Table 1.

Inclusion/Exclusion criteria and rationale for the study of elective total hip/knee arthroplasty (THA/TKA) readmissions

Inclusion criteria	Rationale
1. Enrolled in Medicare fee-for-service	Hospital claims data are regularly available only for Medicare fee-for-service beneficiaries.
2. Age 65 or older	Medicare patients younger than age 65 qualify for Medicare due to severe disability, making them distinctly different from the elderly Medicare population.
3. Discharged from a non-federal acute care hospital alive	Only those patients who are alive at time of hospital discharge are eligible for a readmission.
4. Enrolled in Parts A and B Medicare for the 12 months prior to the date of the index admission	Including Medicare Part A beneficiaries ensures there are no Medicare Part C (Medicare Advantage patients) in the data. Enrollment in Medicare in the 12 preceding months ensures 1 year of administrative data for risk adjustment purposes.
5. Have a qualifying elective primary THA/TKA procedure, without any of the following:	Elective primary THA/TKA is the procedure of interest in this study.
(a) Femur, hip or pelvic fractures coded in the principal or secondary discharge diagnoses fields of the index admission	Procedures to correct an orthopedic fracture are considered non-elective. Patients with orthopedic fracture tend to have higher mortality, complication and readmission rates.
(b) Partial hip arthroplasty procedures with concurrent THA/TKA	Partial hip arthroplasty are primarily indicated for hip fractures.
(c) Revision procedures with a concurrent THA/TKA	Few hospitals perform THA/TKA revision procedures and are associated with higher mortality, complication and readmission rates.
(d) Resurfacing procedures with a concurrent THA/TKA	Resurfacing procedures are distinctly different than THA/TKA and are primarily indicated for younger, healthier patients.
(e) Mechanical complication of the pelvis, sacrum, coccyx, lower limbs, or bone/bone marrow or disseminated malignant neoplasm coded in the principal discharge diagnosis field	A mechanical complication was likely present on admission and may require more technically complex procedures to correct. Patients with malignant neoplasms undergoing a THA/TKA are likely not elective and the patients are more likely to have a readmission.
(f) Removal of implanted devices/prostheses	Removal of implanted device/prostheses may be more complicated.
(g) Transfer from another acute care facility for THA/TKA	Transfers from another acute care facility for THA/TKA is likely not elective.
Exclusion criteria
1. Without at least 30 days post-discharge enrollment in fee-for-service Medicare	Since readmissions are identified using claims data, 30 days of post-discharge enrollment in Medicare fee-for-service is required.
2. Discharged against medical advice (AMA)	Patients leaving AMA may not allow providers to deliver complete and full care to prepare the patient for discharge.
3. Admitted for the index procedure and subsequently transferred to another acute care facility	Including these cases in the readmission measure makes it difficult to determine to which hospital the readmission outcome should be attributed.
4. With more than two THA/TKA procedure codes during the index hospitalization	More than two THA/TKA procedures likely reflects an error in coding.

Source: Suter et al. [10].