This clinical trial aims to evaluate whether continuous passive motion (CPM) can prevent ankle joint contracture and muscle atrophy in critically ill patients receiving mechanical ventilation in the ICU. The study will also assess the feasibility and safety of implementing CPM therapy in this population.

The primary objectives are:

To determine whether CPM preserves ankle dorsiflexion range of motion during ICU immobilization.

To assess whether ultrasound can detect changes in tibialis anterior muscle morphology in response to CPM.

In this within-subject design, each participant will receive CPM therapy on one ankle while the contralateral ankle serves as the control. Outcomes related to joint mobility and muscle condition will be compared between the two sides.

Participants will:

Receive CPM treatment on one ankle for 30 minutes, twice daily, for up to 7 days or until ICU discharge.

Undergo goniometric and ultrasound assessments at baseline and after the intervention.

Continue to receive standard ICU care throughout the study period.

Critically ill patients commonly experience neuromuscular complications, notably intensive care unit-acquired weakness (ICU-AW) and joint contractures. ICU-AW affects up to 80% of patients requiring prolonged mechanical ventilation and is associated with prolonged hospitalization, delayed functional recovery, and increased mortality. Concurrently, immobility during ICU stays contributes significantly to joint contractures, affecting approximately one-third of patients experiencing extended ICU admissions. Among these complications, ankle joint plantar-flexion contractures (foot drop) are particularly debilitating, severely impacting patients' balance, gait retraining, and overall functional recovery after ICU discharge.

Although early mobilization is widely recognized as beneficial, leading to reduced ICU stays, lower incidence of delirium, preservation of muscle integrity, and enhanced quality of life post-discharge, its implementation remains challenging. Many critically ill patients are unable to participate in early active mobilization due to sedation, hemodynamic instability, or other medical contraindications. Furthermore, evidence suggests that early mobilization might carry increased risks of adverse events for certain patient populations. Thus, alternative strategies are essential for patients unsuitable for early active rehabilitation, emphasizing preservation of joint mobility and muscle integrity to facilitate future rehabilitation opportunities.

Continuous passive motion (CPM) therapy has emerged as a viable intervention designed initially for postoperative orthopedic rehabilitation. CPM passively moves joints through a controlled range, potentially maintaining flexibility by inhibiting periarticular collagen cross-linking, preserving soft tissue extensibility, and maintaining muscle-tendon compliance. However, its effectiveness in critical illness settings remains uncertain, with limited evidence suggesting potential benefits in reducing muscle atrophy, such as that of the tibialis anterior muscle, in ICU patients unable to actively mobilize, while other studies have reported minimal effects. Thus, rigorous evaluation of CPM's impact on joint mobility preservation and muscle atrophy prevention is warranted.

This study aimed to evaluate whether CPM therapy effectively mitigates passive range of motion (PROM) loss at the ankle joint in sedated, mechanically ventilated ICU patients. Additionally, muscle structural changes were assessed via ultrasound imaging to determine if CPM influences muscle morphology compared to limbs receiving standard care alone. Ultrasound parameters, including muscle thickness (MT), cross-sectional area (CSA), echointensity (EI), and pennation angle (PA), were used to comprehensively monitor morphological changes and provide insights into the functional implications of observed alterations.

Inclusion Criteria:

- Eligible participants were adults (≥18 years) with acute respiratory failure expected to require mechanical ventilation for >5 days.

Exclusion Criteria:

• Neuromuscular disorders
• Recent lower limb surgery or trauma
• Critical limb ischemia
• Limb amputation
• Deep vein thrombosis
• Significant leg wounds
• Pregnancy.