Abstract
OpenCap (Stanford University) uses standard smartphone cameras and computer vision algorithms to estimate joint kinematics without markers. With affordable equipment and reasonable setup procedures, it may provide an alternative to visual assessment of movement impairments in the clinic. Subtle alterations in joint kinematics can be relevant to the interpretation of recovery progress following musculoskeletal injury or surgery such as anterior cruciate ligament reconstruction (ACLr). It is important to understand the level of agreement between new tools for assessment and gold standard kinematic measures. PURPOSE: To determine concurrent validity of kinematic data collected using OpenCap and gold standard technologies during a single limb squat in patients post ACLr. METHODS: Kinematic data were collected concurrently with 12 infrared (marker) and 3 iPhones while 19 individuals (26.8 ± 4.2 years; 122.3 ± 12.5 days post ACLr) performed single limb squats. Kinematic models created from pose estimations based off marker (Qualisys) and video data (OpenCap) were used to calculate peak hip, knee and ankle sagittal plane angles for surgical (Sx) and non-surgical (NSx) limbs. Individual trials (1-3) were used to examine the relationship (linear regression, R2) and agreement (ICC 3,1) between methods. Bias and limits of agreement (LOA) were calculated. 8 trials were excluded due to poor Open Cap reconstruction. RESULTS: ICC and R² values were 0.93 and 0.93 for the knee, 0.72 and 0.72 for the ankle, and 0.76 and 0.79 for the hip, respectively. For knee flexion, LOA ranges from 9.9° to -9.45° (Sx) and 8.8° to -11.22° (NSx); for ankle variables, 10.9° to -3.7° (Sx) and 13.9° to -7.3°(NSx); and for hip variables, 21.67° to -24.2° (Sx) and 16.3° to -21.6°(NSx). CONCLUSION: The data indicate excellent agreement between systems for knee variables, but only good and moderate agreement was observed for hip and ankle variables. These findings show promise for application of OpenCap in the clinic for testing knee functional performance post ACLr. However, the range in LOA indicate that it may be most effective in detecting larger flexion deficits.
Recommended Citation
Chen, Alexander; Wang, Jiaqi; Sigward, Susan; Ma, Willa; and Choi, Grace
(2025)
"Comparison of Lower Limb Sagittal Plane Kinematics Measured Using OpenCap and Traditional MoCap During Single Limb Squat Analysis in Patients Post-ACLr,"
International Journal of Exercise Science: Conference Proceedings: Vol. 14:
Iss.
5, Article 13.
Available at:
https://digitalcommons.wku.edu/ijesab/vol14/iss5/13
Included in
Health and Physical Education Commons, Medical Education Commons, Sports Sciences Commons