The Lower Body Positive Pressure Treadmill for Knee Osteoarthritis Rehabilitation

Summary

Here, based on a clinician’s point-of-view, we propose a two-model lower body positive pressure (LBPP) protocol (walking and squatting models) in addition to a clinical, functional assessment methodology, including details for further encouragement of the development of non-drug surgical intervention strategies in knee osteoarthritis patients. However, we only present the effect of LBPP training in improvement of pain and knee function in one patient through three-dimensional gait analysis. The exact, long-term effects of this approach should be explored in future studies.

Abstract

Here, based on a clinician’s point-of-view, we propose a two-model lower body positive pressure (LBPP) protocol (walking and squatting models) in addition to a clinical, functional assessment methodology, including details for further encouragement of the development of non-drug surgical intervention strategies in knee osteoarthritis patients. However, we only present the effect of LBPP training in improvement of pain and knee function in one patient through three-dimensional gait analysis. The exact, long-term effects of this approach should be explored in future studies.

Introduction

Knee osteoarthritis (OA) is a progressive degenerative joint condition and a major cause of pain and locomotor disability in people all over the world¹. Knee OA is characterized by osteophyte and cyst formation, narrow joint spacing, and subchondral bone sclerosis². These pathological changes make it difficult to perform essential activities of daily living such as walking, squatting, and going up and down stairs³. However, physical activity is recommended as an essential component of first-line knee OA management⁴. Exercise intervention for knee OA rehabilitation is affected by several factors: (1) limited knee joint movement caused by pain and minor knee structural changes; (2) muscle atrophy associated with maintaining knee stability and a decrease in muscle strength⁵; and (3) the above reasons lead to a reduction in exercise and an increase in body mass index (BMI), which further increases the burden on the knees, thus creating a vicious cycle⁶.

In response to the above mentioned issues, the body weight-supported training system (BWSTT) has gradually addressed bone and joint disease-related rehabilitation⁷. In recent years, one of the emerging body weight-supported training technologies is called the lower body positive pressure (LBPP) treadmill⁷. This technology uses a waist-high inflatable balloon to achieve positive lower limb pressure and accurately adjust the air pressure to regulate body weight with the aim of achieving weight reduction. The system is also equipped with a running platform that can concurrently perform treadmill-related activities under the control of body weight⁸. Meanwhile, the pressure generated in the inflated enclosure provides a lifting force against the body. Because the pressure is only slightly above atmospheric pressure and is evenly distributed, the force on the lower body is almost imperceptible. Thus, the LBPP running platform provides a higher level of comfort and is more suitable for long-term training compared with the traditional BWSTT⁹. Peeler et al. performed an LBPP treadmill intervention on 32 knee OA patients and showed that the LBPP treadmill can effectively relieve knee pain, improve daily life functions, and produce an increase in thigh muscle strength¹⁰. The potential mechanism might be related to achievement of effective knee joint activity while reducing knee joint torque¹¹. On the other hand, since the age of onset of knee OA patients is mostly over 45 years old¹², onset may also be associated with cardio-pulmonary diseases. Studies have shown that LBPP allows people to achieve walking as exercise with relatively low heart rate, blood pressure, and oxygen consumption and achieve safer and more effective aerobic exercise than full-weight flat walking; this type of walking is another advantage of LBPP when compared with traditional BWSTT¹³.

However, due to the relatively new application of this system to knee OA intervention, the relatively few existing studies have greatly limited the clinical application of this technology in knee OA rehabilitation. The LBPP protocol proposed in this article aimed to explore the clinical non-drug and surgical knee OA treatment using the LBPP treadmill.

Protocol

The clinical project was approved by the Medical Ethics Association of the Fifth Affiliated Hospital of Guangzhou Medical University and has been registered at the China Clinical Trial Registration Center (No. ChiCTR1800017677 and entitled “Effect and Mechanism of Anti-gravity Treadmill on Lower Limb Motor Function in Patients with Knee Osteoarthritis”).

