal-backed cups with cemented or cementless fixation).

In addition to the articulating surfaces, wear is also generated at the interfaces between the components of modular implants—in particular between the backside of a polyethylene liner and its metal backing. This backside wear is a result of the gradual loosening of the modular locking mechanisms with repeated load over time. These wear particles, in addition to the unavoidable articular wear, can lead to increased osteolysis and subsequent increased component loosening and failure.

To address this issue, the stability of various locking mechanisms in commercially available metal-backed acetabular cups was determined as a function of the temperature and force of insertion, and under long-term cyclic loading. Excelen is developing innovative, second-generation locking mechanisms of polyethylene inserts to their metal backing based on shape memory alloys. In femoral components, a study was conducted to determine the effect of design features of Morse tapers on locking stability, which can affect subsequent wear and corrosion.

Adequate stability of the fixation of prosthetic components to bone must be obtained for a successful outcome of joint replacement. In vitro studies were performed to determine the stability of knee and hip replacement components as a function of various design and physiologic factors such as short sterms versus long sterms, osteoporotic bone versus normal dense bone, cemented versus uncemented fixation with packed allograft or autograft, and revision versus primary replacement.

The problem of infections is extremely serious with a high degree of morbidity, particularly when fracture fixation and joint replacements (implants) are involved. Bacteria are attracted by implants and colonize their surfaces, which complicates their treatment and eradication. Infection destroys bone, prevents fractures from healing, and causes joint arthroplasty components to loosen. In addition, there is evidence that the presence of an implant affects the immune system and its ability to fight off an infection.

The orthopaedic and infectious disease physicians collaborating with the Excelen Orthopaedic Biomechanics Laboratory are in the national and international forefront of the treatment of musculoskeletal infection. a serious, expensive, and life-threatening problem. The Musculoskeletal Sepsis Unit of Hennepin County Medical Center, directed by infectious disease expert Dr. Dean Tsykayam, is a multi-state referral center for orthopaedic infection. Drs. Tsukayama, Gustilo, Schmidt and Kyle have developed widely accepted algorithms for treating infections in hip and knee arthroplasty. These treatment protocols have been successfully implemented around the world.

This wide-ranging clinical activity is coupled with extensive laboratory research. A number of biochemical studies have been conducted to determine how the presence of an implant affects the immune system, rendering it less effective in combating an infection. Excelen has designed and fabricated the only mold that allows surgeons to customize beads impregnated with antibiotics for implantation at infection sites.