Background: Choice of agent for venous thromboembolism prophylaxis (VTEP) after joint arthroplasty is a complex decision, the difficulty of which has been compounded by divergent guidelines. Specifically, the adequacy of aspirin monotherapy (ASA) for VTEP has long been debated between the American Academy of Orthopaedic Surgeons (AAOS) and the American College of Chest Physicians (ACCP). AAOS endorsed ASA in 2009; it was not until 2012 that ACCP supported ASA over no prophylaxis. Yet, many hospitalists remain unfamiliar with this practice, and as Orthopaedics co-management services become more common, hospitalists will increasingly share this challenging decision. As such, we investigated the impact of the convergence of AAOS and ACCP guidelines in 2012 to support ASA for VTEP. Our hypothesis was that ASA prescribing would increase after convergence of AAOS and ACCP guidelines.

Methods: This is a retrospective, IRB-approved chart review of patients at two tertiary care teaching centers located in the New York Metropolitan area. We collected data to assess preoperative VTE risk and examined VTEP prescriptions on postoperative day 1 (POD1) and discharge (D/C) from 7/2008 to 12/2011 (pre-period) and 1/2012 to 7/2014 (post-period), the periods pre- and post-convergence of guidelines. Statistical analyses included Chi square test to compare rates of ASA VTEP between the pre- and post- periods. Inclusion: adults, primary/revision TKA by ICD9, and CPT codes. Exclusions: preoperative full dose anticoagulation and hypercoagulability. The primary comparison was change in ASA monotherapy for VTEP between the pre- and post-periods.

Results: Of 368 records reviewed, 329 were included in analysis. There were no differences between the pre- and post-period groups for age, sex, BMI, estrogen therapy, malignancy, smoking status, prior VTE, bilateral procedures, or surgery within 3 months. On POD1, in the pre-period, 4.6% were prescribed ASA monotherapy vs 41.8% in the post-period (p<.0001). On D/C, in the pre-period,14.5% were prescribed ASA vs 53.1% in the post-period (p<.0001). In the pre-period, the most commonly prescribed class of agents were vitamin K antagonists (VKA) (POD1:35.3%, D/C: 42.1%) and Xa inhibitors (POD1: 29.0%, D/C: 23.0%). In the post-period, ASA predominated at both time points. There was a strong, inverse relationship between VKA and ASA use over the study period.

Conclusions: Our results indicate a significant change in orthopaedist prescribing patterns between the pre- and post-periods, with no apparent change in VTE risk in the populations studied. Once its role in VTEP, previously AAOS-endorsed, was supported by the ACCP, it appears that orthopaedic providers readily incorporated ASA into clinical practice. ASA may be favored over other VTEP agents for its lower bleeding risk profile and cost. The robust effect found in this study suggests that aligned guidelines have a powerful impact. Considering the growing practice of co-management, this may foreshadow a change in co-management hospitalist prescribing patterns.