Can an orthopaedic total joint arthroplasty (TJA) surgeon with modern implants, proper technique, and postoperative management achieve the desired result 100 percent of the time? This certainly seems to be the goal of both consumer advocates and government regulators, as the following examples show.
- The Consumers Union, the advocacy and public policy arm of Consumers Report, recently published a statement asking orthopaedic device manufacturers to issue 20-year warranties on hip and knee implants. The warranty documents would be given to the patient as part of the implant procedure and would cover any failure of materials and the cost of replacement prostheses.
- The Centers for Medicare and Medicaid Services (CMS) has stated that deep venous thrombosis (DVT) and pulmonary embolism (PE) after TJA are “never events,” complications that should never happen. Periprosthetic infection has also been targeted as a “never event.”
But is it feasible to guarantee the success of a total hip (THA) or total knee arthroplasty (TKA) for every individual? Is it possible (at least from the federal government’s point of view) to have no complications after a THA or TKA procedure if the surgeon performs the surgery in a perfect manner 100 percent of the time?
Obstacles to perfection
A TJA is a very complex procedure, and its success is based on numerous factors. Some of these factors are within the control of the surgeon, but many others deal with patient variables that are outside the surgeon’s control.
In addition, many issues pertaining to the cellular mechanisms of why a TJA fails or becomes infected, or why certain patients may be more susceptible to poor outcomes than others remain to be determined or are currently under investigation.
A blood clot can develop after TJA even in patients without other known risk factors. This is presumably due to stasis and mechanical or physical effects imparted to the vein during surgery. To prevent a blood clot, antithrombotic agents, in combination with mechanical prophylaxis, are used. Despite the use of these agents, a finite risk of development of a clot and a PE after TJA remains.
The risk of a patient’s incurring DVT and PE can be lowered by mechanical or pharmacologic prophylaxis, but it can never be completely eliminated. Additionally, many of the pharmacologic agents recommended for lowering the risk of DVT and PE are associated with increasing the risk of bleeding that can lead to hematoma formation and wound infection.
Infection after TJA is an unfortunate and sometimes disastrous occurrence. The presence of a foreign body as large as a prosthesis makes the patient susceptible to the development of an infection. The ability of organisms to form a glycocalyx often precludes eradication of an infection without removing the prosthesis.
Despite the use of multiple interventions to lower the rate of infection—including antibiotic prophylaxis, screening (nasal swabs) for methicillin-resistant Staphylococcus aureus (MRSA), and the use of space suit operating garb, laminar air flow, and silver impregnated dressings—a zero rate of infection has never been achieved. Current scientific knowledge is insufficient to totally eliminate periprosthetic infection. Although the science is constantly being advanced, orthopaedic surgeons still do not know all of the patient variables or have the bacterial-resistant technology to ensure that a periprosthetic infection is a never event.
Patient factors have also been associated with an increased risk of periprosthetic infection. A study of more than 56,000 TKAs found that the following patient characteristics were all associated with a significantly increased number of deep surgical site infections:
- body mass index greater than 35
- diabetes mellitus
- ASA score greater than 3
- diagnosis of osteonecrosis
- posttraumatic arthritis
Another study, involving more than 40,000 THA patients, showed that an increased risk of periprosthetic infection was associated with rheumatologic disease, obesity, coagulopathy, and preoperative anemia. Patients who are obese have an increased rate of complications—including infections—after THA or TKA.
Long-term studies of TJA patients show that 5 percent to 10 percent of implants will have failed by 10 years after surgery. Several patient factors that are largely outside a surgeon’s control are associated with TJA failures.
For example, patients who require TJA are frequently older and many have significant comorbidities. A recent study based on Medicare data showed that depression, rheumatologic disease, psychosis, and renal disease were all associated with an increased risk of revision after THA. Poor function after TKA has been associated with older age, BMI greater than 40, low emotional health scores, and poor quadriceps strength.
Other patient factors linked with poor outcomes or higher rates of complications after TJA include renal failure, malnutrition, low albumin levels, low vitamin D levels, and low total lymphocyte counts.
