SICOT e-Newsletter

Issue No. 67 - April 2014

Worldwide News

Young Age and Total Knee Arthroplasty: What is new in the Literature?

Kamal Bali
SICOT Newsletter Editorial Board Member - University of Western Ontario, Canada

As the indications for knee replacement expand, total knee arthroplasty (TKA) in young patients is increasingly becoming an area of utmost research and discussion in the domain of joint reconstruction. The current issue of JBJS America (April 2014) carries two research articles focused on the subject. The abstracts of these articles has been summarised below.

ARTICLE 1:

Younger age is associated with a higher risk of early periprosthetic joint infection and aseptic mechanical failure after total knee arthroplasty.

by Meehan JP, Danielsen B, Kim SH, Jamali AA, White RH.
in J Bone Joint Surg Am. 2014 Apr 2;96(7):529-35. doi: 10.2106/JBJS.M.00545.

Background:

Although early aseptic mechanical failure after total knee arthroplasty has been reported in younger patients, it is unknown whether early revision due to periprosthetic joint infection is more or less frequent in this patient subgroup. The purpose of this study was to determine whether the incidence of early periprosthetic joint infection requiring revision knee surgery is significantly different in patients younger than fifty years of age compared with older patients following primary unilateral total knee arthroplasty.

Methods:

A large population-based study was conducted with use of the California Patient Discharge Database, which allows serial linkage of all discharge data from nonfederal hospitals in the state over time. Patients undergoing primary unilateral total knee arthroplasty during 2005 to 2009 were identified. Principal outcomes were partial or complete revision arthroplasty due to periprosthetic joint infection or due to aseptic mechanical failure within one year. Multivariate analysis included risk adjustment for important demographic and clinical variables. The effect of hospital total knee arthroplasty volume on the outcomes of infection and mechanical failure was analyzed with use of hierarchical modeling.

Results:

At one year, 983 (0.82%) of 120,538 primary total knee arthroplasties had undergone revision due to periprosthetic joint infection and 1385 (1.15%) had undergone revision due to aseptic mechanical failure. The cumulative incidence in patients younger than fifty years of age was 1.36% for revision due to periprosthetic joint infection and 3.49% for revision due to aseptic mechanical failure. In risk-adjusted models, the risk of periprosthetic joint infection was 1.8 times higher in patients younger than fifty years of age (odds ratio = 1.81, 95% confidence interval = 1.33 to 2.47) compared with patients sixty-five years of age or older, and the risk of aseptic mechanical failure was 4.7 times higher (odds ratio = 4.66, 95% confidence interval = 3.77 to 5.76). The rate of revision due to infection at hospitals in which a mean of more than 200 total knee arthroplasties were performed per year was lower than the expected (mean) value (p = 0.04).

Conclusions:

Patients younger than fifty years of age had a significantly higher risk of undergoing revision due to periprosthetic joint infection or to aseptic mechanical failure at one year after primary total knee arthroplasty.

ARTICLE 2:

Revision total knee arthroplasty in the young patient: is there trouble on the horizon?

by Aggarwal VK, Goyal N, Deirmengian G, Rangavajulla A, Parvizi J, Austin MS.
in J Bone Joint Surg Am. 2014 Apr 2;96(7):536-42. doi: 10.2106/JBJS.M.00131.

Background:

The volume of total knee arthroplasties, including revisions, in young patients is expected to rise. The objective of this study was to compare the reasons for revision and re-revision total knee arthroplasties between younger and older patients, to determine the survivorship of revision total knee arthroplasties, and to identify risk factors associated with failure of revision in patients fifty years of age or younger.

Methods:

Perioperative data were collected for all total knee arthroplasty revisions performed from August 1999 to December 2009. A cohort of eighty-four patients who were fifty years of age or younger and a cohort of eighty-four patients who were sixty to seventy years of age were matched for the date of surgery, sex, and body mass index (BMI). The etiology of failure of the index total knee arthroplasty and all subsequent revision total knee arthroplasties was determined. Kaplan-Meier survival curves were used to evaluate the timing of the primary failure and the survivorship of revision knee procedures. Finally, multivariate Cox regression was used to calculate risk ratios for the influence of age, sex, BMI, and the reason for the initial revision on survival of the revision total knee arthroplasty.

