This document details the methodology for the Elective Primary Hip Arthroplasty measure and should be reviewed along with the Elective Primary Hip Arthroplasty Measure Codes List file, which contains the medical codes used in constructing the measure.
Episode-based cost measures represent the cost to Medicare for the items and services provided to a patient during an episode of care (“episode”). In all supplemental documentation, “cost” generally means the standardized1 Medicare allowed amount,2 and claims data from Medicare Parts A and B are used to construct the episode-based cost measures.
The Elective Primary Hip Arthroplasty episode-based cost measure evaluates a clinician’s risk-adjusted cost to Medicare for patients who receive an elective primary hip arthroplasty during the performance period. The measure score is the clinician’s risk-adjusted cost for the episode group averaged across all episodes attributed to the clinician. This procedural measure includes costs of services that are clinically related to the attributed clinician’s role in managing care during each episode from 30 days prior to the clinical event that opens, or “triggers,” the episode through 90 days after the trigger.
The 2010 prevalence of total hip arthroplasties in the United States population was 0.8%, increasing with age to 1.5% at 60 years and 5.9% by 90 years of age.3 There were an estimated 2.5 million individuals with a total hip arthroplasty in 2010, and the demand for primary hip arthroplasties is estimated to grow by 174% between 2005 and 2030.4 Currently, there is a high degree of variability in hip arthroplasty treatment, offering an opportunity to improve the quality of care and cost savings. Opportunities for improvement for elective primary hip arthroplasty include appropriate use of institutional post-acute care (e.g., having patients receive post-procedure treatment in a home health or outpatient therapy setting), improving adherence to correct treatment guidelines, and increasing the use of optimal surgical techniques.
The Elective Primary Hip Arthroplasty episode-based cost measure was selected for development based on input from an expert clinician committee—the Musculoskeletal Disease Management - Non-Spine Clinical Subcommittee—because of its impact in terms of patient population and clinician coverage, and the opportunity for incentivizing cost-effective, high-quality clinical care in this clinical area. Based on the initial recommendations from the Clinical Subcommittee, the subsequent measure-specific clinician expert workgroup provided extensive, detailed input on this measure.
The cost measure numerator is the sum of the ratio of observed to expected5 payment-standardized cost to Medicare for all Elective Primary Hip Arthroplasty episodes attributed to a clinician. This sum is then multiplied by the national average observed episode cost to generate a dollar figure.
The cost measure denominator is the total number of episodes from the Elective Primary Hip Arthroplasty episode group attributed to a clinician.
The Elective Primary Hip Arthroplasty cost measure uses the following data sources:
- Medicare Part A and B claims data from the Common Working File (CWF)
- Enrollment Data Base (EDB)
- Long Term Care Minimum Data Set (LTC MDS)6
Methodologically, the Elective Primary Hip Arthroplasty cost measure can be triggered based on claims data from: acute inpatient (IP) hospitals, hospital outpatient departments (HOPD), ambulatory/office-based care centers, and ambulatory surgical centers (ASC).
The cohort for this cost measure consists of patients who are Medicare beneficiaries enrolled in Medicare fee-for-service and who receive an elective primary hip arthroplasty that triggers an Elective Primary Hip Arthroplasty episode.
The cohort for this cost measure is also further refined by the definition of the episode group and measure-specific exclusions (refer to Section 4).
1 Claim payments are standardized to account for differences in Medicare payments for the same service(s) across Medicare providers. Payment standardized costs remove the effect of differences in Medicare payment among health care providers that are the result of differences in regional health care provider expenses measured by hospital wage indexes and geographic price cost indexes (GPCIs) or other payment adjustments such as those for teaching hospitals. For more information, please refer to the “CMS Part A and Part B Price (Payment) Standardization - Basics" and “CMS Part A and Part B Price (Payment) Standardization - Detailed Methods” documents posted on theCMS Price (Payment) Standardization Overview page. (
2 Cost is defined by allowed amounts on Medicare claims data, which include both Medicare trust fund payments and any applicable beneficiary deductible and coinsurance amounts.
3 Kremers et al. (2015). “Prevalence of Total Hip and Knee Replacement in the United States.” Journal of Bone and Joint Surgery 97(17):1386-97.
4 Kurtz et al. (2007). “Projections of primary and revision hip and knee arthroplasty in the United States from 2005 to 2030.” Journal of Bone and Joint Surgery 89(4):780-5.
5 Expected costs refer to costs predicted by the risk adjustment model. For more information on expected costs and risk adjustment, please refer to Section 4.5.
6 For information on how LTC MDS data are used in risk adjustment, please refer to Section 4.5.