Biomechanical evaluation of the impact of collared cementless total hip arthroplasty stems on implant subsidence: a cadaveric in German

Background: With the increasing use of cementless total hip arthroplasty (THA), stem subsidence has emerged as one of the primary complications. Although electron beam melting (EBM)-manufactured stems have been demonstrated to prevent subsidence, there has been limited investigation into the comparative biomechanical impact of collarless and collared EBM cementless stems on stem subsidence in veterinary medicine. Aims: This study aimed to compare the stem implant resistance and failure mechanical properties between collarless and collared EBM-manufactured stems. Methods: Seven pairs of femurs were harvested from canine cadavers. In each pair of femurs, the left femur was implanted with a collarless, and the right femur with a same-sized collared cementless stem. Specimen constructs were mounted to the loading frame of a testing machine and load was transferred to the femoral stem parallel to the longitudinal axis of the femur until the stem subsided 5 mm. Load and stem displacement data acquired during the tests were used to generate load-displacement curves and obtain stiffness, yield, and failure data for each specimen construct. Yield and failure energies were calculated as the areas under the load-displacement curves to the respective points. The effects of implant type and load during subsidence were analyzed using paired t-tests. Results: The yield and failure loads for the collared stems were approximately 40% greater than for the collarless stems (156.39 +/-; 43.63 kgf vs. 112.01 +/- 59.83 kgf, P<0.05). Conclusion: This study supported the advantages of collared EBM stems, including subsidence prevention and better initial stability for early osteointegration.