Previous investigators have characterized TKA outcomes at the population level for the Medicare population [3, 17]. It has also been documented that TKA results in decreased pain and improved function in patients who have disabling arthritis of the knee . However, complications requiring revision surgery within the first 12 months after primary TKA are associated with increased costs and poor clinical outcomes. Identifying risk factors for early failure is important for informing shared medical decision-making for elderly patients who are considering elective TKA for treatment of advanced knee osteoarthritis and for risk stratification of publicly reported outcomes.
Our study has several notable limitations. First, we relied on administrative claims data (which do not indicate laterality) to identify revisions and risk factors for early failure. However, previous investigators have reported reasonable correlation between administrative claims and the clinical record when evaluating causes and types of revision total joint arthroplasties . Second, our study was limited to Medicare patients; further study using different data sets will be needed to determine whether our findings are generalizable to younger patients who undergo primary TKA. Finally, our findings are limited to risk factors for failures that occur during the first 12 months after primary TKA, and therefore it is uncertain whether the same or other risk factors are associated with an increased long-term risk of revision TKA. However, the impact of patient comorbidities on the risk of early failure after TKA has important clinical and policy implications for surgeons, hospitals, and patients.
Risk factors for complications and revision after TKA have been identified by previous investigators. Mortazavi et al.  investigated risk factors for revision after infection after primary TKA and found revision for infection, higher Charlson index greater than 3 (odds ratio [OR], 2.48; 95% CI, 1.33-4.65), and diagnosis other than osteoarthritis (OR, 3.90; 95% CI, 1.55-9.82) at the time of primary TKA were predictors. Heck et al.  investigated the odds of revision TKA among Medicare patients and found that male sex, younger age, longer length of stay, more diagnoses at the time of primary TKA hospitalization, unspecified arthritis type, surgical complications during hospitalization, and surgery done at an urban hospital were all independently associated with an increased risk of revision within 2 years. Kapadia et al.  compared outcomes of 531 patients undergoing TKA who had a history of tobacco use with nonsmokers at a single institution and found there was a statistically significant difference in survivorship (p < 0.001) at the time of their most recent followup. Sheng et al.  found age was a predictor of survivorship of 2637 revision TKAs from the Finnish Arthroplasty Registry. Patients who were older than 70 years of age had better rates of survival (p < 0.005).
As healthcare delivery and payment systems shift from volume-based to value-driven [5, 9, 21], increased emphasis will be focused on public reporting of physician performance and patient outcomes, including complication and revision rates for elective surgical procedures such as TKA. Furthermore, the United States has initiated a TKA outcomes registry, the American Joint Replacement Registry, which will be used to evaluate revision rates among patients undergoing TKA in the United States. It is important that publicly reported TKA outcomes and TKA registry results be appropriately risk-adjusted for factors beyond the control of the surgeon such as patient comorbidities, which are known to influence patient outcomes. The patient comorbidities identified in our study could be used in risk-adjustment models for public reporting of TKA outcomes and total joint arthroplasty registries to appropriately account for the patient characteristics that are associated with an increased risk of revision TKA.
In conclusion, chronic pulmonary disease, depression, alcohol abuse, drug abuse, renal disease, hemiplegia or paraplegia, and obesity are associated with an increased risk of early revision after primary TKA in Medicare patients. This information can be useful in shared medical decision-making when counseling elderly patients with modifiable and non-modifiable risk factors who are considering elective TKA regarding the risk of early failure and for risk-stratifying publicly reported outcomes in Medicare patients undergoing TKA.
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