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Total Hip Joint Replacement

National Institutes of Health
Consensus Development Conference Statement
March 1-3, 1982

Conference artwork, a diagram of an artificial hip replaced into the hip joint.

This statement is more than five years old and is provided solely for historical purposes. Due to the cumulative nature of medical research, new knowledge has inevitably accumulated in this subject area in the time since the statement was initially prepared. Thus some of the material is likely to be out of date, and at worst simply wrong. For reliable, current information on this and other health topics, we recommend consulting the National Institutes of Health's MedlinePlus http://www.nlm.nih.gov/medlineplus/.

This statement was originally published as: Total Hip Joint Replacement. NIH Consens Statement 1982 Mar 1-3;4(4):1-11.

For making bibliographic reference to the statement in the electronic form displayed here, it is recommended that the following format be used: Total Hip Joint Replacement. NIH Consens Statement Online 1982 Mar 1-3 [cited year month day];4(4):1-11.

Introduction

A Consensus Development Conference was held at the National Institutes of Health on March 1, 2, and 3, 1982, to seek a position on issues involving total hip joint replacement (THR).

At NIH, Consensus Development Conferences bring together investigators in the biomedical sciences, practicing physicians, consumers, and advocate groups to provide a scientific assessment of technologies, including drugs, devices, and procedures, and to seek agreement on their safety and effectiveness.

On the first two days of the meeting, a Consensus Development Panel and members of the audience heard evidence presented on the following key questions:

  • What are the indications and contraindications for total hip joint replacement?
  • What are the current scientific principles guiding selection of materials, devices, and procedures for total hip joint replacement?
  • What is the short-term and long-term prognosis for medical status and functional activity after total hip joint replacement?
  • What are the medical and surgical complications of total hip joint replacement?
  • What are the problems related to revision surgery for total hip joint replacement?
  • In what directions should the science base and techniques of total hip joint replacement be advanced?

 

Members of the panel included physicians and scientists representing biomedical research, diagnostic radiology, orthopedic surgery, biomechanics, biomaterials, clinical medicine, rheumatology, epidemiology, biostatistics, public health, hospital management, medical rehabilitation, family practice, consumer interests, and other fields relevant to a discussion of THR.

What Are the Indications and Contraindications for Total Hip Joint Replacement?

THR is a relatively common procedure, with an estimated 75,000 THR's performed on 65,000 patients annually in the United States. About 60 percent of the procedures are performed on patients over 65 years old, with another 25 percent performed on patients between 55 and 64 years old. The most common reasons for THR are osteoarthritis (60 percent), fracture-dislocations (11 percent), rheumatoid arthritis (7 percent), aseptic bone necrosis (7 percent), and revision of previous hip operations (6 percent).

Medical Management Programs

Most THR's are performed on patients with arthritis of the hip. Before considering such patients for THR, a comprehensive medical program should be undertaken. Current therapeutic modalities for hip arthritis should consist of a carefully coordinated, multidisciplinary effort. Factors affecting therapeutic decisions include precise diagnosis, stage and extent of arthritis, pathogenesis of symptoms (inflammatory or mechanically induced), and the age and expectations of the patient. Short- and long-term goals include relief of pain and stiffness and restoration (or maintenance) of function.

General therapeutic approaches to arthritis of the hip include patient and family education, proper rest and protective devices (canes, crutches, walkers), elimination of suspected aggravating factors (obesity, over-exercise), utilization of accepted physical therapy programs designed to relieve pain, maintenance and restoration of joint motion and muscle strength, and advice to patients regarding aids for daily living. Sexual counseling and discussion with vocational advisors are integral to this comprehensive program.

Drug therapy is designed to reduce pain and minimize the consequences of inflammation when present. Whereas no specific agents are available for clinical use to prevent, retard, or reverse osteoarthritis, remittive agents such as gold and D-penicillamine have been used successfully to treat many patients with rheumatoid arthritis.

All pharmacologic agents currently available for use in arthritic disorders have potential side effects and require careful monitoring. Many patients can be managed successfully for long periods of time using these modalities.

Patient Selection

Candidates for THR are those patients who have disabling pain and functional limitation of the hip(s) in spite of adequate medical therapy. Symptomatic arthritis and major disruption of the anatomy of the hip are the usual indications. The use of THR in patients with malignancy must be weighed against considerations of life expectancy and possible alternative procedures to relieve pain. Failed previous hip surgery also constitutes an indication.

The relative contraindications of youth, obesity, and neurological disease must be weighed against the disability caused by the clinical problem. Aside from medical emergencies such as myocardial infarction and respiratory failure, or the presence of active hip infection, there are no absolute contraindications.

