The modern era of total joint arthroplasty began in the 1960s with Sir John Charnley’s development of total hip replacement consisting of a stainless steel femoral head articulating with a polyethylene acetabular implant, both secured to supporting bone by polymethylmethacrylate (PMMA) cement. The procedure has relieved joint pain and increased the quality of life for millions of people. Before the development of this hip replacement surgery, patients with debilitating degenerative arthritis of the hip were forced to either suffer with the condition or undergo hip joint fusion (called arthrodesis). Now, 40 years later, 10- to 15-year success rates close to 90% are being reported for total hip and total knee arthoplasty. The high rate of this early technique of fixation makes it the gold standard to which all subsequent methods should be compared.

Despite great strides in the development of better component designs, biomaterials, and surgical techniques, the life span of total joint-arthroplasty is limited by, among other things, the long-term mechanical properties of the implant and wear debris. Failures do occur, more frequently in young,active patients. The forces imposed on the joint make maintenance of implant fixation difficult; component loosening and migration are not uncommon. High joint reaction forces also produce relatively high frictional forces at the metal-plastic interface. Over time, frictional wear debris, both metallic and polyethylene, elicits biologic responses that resorb bone and may further compromise implant stability. Improving the fixation and wear characteristics of total joint components is a major focus of orthopaedic research.

The clinically significant loosening rates of implants, especially in younger, active persons, have led many investigators to pursue methods of alternative fixation. New biomaterials and innovative designs are two promising approaches which will improve this type of fixation. The loads imposed on bones and joints are dramatic as a result of the mechanical disadvantage under which they function. Forces at the hip can easily exceed fivefold body weight. Modification of the load transfer between joint components after total joint replacement therapy is also believed to cause stress shielding, a mechanism by which bone tissue adapts to mechanical loading in a negative way that ultimately leads to bone resorption and subsequent implant loosening. Historical data on partial joint implants for the femoral head and the tibial plateau provide evidence of such a mechanism.

Noteworthy is the fact that knee replacement surgery is performed on more than 250,000 Americans annually, followed by total hip joint replacement (>350,000), and around 700,000 spinal fusions. Yet less technology is brought to bear on this issue than on the development of common household appliances. As a whole, more engineering analysis goes into the washing machine in everyone’s home than into the artificial joints implanted in people. This may explain why the fixation of orthopedic implants has been one of the most difficult and challenging problems. As younger, more active patients are diagnosed with joint osteoarthritis, the restricted life span and functional limitations of artificial joints are becoming an increasing concern for the medical community.  The average age of a patient needing a lumbar disc replacement is about 35 years. It has been estimated that an individual takes 2 million steps per year and bends 125,000 times; therefore, over the 50-year life expectancy of the artificial disc, there would be over 106 million cycles. This estimate does not even include the subtle disc motion that occurs with the 6 million breaths we each take per year. Thus, artificial joint components should be both strong and durable. Adding to the problem are high complication rates for repeat surgery.  If revision surgery fails, alternatives include joint fusion, which does not permit the knee to bend, or amputation and fitting with a prostheses.

Due to increasing life expectancy and our elderly population, expected to double in the next 20 years, clinical problems such as osteoporosis and osteoarthritis are expected to topple our health care system. Considerable improvements have to be made in total joint replacement surgery and joint reconstruction to increase the longevity of such joints, reduce the number of revision surgeries and attributed risks, and subsequently reduce costs to make these types of surgery available to everyone. Revision surgeries are associated with a high mortality rate, especially in the elderly population. New approaches have to be identified in implant fixation, load transfer between joint components, and material properties. In addition, gene therapy in combination with tissue engineering may allow re-engineering of joints altogether to eliminate joint replacement surgery in the first place.

There are numerous reports in the literature on different designs that have been tested; however, there is limited information available on how the joints actually work and how load is transferred between joint components. This is particularly significant if a radically new design is sought to overcome current limitations.
 
 

The following outlines the main elements expected in the presentations and final reports, which will be an essential part of your overall grade. As part of the design process, several considerations have been taken into account; some of them are scientific and others are non-scientific considerations.

As part of the project, some teams will identify shortcomings of total joint replacement implants currently available in order to develop a novel concept for future generations of implants (odd team numbers). The other teams (even numbers) will need to gain knowledge on the biomechanics of the normal joint and on the development of the disease leading to total joint replacement with the aim of designing an ideal natural joint which may be realized through genetic manipulation.

