Multimorbidity Definitions May Improve Clinical Decision-Making for Older Patients

Which older patients with multiple comorbidities have the greatest mortality risk after an inpatient orthopaedic procedure? And which comorbidities are responsible for that risk?

The answers have not always been clear cut: Conventional multimorbidity definitions have limited clinical usefulness because they label the majority of older patients as “multimorbid,” do not specify which comorbidities are contributing to the risk, and do not incorporate the patient’s functional status.

Now, researchers from the University of Pennsylvania Perelman School of Medicine in Philadelphia have developed and validated better surgical, specialty-specific multimorbidity definitions based on distinct high-risk comorbidity combinations. They have done this not only for older patients undergoing inpatient orthopaedic procedures, but also for older general surgery and vascular surgery patients.

The new definitions, which also address functional status, can help in clinical decision-making and offer more-accurate comparisons of performance from one hospital to another, according to the authors of the study, which has been published online ahead of print by the Journal of the American College of Surgeons.

“Ultimately, our multimorbidity methodology is a powerful way to assess risk and it’s easy to apply because it uses administrative datasets,” said the study’s lead author Omar I. Ramadan, MD, MSc, a general surgery resident at the Perelman School of Medicine.

Multimorbidity Definitions

For the first step in developing the multimorbidity definitions, the researchers analyzed Medicare claims data on patients aged 66 to 90 who underwent inpatient orthopaedic, general, or vascular surgery between 2016 and 2017. The definitions were validated using Medicare claims data for patients who underwent these procedures between 2018 and 2019.

Patients were categorized into clinically relevant groups by ICD-10 principal procedure codes. The researchers did not include patients with metastatic cancer or Alzheimer’s disease and related dementias or patients who were aged 90 or older. Their reason: These conditions and that age group are already associated with high mortality rates, and these patients would likely have different goals of care if faced with severe postoperative complications. However, patients with metastatic cancer or Alzheimer’s disease and related dementias and those aged 90 and older were studied using the new multimorbidity definitions.

The researchers defined multimorbidity as the presence of 1 or more qualifying comorbidity sets (QCSs). The QCSs, in turn, were defined as combinations of 1 to 3 comorbidities that were associated with at least 2-fold (for orthopaedic and general surgery patients) or 1.5-fold (for vascular surgery patients) greater risk of 30-day mortality compared with patients in the same age group undergoing the same procedure.

For further validation, the researchers tested whether patients with multimorbidity had different outcomes based on hospital quality, as it is well established that higher-quality hospitals are associated with better outcomes for high-risk patients. The researchers defined higher-quality hospitals as those with a nursing skill mix and surgical, specialty-specific patient volume above the median, as well as a resident-to-bed ratios (>0.25) characteristic of major or very major teaching hospitals.

Key Study Findings

Compared with conventional multimorbidity definitions, the new definitions labeled far fewer patients as multimorbid:

  • For orthopaedic surgery, the new definition identified 40.2% of the older population as multimorbid versus 55.9% of patients when using a conventional definition.
  • For general surgery, the new definition identified 55.9% of the older population as multimorbid compared with 85.0% with the conventional definition.
  • For vascular surgery, the new definition identified 52.7% of the older population as multimorbid versus 96.2% with the conventional definition.

Thirty-day mortality was also higher with the new definition:

  • 1.68% with the new definition versus 1.13% with the old definition for orthopaedic surgery
  • 5.64% with the new definition versus 3.96% with the conventional definition for general surgery
  • 7.00% with the new definition versus 4.43% with the conventional definition for vascular surgery

The researchers also found that higher-quality hospitals offered significantly greater mortality benefits than other hospitals for multimorbid versus non-multimorbid orthopaedic and general surgery patients, but not vascular surgery patients, in keeping with prior literature.

The highest risk (30-day mortality) QCSs were:

  • Protein-calorie malnutrition for orthopaedic surgery
  • Home hospital bed or wheelchair use combined with thrombocytopenia and other hematological disorders for general surgery
  • Acute heart or respiratory failure for vascular surgery

Possible Benefits of the New Definition

The new multimorbidity definitions will help surgeons better explain the risks associated with any given procedure to patients and make better care decisions, Dr. Ramadan said. For policymakers and hospital systems, the definitions offer a better way of benchmarking and accurately comparing the performance of one hospital with that of another, he aid.

Research using the new multimorbidity definitions is continuing in several areas, including how to use the definitions to compare hospital systems with each other, and how to use them to quickly assess a patient’s risk for any given surgical procedure, Dr. Ramadan said.


Ramadan OI, Rosenbaum PR, Reiter JG, et al. Redefining multimorbidity in older surgical patients. J Am Coll Surg. 2023 Mar 15:e000659. doi: 10.1097/XCS.0000000000000659. Online ahead of print.

Leave a Reply

CME Updates