Evaluation by the orthopedic surgeon will allow consideration of options such as THR, nonoperative treatment, delayed operation after modification of a relative contraindication, or alternative operations such as arthrodesis, femoral osteotomy, pelvic osteotomy, resection arthroplasty, and hemiarthroplasty. The effects of possible complications of the hip surgery must be considered.

The primary care physician and orthopedist should assess the emotional and mental capabilities of the patient and family and consider their expectations of and commitment to rehabilitation. When the hospitalization process overwhelms the mental, physical, or emotional resources of the patient, the operation may be a technical success but a practical failure.

Once the decision has been made to perform a THR, a comprehensive medical evaluation is indicated.

The ultimate decisions regarding management must be made after consideration of all these factors, realizing that there are numerous variables and very few absolutes.

What Are the Current Scientific Principles Guiding Selection of Materials, Devices, and Procedures for Total Hip Joint Replacement?

Design and Materials Considerations

The motion requirements for a THR are well understood and do not present serious design limitations. Data on hip implant forces are less well defined but are being generated by gait analysis and direct measurement using instrumented prostheses. Gait analysis is a combined experimental and analytical approach which uses measurements of ground reaction forces and body motions to predict the resultant hip joint forces. The predictive process is complicated by many unknown and currently unmeasurable muscle forces. Direct force measurements using instrumented prostheses in a few selected patients have emphasized the variations in hip joint forces that can occur with different activities.

Assessment of hip implant stress distributions are being used to study component fracture and permanent deformation, cement fracture, interface loosening, and stress-related bone resorption and remodeling. Stresses depend on joint loading and geometry, material properties and boundary (interface) conditions, and thus are influenced by implant design, choice of materials, and fixation techniques. The importance of these parameters can be evaluated by analytical and experimental techniques and their combinations. However, the development of truly optimized hip implants is impeded by an imperfect understanding of many aspects of the complex behavior of the hip implant structure. In particular, objective criteria of failure for the tissues are not available and the complicated clinical aspects of the procedure are difficult to describe.

Stress analyses can, however, add to an understanding of this complicated structure by quantifying and interrelating parameters and phenomena. Moreover, finite element methods can be used to predict objectively the mechanical performance of different devices on a relative basis. Finally, stress analyses can provide guidelines to assess consequences of design choices and surgical compromises. For instance, the relative contributions of parameters such as cement layer thickness, stem stiffness, stem length, and stem cross-sectional shape have been established and quantified.

The progress with stress analysis has not been such that design and manufacturing standards on geometries and dimensions are available at this time. No standards are used for dimensional parameters such as head size, although such standards might improve the potential for interchangeability. Manufacturers apply quality control related to the strength of the prosthetic components on an individual basis although the extent and uniformity of application is unclear.

Synthetic biomaterials used in current THR's include alloys such as the iron, cobalt, and titanium base systems; polymers such as polymethylmethacrylate and polyethylene; carbons; and ceramics. The evolution and application of these biomaterials have established an extensive base of knowledge on short- and long-term biocompatibility.

Alloy development for total hip prostheses has resulted in substantial improvements in mechanical properties. The traditional wrought stainless steel and cast cobalt-chromium-molybdenum alloys are being replaced in part by the wrought, hot isostatically pressed, or thermo mechanically strengthened cobalt base alloys, by chemical modifications of stainless steel, and by titanium base alloys.

The selection of biomaterials depends upon the physical, mechanical, chemical, and electrical properties related to biocompatibility. Laboratory methods for determining chemical analyses, static mechanical properties, and surface finish are well established for biomaterials in current clinical use. Dynamic measurements of properties such as material fatigue, friction, creep, wear, an biodegradation require further research and standardization to establish a complete series of quantitative correlations with clinical applications.

There is considerable evidence to support the concept that the materials used today in THR are highly compatible with human tissues. A certain degree of wear of those substances is inevitable but the degree thus far recognized has been minimal and therefore the debris accumulated in the surrounding tissues is very small.

Although sensitivity to alloy wear products has been suspected to produce loosening of the prosthetic implant, no evidence exists to confirm this suspicion. Small metallic particles and staining noted in tissues surrounding a hip prosthesis have produced neither neoplasms nor harmful tissue reactions. Allergic reactions to alloys have been suspected in some instances but the frequency has been low.

Surgical Considerations

Polymethylmethacrylate cement has been the foundation upon which the success of THR has rested. Its relative inertness, mechanical properties, and ease of applicability have guaranteed its popularity and wide acceptance. Its mechanical properties, different from those of the bone and metallic implant, serve as a buffer to dissipate the stresses to which the composite structure is necessarily subjected during the activities of daily living.

