Acetabular Cup Fixation in Total Hip Arthroplasty Evaluated Using Laser Resonance Frequency Analysis

The initial fixation of the acetabular cup is crucial for outcomes in total hip arthroplasty (THA); however, stability is evaluated subjectively. We developed a Laser Resonance Frequency Analysis (Laser-RFA) system using low-output laser-induced vibration to objectively assess fixation. This study demonstrates the relationship between fixation strength and vibrational characteristics and evaluates surgeons' tactile assessment. In laboratory experiments, acetabular cups were press-fit into polyurethane simulated bone and stimulated with frequency-swept laser irradiation (preliminary laboratory experiment: 1500-4500 Hz; modified-condition: 2250-2750 Hz). Peak frequencies measured by the Laser Doppler vibrometer were correlated with fixation strength. In the clinical study, peak frequencies from microphone-recorded vibrations were compared between cases with and without screw fixation based on intraoperative tactile assessment. In a supplemental experiment, surgeons were divided into skilled and non-skilled groups. Participants implanted an acetabular cup into simulated bone, and tactile fixation strength was quantified. Periodic waveforms were identified in the preliminary experiment, and six peaks (Waves A-F) were defined in the modified-condition laboratory experiment. Waves A and B showed negative correlations with fixation strength, whereas Waves C-F showed positive correlations. Clinically, peak frequencies were lower in cases requiring screw fixation than in those not requiring screw fixation (approximately 2900 vs. 3050 Hz; p < 0.003). The supplemental experiment showed significant differences in fixation strength across all tactile assessment levels in the skilled group, whereas no significant differences were observed in the non-skilled group. These findings indicate Laser-RFA objectively assesses acetabular cup fixation and reflects the tactile assessment of experienced surgeons.