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    REGISTRY REVIEW: Primary Total Knee Arthroplasty in the US

    Surgeons who participate in the American Joint Replacement Register (AJRR) have contributed the details on nearly 1 million primary total knee arthroplasties (TKA) performed in the US, providing a snapshot of trends in this common orthopaedic procedure.

    Data in the AJRR’s 2020 Annual Report show that between 2012 and 2019:

    Women were more likely than men to undergo primary TKA. About 60% of TKA patients in the youngest 3 age groups – under 50, 50 to 59, and 60 to 69 – were women and 40% were men. By age 70, the percentage of men dropped to less than 40%, and then to under 35% by age 90. This is not surprising, as women typically have a longer lifespan than men. The AJRR data confirm that correspondingly, the percentage of women undergoing TKA grows as the population ages.

    Cruciate retaining implants are catching up to posterior stabilized implants. Each year between 2012 and 2017, at least 50% of primary TKAs were performed with a posterior stabilized implant. That changed in 2018 and 2019, when posterior stabilized implants were used for 48.8% and 45%, respectively, of primary TKAs. During those 2 years, the use of cruciate retaining implants was on the rise – up to 40.8% in 2018 and 43.2% in 2019 – as was the use of ultracongruent implants. Use of the latter type of implant had nearly doubled, growing from just 5.0% in 2012 to 9.4% in 2019.

    Use of antioxidant polyethylene inserts has exploded. Although highly cross-linked polyethylene remains the material of choice for inserts, it’s losing ground to antioxidant polyethene. Use of highly cross-linked polyethylene has dropped from a high of 59.7% of polyethylene inserts used in 2012 to 47.5% in 2019, while the use of antioxidant polyethylene has grown from 4.8% in 2012 to 29.3% in 2019. The share of conventional polyethyene has shrunk from 35.5% in 2012 to 23.2% in 2019.

    Cemented implant fixation is still the norm, but cementless fixation is growing. In most cases, surgeons cement the tibial and femoral components in a primary TKA, with cementless fixation accounting for only 9.9% of primary TKAs in 2019. However, the percentage of cementless TKAs has seen significant growth since 2012, when it was at only 1.9%. Interestingly, hybrid cemented/cementless fixation seems to be losing favor: From a high of 4.7% in 2013, hybrid fixation was used in only 2.5% of primary TKAs in 2019.

    Higher BMI may put patients at greater risk for revision TKA. According to the AJRR data, obesity has an impact on revision rates: Having an increased BMI was associated with an increased cumulative percent revision of primary TKAs. Patients with a BMI of 40 or more (categorized as Obesity Class III) had a 1.3 times higher risk for needing a revision TKA than patients with a normal BMI (18.5 to 24.9) after adjusting for sex and age.

    In 2019, 3 of the top 5 most commonly used tibial and femoral combinations included a posterior stabilized component. However, the most common combination used a cruciate retaining component. Between 2012 and 2017, the Triathlon/Triathlon PS was the top tibial/femoral combination for primary TKA. Then in 2018, it was eclipsed by the Triathlon/Triathlon CR, which pulled away in 2019. Rounding out the top 5 in 2019 were the Persona/Persona CR, the Persona/Persona PS, and the Attune/Attune PS. With cruciate retaining implants trending up, it will be interesting to see whether these data change in the 2021 report.

    The revision rates for the top 5 posterior stabilized and top 5 cruciate retaining implants have been quite low. Not only were the rates low, but they were also similar among implant types.

    Top 5 Posterior Stabilized Implants

    Based on data from the 2020 Annual Report from the American Joint Replacement Registry

    Top 5 Cruciate Retaining Implants

    Based on data from the 2020 Annual Report from the American Joint Replacement Registry

    Most patients were discharged home after primary TKA. With the emphasis on reducing costly post-discharge services, it’s not surprising that by 2019, 87.2% of patients were being discharged home with or without home healthcare. The other 12.8% of patients received post-discharge care at a skilled nursing facility, inpatient rehabilitation facility, or other type of facility.

    The 2020 Annual Report from AJRR can be found here.