Experience has indicated that failure of the cement may be responsible for loosening of the prosthetic implants and the ensuing pain and disability encountered in a percentage of cases. There is strong evidence, however, that improved cementing techniques and prosthetic implantation developed during the past decade have reduced the incidence of complications related to failure of the acrylic material. Over 20 years of usage of the material have failed to reveal any evidence of carcinogenic or significant toxic effects. It's fragmentation--brought about by mechanical forces--has been thought to produce local tissue reactions and wear phenomena. Some concern exists regarding the possible degradation of the acrylic cement in vivo with time, and the resulting loss of it's mechanical integrity and supportive role.

Significant improvements in surgical techniques have resulted in an increased success rate with THR. In an effort to control the stresses on the bony and artificial structures about the hip joint, various surgical techniques have been developed. Barring specifically indicated correction of gross anatomic deficiencies, transplantation of the greater trochanter does not significantly benefit gait, but the osteotomy involved improves surgical exposure.

Proper implantation of the prosthetic components appears to be of paramount importance in the prevention of early as well as late complications. The preparation of the bony structures prior to the implantation must be carried out with considerable care and precision to insure the most desirable mechanical environment. Placement of the prosthetic components influences the biological environment of the adjacent bone and, therefore, its subsequent survival.

Since surgical technique may influence late loosening, this complication requires further study. The preservation or sacrifice of the subchondral bond is still a subject of controversy, although it is agreed that thorough coverage of the plastic implant and firm cementation of the parts are desirable.

Prevention of loosening of the femoral component seems to be enhanced by good cementing techniques, by removal of cancellous bone, particularly from the superior-medial aspect of the femur, and by the placement of the prosthesis in an attitude that guarantees an adequate cement mantel around it's stem. The long-term benefits of techniques used in the preparation of the femur and the insertion of the cement have not yet been documented, although there are indications that cement pressurization and bone cleansing are desirable.

Numerous surgical techniques and instrumentation have been developed to permit the reconstruction of the severely damaged acetabulum and proximal femur. Bone grafting for acetabular defects has made prosthetic replacement possible in many instances. Various metallic reinforcement rings have been developed to obtain greater stabilization of the prosthetic parts in difficult cases.

Considerable evidence exists to support the belief that the use of perioperative antibiotics and clean air operating rooms have reduced the incidence of infection to less than 1 percent.

Rehabilitation of patients who are candidates for THR can be expedited by a program of physical therapy prior to surgery. Rehabilitation processes should be individualized and appropriate for the patient's age and medical condition, surgical approach, and expected accomplishment of both short- and long-range goals.

Early postoperative care should provide a balance of rest and therapeutic regimens, with primary consideration given to restoring medical stability and accomplishing basic activities of daily living. Instruction in pulmonary exercises, proper positioning, and the use of vascular support for the lower extremities are examples of physical measures used. The progression of exercise and ambulation during this phase is geared to surgical considerations and to the individual tolerance of each patient. In-hospital care can be terminated when the short-range goal of independent ambulation with a suitable and stable gait is accomplished, and when the patient has learned appropriate dynamic and static strengthening exercises and can demonstrate the ability to function adequately in a home environment.

There is no question about the initial success of THR and the overwhelming benefits that this surgical intervention has brought to numerous people throughout the world. The operation is a major surgical undertaking, however, and should be performed in institutions which are appropriately staffed and equipped to satisfy the needs of the complicated as well as the uncomplicated procedure. A common factor associated with many late complications, such as loosening and component breakage, is outmoded surgical techniques. Therefore, it may be concluded that THR should be performed by orthopedic surgeons with special interest and expertise in this area and in hospitals where the operation is performed frequently and the necessary equipment and staffing exist. Continuing interdisciplinary education of the orthopedist and the surgical team concerning new techniques and developments is essential.

What is the Short-term and Long-term Prognosis for Medical Status and Functional Activity After Total Hip Joint Replacement?

THR, when done for incapacitating pain and dysfunction, is a procedure which gives a predictably excellent result in the vast majority of patients. Relief of pain and return to useful function can be expected.

Following hospitalization for 2 to 3 weeks, and several more weeks using walking aids and physical therapy methods, the usual patient can become reasonably independent in about 3 months. A gradual progression in improvement in strength, pain relief, and mobility can be expected during the next several months.

Complications, which adversely affect recovery and may alter an otherwise good result, can occur during the early postsurgical period.

The patient's activities after recovery should include all those involved in daily living--unlimited walking, driving a motor vehicle, dancing, sex, etc. To be avoided are repetitive activities which overload the hip, such as jogging, jumping, and racquet sports. Excessive hip flexion, such as squatting, should also be discouraged, but general physical fitness is encouraged.