Increased mortality within 90 days after THA has been associated with congestive heart failure, metastatic cancer, psychosis, renal disease, dementia, hemiplegia, cerebrovascular disease, and chronic pulmonary disease.
Whether TJA implants can realistically be guaranteed for 5 years—let alone 20 years—is also questionable. Catastrophic implant failures can mechanically occur in the absence of a design or manufacturing flaw.
The knee or hip implant can be subjected to loads up to five times body weight. When patients participate in activities not recommended by the surgeon, or when a patient is overweight or obese, the implant is at risk.
In some scenarios, the bone surrounding the implant has been damaged by trauma or is osteoporotic. Mechanically, a poorly supported prosthesis placed in a bone-deficient acetabulum or tibial plateau may increase the risk of catastrophic or early aseptic failure. A diligent surgeon can attempt to improve local bone stock with bone grafting or use of bone growth stimulating agents, such as bone morphogenetic protein, but the individual patient response is a biologic phenomenon that is not completely understood and is based, to some degree, on individual, patient-specific variables.
Morbid obesity has been associated with catastrophic failure of implants. As a patient gains weight—a factor outside the surgeon’s control—loads on certain types of implants can increase, resulting in local damage and corrosion of the implant material. These local effects of increased tribocorrosion and release of wear debris seem to be, to a certain extent, variables that affect some patients more than others.
Total joint implant wear is a physical reality. There are no known articulations that have absolutely no wear. Osteolysis about a prosthesis is related to the body’s response to particulate wear, especially submicron polyethylene particles. Bone loss is modulated through protein receptors that mediate osteoclastogenesis.
Current research points toward genetic factors that may make certain patients more susceptible to osteolysis. The loss of supporting bone surrounding a prosthesis can lead to premature loosening or catastrophic failure. Again, this is one of many individual, patient-related factors that can decrease the longevity of total joint replacement and is out of the control of either the surgeon or the manufacturer.
The blame game?
Clearly the success or failure of a THA or TKA depends on numerous factors related to the surgeon, implant manufacturer, and the patient. Patient factors are volitional and genetic. Implants have a finite, measurable rate of failure that will never be zero.
Making surgeons, hospitals, or manufacturers responsible for the failure of a total joint implant when some factors are outside their control places an unfair burden on these entities and may be deleterious to the patient.
If hospitals and physicians are penalized for factors and conditions outside their control, there is a danger that patients with comorbidities may be denied surgery or have significant difficulty in obtaining these procedures. For example, patients who are obese—as more than one in four Americans are—may be unable to lose weight as their physicians recommend. Even though the results of TJA are good in this patient population, they are not as good as in a population of normal weight patients.
A similar argument exists for patients who have inflammatory arthropathy, diabetes, or renal disease. These patients could be at risk for denial of elective hip or knee arthroplasty because their conditions may be poorly controlled and are associated with poor outcomes.
As long as human variables are associated with surgical outcomes, a small but finite risk of complications and failure of THA and TKA will always be present. This is undeniable and must be realized by patients and payers. The results of joint arthroplasty using modern techniques, care pathways, and implants are excellent and continue to improve, but it is unreasonable to believe they will ever reach perfection.
References for the studies and statistics cited in this article can be found in the online version, available at www.aaosnow.org
Mark H. Gonzalez, MD, MEng, and William M. Mihalko, MD, PhD, are members of the AAOS Biomedical Engineering Committee. Dr. Mihalko is also the current chair of the Orthopaedic Device Forum.
Disclosure information: Dr. Gonzalez—Johnson & Johnson, Smith & Nephew, Ortho Sensing Technology, American Society for Surgery of the Hand; Dr. Mihalko—Aesculap/B.Braun; Medtronic; Smith & Nephew; Stryker; Saunders/Mosby-Elsevier; Springer; Journal of Arthroplasty; Reconstructive Review; American Orthopaedic Association; ASTM International
- Several factors related to the surgeon, hospital, manufacturer, and patient contribute to the longevity of total joint implants, as well as to the potential for complications such as DVT, PE, and periprosthetic infections.
- Despite advances in techniques and understanding of disease processes, it may be impossible to eliminate implant failures and certain complications due to factors out of the surgeon’s control.
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