Evaluating Stumble Recovery Functions of Prosthetic Knees

Primary outcomes

1. User-Perceived Safety During Use of Stumble Recovery Function Assessed by 3-Point Scale

   Time frame: Assessed at the end of each device exposure period within formative (1 day use), verification (1 day use), validation (1 day use), and crossover phases (1-3 weeks use per exposure), at scheduled visits.

   Safety perception will be assessed using a study-specific 3-point scale. Participants will rate their perception of safety when using the investigational device with the stumble recovery function enabled, compared to either a previous device version without this function or other similar devices. For each aspect of the new function, users will report a score: worse (0), neutral (1), or better (2).

2. Expert-Perceived Safety of Stumble Recovery Assessed by 3-Point Scale

   Time frame: Assessed at the end of each device exposure period within formative (1 day use), verification (1 day use), validation (1 day use), and crossover phases (1-3 weeks use per exposure), at scheduled visits.

   Safety perception will be assessed by researchers or engineers using a study-specific 3-point scale. Experts will rate the safety of the investigational device with the stumble recovery function enabled, compared to either a previous device version without this function or other similar devices. For each aspect of the new function, experts will report a score: worse (0), neutral (1), or better (2)

3. User-Perceived Stability and Confidence

   Time frame: Assessed at the end of each device exposure period within formative (1 day use), verification (1 day use), validation (1 day use), and crossover phases (1-3 weeks use per exposure), at scheduled visits.

   Stability and confidence rated by users (worse/neutral/better) via observation and feedback after using the new function.

4. Fall Rate Following Induced Perturbation Events Assessed by Direct Observation

   Time frame: Assessed at the end of each device exposure period within formative (1 day use), verification (1 day use), validation (1 day use), and crossover phases (1-3 weeks use per exposure), at scheduled visits.

   The outcome will be measured as the fall rate following induced perturbation events during use of the stumble recovery function. The fall rate is defined as the number of perturbation events resulting in falls divided by the total number of perturbation events, assessed by direct observation and/or video recording during controlled laboratory testing. The reduction in fall rate will be compared to baseline conditions, which may include use of non-microprocessor-controlled knees (NMPKs) or microprocessor-controlled knees (MPKs) without the stumble recovery function.

5. Stumble and Fall Detection Rate Assessed by Device Log Analysis

   Time frame: Assessed at the end of each device exposure period within formative (1 day use), verification (1 day use), validation (1 day use), and crossover phases (1-3 weeks use per exposure), at scheduled visits.

   The detection rate will be measured as the proportion of induced stumbles and falls (during controlled perturbation events) that are automatically identified by the knee's stumble recovery system. Detection will be confirmed via analysis of device event logs, which record when the system recognizes a stumble or fall. The successful detection rate is defined as the number of correctly detected stumbles and falls divided by the total number of perturbation events.

6. Stumble and Fall Response Trigger Rate Assessed by Device Log Analysis

   Time frame: Assessed at the end of each device exposure period within formative (1 day use), verification (1 day use), validation (1 day use), and crossover phases (1-3 weeks use per exposure), at scheduled visits.

   The response trigger rate will be measured as the proportion of detected stumbles and falls that result in the knee successfully initiating the appropriate response, as confirmed by device event logs. For each instance where a stumble or fall is detected by the knee's system, device logs will be analyzed to verify whether the corresponding response (e.g., stumble recovery activation, fall dampening) was triggered. The trigger rate is defined as the number of successful response triggers divided by the total number of detected stumbles and falls.

7. Stumble and Fall False Detection Rate Assessed by Device Log Analysis

   Time frame: Assessed at the end of each device exposure period within formative (1 day use), verification (1 day use), validation (1 day use), and crossover phases (1-3 weeks use per exposure), at scheduled visits.

   The false detection rate will be measured as the proportion of incorrectly detected stumbles or falls by the knee's system, as determined through analysis of device event logs during controlled testing sessions. A false detection is defined as a device-logged stumble or fall event that does not correspond to an actual perturbation or loss of balance observed by study personnel. The false detection rate is calculated as the number of incorrect detections divided by the total number of detections of stumbles and falls.

8. Stumble Recovery False Trigger Rate Assessed by Device Log Analysis Stumble Recovery False Trigger Rate Stumble Recovery False Trigger Rate

   Time frame: Assessed at the end of each device exposure period within formative (1 day use), verification (1 day use), validation (1 day use), and crossover phases (1-3 weeks use per exposure), at scheduled visits.

   The false trigger rate will be measured as the proportion of incorrect activations of the knee's stumble recovery function, determined by analysis of device event logs during controlled testing sessions. A false trigger is defined as activation of the stumble recovery response by the device in the absence of a true stumble or fall event, as verified by study personnel or video review. The false trigger rate is calculated as the number of incorrect triggers divided by the total number of stumble recovery activations.

   Measures how often the knee's stumble recovery is incorrectly activated during testing.

9. Fear of Falling Reduction Assessed by Falls Efficacy Scale-International (FES-I)

   Time frame: Assessed at the end of each device exposure period within formative (1 day use), verification (1 day use), validation (1 day use), and crossover phases (1-3 weeks use per exposure), at scheduled visits.

   Changes in fear of falling will be assessed using the Falls Efficacy Scale-International (FES-I) questionnaire. The FES-I provides a total score representing the participant's concern about falling during social and physical activities. Scores range from 16 (no concern about falling) to 64 (severe concern about falling); higher scores indicate a greater fear of falling. The outcome will be measured as the change in FES-I score from baseline (prior to use of the stumble recovery function) to after using the device with the stumble recovery function enabled.

10. Perceived Safety and Balance Assessed by Activities-specific Balance Confidence (ABC) Scale

    Time frame: Assessed at the end of each device exposure period within formative (1 day use), verification (1 day use), validation (1 day use), and crossover phases (1-3 weeks use per exposure), at scheduled visits.

    Perceived safety and balance will be assessed using the Activities-specific Balance Confidence (ABC) Scale questionnaire. The ABC Scale measures an individual's confidence in maintaining balance during various daily activities. Scores range from 0% (no confidence) to 100% (complete confidence); higher scores indicate better perceived safety and balance. The outcome will be measured as the change in ABC Scale score from baseline (using the prescribed or previous knee) to after using the device with the stumble recovery function enabled. Non-inferiority will be established if the change in score is within the minimal detectable change (MDC), set at 11.56 percentage points.

11. Stumble Recovery Ability Assessed by Motion Capture or Wearable Sensor Analysis

    Time frame: Assessed at the end of each device exposure period within formative (1 day use), verification (1 day use), validation (1 day use), and crossover phases (1-3 weeks use per exposure), at scheduled visits.

    Improvement in stumble recovery ability will be assessed by measuring recovery time, defined as the duration from stumble onset to regaining stable posture. Recovery time will be recorded during controlled perturbation events using motion capture technology or wearable sensors. Shorter recovery times indicate enhanced ability to recover from stumbles with the stumble recovery function enabled, compared to baseline device conditions.