Why the measurements matter clinically
 

After total knee arthroplastyTKA
A combination of slower walking speed, shorter operated-side stance, reduced knee flexion during loading response, increased trunk compensation, and prolonged five-times sit-to-stand performance can document a guarded functional pattern. Possible clinical contributors include pain inhibition, effusion, quadriceps weakness, reduced confidence, restricted range of motion, or insufficient rehabilitation progression.
That pattern is not diagnostic. The same findings can result from contralateral arthritis, lumbar or neurologic disease, cardiopulmonary limitation, fatigue, fear of falling, assistive-device use, or a technically inadequate recording.
Reduced swing-phase knee flexion may help direct examination toward knee stiffness, pain, reduced foot clearance, ankle dorsiflexor weakness, or a stiff-knee strategy. It does not establish a mechanical implant problem. A clinically appropriate assessment might include knee range of motion, extensor mechanism function, quadriceps strength, effusion, pain location, ankle motor and sensory examination, video review, and radiographs when indicated.
Improving walking speed with persistent or increasing trunk lean is also clinically relevant. It may indicate that the patient is achieving better performance through compensation rather than normalized movement. This can guide rehabilitation toward quadriceps control, hip-abductor function, balance, endurance, or assistive-device review without labeling the finding as a complication.
 

After total hip arthroplasty
Reduced operated-side terminal-stance hip extension may reflect a persistent flexed walking strategy. Possible contributors include slow walking speed, hip-flexor discomfort, flexion contracture, weakness of the hip extensors, fear of loading, anterior soft-tissue symptoms, pelvic tilt, or lumbar compensation. The camera-derived angle is not a measurement of implant anteversion, cup inclination, stem position, or anterior instability.
Pelvic obliquity accompanied by ipsilateral trunk lean can support targeted evaluation of hip-abductor function. The differential includes pain inhibition, gluteus medius or minimus weakness, abductor tendon pathology, superior gluteal nerve dysfunction, leg-length or offset concerns, lumbar deformity, balance impairment, contralateral disease, and camera-plane error. Published THA gait studies likewise show that gait and compensatory abnormalities can persist despite overall clinical improvement.
A declining walking speed associated with new pain, an abrupt change in stance tolerance, inability to complete the task, or rapidly increasing compensation requires conventional clinical reassessment. Depending on the presentation, this may include examination, radiographs, inflammatory markers, joint aspiration, venous thromboembolism assessment, neurologic evaluation, or urgent emergency investigation. OrthoGait JR should document the functional change, not determine the cause.
Sit-to-stand performance
Sit-to-stand testing adds information about lower-extremity strength, movement strategy, balance, confidence, and task-level functional capacity. Markerless analysis has been studied for kinematic classification of sit-to-stand after TKA, supporting its potential as an objective functional-assessment method.
 

Interpretation must account for:
chair height and stability;
use of armrests or hands;
foot position;
footwear;
external assistance;
number of completed repetitions;
timing definition;
pain;
balance loss;
fatigue; and
whether the same protocol was used at baseline.
 

A faster result obtained using the arms cannot be treated as equivalent to a slower arms-crossed baseline. A missing or aborted result is not zero.
Important app-specific interpretation rules
The reviewed OrthoGait JR asymmetry calculation is:
Asymmetry magnitude= 
(∣L∣+∣R∣)/2
∣L−R∣
​    
×100
Because the calculation uses the absolute difference, it reports the magnitude of asymmetry but discards its direction. Therefore, every asymmetry percentage should be reviewed with the underlying left and right values, operated side, symptoms, and video.
Direct 10-m walking speed is valid only when:
a physical 10-m course has been measured;
the accepted timing interval represents that course;
acceleration and deceleration rules are standardized;
task completion is confirmed; and
the same timing convention is retained at follow-up.

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