Impact of surface structure and screw fixation on primary stability in three acetabular cup systems: A biomechanical...

Primary stability is essential for successful uncemented total hip arthroplasty (THA), as it facilitates early osseointegration and reduces the risk of implant failure. Acetabular cup design, surface morphology, and fixation strategy significantly influence this initial stability. This biomechanical study assessed the primary stability of three uncemented acetabular cup systems - Allofit-S®, EcoFit®-Epore®, and Revisio®-S - each with distinct surface characteristics and materials.

Using a standardized polymethacrylimide bone model and a custom-built hip acetabulum simulator, micromotions were measured under physiological torque. Rotational, translational, and total micromotion were evaluated across four screw fixation configurations (0-3 screws) using eddy current sensors with 0.1 μm precision. Statistical analysis included ANOVA and post-hoc LSD tests with Bonferroni correction (α = 0.05).

Rotational micromotion did not show any significant variation with the number of screws (p > 0.05). Translational and total micromotions varied significantly across implant types and fixation levels. EcoFit®-Epore® displayed the highest initial micromotion, which was noticeably reduced with screw augmentation (p = 0.003, p = 0.018). In contrast, Allofit-S® and Revision®-S demonstrated superior intrinsic stability with minimal benefit from screw fixation.

Implant design and surface morphology critically affect primary acetabular cup stability. Macrostructured and roughened surfaces (Allofit-S®, Revisio®-S) provide greater inherent stability, while highly porous implants (EcoFit®-Epore®) benefit evidently from screw fixation. These findings support tailored implant selection and fixation strategies based on patient-specific anatomy and surgical context to optimize outcomes in uncemented THA.