Results:

The most common reason for the initial revision was aseptic loosening (27%; 95% confidence interval [CI] = 19% to 38%) in the younger cohort and infection (30%; 95% CI = 21% to 40%) in the older cohort. Of the twenty-five second revisions in younger patients, 32% (95% CI = 17% to 52%) were for infection, whereas 50% (95% CI = 32% to 68%) of the twenty-six second revisions in the older cohort were for infection. Cumulative six-year survival rates were 71.0% (95% CI = 60.7% to 83.0%) and 66.1% (95% CI = 54.5% to 80.2%) for revisions in the younger and older cohorts, respectively. Infection and a BMI of â¥40 kg/m2 posed the greatest risk of failure of revision procedures, with risk ratios of 2.731 (p = 0.006) and 2.934 (p = 0.009), respectively.

Conclusions:

The survivorship of knee revisions in younger patients is a cause of concern, and the higher rates of aseptic failure in these patients may be related to unique demands that they place on the reconstruction. Improvement in implant fixation and treatment of infection when these patients undergo revision total knee arthroplasty is needed.

A commentary by esteemed arthroplasty surgeon, Dr Kelly G. Vince, follows these articles and focuses on the key points highlighted by these research articles. Although both articles are level 3 studies, one is an institutional study (Aggarwal et al) while the other one (Meehan et al) is a large population-based study evaluating data all over the California state of the United States. Despite being completely different methodologically, both articles clearly document higher rates of aseptic failure in total knee arthroplasty patients under the age of 50 years. This is understandable as the younger population is likely to wear out a TKA sooner than their older counterparts.

With the advancement in the bearing surfaces and implantation techniques, the likelihood of early catastrophic mechanical failure of TKA even in a young active population group is very low. As Dr Vince points out, a well done primary TKA and a good first revision surgery should be able to serve a young patient through a lifetime with acceptable function. Unfortunately, this has not been consistently seen in these two studies as many young patients in the two studies faced their first revision within a year, rather than enjoying years of service by the artificial joint, because of infection or unsatisfactory function. To add to the pessimism as far as outcomes of TKA in young are concerned, Aggarwal et al also reveal the data on the number of first revisions that failed prematurely and eventually placed the limb in jeopardy.

One outcome, reported by Meehan et al, that is difficult to explain is the higher incidence of periprosthetic infection in the younger patients as compared to the older patients even after eliminating the confounding variables. Normal logic would imply higher immunity and protection from infection in youth. One explanation that these authors put forward is the higher incidence of post-traumatic arthritis in young patients. Specifically a previous history of arthrotomy, a recognised risk factor for infection, is likely to be more common in young patients with post-traumatic arthritis. However, a clear relationship between previous arthrotomy and aseptic loosening has not been established in the literature, and implant fixation issues in young (cemented vs. uncemented) are more likely to play a role in the pathogenesis of aseptic failure in this group of patients.

These studies reiterate the importance of patient education and understanding patient expectations. Knee arthroplasty continues to remain a good and reliable procedure for older patients as far as pain relief and function is concerned. Early failures reported in young patients due to unacceptable function are in part likely to result from unfulfilled âunique expectationsâ than from high activity levels. Thus, the fact that an artificial knee joint can never match the performance of a normal human knee joint needs to be communicated to all patients (especially young active individuals) with utmost clarity.

Both studies are limited by their retrospective design and reliance on administrative data. Both are unable to draw any conclusions regarding survivorship of specific implant designs or knee fixation techniques in young patients. Although the study by Meehan et al (unlike Aggarwal et al) involves patient population operated all over the California state by multiple surgeons, it fails to identify the effect of individual surgeons. However, Meehan et al do identify decreased incidence of periprosthetic infections at high volume hospitals, which supports the concept of utilising specialty service hospitals in reducing the incidence of complications following TKA.

Despite their limitations, both these studies are an invaluable addition to the limited literature on outcome of TKA in young adults and are a must read for anyone with interest and a predominant practice in knee arthroplasty surgery.