The goal of this clinical trial is to learn if continuous passive motion (CPM) helps prevent ankle joint contracture and muscle loss in critically ill, mechanically ventilated ICU patients. It will also evaluate the feasibility and safety of implementing CPM in this population. The main questions it aims to answer are:

Does CPM help preserve ankle dorsiflexion range of motion during immobilization in the ICU?

Can ultrasound measurements detect changes in tibialis anterior muscle condition in response to CPM?

Researchers will compare one ankle receiving CPM to the other ankle without intervention in the same patient to assess differences in joint mobility and muscle morphology.

Participants will:

Receive CPM therapy on one ankle for 30 minutes, twice daily, over a 7-day period or until ICU discharge

Undergo goniometric and ultrasound assessments at baseline and at the end of the intervention

Remain under usual ICU care and monitoring while enrolled in the study

Inclusion Criteria:

• Adults aged ≥ 18 years
• Admitted to the ICU with acute respiratory failure requiring mechanical ventilation
• Expected to remain mechanically ventilated for at least 7 days
• Sedated and unable to participate in active mobilization
• No contraindications for passive ankle movement
• Informed consent obtained from legal representative

Exclusion Criteria:

• Pre-existing neuromuscular disorders affecting lower limb mobility (e.g., stroke with hemiparesis, myasthenia gravis)
• Recent orthopedic surgery or trauma involving the lower limbs
• Presence of lower limb amputation
• Peripheral vascular disease with critical limb ischemia
• Active deep vein thrombosis in either leg
• Significant wounds, pressure ulcers, or skin breakdown at the heel
• Pregnancy

The individual participant data (IPD) will not be shared due to the small sample size and the risk of re-identification, especially in a critically ill ICU population. The study was not designed with data sharing infrastructure in place.