Comorbidities as Predictors of Pain Outcomes After Primary and Revision Total Knee Arthroplasty
By Geetha Achanta, Ph.D.
Total knee arthroplasty (TKA) is the most common joint arthroplasty performed in the United States. An estimated 672,000 TKAs were performed in 2009 alone1 and the annual volume of primary TKAs is projected to grow six-fold between 2005 and 2030.2 Studies have shown that medical comorbidities can have adverse effects on outcomes such as pain and function and are associated with perioperative complications and longer hospital stays.
To identify the medical and psychological comorbidities that are associated with poor pain outcomes after primary or revision TKA, Jasvinder A. Singh, M.D., and his colleagues at the University of Alabama Center for Education and Research on Therapeutics (UAB CERT) and the Mayo Clinic conducted a study3 using prospectively collected data from the Mayo Clinic Total Joint Registry. The team selected patients who had undergone primary or revision TKA between 1993 and 2005 and had responded to a standardized followup questionnaire to assess post-TKA knee pain and function at 2 or 5 years.
The medical comorbidities assessed by the UAB CERT team were based on the Deyo-Charlson Comorbidity Index and included six disease groups hypothesized to be associated with moderate to severe pain—heart disease, peripheral vascular disease, renal disease, chronic obstructive pulmonary disease, diabetes, and connective tissue disease. Psychological comorbidities of interest included anxiety and depression.
"To our knowledge, ours was among the first studies that simultaneously assessed the association between various medical and psychological comorbidities and an increased risk for pain outcomes in a large cohort of patients who had undergone TKA," explained Dr. Singh.
Patients who had undergone primary or revision TKA were characteristically similar in age (mean age of 68 vs. 69 years), sex (55% vs. 50% female), and weight (87% were overweight or obese in both surgical groups). However, they differed with regard to their underlying diagnoses and comorbidities.
Among patients in the primary TKA group, the predominant underlying diagnosis was osteoarthritis (94%) followed by rheumatoid arthritis (4%) and other diagnoses (2%). Among the patients in the revised TKA group, the underlying diagnoses were more diverse and included loosening, wear, or osteolysis in the knee joint (62%), dislocation, bone or prosthesis fracture, instability, or nonunion (25%), and a previous failed arthroplasty or infection (12%).
Medical and psychological comorbidities were common in both TKA groups. In the primary TKA group, these included peripheral vascular disease (5%), chronic obstructive pulmonary disease (11%), anxiety (6%), and depression (11%). In the revision TKA group, these included diabetes (10%), chronic obstructive pulmonary disease (9%), anxiety (5%), and depression (8%).
The UAB CERT team used the data from the 2-year and 5-year followup questionnaires to analyze the association between the comorbidities and pain, with some important findings. "In our study, anxiety was found to be a significant predictor of poor pain outcomes 2 years after primary TKA, while anxiety, depression, and heart disease were significant predictors of poor pain outcomes 5 years after primary TKA. Additionally, depression was found to be a significant predictor of poor pain outcomes 2 years after revision TKA." No significant associations between medical and psychological comorbidities and the risk of moderate to severe pain were found at 5 years after revision TKA.
Although the study analyses made adjustments for age, sex, body mass index, distance from a medical center, operative diagnosis, and implant fixation, other factors were not controlled. These factors, which can influence pain outcomes, include TKA-related complications, adherence to rehabilitation programs, and patient expectations and satisfaction. In addition, the questionnaire response rates were low at 5 years (57% for primary TKA vs. 48% for revision TKA), which reduces confidence in the estimates at the 5-year follow-up.
"The findings of our study have several implications for clinical practice," noted Dr. Singh. "First, we need to inform patients, who have any of the comorbidities identified in our study that are predictive of poor pain outcomes, of the increased risk of moderate to severe pain before their surgery. Second, this research may lead to development of a patient-specific risk score for persistent pain that should be calculated before surgery that gives patients realistic expectations of pain outcomes after TKA and allows them to truly weigh the benefits and risks of undergoing the procedure. And third, future studies should be conducted to determine if optimal management of comorbidities in the preoperative or perioperative period might improve TKA-related pain outcomes."
Dr. Singh added that he is interested in the association between psychological comorbidities (anxiety and depression) and an increased risk of poor post-TKA pain outcomes because these comorbidities are modifiable if optimally treated. In future studies, he and his team hope to examine whether early recognition of these psychological comorbidities and their optimal management might improve outcomes after TKA.
The Centers for Education and Research on Therapeutics (CERTs) are a nationwide network of six research centers and a coordinating center that receive core financial support from the Agency for Healthcare Research and Quality. The CERTs conduct research and provide education that will advance the optimal use of drugs, medical devices, and biological products; increase awareness of the benefits and risks of therapeutics; and improve quality while cutting the costs of health care.
Wier LM, Pfuntner A, Maeda J, et al. HCUP Facts and Figures: Statistics on Hospital-Based Care in the United States, 2009. Rockville, MD: Agency for Healthcare Research and Quality; 2011. Available at http://hcup-us.ahrq.gov/reports/factsandfigures/2009/pdfs/FF_report_2009.pdf.
Kurtz S, Ong K, Lau E, et al. Projections of primary and revision hip and knee arthroplasty in the United States from 2005 to 2030. J Bone Joint Surg Am. 2007 Apr;89(4):780-5. PMID: 17403800. PMID: 17403800
Singh JA, Lewallen DG. Medical and psychological comorbidity predicts poor pain outcomes after total knee arthroplasty. Rheumatology (Oxford). 2013 May;52(5):916-23. PMID: 23325037.