The program for each patient should be individualized according to medical conditions existing prior to surgery. For example, the postoperative program will be altered by preexisting hip weakness, osteoporosis, and the condition of other joints.

Patients with THR should be followed according to a definite protocol. This includes at least a review at 1 year, 5 years, 10 years, and longer after the operation. This followup helps diagnose potential and actual problems (complications) which may arise. Most of these complications are mechanical. All THR's are mechanical devices and, therefore, may fail under stress and with time. Long-term followup studies also serve to obtain data for assessment of real and potential complications and to assess risk resulting from patient characteristics which were measured at the time of operation. However, long-term evaluations done today assess the state of the art when the surgery was done 10 or more years ago.

From these long-term studies, loosening of components emerges as the most frequent complication of THR. Acetabular loosening may occur in up to 10 percent of patients by the 10th year, and will probably increase in incidence with time. About one-half of these loose acetabular components are painful and may require revision surgery. The incidence of loosening is much higher in younger patients, and is also higher in patients with rheumatoid arthritis.

The femoral component is subject to loosening in two areas--the cement-bone junction and the metal-cement junction. Although up to 40 percent of femoral components followed for 10 years in a large series of patients have been judged to be radiographically loose, only 6 percent required revision. Fortunately, the incidence of femoral component loosening tends to plateau with time.

Femoral stems may fracture, necessitating removal, and this is usually preceded by loosening. The rate is low (0.5 percent in one large series), and is expected to become even lower with improved design, technique of manufacture, and advances in surgical technique.

What Are the Medical and Surgical Complications of Total Hip Joint Replacement?

Local complications include:

Deep infection

This occurs in approximately 1 percent of THR's in large series undertaken by experienced hip surgeons in an optimal environment. It is catastrophic when it occurs. Patients who may be at increased risk include severe rheumatoid arthritics on steroids, patients with prior hip surgery, and patients with a prior history of infection in or about the hip.

Deep infection may be classified into (1) 40 percent acute, evident early in the postoperative period; (2) 45 percent delayed, which expresses itself 2 to 24 months after surgery; and (3) 15 percent late by hematogenous spread, which develops in previously asymptomatic patients 2 to 5 years after surgery.

The diagnosis of delayed deep infection can be difficult. Pain is the predominant symptom. An elevated sedimentation rate may help in diagnosis. Conventional radiographs cannot differentiate septic from aseptic loosenings. Scintigraphic evaluation is sensitive for loosening and infection, but is not specific. Aspiration and culture for microbial organisms is frequently diagnostic; arthrography can confirm that the aspiration needle is indeed placed within the pseudocapsule. Histological examination (frozen section) at surgery is an effective means of establishing the diagnosis.

Dislocation

The rate of dislocation varies between 0.8 and 2.4 percent. It is particularly low in standard THR's performed in institutions in which reasonably large numbers of the procedures are done. It is higher in reoperations.

Heterotopic bone formation

Although heterotopic bone formation may be seen on X-rays in up to 40 percent of patients, less than 2 percent exhibit a concomitant functional limitation.

Other

Fracture of the femur, perforation of the femur or acetabulum, vascular complications, nerve palsy, and trochanteric problems may occur.

Systemic complications include:

Death

Operation-related mortality is less than 1 percent in this major operative procedure undertaken in a population that is, for the most part, at middle age or beyond.

Thromboembolic disease

Thromboembolic disease is a major complication of THR. The incidence of venous thrombosis varies according to the diagnostic technique utilized and has been reported to be as high as 50 percent. Pulmonary embolism is infrequent and fatal pulmonary embolism is rare when appropriate prophylactic measures are used. Elevation of lower extremities, elastic support of lower extremities, and pump pressure techniques are among the physical measures used in prevention. Prophylactic use of coumadin, low molecular weight dextran, and aspirin have proved valuable, but use must be carefully supervised and regulated.

Urological complications

Urinary retention and infection occur in 15 to 30 percent of patients. These can and should be reduced by prophylactic measures undertaken prior to THR.

Other

Pulmonary, cardiovascular, and gastrointestinal complications are infrequent. Occasional allergic reactions to drugs and blood occur.

Late Biomechanical Complications

Potential modes of biomechanical failure include loosening, component fracture, and excessive wear. Loosening constitutes one of the most serious long-term complications. The integrity of the bone/cement/prosthesis interfaces is crucial to success of the arthroplasty.

Fibrous tissue at the bone-cement interface is a widespread finding and is seen as a radiolucent line in radiographs. Radiolucency is seen in a relatively large number of patients, but symptomatic loosening occurs less often. However, there are indications that radiographic loosening may become symptomatic in the course of time. Loosening of the femoral component is influenced by poor cementing technique, varus position, calcar resorption, inadequate prosthetic design, excessive patient weight and level of activity, and cement-layer fracture. The mechanical action of motion and the presence of abraded particles from the cement can lead to the development of granulomata and to progressive bone resorption.

