Mid-term outcomes of the cementless collarless Paragon™ hip system in total hip arthroplasty

Background: The role of the collared stem in cementless total hip arthroplasty remains controversial. Registry publications suggest that collared stems may reduce revision rates; however, stem geometry and surface preparation may provide stability without the use of a collar even in patient cohorts of >75 years of age. This is seen as a survivorship rate equal to or better than cemented stems. Methods: We conducted a retrospective cohort study of 518 primary total hip replacements performed between January 2012 and October 2022 using the cementless collarless Paragon™ stem by a single surgeon regardless of age, gender, American Society of Anesthesiologist grade or Body Mass Index (BMI). Outcomes were compared using the Australian Orthopaedic Association National Joint Replacement Registry. Results: Analysis showed the cumulative percentage revision rate for the whole Paragon™ group was 2.4% at 8 years compared to 4.1% for all other stems by other surgeons recorded by the registry. Ten revisions (1.9%) were recorded, with only one involving the femoral stem (0.2%). The 8-year survivorship was 99.7%. Subgroup analysis showed no revisions among Class 3 obese patients (BMI ≥ 40, n = 41) and comparable outcomes in patients ≥60 years, challenging previous registry findings associating collarless stems with higher revision risk in elderly and obese cohorts. Conclusion: The results show comparable or superior outcomes to collared stems and survivorship regardless of patient age, gender, or BMI. Some findings suggest that the addition of a collar can benefit some designs, but the Paragon™ system demonstrates that an optimized stem geometry, without a collar, may not be essential for a stable fixation.