Study examines impact of patient comorbidities

Maureen Leahy

With patients living longer, more active lives, the demand for total knee arthroplasty (TKA) is increasing. However, elderly TKA patients with certain comorbidities are at increased risk of early revision, according to data presented at the 2012 annual meeting of the American Association of Hip and Knee Surgeons.

“Patient-related risk factors for early TKA failure are poorly understood, particularly in older patients,” said presenter Harry E. Rubash, MD, chief of orthopaedic surgery at Massachusetts General Hospital in Boston. “The purpose of our study was to identify specific demographic and clinical characteristics associated with an increased risk of early revision following primary TKA in Medicare patients.”

Rating the risks
Using data from the National Medicare 5 percent sample covering the period 1998–2008, ­Dr. Rubash and his fellow researchers calculated the relative risk of revision within 12 months of primary TKA as a function of baseline medical comorbidities in 117,903 patients. They used a Cox Regression Model to examine the impact of 29 comorbid conditions on the risk of early revision, controlling for age, sex, race, census region, socioeconomic status, and all other baseline comorbidities. Adjusted hazard ratios (HR) were constructed for each condition, and Wald’s X2 statistic was used to rank the degree of association of comorbidities with the risk of early revision.

The researchers found that the most significant comorbidities associated with early revision (in order of significance, P < 0.040, for all comparisons) were the ­following:

• chronic pulmonary disease (HR = 1.32)
• depression (HR = 1.30)
• alcohol abuse (HR = 1.80)
• drug abuse (HR = 2.08)
• renal disease (HR = 1.25)
• hemiplegia/paraplegia (HR = 1.91)
• obesity (HR = 1.19)

“Knowing that these conditions are associated with an increased risk of early revision is important when counseling elderly TKA patients regarding their individual risks of early failure,” said Dr. Rubash. “It is also helpful for risk-stratifying publicly reported outcomes in Medicare TKA patients.”

Dr. Rubash’s coauthors of “Risk Factors for Early Revision Following Primary TKA in Medicare Patients” are Kevin J. Bozic, MD, MBA; Edmund Lau, MS; Kevin L. Ong, PhD; Vanessa Chan, MPH; Steven M. Kurtz, PhD; Thomas P. Vail, MD; and Daniel J. Berry, MD.

Disclosures: Dr. Rubash—Pipeline; Biomet; Zimmer; Wolters Kluwer Health–Lippincott Williams & Wilkins; Hip Society. Dr. Bozic—AAOS; American Association of Hip and Knee Surgeons (AAHKS); American Joint Replacement Registry; American Orthopaedic Association; California Joint Replacement Registry Project; California Orthopaedic Association; Harvard Business School; Orthopaedic Research and Education Foundation. Mr. Lau—Stryker; Kyphon; Amgen; Alcon. Dr. Ong—Stryker; Medtronic; Biomet; Journal of Arthroplasty. Dr. Kurtz—Stryker; Zimmer; Biomet; DePuy; Medtronic; Invibio; StelKast; Ticona; Formae; Kyocera Medical; Wright Medical Technology; CeramTec; DJO; Journal of Arthroplasty; AAOS Exhibits Committee. Dr. Vail—DePuy, A Johnson & Johnson Company; Journal of Arthroplasty; American Board of Orthopaedic Surgery, Inc.; AAHKS; Knee Society. Dr. Berry—DePuy, A Johnson & Johnson Company. Ms. Chan—no disclosures.

Maureen Leahy is assistant managing editor of AAOS Now. She can be reached at leahy@aaos.org

Bottom Line

• Clinical characteristics associated with an increased risk of early revision following primary TKA are poorly understood, especially in older patients.
• This retrospective study found that chronic pulmonary disease, depression, alcohol abuse, drug abuse, renal disease, hemiplegia/paraplegia, and obesity are significant risk factors for early revision TKA in Medicare patients.
• This information is important for orthopaedic surgeons when counseling elderly TKA patients regarding their individual risks for early failure, and for risk-stratifying publicly reported outcomes in Medicare TKA patients.