There were at least 500,000 total knee replacements in the last year, and well in excess of 100,000 hip replacements. Why so many?
Aging
As a nation, we’re getting older and wearing out our knees, and to a somewhat lesser degree, our hips. Not as many of us are dying before these joints begin to cause us trouble. Furthermore, the age at which clinicians are willing to recommend getting a replacement knee has been dropping, so that it is no longer unusual for a person in their 40’s to get one. Most knees (and hips) are however, still going to people over 60, with the 70’s now the most common age of recipients.
Obesity
As a nation, we’re also getting fatter as we get older. Obesity , typically owing to overeating and a relative lack of even moderate exercise, is now probably the prime contributing cause of the severe osteoarthritis that causes most patients to see an orthopedic surgeon.
Wear & Tear From Sports or Occupation
Curiously, dedicated joggers and runners are getting new knees (and hips) as well. While the improved life expectancy through cardiovascular benefits and avoidance of metabolic syndrome, of regular aerobic exercise like running far outweigh the hazards of the joint jarring wear-and-tear of these activities, it is no longer uncommon to see fit patients after a decade or two of running (or basketball) in need of replacements, particularly as they too, age into their fifties.
Favorable Cost-Benefit Ratios, Insurance Coverage & Sick Leaves
Study after study shows that replacement of the joints of the lower extremities, particularly the knees, results in significant benefits in longevity and quality of life. Patient resistance to the idea is far less common, and most insurance plans now have so many subscribers of the target age for these arthroplasties, that covering them is a must for the plans to stay competitive. Of particular note, Medicare coverage for these procedures is almost automatic, given their increasing frequency and demonstrable success. Furthermore, in part because of the Family & Medical Leave Act, and in part because of the cost of training new replacementworkers, companies are now more willing to see replacement surgeries as an opportunity to get a more mobile and less medicated employee back to work, not as an occasion that marks the patient as someone they should try to retire.
More Historically Underserved Minorities Are Now Getting Replacements
Disparities in having the surgery by gender, race, and socioeconomic status are beginning to shrink. It was not uncommon in the past for more women than men to have knee replacements, but that has faded. Whites had more knee replacements than Hispanics, who in turn had more than blacks, but this too is changing. There is still a long way to go.
Is the Operation Risk-Free?
No, but the case of fatalities is in the low single digits per thousand cases. (Given the age group concerned, their mortality without ever having the surgery is not much better than that). The general nature of complications of this surgery have remained about the same over the last thirty years, although at substantially lower rates per thousand procedures. Infection remains number one, failure or misalignment of the joint is second, and emboli and venous thrombosis and nerve damage follow at a distance.
How Best to Reduce Risk & Get More Favorable Outcomes?
The answer to this question is becoming clearer: Use a doctor who annually performs a lot (ideally over 100; many today do several hundred) of these procedures, at a hospital where every year, hundreds of patients have the procedure done. Practice and experience in both surgeon and surgical department seem to be the best predictors of success for the patient.
Can a Replacement Be Replaced?
There are between 25,00-30,000 “revisions” (overwhelmingly outright replacement) of prior arthroplasties annually. The initial artificial joints fail for the same reasons the biological joint failed: wear, often exacerbated by obesity. A secondary, but related reason is increasing imbalance in the knee or in the patient’s posture or gait, as a whole. The amount of hardware and type of replacement joint is often larger, in the sense that it is longer and needs to be better anchored, given that some native bone matrix has deteriorated. The outcomes in enhanced mobility from revisions tend to be somewhat less dramatic than from the first replacement, but still tend to overwhelm considerations of risk and cost.
