Abstract
BACKGROUND: Degenerative lumbar disease (DLD) affects older adults, causing lumbar degeneration and lower extremity dysfunction. The five-times sit-to-stand test (5xSTS) reveals kinematic changes associated with DLD. While marker-based motion capture systems detect these changes, their complexity limits clinical use. Markerless motion capture offers a portable alternative, yet its functional assessment applications in DLD remain underexplored. Thus, the aim of this study is to evaluate the reliability and validity of markerless motion capture for assessing functional tests in DLD patients. METHODS: This study included 11 healthy individuals (mean age: 27.28 ± 6.92 years) and 10 with DLD (mean age: 70.00 ± 8.08 years). Participants performed the 5xSTS while being recorded by marker-based (VICON) and markerless (MediaPipe) systems using two synchronized cameras. Test-retest reliability was assessed over one week via the intraclass correlation coefficient (ICC). Concurrent validity and agreement between VICON and MediaPipe were evaluated via Pearson/Spearman correlation coefficients, systematic bias, and the root mean square error (RMSE). Movement time, joint excursions, and angular velocities were also analyzed and compared across two groups. RESULTS: Both systems showed high test-retest reliability (ICC: 0.81-0.99) and strong correlations (r: 0.75-0.99). The highest RMSE was observed at the ankle in the anterior-posterior (A-P) direction in the DLD group (54.55 mm) and at the hip A-P axis in the control group (51.20 mm). The lowest RMSE was found at the knee medial-lateral (M-L) axis in the DLD group (7.88 mm) and at the ankle M-L axis in the control group (8.54 mm). Bias values ranged from 0.30 mm (hip vertical in control group) to +53.47 mm (ankle A-P in DLD group), with underestimation more common at the hip and overestimation at the ankle. The control group demonstrated a faster 5xSTS completion time (5.89 ± 0.69 s vs. 8.13 ± 1.96 s, p < 0.05), greater hip joint excursions during sit-to-stand (65.07 ± 25.94° vs. 38.13 ± 9.84°, p < 0.05) and stand-to-sit (62.56 ± 24.74° vs. 27.85 ± 11.45°, p < 0.05) tests, and higher angular velocities compared to the DLD group. CONCLUSION: MediaPipe markerless motion capture can quantify 3D kinematic changes in DLD patients during functional performance. It enables a clinical evaluation with minimal setup, offers potential for remote assessment, and accurately detects sagittal plane movement. The two-camera system provides 3D kinematic data comparable to multi-camera systems, suitable for home rehabilitation and assessment.