Inter‐Session Repeatability of a Smartphone‐Based Markerless System to Measure Segment Length and Lower‐Limb Kinematics in Patients With End‐Stage Knee Osteoarthritis
4 affiliations
- 1Department of Orthopedic Surgery and Orthopedic Research Institute West China Hospital, Sichuan University Chengdu Sichuan Province China
- 2School of Physical Education Tianfu College of Southwestern University of Finance and Economics Mianyang Sichuan Province China
- 3Information Technology Center West China Hospital, Sichuan University Chengdu Sichuan Province China
- 4Department of Orthopedic Surgery and West China Biomedical Big Data Center West China Hospital, Sichuan University Chengdu Sichuan Province China
Abstract
Background: While kinematic analysis is crucial to characterize multi‐planar functional deficits in end‐stage knee osteoarthritis (OA), traditional laboratories impose severe physical burdens on patients. In‐field markerless systems like OpenCap offer an accessible alternative, yet their repeatability in this population remains underexplored. The objective of this study was to assess the inter‐session repeatability of OpenCap for quantifying segment lengths and lower‐limb kinematics during gait and sit‐to‐stand tasks in end‐stage knee osteoarthritis (OA) patients.
Methods: Twenty‐three patients with end‐stage knee OA scheduled for total knee arthroplasty performed gait and sit‐to‐stand tasks while wearing street clothes across two visits. Segment lengths obtained from static calibration were compared between sessions, while waveform repeatability of lower‐limb joint angles was assessed using root mean square deviation (RMSD) and intraclass correlation coefficient (ICC). Additionally, the standard error of measurement (SEM) and minimal detectable change (MDC) were calculated for discrete kinematic parameters.
Results: The segment lengths exhibited moderate to excellent repeatability between sessions (mean ICC: 0.79). Measurement bias was generally minimal (< 0.5 cm, except for the upper arm), with the overall 95% limits of agreement ranging from −4.51 to 3.98 cm. For gait, the average RMSD and ICC values were 4.0° (SD: 0.9) and 0.82 (SD: 0.07), respectively, whereas for the sit‐to‐stand task, these values were 5.2° (SD: 1.1) and 0.69 (SD: 0.08), respectively. The average SEM and MDC values for gait were 2.9° and 8.0°, and for sit‐to‐stand, 3.0° and 8.4°, respectively.
Conclusions: OpenCap demonstrates moderate to good inter‐session repeatability for static anatomical measurements and gait kinematics in patients with end‐stage knee OA, showing promise as a low‐burden clinical assessment tool. However, the higher variability observed during the sit‐to‐stand task necessitates cautious, task‐specific interpretation, underscoring the need for further improvements before expanding its use across broader functional assessments.
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BibTeX
@article{ye2026intersession,
title = {{Inter‐Session Repeatability of a Smartphone‐Based Markerless System to Measure Segment Length and Lower‐Limb Kinematics in Patients With End‐Stage Knee Osteoarthritis}},
author = {Chunping Ye and Renxin Ding and Junqing Wang and Yong Nie and Kang Li},
journal = {Orthopaedic Surgery},
year = {2026},
month = sep,
doi = {10.1111/os.70431},
url = {https://doi.org/10.1111/os.70431},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - JOUR
TI - Inter‐Session Repeatability of a Smartphone‐Based Markerless System to Measure Segment Length and Lower‐Limb Kinematics in Patients With End‐Stage Knee Osteoarthritis
AU - Chunping Ye
AU - Renxin Ding
AU - Junqing Wang
AU - Yong Nie
AU - Kang Li
PY - 2026
DA - 2026/09/17
JO - Orthopaedic Surgery
DO - 10.1111/os.70431
UR - https://doi.org/10.1111/os.70431
AB - Background: While kinematic analysis is crucial to characterize multi‐planar functional deficits in end‐stage knee osteoarthritis (OA), traditional laboratories impose severe physical burdens on patients. In‐field markerless systems like OpenCap offer an accessible alternative, yet their repeatability in this population remains underexplored. The objective of this study was to assess the inter‐session repeatability of OpenCap for quantifying segment lengths and lower‐limb kinematics during gait and sit‐to‐stand tasks in end‐stage knee osteoarthritis (OA) patients. Methods: Twenty‐three patients with end‐stage knee OA scheduled for total knee arthroplasty performed gait and sit‐to‐stand tasks while wearing street clothes across two visits. Segment lengths obtained from static calibration were compared between sessions, while waveform repeatability of lower‐limb joint angles was assessed using root mean square deviation (RMSD) and intraclass correlation coefficient (ICC). Additionally, the standard error of measurement (SEM) and minimal detectable change (MDC) were calculated for discrete kinematic parameters. Results: The segment lengths exhibited moderate to excellent repeatability between sessions (mean ICC: 0.79). Measurement bias was generally minimal (< 0.5 cm, except for the upper arm), with the overall 95% limits of agreement ranging from −4.51 to 3.98 cm. For gait, the average RMSD and ICC values were 4.0° (SD: 0.9) and 0.82 (SD: 0.07), respectively, whereas for the sit‐to‐stand task, these values were 5.2° (SD: 1.1) and 0.69 (SD: 0.08), respectively. The average SEM and MDC values for gait were 2.9° and 8.0°, and for sit‐to‐stand, 3.0° and 8.4°, respectively. Conclusions: OpenCap demonstrates moderate to good inter‐session repeatability for static anatomical measurements and gait kinematics in patients with end‐stage knee OA, showing promise as a low‐burden clinical assessment tool. However, the higher variability observed during the sit‐to‐stand task necessitates cautious, task‐specific interpretation, underscoring the need for further improvements before expanding its use across broader functional assessments.
SN - 1757-7853
SN - 1757-7861
ER -