Does the End of the Surgery End the Problem By Itself? Postsurgical Physical Therapy
Most patients who have had arthroplasties will be referred to physical therapists (aka “physical terrorists”) who will virtually force (sometimes using football-coach-like or drill sergeant challenge talk) the patient to optimize the use of their new joint (and thereby accelerate their own recovery) through a pattern of training and exercises. Ideally, this can include as many as two sessions a day at an inpatient rehabilitation facility. But more often after discharge from an acute-care hospital, there will be three weekly in-home sessions with a visiting physical therapist or three weekly trips to an outpatient physical therapy clinic. The often painful exertions that ensue focus on flexion (getting the knee to bend to 100 degrees or over, ideally about 120 degrees), extension (straightness in terms of degree from 180 degrees, ideally zero deflection or only one or two percent) and range of motion (ideally with knees, the ability to use an exercise or actual bicycle. While these physical therapists will initially train patients to use better assistive devices like walkers, crutches, and canes, and advocate for the safe use of adaptive technology (sometimes as simple as raised “handicapped person’s ” toilets) their long term goal is to get the patient to tolerate any pain or stiffness that cannot be reduced safely and effectively by medications (one should not stay on oxycontin or percocet forever), so as to master once again activities like stair climbing, using regular toilets, and safe driving (particularly in right-side replacements where the gas and the brake pedals are being put to work constantly .
Continuous Passive Motion Machines
A very common technology used alongside this active physical therapy, often within a day or two of the actual surgery, is a continuous passive motion machine (a “CPM’). This is a portable bedside device, which is employed with the patient laying down on his or her bed, ideally in a comfortable position that allows for reading a book, watching TV and even sleeping in some cases. The patient’s leg is placed into a mechanized (but often lamb’s wool padded) brace that is mounted on a frame with an electric motor underneath, in the base which rests on the bed, and serves as an anchor. When the machine is turned on it causes the now strapped-in leg to bend at the replaced knee and then straighten in a slow rhythmic manner on a repeating basis. While the speed of these cycles of motion is rarely adjusted, the angle of flexion is usually progressively increased in terms of degrees on the theory that this promotes a quicker return to voluntary flexion. This assumption is widely held within the orthopedic surgical community, and among physical therapists, even though there are some studies that show that it does not significantly aid in enhanced mobility or reduced pain in the long run. (After three months, a commonly used measure, patients without CPM do about as well.) Nonetheless, current clinical practice overwhelmingly favors CPM, and the rental of these machines for home use (usually for three weeks after discharge from the hospital) is covered by most insurance plans.
Research into Improved Equipment and Procedures Continues Apace
According to ClinicalTrials.gov, there are 105 ongoing studies, usually based at university-associated medical centers, dealing with arthroplasties of the knee alone. The majority are comparison tests between differing models of replacement joint, or of differing ways of attaching them. A strong emphasis is placed on reducing the wearing of surfaces, so as to extend joint life. Minimally invasive surgeries (usually involving smaller incisions and replacement of only one part of the knee joint, are increasingly popular research topics, given that they often avoid having to cut the femoral quadriceps muscle. (This approach represents only single digit percentages of current practice today.) The timing and extent of physical therapy, including the seemingly unorthodox notions that it should begin even before the surgery, or is best postponed until six weeks after the surgery (on the theory that most patients are in severe pain for the first six weeks and will not voluntarily make much progress in flexion, extension, and range-of-motion) are all under study, as is the use of CPMs. In sum, the situation with joint replacement surgery is already quite upbeat, but it is trying continuously, to make sure of its underlying scientific footing. (Pun definitely intended).
Conflict of interest disclosure: This author has been on medical leave and away from this blog for almost three months, while he focused on recovering from revision right total knee arthroplasty. While a classic patient in terms of underlying etiology – i.e. morbid obesity, relative physical inactivity, etc. -his own experiences with his surgeon, rehabilitation hospital, and physical therapists, have been uniformly positive, even when they involved overcoming sometimes great pain and stiffness in the interest of regaining a more active life. (My physical therapist told me to write that!) To him, it has all seemed quite worth it, and quite consonant with the bulk of the literature reports.
Tony Stankus, FSLA, tstankus@uark.edu
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