REGISTRY REVIEW: An Overview of Hip and Knee Arthroplasty in the US

    The 2020 Annual Report from the American Joint Replacement Registry (AJRR) contains a wealth of data on hip and knee arthroplasty procedures performed in the US between 2012 and 2019.

    “Our primary goal is to provide data that is actionable to orthopaedic surgeons in their journey to improve the lives of millions of Americans who suffer from hip and knee arthritis,” said Bryan D. Springer, MD, chair of the AJRR Steering Committee. “The information in this year’s report gives the most comprehensive picture to date of patterns of hip and knee arthroplasty practice and outcomes in the United States.”

    Over the next few months, we’ll examine some of the more interesting data points, starting with this high-level overview of hip and knee arthroplasty:

    Breakdown of Procedures

    Elective total hip arthroplasty (THA) was the most commonly performed hip arthroplasty in 2019, with 91,814 procedures done by 3145 surgeons. This was followed by:

    • 8963 hemiarthroplasties performed by 2060 surgeons
    • 3644 revision THAs performed by 1216 surgeons
    • 2834 THAs for hip fracture performed by 1143 surgeons
    • 248 hip resurfacings performed by 34 surgeons

    Not surprisingly, primary total knee arthroplasty (TKA) was far more common than partial or revision knee arthroplasty, with 139,991 procedures performed by 3639 surgeons in 2019. This was followed by:

    • 11,460 revision TKAs performed by 2112 surgeons
    • 6507 partial knee replacements performed by 1123 surgeons

    The AJJR defines “partial knee replacement” as medial unicompartmental, lateral unicompartmental, and patellofemoral arthroplasty.

    Interestingly, far fewer surgeons who perform primary THA or TKA also perform revision procedures, suggesting that general orthopaedic surgeons who are comfortable with the primary procedures are referring patients to surgeons who specialize in joint replacement for the revision procedures.

    In addition, the AJRR data confirm what’s generally been known for years: Very few surgeons are still performing hip resurfacing, and when they do so, it’s indicated for a small population. Similarly, partial knee arthroplasty is a more narrowly indicated procedure, with fewer candidates and fewer surgeons choosing to perform partial knee arthroplasty.

    Mean Patient Age

    The mean age of the 625,097 patients who underwent elective primary THA between 2012 and 2019 was 66 years, and the mean age of the 57,970 patients who underwent revision THA during that period was just a little bit older at 66.9 years.

    For knee arthroplasty, the mean age of the 995,410 patients who underwent elective primary TKA between 2012 and 2019 was 66.9 years, and the mean age of the 57,970 patients who underwent revision TKA during that period was slightly younger at 65.4 years.

    These data suggest that primary and revision THA and TKA are increasingly being offered to younger patients to restore function and relieve pain.

    The younger mean age for revision TKA is interesting and may reflect the younger mean age of patients undergoing partial knee arthroplasty – 64.5 years. Research has shown that many partial knee arthroplasty patients need a revision procedure within a few years of the index surgery, although more-recent data show longer-term survivorship of partial knee arthroplasty. [1]

    Hip resurfacing was reserved for younger patients (mean age 53.6 years), while older patients typically underwent hemiarthroplasty and THA for hip fracture (mean age 82.4 years and 72.4 years, respectively).

    Length of Stay

    Mean length of stay (LOS) for elective primary THA has dropped from 2.7 days in 2012 to just 1.9 days in 2019. For elective primary TKA, mean length of stay has decreased considerably, from 2.9 days in 2012 to 1.9 days in 2019.

    These data parallel the adoption of rapid recovery protocols that have the goal of reducing LOS without sacrificing patient safety. In addition, the Centers for Medicare and Medicaid Services has removed TKA and THA from the Inpatient Only list, making further decreases in LOS possible in the next few years.

    The mean LOS for hemiarthroplasty and for THA for hip fracture were also reduced between 2012 and 2019, but not as dramatically: from 5.7 days to 5.4 days for hemiarthroplasty (after increasing to 6.0 in 2015) and from 4.8 days to 4.5 days (after increasing to 5.1 in 2015) for THA for hip fracture.

    Similarly, mean LOS for revision TKA decreased slightly from 2012 to 2019, from 3.7 to 3.3 days (after increasing in 2014, 2015, and 2018). Partial knee arthroplasty had the most significant reduction in mean LOS: from 2.3 days in 2012 to 1.0 day in 2016.

    The 2020 Annual Report can be found here.


    1. Tan MWP, Ng SWL, Chen JY, Liow MHL, Lo NN, Yeo SJ. Long-term functional outcomes and quality of life at minimum 10-year follow-up after fixed-bearing unicompartmental knee arthroplasty and total knee arthroplasty for isolated medial compartment osteoarthritis. J Arthroplasty. 2020 Nov 1;S0883-5403(20)31148-7. doi: 10.1016/j.arth.2020.10.049. Online ahead of print.