| Requirement | Specification | Justification |
| 1. The device must allow adjustment of plantarflexion and dorsiflexion to match the patient’s current phase of rehabilitation. | Three discrete, clinician-supervised ROM settings for plantarflexion and dorsiflexion angles. | – Current treatments progress from full immobilization (casting, walking boot) to semi-rigid bracing and then to functional rehab devices. – Adjustable ROM improves compliance and reduces stiffness, muscle wasting, and reinjury risk compared to rigid immobilization. |
| 2. The device must allow adjustment of abduction and adduction to match the patient’s current phase of rehabilitation. | Three discrete, clinician-supervised ROM settings for abduction and adduction angles. | – Midfoot and forefoot motion (abduction/adduction) contributes to ankle instability and functional deficits after sprain. – Ignoring transverse control can increase the chance of reinjury. |
| 3. The device must allow adjustment of inversion and eversion to match the patient’s current phase of rehabilitation. | Three discrete, clinician-supervised ROM settings for inversion and eversion angles. | – Lateral stability and support is key for reducing risk of reinjury. – Lateral bracing for functional recovery increases patient satisfaction. |
| 4. The device must actively assist the ankle range of motion during the active recovery phase. | A) Actively support patient rehabilitation from near immobilization stage to near full mobility stage. B) Limit assisted angular velocity. | – Powered ankle orthoses significantly increased the patient range of motion and gait when combined with neuromuscular training. – Managed angular velocity to prevent reinjury and assist recovery. |
| 5. The device must tolerate loads without loss of structural integrity. | A) Withstand loads of up to 3-5× patient body weight. B) Safe use for patients up to 250 lbs. | – Failure under normal loads would compromise ankle support and increase reinjury risk. – Reliable load capacity is critical for safe, everyday use. |
| 6. The device must be lightweight. | A) Limit device weight to less than 2 kg. B) Limit distal weight. | – Excessive weight alters gait patterns and can cause injuries in the knees or hips. – Excess weight at the distal end negatively affects the metabolic cost of the swing phase. – Lightweight devices improve compliance and user comfort. |
| 7. The device must be comfortable. | A) Limit ankle-device interface pressure. B) Continuous use for ≤8 hours per day without tissue damage. | – Comfort and fit are among the most important factors in compliance. – Poor comfort leads to noncompliance rates up to 80% in lower-limb orthotic users. – Patient adherence is essential to recovery. |
| 8. The device must allow fast switching between the three rehabilitation phase modes. | A) Acute Phase: Near Zero Mobility B) Sub-Acute Phase: Partial Mobility C) Functional Phase: Near Full Mobility D) Time for manual clinician adjustment between modes is less than 1 minute | – Current treatments progress from full immobilization (casting, walking boot) to semi-rigid bracing and then to functional rehab devices |
| 9. The device must constrain the range of motion of the ankle to match the patient’s current phase of rehabilitation. | A) Acute Phase: 0-5° in all axes B) Sub-Acute Phase: Clinician Defined C) Functional Phase: i. 15-20° / PF 45-50° ii. Inv: 30° / Ev: 30° iii. Abd: 15° / Add: 35-40° | – Powered ankle orthoses significantly increased the patient range of motion and gait when combined with neuromuscular training |
| 10. The device must provide a controllable active element capable of assisting the patient through a prescribed range of motion during the sub-acute phase. | A) Patient rehabilitation ROM: (Range for Set Points) i. DF 0-20° / PF 0-50° ii. Inv: 0-30° / Ev: 0-30° iii. Abd: 0-15° / Add: 0-40° B) Limit assisted ankle angular velocity to ≤10°/sec (clinician-adjustable) | Adjustable ROM improves compliance and reduces stiffness, muscle wasting, and reinjury risk compared to rigid immobilization. |
| 11. The device must allow clinicians to set a custom range of motion boundary for each plane of motion within the sub-acute phase. | A) Sub-Acute Phase: Partial Mobility i. DF 0-20° / PF 0-55° ii. Inv: 0-30° / Ev: 0-30° iii. Abd: 0-15° / Add: 0-40° B) Clinician-prescribed adjustment. | – Clinician-defined ROM limits enable personalized progression based on patient tolerance and recovery metrics. |
| 12. The device must include a fail-safe that prevents motion beyond clinician-set limits. | A) Independent hard-stop that physically enforces the ROM limits regardless of software/electronics. B) Not exceed more than .5 degrees beyond the constrained range of motion. | – A hard-stop provides safety independent of power, preventing over-rotation and unintended progression between phases. |
| 13. The device must include an emergency shut-off mechanism that rapidly stops all powered motion. | A) One single-action control (button/toggle) must cut power or pressure to the active components of the system. B) Located within easy reach of the user. C) Cuts the operation of the device within less than 5 seconds. | – Rapid interruption of powered motion is critical for patient safety during active rehab. A clearly marked shut-off allows for immediate response to unexpected pain or malfunction. |