Fracture of the femoral component is less common, although clinical consequences are far more immediate than with radiographic loosening. Fracture has been reported in all materials used, but is extremely uncommon with appropriate designs and use of newer alloys. It occurs mostly in heavy, active patients and is correlated with limitation of hip-joint motion, bilateral hip disease, loosening, and varus position. Fracture is usually caused by metal fatigue, and often microstructural defects have been found at the fracture site.

What Are the Problems Related To Revision Surgery for Total Hip Joint Replacement?

If THR fails, as it has in over 10 percent of patients, can a subsequent operation (revision) be done? The answer is yes--but the type of revision surgery and its outcome depend in part on whether the failure is for purely mechanical reasons or because of associated infection.

The mechanical failure in one study showed the average time interval from insertion to failure because of loosening of the femoral component was 3 years, for loosening of the acetabular component, 4 1/2 years, and for fractured femoral stems, 3 years.

The ultimate clinical result from revision or secondary surgery is generally less good than from primary surgery, and failure of this revision surgery may also occur. The infection rate in revision surgery is twice that for initial surgery, and trochanteric complication three times more common. In addition, about one-fourth of these revised hips show progressive radiolucent lines portending possible subsequent failure of this revision. Thus, only about 60 percent have satisfactory functional results after revision for mechanical failure. Revision is usually hampered by lack of sufficient bone stock and by bone inadequate for cement fixation.

If revision surgery is required because of infection, a satisfactory result is further jeopardized. Not only are there mechanical difficulties, but infection must either be completely controlled or eradicated. The diagnosis of infection must first be made--not always an easy task.

Isolation of the infecting organism is essential. This should be first attempted by culturing aspirated fluid from the hip pseudocapsule, or from tissue at time of operation. Histologic confirmation is essential. The isolate must then be tested for antibiotic sensitivity.

Neosurgical infections are handled in customary fashion with adequate drainage and antibiotics. It is the delayed and late infection which requires extensive surgery with removal of the components.

The surgical problems in revision surgery of the failed THR are unique whether or not there is infection. For the infected THR, eradication of infection demands priority consideration, and requires removal of components and cement (as in the mechanically failed hip) and, in addition, a thorough and complete debridement of all infected tissue.

Two methods of dealing with the infected THR are then available. The reimplantation may be delayed until evidence of complete healing and eradication of infection occurs. At that time--months or even years later--implantation of another THR may be contemplated. This indirect or delayed method yields over 90 percent freedom of subsequent infection even in the presence of antibiotic-resistant organisms.

The second method is that of direct transfer in one operation. Old prostheses are removed and new ones are reimplanted at a single setting. Concomitantly, the surgeon uses appropriate systemic antibiotics and antibiotic-impregnated acrylic (as advocated from abroad). This method may well succeed in patients with less virulent organisms and high antibiotic sensitivity.

Thus, the procedure to be followed depends in most part on the sensitivity of the organisms. Other factors, such as the biological state of the soft tissue and bone, are also important.

Whether the area is infected or not, special techniques must be employed both for removal of the old components and the acrylic, and to reimplant the new components. In such cases, the bone has been altered by abnormal stress and often by osteomyelitis, and return of the trochanter to healthy bone is often impossible. Bone grafting of defects in the acetabulum must be anticipated. Special femoral and acetabular prostheses of varied design must be readily available. Muscle integrity should be restored as well as possible.

When all the difficulties of revision have been considered, it may be better judgment not to reoperate, but to leave the hip as a resection-arthroplasty (Girdlestone). The medical, social, and economic factors may be overwhelmingly against yet another major operation. Although walking aid is required, a resection-arthroplasty of the hip may be painless, and reasonably good function may be possible. The decision regarding further surgery must be primarily the patient's, with the surgeon acting as advisor.

Thus, the optimum time for a properly executed THR is the initial operation, and revision surgery is usually less satisfactory.

In What Directions Should the Science Base and Techniques of Total Hip Joint Replacement Be Advanced?

The existing technologies for THR are at a stage where clinical applications show up to 90 percent of devices to be functional at 10 years postsurgery. Although THR is a highly successful procedure, some complications do occur and the life expectancy of the devices may be limited. Most improvements which are being considered concern fixation techniques, although new materials and devices are also being investigated. To enhance the stabilizing effects of the acrylic cement, new techniques of pressurization are being studied. A concern exists, however, regarding the biological effects and long-term mechanical consequences of the deeper penetration of acrylic cement into bone.

