Accessibility Tools
Characterizing Comorbidities in Total Joint Arthroplasty Patients in a Safety-Net Hospital Using the Age-Adjusted Charlson Comorbidity Index


Total knee and hip arthroplasty is often performed for severe cases of osteoarthritis. It is generally performed on older patients, usually over 55 years of age, and is more common in obese patients (“Hip and Knee Replacement Surgery FAQs,” n.d.; Namba et al. 2005) It is well documented that joint arthroplasty population has a high number of comorbidities at the time of surgery, which can greatly affect surgical outcomes. The presence of multiple comorbid diseases has been shown to increase patient’s length of stay and lead to greater utilization of resources after a total knee arthroplasty (Pugely et al. 2014). It may also delay diagnosis, alter treatment, lead to complications, influence survival, and confound analysis of outcomes (Feinstein1970). The goal of the present study is to analyze the distribution of comorbid diseases in patients who have undergone total joint arthroplasty at BronxCare Health System, which serves the poorest congressional district in the United States. We hypothesize that patients in this large, closed urban setting have a high incidence of comorbidities, calculated as both total number of conditions using the hospital’s internal comorbidity formula and scoring system, and using the Age-Adjusted Charlson Comorbidity Index (ACCI), thus requiring a shift in the bundled payment structure to account for the actual resource use as a result of the pre-existing comorbidities.


A retrospective analysis was conducted reviewing consecutive total joint arthroplasty patients at BronxCare Hospital System receiving surgery between 2008 and 2018 (N=1836). All procedures were performed by two fellowship-trained joint replacement surgeons. The total number of conditions per person was determined using the department’s own formula which takes into account additional comorbidities and risk factors common in our particular patient population proven to increase risk of complications such as obesity, anemia or smoking status, but does not weight the comorbidities by severity. Additionally, the relevant comorbidities were used to calculate the Age-Adjusted Charlson Comorbidity Index (ACCI), which is includes fewer comorbidities, but weights them based on severity. From this, we determined the score distribution of both the hospital score and of the ACCI of the population. The most frequent conditions present were also identified. Descriptive statistical analysis was performed to find central tendency and variance.


Within the patient population, 5% had no comorbidities, 36.7% had between 1 and 4, 41.6% had between 5 and 9, and 16.8% had over 10 comorbid conditions (mean: 6; sd: 3.66; mode: 4) [Graph 1]. Regarding AACI scores, 5.5% of the patient population scored 0, 48% scored between 1 and 4, 43% scored between 5 and 9, and 4% scored above 10 (mean: 4.4; sd: 2.6; mode: 4) [Graph 2]. Out of the total patient population, 26% presented with one or more psychiatric issues. The most frequently occurring comorbid conditions according to the hospital criteria in this population were hypertension (N=1228), obesity (N=755), diabetes (N=583), anemia (N=533), and valve disorder (N=522).


Using the described methodology, our analysis uncovered the presence of a high incidence of comorbidities in the BronxCare Orthopedics total joint replacement patient population. We had previously observed this, but had not statistically confirmed it to date. Total joint arthroplasty is a common procedure performed worldwide and it is well known that comorbidities can influence outcomes. Additionally, it has been shown that safety net hospitals that serve patients of lower socioeconomic status, like BronxCare, have a patient population with increased comorbidities (Balasubramanian et al. 2017). It is possible that the greater occurrences of comorbidities in total joint arthroplasty patients is in part due to the trend that this procedure is more commonly required in older and obese osteoarthritis patients. Both age and obesity are risk factors for other comorbidities such as hypertension and diabetes, which can impact surgical complications and outcomes and often require more extensive care (Namba et al. 2005). Thus, regardless of the reason for increased rate of comorbidities, it is critical that joint replacement centers properly assess the pooled severity of comorbid conditions in their patient population for two main reasons. First, awareness of increased comorbidities dictates the care delivery process required to achieve quality outcomes. Spotlighting certain especially risk-associated comorbidities that were previously unknown also allows for the enactment of special protocols. Second, this information is useful to assist in calculating the total cost of procedures used for value-based healthcare payments. As total joint arthroplasty becomes more common, gaining a better understanding of the severity of pooled comorbidities within a hospital’s respective patient population can lead to a more accurate assessment in developing efficacious payment systems adopted for the procedure (Wolford et al. 2015). It has been studied and declared that bundled payments for total joint payments are promising forkeeping costs down and quality up, but require additional attention and risk adjustment of complexities for patients with high comorbidity burdens (McLawhorn and Buller 2017). In our opinion it is critical that the Center for Medicare and Medicaid Services (CMS) and commercial payors include these risk adjustments for pooled comorbidities so that hospitals with medically complex patients, such as BronxCare and other safety net hospitals, are not penalized or disadvantaged (Ellimoottil et al. 2016). Therefore, rather than stratifying individuals for individual payment, pooled comorbidity information can be used to better inform bundled payments for joint replacements based on severity of comorbidities of the population served by the center. Our suggestion is that joint replacement centers, especially hospitals similar to BronxCare across the nation, go through the exercise described and carried out here in order to understand the severity of the pooled comorbidities in their patients. Not only is it important for these surgical centers to be more aware of the health problems present in their patients, but they should also use this information to better assess total cost of procedures.

Noshin Nuzhat 1, Melanie Anaya 1, Gabriela de Queiroz Campos 1, Ariel R.C. Silverman 2, Kylen Soriano 3, Ronald Huang 4, Morteza Meftah 4, Ira H. Kirschenbaum 4

1 Brown University, 2 McKinsey Consulting, 3 University of California San Francisco, 4 Orthopaedic Surgery, BronxCare Health System