1. Recruitment

1. Recruit patients presenting with radiographic evidence of mild-to-moderate (Kellgren & Lawrence grades II or III) knee OA in one or both knees and knee pain when walking, squatting, and/or kneeling (the minimum level 3/10 on numerical pain rating scale [NPRS] before inclusion).
2. Ensure that these patients have no severe knee OA (Kellgren & Lawrence grade IV), retropatellar arthritis or any medical condition that would prevent them from tolerating progressive training.
3. Obtain written informed consent from each patient before their participation.

2. Pre-training evaluation

1. Complete demographic forms of the patient including weight, height, past medical history and any past or current medications.
2. Clinical assessment
   1. Conduct the numerical rating scale (NRS)¹⁴. Ask the patient to describe the pain intensity with 11 numbers from 0 to 10, where 0 is no pain and 10 is the worst pain.
   2. Conduct the active/passive knee joint range-of-motion (ROM) assessment¹⁵ using a handheld 2-arm goniometer (26-cm arms with 2° markings).
   3. Conduct the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC)¹⁶. Ask the patient to mark the corresponding position of pain or limited function on a straight line for 5 pain-related items, 2 stiffness items, and 17 functional items. “0” indicates no pain or no function limitation. “10” indicates severe pain or extreme limited function.
   4. Conduct the Knee Injury and Osteoarthritis Outcome Score (KOOS)¹⁷ (optional). Ask the patient to finish the self-evaluation questionnaire with five-level for each item in five subscales: pain, other symptoms, activities of daily living, sports, and recreation.
   5. Conduct the European five-dimensional health scale (EQ-5D)¹⁸ (optional). Ask the patient to mark the three-level for five dimensions: mobility, self-care, usual activities, pain/discomfort, and anxiety/depression.
   6. Conduct the 10-meter walk test (10 MWT)¹⁹. Ask the patient to perform three consecutive 10 MWT trials at a self-selected pace for safety and comfort. Ask the patient to walk without assistance for 10 m and measure the time taken for the middle 6 m (to exclude acceleration and deceleration effects).
   7. Conduct the timed up and go (TUG) test²⁰. Ask the patient to perform three consecutive TUG trials (stand up, walk 3 m, turn, walk back, and sit down) at a self-selected pace (for safety and comfort).
3. Perform the three-dimensional (3D) gait analysis (optional).
   NOTE: 3D gait and concurrent electromyography (EMG) analyses are not required for this LBPP training protocol, but can be used for further objective assessments as needed.
   1. Position twenty-two spherical markers on the patient’s anatomical landmarks based on the Davis protocol²¹.
   2. Position six surface EMG electrodes on the bilateral rectus femoris, semitendinosus, and long head biceps femoris of the patient.
   3. Perform calibration in the standing position. Ask the patient to hold an orthostatic position for at least 3−5 s with the feet aligned in order to avoid having one foot in a more anterior or posterior position with respect to the other.
   4. Instruct the patient to walk with a self-selected speed along the 5-m walkway, five times.
   5. Remove all the spherical markers and EMG electrodes from the patient. Save all the collected data for data processing later following the instructions in section.

3. LBPP training

NOTE: An anti-gravity treadmill (Table of Materials) was used for this LBPP training protocol and shown in Figure 1. For patient safety, a therapist is required to set up the patient in the LBPP and supervise the whole treatment process.

