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    REGISTRY REVIEW: Primary Total Hip Arthroplasty in the US

    In 2007, the editors of The Lancet dubbed total hip arthroplasty (THA) the “operation of the century,” noting that when THA was introduced in the 1960s, it “revolutionised management of elderly patients crippled with arthritis, with very good long-term results.” [1]

    Today, THA is one of the most frequently performed orthopaedic operations. Surgeons who participate in the American Joint Replacement Registry (AJRR) have contributed the details on nearly 625,000 primary THAs 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:

    Up to age 60, men were more likely than women to undergo THA. More than 50% of elective primary THA patients in the 2 youngest age groups in the AJRR database were men: 55.4% for under age 50 and 52.2% for ages 50 to 59. That changed pretty dramatically by age 60, with women accounting for 55.1% of procedures performed in the 60 to 69 age group. The percentage of women continued to climb with each decade, hitting 70.5% by age 90.

    The most commonly used femoral neck head size was 36 mm. The AJRR data show a strong preference for 36-mm femoral heads: In 2019, this head size was used in 61.2% of primary THAs, compared with 20.4% for 32-mm femoral heads. Use of the 36-mm heads has steadily increased since 2012, while the use all other head sizes has steadily decreased.

    Interestingly, dual mobility bearings have been gaining ground in primary THA, especially in patients at both ends of the age spectrum. Overall, the percentage of dual mobility bearings used in primary THAs more than doubled between 2012 and 2019, from 4.1% of all reported procedures to 8.6%. Surgeons were more likely to use dual mobility bearings in patients under age 50 (8.1%) and in those between ages 80 and 89 (7.5%) and age 90 and older (9.6%), according to the AJRR data.

    Cobalt chromium femoral heads have, not surprisingly, fallen out of favor – except in older patients. By 2014, ceramic had overtaken cobalt chromium heads as the material of choice for femoral heads, no doubt due to concerns over trunionosis and taper corrosion. The use of ceramic heads increased from 38.4% in 2012 to 67.8% in 2019, while the use of cobalt chromium decreased from a high of 56.1% in 2012 to just 24.3% by 2019. The majority of cobalt chromium heads were implanted in patients in the 2 oldest age groups: 63.8% of procedures in patients ages 80 to 89 and 77.5% of procedures in patients age 90 and older. Similarly, the use of ceramic-on-polyethylene bearing surfaces has risen significantly since 2012, while use of metal-on-polyethylene implants has dropped dramatically.

    Antioxidant polyethylene is not making much progress as a liner material; surgeons vastly prefer highly cross-linked polyethylene liners. There has been growing interest in the use of antioxidant polyethylene in primary total knee arthroplasty. That has not been the case in primary THA: The AJRR data show that usage of antioxidant polyethylene grew from 2012 to 2015 but then leveled off and has been holding fairly steady at around 12.5% of procedures since then.

    Although cementless stem fixation nearly doubled between 2012 and 2019, it was used in only a small percentage of elective primary THAs. Surgeons have “rediscovered” cementless fixation for primary THA: Use of cement increased from 2.7% of elective procedures in 2012 to 5.3% in 2019. As with the use of cobalt chromium heads, patients in the 2 oldest age groups were more likely to have cementless stem fixation than younger patients: 13.7% of procedures in patients ages 80 to 89 and 32.7% of procedures in patients age 90 and older.

    Given the popularity of ceramic-on-polyethylene bearing surfaces, it’s not surprising that 7 of the 8 most commonly used femoral stem/acetabular cup/bearing surface combinations included ceramic-on-polyethylene bearings. Since 2014, the most commonly implanted combination has been the Accolade II stem and Trident cup with a ceramic-on-polyethylene bearing surface. However, the AJRR data show that as of 2019, 2 other combinations were catching up: the Corail stem/Pinnacle cup with a ceramic-on-polyethylene bearing surface and the Summit stem/Pinnacle cup with a ceramic-on-polyethylene bearing surface. Accolade II overtook Corail as the most commonly used femoral stem as of 2014, while Pinnacle has been the most commonly used acetabular cup since 2012.

    The revision rates associated with the 6 most commonly used cementless hip constructs were relatively low.

    Top 6 Cementless Hip Constructs

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

    As with primary total knee arthroplasty, increasing BMI was associated with a greater risk of revision THA. Obesity has an impact on revision rates, according to the AJRR data: All obesity classes were associated with an increased cumulative percent revision of primary THAs. Patients with a BMI of 40 or more (categorized as Obesity Class III) had a 2.4 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.

    Most patients were discharged home after primary THA, as was seen with discharge after primary total knee arthroplasty. In line with efforts to decrease the use of expensive post-discharge services, 85.8% of primary THA patients were discharged home with or without home healthcare in 2019. The other 14.2% 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.

    Reference

    1. Learmonth ID, Young C, Rorabeck C. The operation of the century: total hip replacement. Lancet. 2007 Oct 27;370(9597):1508-19. doi: 10.1016/S0140-6736(07)60457-7.