Surface replacement arthroplasty to date has failed to demonstrate superiority over other conventional total hip procedures. Experience in most centers throughout the world has indicated increased and accelerated failure rates, primarily from loosening of the prosthetic parts and fracture of the femoral neck. Metal backing of acetabular components has been investigated both clinically and analytically, and the results suggest potential improvement over the traditional approaches. However, the clinical series are relatively small, and the results of the stress analyses subject to uncertainties. Although these studies are promising in concept, further analysis and clinical evaluation are necessary.

Numerous material innovations also have been introduced. These include microporous and macroporous interfaces for fixation, the use of reactive or biodegradable compounds to influence tissue responses, and the development of new combinations and composites of materials. Although many of these methods are quite promising, further in vitro, in vivo, and clinical investigations are recommended. The details of biomaterial surface chemistries and local and systemic tissue responses to dilute biodegradation products should be investigated further and expanded to include possible allergic and hypersensitive reactions.

Further improvements in THR will depend on a coordinated approach to the study of long-term implant performance. Prospective and retrospective clinical studies should continue to examine implant performance using radiographic and other clinical assessment techniques. This approach has provided invaluable clinical data but is a relatively expensive and inefficient means for the investigation of implant failure because of the low failure rates at any one institution.

Implant failure mechanisms should also be studied using device retrieval and analysis, preferably on a multi-institutional or regional basis. Data obtained from implants removed during revision surgery or at the death of the patient can provide valuable additional insights into in vivo implant performance. Such studies might well substantiate the conclusions of clinical evaluations.

To answer many questions about the successes and failures of THR, it is essential to have a large, multi-institutional data base to assess risks and benefits for different groups of patients, prosthetic designs, materials, methods of insertion, and postoperative protocols. To develop such a data base, standard definitions for terms such as "loosening" and "activity level" are needed as well as standard specifications for prostheses, and a minimal essential set of data elements. Epidemiologic estimates of unmet need, however, will require collection of data from defined populations. In addition, the potential importance of the study of functioning implants removed at the time of death suggests that a national network of potential implant donors be developed.

Improved quantitative methods for the functional evaluation of hip replacement patients should also be utilized and further developed since the primary goals of THR are to reduce pain and to improve functional performance. Such studies can serve to (1) refine preoperative diagnoses, (2) improve the precision of specific patient evaluations, (3) provide comparisons between implant designs, and (4) increase the understanding of the basic biomechanics of gait patterns associated with THR. Of the few reported studies, most have concentrated on comparative implant performance, with studies of energetics and kinesiology showing few differences between implant types. Available evidence also indicates that the gait of hip implant patients improves considerably from presurgical measures but may never reach normal values.

Long-term improvements in THR will depend ultimately on a rational approach to the design and development process. Such an approach must be cognizant of the unique features of design within the musculoskeletal environment and the need to incorporate workable surgical techniques as part of the design. The design and development process is closely linked to the process of modeling which is used to integrate and extend the range of applicability of experimental results. A multifaceted approach should be pursued, including the use of analytical models of varying complexity, in vitro tests using cadaver bones and representative supportive structures, and in vivo animal experiments. The most valuable contributions will be those which relate results to predictions available in the literature. Attempts to standardize model geometries and material properties and to arrive at uniform in vitro testing configurations should be developed where feasible. Particular emphasis should be given to improving our understanding of bone remodeling and ingrowth mechanisms and to the failure mechanisms associated with the bone/cement/prosthesis interfaces.

This conference was sponsored by the National Institute of Arthritis, Diabetes, and Digestive and Kidney Diseases. The NIH Office for Medical Applications of Research provided assistance in the planning and conduct of the meeting.

