Published 5/1/2017
Terry Stanton

Identifying Risk Factors for Unplanned Readmissions Following TJA

A study that sought to identify trends and risk factors for unplanned readmission following total joint arthroplasty (TJA) found that increasing body mass index (BMI), an American Society of Anesthesiologists (ASA) score of ³3, and discharge to an inpatient rehabilitation facility were independent risk factors for early unplanned readmissions.

The study, presented at the AAOS Annual Meeting by Leah Herzog, MD, covered 1,615 primary total hip (511) and knee (654) procedures identified from a database at a large urban academic hospital for all patients who underwent elective primary total hip arthroplasty (THA) and total knee arthroplasty (TKA) from 2004 through 2013. Patients who died during the index admission, had bilateral TJA or unicondylar knee arthroplasty (UKA) procedures, or were returning for a subsequent planned elective TJA procedure were excluded. A combination of administrative data mining and retrospective chart reviews were used to collect patient demographic, clinical, and surgical data.

BMI, insurance type (government-based versus private), length of stay, ASA physical status scores, anesthesia technique (general versus neuraxial), relevant medical comorbidities, and discharge disposition status (inpatient rehabilitation versus home) were among the parameters obtained. Medical comorbidities were initially obtained via diagnosis codes from the hospital's administrative database; these were supplemented and modified as necessary by verifying each diagnosis with the history and physical examination document associated with the index admission.

Surgical variables collected included total time spent in the operating room, total surgical times, total tourniquet times for all TKA procedures, estimated blood loss during the operation, and perioperative transfusion rates. For the latter, the authors wrote, "we combined intraoperative and postoperative blood transfusions into one 'perioperative' category, and any instances of multiple or subsequent blood transfusions for the same patient were not factored into the analysis."

The risk factors
The study found that an ASA score of ³3 correlated with risk of unplanned readmission at both 30 and 90 days after surgery. The authors noted that a high ASA score as a predictor of early unplanned readmission "is becoming an increasingly popular topic in the orthopaedic literature." A correlation has previously been found in studies or readmission rates for orthopaedic trauma patients and for those undergoing elective anterior cervical diskectomy and fusion, while "the relationship between higher ASA scores and risk of early unplanned readmission is not well delineated with respect to TJA literature."

Discharge to inpatient rehabilitation, use of anesthesia for the operation, and increasing BMI levels were all associated with increased likelihood of readmission at 30 days. With the exception of general anesthesia, each of these factors also demonstrated statistical significance in the adjusted model at 90 days. Although several medical comorbidities trended toward statistical significance, only congestive heart failure reached statistical significance at the 90-day time period.

The authors wrote that to their knowledge, no study has reported general anesthesia as an independent risk factor for unplanned readmission to the hospital within 30 days. Aside from general anesthesia, no other surgical factors were found to be independently associated with an increased likelihood of readmission during the study period.

Patient discharge disposition, the authors note, "remains a controversial topic with respect to risk of early unplanned readmission." They write, "Over the last 20 years, there has been a gradual shift away from discharging the majority of patients to inpatient rehab facilities in favor of sending more patients home with home health services (HHS) or home under self-care (HUSC). From 1998 to 2009, reported discharge rates to home with HHS increased from 15 percent to 35 percent. Our institution also followed a similar trend from 2004 to 2013, with the annual percentage of primary elective TJA patients being discharged home increasing from fewer than 15 percent to almost 65 percent. This is likely explained by more early, aggressive physical therapy regimens that are started quickly after surgery, and an increasingly active role from the social services department in coordinating the utilization of home health services and outpatient physical therapy programs."

With respect to BMI, the authors write that "BMI values and the various obesity categories being reported as independent risk factors for unplanned readmission following elective TJA remain controversial, heterogeneous in nature, and largely inconclusive." A limitation of reporting BMI information, they noted, is that the ICD-9 diagnosis coding system comprises two separate BMI coding systems, the first being the diagnosis codes that establish overweight, obese, morbidly obese, and super obese categories and the second system being V-codes that record BMI in 5 to 10 unit increments.

The authors conclude: "Unplanned readmission rates are being used as quality performance indicators, and all institutions will eventually be held to the regional and national standards. Understanding the relevant risk factors in the context of unique populations served will better help individual hospitals and orthopaedic surgeons stratify patients appropriately based on the potential risk of unplanned early readmission. … We advocate for future studies to consider reporting from the perspective of the entire 90-day post-discharge period."

Dr. Herzog's coauthors of "Ten-Year Trends and Independent Risk Factors for Unplanned Readmission Following Elective Total Joint Arthroplasty at a Large Urban Academic Hospital" are Matt Varacallo, MD; Nader Toosi, MD; and Norman Johanson, MD.

The authors' disclosure information can be accessed at www.aaos.org/disclosure

Terry Stanton is the senior science writer for AAOS Now. He can be reached at tstanton@aaos.org