Knee Flexionater to Avoid Motion Restoring Surgery

Comparing High Intensity Stretch Device Combined With Physical Therapy Versus Physical Therapy Alone to Prevent Motion-Restoring Surgery Following Primary Total Knee Arthroplasty: Study Protocol for a Randomized Controlled Trial

The goal of this clinical trial is to learn whether adding a stretching device to standard physical therapy can help people regain knee bending after total knee replacement surgery.

Some people have difficulty bending their knee during recovery. When this happens, doctors may recommend another procedure called motion-restoring surgery to improve knee movement.

This study aims to answer two main questions. First, does adding a hydraulic high-intensity stretching device to physical therapy help people regain knee bending after surgery? Second, does using the device affect recovery, daily activities, or the chance of needing another procedure?

Researchers will compare two treatment approaches. One group will receive standard physical therapy alone. The other group will receive standard physical therapy and will also use a hydraulic high-intensity stretching device called the Ermi Knee Flexionater at home.

Participants who receive the device will use it at home each day in addition to attending their physical therapy sessions. Researchers will measure how well participants can bend their knee and will ask questions about pain, daily function, and activity level. Participants will also complete simple walking and mobility tests.

Study visits will occur about four weeks after surgery when participants enroll, and again at about eight weeks, twelve weeks, six months, one year, and two years after surgery. Researchers will compare results between the two groups to see whether the stretching device improves recovery after knee replacement.

Study Overview

• Status: Recruiting
• Conditions: Joint Contractures; Total Knee Anthroplasty; Knee Arthrofibrosis
• Intervention / Treatment: Other: Standard Physical Therapy; Device: Hydraulic high Intensity Stretch Device

• Study Type: Interventional
• Enrollment (Estimated): 150
• Phase: Not Applicable

Contacts and Locations

Study Locations

• United States
  • Texas
    • Houston, Texas, United States, 77043
      • Recruiting
      • Inov8 Orthopedics
      • Contact: Director of Research; Phone Number: 832-240-5974; Email: bpeace@inov8hc.com

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria:

• Age 40 years or older
• Undergoing primary total knee replacement surgery
• Knee flexion less than 105 degrees at approximately 4 weeks after surgery
• Considered a candidate for motion-restoring surgery, with any surgery delayed until after 2 months of nonoperative treatment

Exclusion Criteria:

• Not willing to participate
• Diagnosis of advanced rheumatoid arthritis
• Neurological deficit affecting the operative leg
• Revision total knee replacement or previous major surgery on the same knee
• Cognitive impairment
• Prior total hip replacement on the same side (ipsilateral total hip arthroplasty)
• Living more than 2 hours from the study site or unwilling to attend required local physical therapy visits

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: None (Open Label)

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Active Comparator: Physical Therapy Only; Participants will receive standard postoperative physical therapy following primary total knee arthroplasty according to the treating clinician's usual rehabilitation protocol.	Other: Standard Physical Therapy; Supervised postoperative physical therapy following primary total knee arthroplasty. Therapy includes range of motion exercises, strengthening, neuromuscular re-education, manual therapy, and functional rehabilitation as determined by the treating clinician.
Experimental: Hydraulic high-Intensity Stretch Device Plus Standard Physical Therapy; Participants will receive standard postoperative physical therapy and will use a hydraulic high-intensity stretch device (Ermi Knee Flexionater) at home in accordance with the study protocol.	Device: Hydraulic high Intensity Stretch Device; A hydraulic high-intensity mechanical stretch device (Ermi Knee Flexionater) used as an adjunct to standard postoperative physical therapy following primary total knee arthroplasty. The device is designed to apply controlled, patient-actuated stretch to increase knee flexion range of motion. Participants assigned to this intervention will use the device at home daily for approximately one hour, in addition to attending prescribed physical therapy sessions. Device use will begin at approximately four weeks postoperatively and continue for up to eight weeks, consistent with the study protocol. Participants will receive in-person instruction on device setup and operation and will record frequency and duration of use in a log. Compliance will be monitored through weekly check-ins.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change from Enrollment in Active and Passive Knee Flexion Range of Motion (Degrees)	Change in active and passive knee flexion measured in degrees using a standard goniometer. Higher values indicate greater knee flexion and improved range of motion.	Baseline (Enrollment at 4 weeks post-operative), 8 weeks post-operative, 12 weeks post-operative, 6 months post-operative, 1 year post-operative, and 2 years post-operative

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change from Enrollment in KOOS Score	Change in Knee injury and Osteoarthritis Outcome Score (KOOS). Scores range from 0 to 100, where 0 represents extreme knee problems and 100 represents no knee problems. Higher scores indicate better knee function.	Baseline (Enrollment), 8 weeks, 12 weeks, 6 months, 1 year, and 2 years post-operative
Change from Enrollment in WOMAC Score	Change in Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Total scores range from 0 to 96, where higher scores indicate worse pain, stiffness, and functional limitation.	Baseline (Enrollment), 8 weeks, 12 weeks, 6 months, 1 year, and 2 years post-operative
Change from Enrollment in Visual Analog Scale (VAS) Pain Score	Change in self-reported pain measured using a 0-10 scale, where 0 indicates no pain and 10 indicates the worst possible pain. Lower scores indicate less pain.	Baseline (Enrollment), 8 weeks, 12 weeks, 6 months, 1 year, and 2 years post-operative
Change from Enrollment in Timed Up and Go (TUG) Test Time (Seconds)	Change in time required to complete the Timed Up and Go test. Lower times (seconds) indicate improved mobility.	Baseline (Enrollment), 8 weeks, 12 weeks, 6 months, 1 year, and 2 years post-operative
Change from Enrollment in Six-Minute Walk Test (6MWT) Distance (Meters)	Change in distance walked during the Six-Minute Walk Test measured in meters. Greater distance indicates improved functional endurance.	Baseline (Enrollment), 8 weeks, 12 weeks, 6 months, 1 year, and 2 years post-operative
Number of Participants Experiencing Adverse Events	Number of participants experiencing any adverse event, including but not motion restoring surgery, limited to infection, pulmonary embolism, rehospitalization, revision surgery, or other complications following enrollment.	From enrollment to 2 years post-operative follow-up

Collaborators and Investigators

• Sponsor: Ermi LLC
• Investigators: Study Director: Shaun K Stinton, PhD, Ermi LLC

Study record dates

Study Major Dates

• Study Start (Actual): December 9, 2025
• Primary Completion (Estimated): December 1, 2029
• Study Completion (Estimated): December 1, 2029

Study Registration Dates

• First Submitted: March 2, 2026
• First Submitted That Met QC Criteria: March 2, 2026
• First Posted (Actual): March 6, 2026

Study Record Updates

• Last Update Posted (Actual): March 6, 2026
• Last Update Submitted That Met QC Criteria: March 2, 2026
• Last Verified: March 1, 2026

More Information

Terms related to this study

• Other Study ID Numbers: RCT-EF-225

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: Yes
• product manufactured in and exported from the U.S.: No