1. Preparation
   1. Patient preparation
      1. Introduce the specific LBPP treadmill training process and related precautions to the patient.
      2. Check the patient’s blood pressure (BP) and heart rate (HR) before training (60 bpm ≤ HR ≤ 120 bpm and 90/60 mmHg ≤ BP ≤ 160/100 mmHg).
      3. Determine the size of the air seal shorts according to the waist circumference of the patient and ask the patient to put on the shorts.
   2. Anti-gravity treadmill setting up
      1. Turn on the treadmill by operating the switch located on the front cover of the system and run the self-testing of the anti-gravity treadmill.
      2. Lower the cockpit and have the patient step into the fabric enclosure of the anti-gravity treadmill.
      3. Lift the cockpit to the appropriate height according to the LBPP training model: the cockpit height should be at the anterior superior iliac spine for the walking model and slightly below the femur’s greater trochanter for the squatting model. Once the cockpit is in place, zip the patient into the anti-gravity treadmill.
      4. Use the safety lanyard supplied with the machine to secure the clip onto patient’s clothing, which is essential for emergency stopping during the training process (in case the patient falls or does not feel well).
      5. Instruct the patient to stand still on the surface of the treadmill belt to allow the system to hold and weigh the patient’s full body weight (BW) without any support from any part of the system and then press the start button to perform an anti-gravity treadmill system calculation for accurate unweighting.
      6. Place three cameras supplied with the machine (in front and bilaterally, Figure 1) and adjust the positions to obtain the synchronized video feedback during the training process; this will help the patient correct abnormal movement patterns.
2. Training session
   NOTE: The whole training session is performed for 30 min, six times a week for two weeks. The main parameters that need to be adjusted with the “+” and “–” button controls in the LBPP console are speed (miles per hour, mph), BW support (%), incline (%) and knee’s active range-of-motion (AROM).
   1. Start the warm-up session with the following settings: 5 min (speed = 0−2.0 mph, BW = 65%, incline = 0%). Increase speed by 0.4 mph and BW support in 7% increments per minute.
   2. Perform the walking model session with the following settings: 15 min (speed = 2.0 mph, BW = 65%, incline = 0%).
   3. Perform the cool-down session with the following settings: 5 min (speed = 2.0−0 mph, BW = 65%−100%, incline = 0%). Decrease speed by 0.4 mph and BW support in 7% decrements per minute.
   4. End up with the squatting model session with the following settings: 5 min (speed = 0 mph, BW = 50%, incline = 0%, AROM = 0°−50° or the maximum tolerable joint range of motion within 50°, 30 s of squatting followed by a 30 s rest period).
      NOTE: In the clinical application, this LBPP training session should be adjusted according to the patient’s tolerance. Moreover, if the patient cannot tolerate the squatting training model, only the walking mode is performed.

4. Post-training evaluation

NOTE: The same therapist completes each patient's pre- and post-evaluation.

1. Re-evaluate the patient after 2 weeks of the LBBP training session, including NRS, active/passive ROM, WOMAC, KOOS, EQ-5D, 10 MWT, TUG and 3D gait analysis.
2. Record patient’s satisfaction and feedback on this LBPP protocol including the degree of enjoyment and self-conscious improvement, desire to continue, and suggestions.

5. 3D gait analysis data processing

1. Run the gait analysis software (Table of Materials) included with the 3D gait analysis system.
2. Define the events of heel-strike (right/left foot initial ground contact) and toe-off (right/left toes are lifted off the ground) in gait cycle for each walking trial (Figure 2).
3. Obtain the spatiotemporal parameters, knee joint kinematics and surface EMG activity parameters.

Results

We show results from a knee OA patient, who was a 60-year-old female (BMI = 22.9) undergoing “more than 3 years of knee osteoarthritis” and severe pain when she was walking (visual analog scale [VAS] = 8/10) and participated in a 2-week LBPP training program at our facility. During the entire intervention, the patient did not take any painkillers to relieve knee pain. The radiological image of her knee joints and the results of clinical function assessments are shown in Figure 3 ...

Discussion

We proposed an LBPP treadmill intervention protocol, which includes both clinical assessment and treatment models, for the rehabilitation of lower extremity motor function in knee OA. Meanwhile, in response to the clinical symptoms and knee OA dysfunction, the treatment model includes not only a training section for walking in the LBPP protocol but also an innovative squatting training section, which aims to solve the daily dysfunction due to thigh muscle weakness and squatting difficulties in knee OA patients. To the be...

Materials

Name	Company	Catalog Number	Comments
AlterG Anti-Gravity Treadmill M320	AlterG Inc, Fremont, CA, USA	1	LBBP training
BTS Smart DX system	Bioengineering Technology System, Milan, Italy	2	Temporospatial data collection
BTS FREEEMG	Bioengineering Technology System, Milan, Italy	3	Surface EMG data collection
BTS SMART-Clinic software	Bioengineering Technology System, Milan, Italy	4	Data processing