Consensus Development Panel

Philip D. Wilson, Jr., M.D.
(Panel Chairman)
Professor of Surgery (Orthopedics)
Cornell University Medical College
Surgeon-in-Chief
Hospital for Special Surgery
New York, New York
Mark B. Coventry, M.D.
Professor of Orthopedic Surgery
Mayo Medical School
Consultant in Orthopedics
Mayo Clinic
Rochester, Minnesota
Joseph D. Croft, Jr., M.D.
Clinical Associate Professor of Medicine
Georgetown University School of Medicine
Washington, D.C.
Matthew Freedman, M.D.
Associate Professor of Diagnostic Radiology
Assistant Professor of Orthopedic Surgery
Director of Orthopedic and Emergency Radiology
University of Maryland
Baltimore, Maryland
Victor Morrison Hawthorne, M.D.
Professor and Chairman
Department of Epidemiology
University of Michigan School of Public Health
Ann Arbor, Michigan
Wilson C. Hayes, Ph.D.
Associate Professor of Orthopedic Surgery
Harvard Medical School
Director, Orthopedic Biomechanics Laboratory
Beth Israel Hospital
Boston, Massachusetts
John J. Hinchey, M.D.
Clinical Professor of Orthopedic Surgery
University of Texas Medical School at San Antonio
San Antonio, Texas
Susan Horn, Ph.D.
Associate Professor
The Johns Hopkins University
School of Hygiene and Public Health
Associate Director
Center of Hospital Finance and Management
Baltimore, Maryland
Rik Huiskes, Ph.D.
Associate Professor of Biomechanics
Department of Orthopedics
University of Nijmegen
Nijmegen, The Netherlands
Jack E. Lemons, Ph.D.
Professor and Chairman
Department of Biomaterials
Assistant Professor
Division of Orthopedic Surgery
University of Alabama in Birmingham
Birmingham, Alabama
Jane R. Mitchell, M.A.
Consumers' Representative, Recommended by American Association of Retired Persons
Casper, Wyoming
Robert W. Richardson, P.T., M.Ed.
Clinical Associate Professor
School of Health Related Professions
University of Pittsburgh
Coordinator of Rehabilitation Services
Department of Comprehensive Medicine and Rehabilitation
St. Margaret Memorial Hospital
Pittsburgh, Pennsylvania
Lawrence A. Rues, M.D.
Assistant Clinical Professor
University of Missouri--Kansas City
Associate Director
Goppert Family Care Center
Baptist Memorial Hospital
Kansas City, Missouri
Augusto Sarmiento, M.D.
Lowman Professor and Chairman
Department of Orthopedics
University of Southern California
School of Medicine
Los Angeles, California
Robert C. Shoemaker, M.D.
Orthopedic Surgeon
Charlestown, New Hampshire

