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general population vs the ESRD population. The lifetime
risk of advanced chronic kidney disease and ESRD is high
and expected to rise with the aging population9; therefore,
an understanding of ATR in this population is important. We
speculate that these conditions may influence the orthopedic surgeon's choice of treatment of ATR in patients with
ESRD. Per American Academy of Orthopaedic Surgeons
Clinical Practice Guidelines, both operative and nonoperative treatments are options for acute ATR; however, clinicians may hesitate to perform surgery, particularly for
patients with ESRD. It is unclear whether ESRD is a valid
contraindication for surgery.
We conducted an epidemiological study using a comprehensive national registry database of patients with ESRD.
Our goals were to (1) estimate the incidence of ATR in the
ESRD population, (2) identify associated risk factors (ie,
age, sex, race, body mass index, cause of ESRD, and comorbidities), and (3) describe treatment type and incidence of
operative site infection (SSI) among patients with ESRD.
We hypothesized that patients waitlisted for transplant
would be less likely to undergo operative repair of ATR
than nonwaitlisted patients because surgery could harm
their chances for a transplant. We also hypothesized that the
rates of surgery would decrease during the study period,
according to documented trends of decreasing rates of operative intervention after publication of randomized controlled trials demonstrating the effectiveness of nonoperative
treatment.23

Methods
This study was deemed exempt from formal review by our
institutional review board. All data were retrieved from the
US Renal Data System, a national registry of all patients
with ESRD in the United States. We included all patients
with ESRD who used Medicare Part A and B as their primary health insurance between January 1, 1999, and
December 31, 2013. Demographic and comorbidity data
were ascertained through the End Stage Renal Disease
Medical Evidence Report, Medicare Entitlement and/or
Patient Registration (form CMS-2728-U3), which must be
filed for all patients within 45 days of an ESRD diagnosis.
All patients were studied from their development of ESRD
until death, end of Medicare primary coverage, or end of the
study. Death was ascertained via the Social Security Death
Master File.

Dialysis vs Transplantation
Patients were categorized into the following 3 groups: (1)
nonwaitlisted (not on the transplant waitlist, never received
a transplant), (2) waitlisted (on the transplant waitlist), or
(3) transplant recipient ("transplanted"). Patients contributed time-at-risk in a time-varying manner in regression

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models. Patients could contribute person-time to multiple
groups. For example, a patient on the waitlist for 2 years
who then lived for 5 years after a transplant would contribute 2 and 5 years to the waitlisted and transplanted categories, respectively.
Patients were categorized in this way to help distinguish
whether group differences in outcomes were the result of
having undergone a transplant as opposed to selection bias.
Patients who are waitlisted for a transplant or receive a
transplant are typically healthier than patients not yet waitlisted for a transplant. In addition, many patients' comorbidities prevent them from being eligible for transplant
consideration. These categories allowed comparisons
between patients of similar health status, with transplant as
an independent variable.

Incidence of and Risk Factors for Achilles
Tendon Rupture
We used Medicare Institutional and Physician/Supplier
claims data to ascertain ATR events. Patients with ESRD
are eligible for Medicare regardless of age, and more than a
half use Medicare as their primary health insurance.29 The
Medicaid claims of patients with ESRD are incorporated
into the US Renal Data System Standard Analysis Files.
ATRs were ascertained using International Classification of
Diseases, Ninth Revision, Clinical Modification25 (ICD9-CM) diagnosis code 727.67 (nontraumatic rupture of
Achilles tendon) and Current Procedural Terminology1
(CPT) codes 27650 (repair, primary, open or percutaneous,
ruptured Achilles tendon) and 27652 (repair, primary, open
or percutaneous, ruptured Achilles tendon; with graft). We
estimated the crude incidence, defined as the number of
ATRs divided by the total time-at-risk, and its 95% confidence interval (CI) by using univariate negative binomial
regression. We subsequently performed multivariate negative binomial regression to estimate the adjusted incidence
rate ratio (aIRR) among nonwaitlisted, waitlisted, and
transplanted groups and to identify risk factors for ATR. We
included all potential confounders available in the database
in our model: age, race, sex, body mass index (BMI) value,
cause of ESRD, comorbidities (hypertension, diabetes, congestive heart failure, atherosclerosis, peripheral vascular
disease, cerebrovascular accident, chronic obstructive pulmonary disease, cancer, smoking status, alcohol dependence, drug dependence, inability to ambulate, and inability
to be transferred), and year of study entry.

Treatment Modality
Among those who sustained an ATR, the patients whose
records indicated a code of CPT 27650 or 27652 within 14
days of ATR diagnosis were considered to have received
operative treatment.8 We performed multivariate logistic

Table of Contents for the Digital Edition of Foot & Ankle International - July 2018