This is a four phase project, in phase I (ends with presentation on February 9), the anatomy of the joint of interest, the biomechanics of the joint, the biomechanics of the diseased joint (even group numbers) or the biomechanics of the bone-implant complex (odd group numbers) with the associated problems are discussed and laid out in a presentation. With the second presentation (on March 2; due date of literature report) to mark the end of phase II, the teams will present the approaches previously taken by others to overcome the joint and implant problems discussed previously. The purpose of the literature review is for you to become expert in this particular field and to gain knowledge and ideas for overcoming current clinical problems. This is an individual effort and will be graded as such. The group midphase presentation on March 2 should also propose a strategy for the development of new implants (odd groups) or reengineered natural joints (even groups).  No solution is expected at this point, only hypothetical strategies are discussed. Feel free to use the audience during the Q&A time after your presentation for brain storming on your ideas. Consult separate handout for details.

During the third phase, the teams will work out concrete strategies for evaluating their novel concepts and a specific plan to test their hypothesis how these joints or joint/implant complex could be improved. These strategies are presented during the phase III presentation on Tuesday, March 28. 

The final phase (final report and final presentation) starts after the evaluation statement of phase III and includes presentation on the evaluation and final decision of a new concept in implant design or joint structure. Arguments need to be made for the design changes and effects on load transfer and longevity should be given in details. For example: instead of just listing that cartilage within the reengineered knee joint will have a vasculature network to allow tissue regeneration, you will need to provide some evidence that suggest that this will prevent damage accumulation in the tissue in the long run. Evidence could be in form of physiological behavior of similar tissue in the body, prediction of force distributions, etc. Critical self-evaluation is a must. In the example above, a vascular network may change the permeability of the cartilage, thereby reducing the load carrying capacity of the tissue. Therefore, other joint parameters will need to be modified. Especially for bone tissue, mechanical adaptation to changes in loads are a big concern and should be considered in the design aspect. It would be advantageous if your team keeps track of ideas and the discussion about them. This is useful information you can use for the final report and final presentation.

Your task for the final presentation: Imagine you are presenting your concept to a group of people to whom you are proposing a new design for investigative research. It is your task as a group to convince the audience that you have thoroughly searched the literature, are aware of current problems associated with your topic, and may have found a way of creating the ideal future generation of treatment. The main focus will be on your specific anatomic region; however, you need to show how it fits into the overall concept.

You are expected to present how you implemented different design considerations in your concepts and how you introduced an evaluation techniques to select you favored design, including a qualitative justification. Provide sketches (preferred 3D rendered images) of your designs and show how it is implemented in the overall design. Keep in mind that we have IronCad 3D modeling software installed at all PC's in the MUD lab, and that manuals are available in Keck 124 (Laboratory of Dr. Liebschner). You also have the option of numerically simulating the load transfer through your model to quantify improvements. A tutorial on how to generate a finite element model and conduct a finite element analysis from IronCad renderings in currently in preparation. In addition, through the School of Engineering you now have access to a 3D color printer with which you can fabricate a three-dimensional model of you concept. Please take a look at:
www.zcorp.com/products/printersdetail.asp?ID=2

Your task for the final report: The report should present critically the subject of the papers selected (strengths, weaknesses, comparison of approaches described, etc.). The main objective of this exercise is for you to become an expert on that topic. The knowledge that you gain through this exercise will be a necessary asset to your group in order to succeed with your project.

Specifically, what we expect is:

Final Report

1. The report should include a general introduction and discussion section.
2. Explain the need for a new/different design (justification of project).
3. Summary of each design consideration (literature review).
4. Details on the concept selection based on quantitative evaluation.
5. Explain details for your selected new concept.
6. Details on the evaluation techniques used to appraise your new and old concepts.
7. Report in the style of a formal proposal to a venture capital firm.
8. Figures and tables are to be at the end of the article.
9. The length of the report should be between 15 and 20 double spaced pages, not including the title page and appendices. Figures and Tables should be included in a separate appendix.

1. All members of the team will take part in the presentation.
2. The presentations will be on Tuesday April 25 and Thursday 27. There will be between two and three presentations per class.
3. Plan for 30 min actual presentation time and 5 min Q&A.
4. The introduction should contain information on the epidemiology of the problem at hand and its expected growth
5. The main section needs to include information on solutions and approaches already published in the literature, and drawbacks and features of previous designs. This part should be equivalent to a summary of the literature reviews.
6. The main section will also introduce the new concept and its advantages in all details.
7. The conclusion should contain a critical evaluation of the design and how it compares to existing implants or the natural joint.

Presentation Evaluation Rubrik: Presentation Rubrik