Speakers

Harlan C. Amstutz, M.D.
"Exposure: Restoration of Functional Biomechanics"
"Emerging Technologies--Status and Future: Resurfacing"
Professor and Chief
Division of Orthopaedic Surgery
University of California, Los Angeles
School of Medicine
Los Angeles, California
Thomas P. Andriacchi, Ph.D.
"Experimental Design and Data Analysis: Functional Evaluation"
Associate Professor and Director of Biomechanical
Research
Rush-Presbyterian-St. Luke's Medical Center
Chicago, Illinois
Bruce J. Brewer, M.D.
"Post-Operative Rehabilitation"
Professor and Chairman
Department of Orthopaedic Surgery
The Medical College of Wisconsin
Milwaukee, Wisconsin
Peter G. Bullough, M.D.
"Biocompatibility and Allegenicity"
Chief, Orthopaedic Pathology
The Hospital for Special Surgery
New York, New York
Albert H. Burstein, Ph.D.
"Performance Standards and Manufacturing Quality Control"
"Strategies for Design and Development"
Director, Department of Biomechanics
The Hospital for Special Surgery
New York, New York
Edmund Y. S. Chao, Ph.D.
"Hip Biomechanical Function"
Professor of Bioengineering and Director of Biomechanics Laboratory
Department of Orthopaedic Surgery
Mayo Clinic
Rochester, Minnesota
Doyt L. Conn, M.D.
"General Medical Consideration"
Chairman
Division of Rheumatology
Associate Professor of Medicine
Mayo Medical School
Mayo Clinic
Rochester, Minnesota
Roy D. Crowninshield, Ph.D.
"Mechanical Factors"
Associate Professor of Orthopaedic Surgery and
Engineering
University of Iowa
Biomechanics Laboratory
Iowa City, Iowa
Nas Eftekhar, M.D.
"Short-term Outcomes"
Associate Professor of Orthopedic Surgery
College of Physicians and Surgeons
Columbia University
Columbia-Presbyterian Medical Center
New York, New York
C. McCollister Evarts, M.D.
"Short-term Risks: Systemic Complications"
Dorris H. Carlson Professor and Chairman
Department of Orthopaedics
University of Rochester School of Medicine and
Dentistry
Rochester, New York
Robert H. Fitzgerald, Jr., M.D.
"Longer-term Risks: Infection and Non-infectious Rejection"
"Infectious Complications"
Assistant Professor of Orthopedic Surgery
Mayo Medical School
Consultant, Orthopedic Surgery
Mayo Clinic
Rochester, Minnesota
Jorge O. Galante, M.D.
"Longer-term Risks: Biomechanical Failure"
Professor and Chairman
Department of Orthopedic Surgery
Rush-Presbyterian-St. Luke's Medical Center
Chicago, Illinois
Harry K. Genant, M.D.
"Longer-term Risks: Radiological Diagnosis"
"Radiological Considerations"
Professor of Radiology and Medicine
Chief of Skeletal Radiology
Department of Radiology
University of California
San Francisco, California
Peter Griss, Dr.med.
"Long-term Outcomes: German/Austria/Switzerland Perspective"
Orthopaedische Klinik Lindenhof
Mannheim
WEST GERMANY
William H. Harris, M.D.
"Emerging Technologies--Status and Future: Metal Backed Socket"
" Technical Problems and Solutions"
Clinical Professor in Orthopaedic Surgery
Harvard Medical School
Chief of Hip and Implant Surgery Unit
Orthopaedic Research Laboratory
Massachusetts General Hospital
Boston, Massachusetts
Richard C. Johnston, M.D.
"Long-term Outcomes: Hip Society Perspective"
Orthopaedic Surgeon
The Hip Society
Iowa Methodist Medical Center
Des Moines, Iowa
Jennifer L. Kelsey, Ph.D.
"Epidemiology"
Associate Professor of Epidemiology
Department of Epidemiology and Public Health
Yale University School of Medicine
New Haven, Connecticut
Jack L. Lewis, Ph.D.
"Experimental Design and Data Analysis: Retrieval Analysis--Engineering Considerations"
Professor of Civil Engineering and Orthopaedic Surgery
Rehabilitation Engineering Program
Northwestern University
Chicago, Illinois
Robin S. M. Ling, M.A.B.M.(Oxon)S.R.C.S.
"Long-term Outcomes: British Perspective"
Orthopaedic Surgeon
Princess Elizabeth Orthopedic Hospital
Exeter, Devon
UNITED KINGDOM
Donald E. McCollum, M.D.
"Bone Deficiencies and Graft Supplementation"
Professor of Orthopaedic Surgery
Duke University Medical Center
Durham, North Carolina
Joseph Miller, M.D., F.R.C.S.(C)
"Fixation: Cements and Cementing Procedures"
"Emerging Technologies--Status and Future: Cementing"
Chairman, Division of Orthopaedic Surgery
McGill University
Orthopaedic Surgeon-in-Chief
Montreal General Hospital
Montreal, Quebec
CANADA
Roland W. Moskowitz, M.D.
"Alternative Patient Management: Nonoperative"
Professor of Medicine
Case Western Reserve University School of Medicine
Director, Division of Rheumatic Diseases
University Hospitals
Cleveland, Ohio
Carl L. Nelson, M.D.
"Short-term Risks: Local Complications"
Professor and Chairman
Department of Orthopaedic Surgery
Head, Section of Reconstructive Surgery
University of Arkansas for Medical Sciences
Little Rock, Arkansas
J. Phillip Nelson, M.D.
"Asepsis and Infection Prevention"
Clinical Instructor
Department of Orthopedic Surgery
University of Colorado Medical School
Denver, Colorado
Robert M. Pilliar, Ph.D.
"Emerging Technologies--Status and Future: Bone Micropore Ingrowth"
Associate Professor
Faculty of Dentistry and Department of Metallurgy and Materials Science
University of Toronto
Toronto, Ontario
CANADA
Robert M. Rose, Sc.D.
"Friction, Wear, and Strength Properties"
"Emerging Technologies--Status and Future: Component Materials"
Mayo Medical School
Mayo Clinic
Rochester, Minnesota
Robert B. Salter, M.D., F.R.C.S.(C)
"Alternative Patient Management: Operative"
Professor and Head of Orthopaedic Surgery
University of Toronto
The Hospital for Sick Children
Toronto, Ontario
CANADA
Eduardo A. Salvati, M.D.
"Non-infectious Complications"
Associate Professor, Clinical Surgery (Orthopedics)
Cornell University Medical Center
Director of Hip Clinic
The Hospital for Special Surgery
New York, New York
David J. Schurman, M.D.
"Retrieval Analysis--Medical Considerations"
Associate Professor
Division of Orthopedic Surgery
Stanford University
Stanford, California
Clement B. Sledge, M.D.
"Orthopedic Considerations"
John B. and Buckminster Brown Professor of
Orthopedic Surgery
Harvard Medical School
Brigham and Women's Hospital
Boston, Massachusetts
Richard N. Stauffer, M.D.
"Long-term Outcomes: Mayo Perspective"
Professor of Orthopedic Surgery
Mayo Medical School
Rochester, Minnesota
Frank E. Stinchfield, M.D.
"Facilities, Staffing, and Training"
Professor and Chairman, Emeritus
Department of Orthopaedic Surgery
Columbia-Presbyterian Medical Center
New York, New York

Conference Sponsors

National Institute of Arthritis, Diabetes, and Digestive and Kidney Diseases
Stephen L. Gordon, Ph.D. Director
Office of Medical Applications of Research

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