Validity and Reliability of Rebee Wearable Sensor to Measure Knee Joint Range of Motion
Conditions: Physical Therapy Modalities
Sponsor: Cairo University

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VALIDITY AND RELIABILITY OF REBEE WEARABLE 
SENSOR TO MEASURE KNEE JOINT RANGE OF MOTION 
 
 
 
 
 
 
 
 
 BY  
Ahmed Mohamed Ahmed Saleh 
B.Sc.in Physical Therapy, 2014 
 
 
 
 
 
 
 A protocol submitted in partial fulfillment of the requirements  
for the master degree in physical therapy for basic science  
Faculty of Physical Therapy  
Cairo University  
November 10, 2020 
      
 

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Supervisors  
Prof. Dr. Wadida Hassan 
Professor of Physical Therapy  
Basic Science Department 
Faculty of Physical Therapy  
                                       Cairo University 
 
 
  Dr. Rania Reda Mohamed 
Lecturer of Physical Therapy  
Basic Science Department 
Faculty of Physical Therapy  
                                       Cairo University 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

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0BContents 
LIST OF ABBREVIATIONS……………………………..4  
CHAPTER I  
INTRODUCTION  
Introduction…………………………………...…………………….  5  
Statement of the Problem …………….…………………...………..  6 
Purpose of the Study……………………………..…………………  6 
Significance of the Study…………….…………………...………..   6 
Hypotheses…………….………………………..………...………..   7 
Basic Assumption…………………….…………………...………..   7  
Delimitations…………….…………………..…………...………..    8 
CHAPTER II 
 LITERATURE REVIEW  
Range of Motion …………….………………...………....                  9 
Causes of ROM Limitation…………….……………...…….              9 
Physical Examination of ROM…………….………………..             10 
Universal Goniometer…………….……..……………...…..              10  
Inclinometer ….……………….………….....……...............              10 
Digital Goniometer …………….…………………..............              12  
Rebee Wearable Sensor ……………………………............              13  
CHAPTER III 
SUBJECTS, MATERIALS AND METHODS  
Design of the Study…………….…………………….....……….....  14  
Participants…………….……………………………......………...... 14  
Selection of Subjects…………….……………………....………......14  
Inclusion Criteria.…………….………………….....…....………......14  
Instrumentation ………………..…………………………………….15  
Procedure for testing Validity …………………….…...………....... 15  
Procedure for testing Reliability …………………….…...………... 16 
Knee Active ROM Measurement …………………….…...………..16 
Steps for Using Rebee Wearable Sensor ………………………….. 18 
Statistical Analysis…………….………………………...………......22 
Ethical Considerations…………….………..…………...………...... 22 
REFERENCES…………….…………...………...…….…..... 23  
APPENDIX 
1BAppendix I: Patient Consent Form…………………………....….    26  
                                                                                                                                                                                     
 
 
 

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       3BLIST OF ABBREVIATIONS 
 
 
 
APPS    : Applications 
 
AROM  : Active Range of Motion 
 
BMI      : Body Mass Index 
 
ROM    : Range OF Motion 
 
UG        : Universal Goniometer 
 
 
 
 
 
 
 
 
 
 
 
 

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4BCHAPTER I  
5B                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         INTRODUCTION 
 
 
       Range of motion (ROM) of the joint is one of the factors that 
determine function of the musculoskeletal system. This parameter should be 
measured and recorded by a valid and reliable method (Yaikwawongs et al., 
2009). It is considered to be an essential component of lower limb physical 
examination, which can be applied using various instruments such as 
goniometers and inclinometers (Pourahmadi et al., 2017). 
 
                 Range of motion of the knee joint is one of the major factors 
determining the outcome after knee injuries. It is also an important 
measurement required by many knee scoring systems to determine the 
preoperative status and postoperative outcome (Anouchi et al., 1996). 
Measurements are used by physical therapists to quantify limitations of 
motion, used to decide an appropriate therapeutic interventions, and document 
the effectiveness of these interventions. The ideal measuring device should 
give reproducible valid and reliable data (Yaikwawongs et al., 2009). 
 
      Two-arm digital goniometer is still widely used in measuring 
uniaxial ROM of joint of extremity, there is high validity, intra rater and 
interrater reliability of the digital goniometer. It is considered valid and 
reliable tool that simplify physical therapists' work (Svensson et al., 2019).   
 
     The measurement of joint ROM is required an essential skill in the 
musculoskeletal assessments commonly performed by physiotherapists. The 
digital goniometer is the most commonly utilized clinical tool for measuring 
joint range of motion, the evolution of sensors technology and applications  
are easy to use, relatively inexpensive, and highly accessible (Keogh et al., 
2019). 

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Rebee is a wearable motion sensor package of sensor with its own 
mobile application, which measures range of joint movement in different 
planes easily which the patient able to wear the sensor and move easily to 
measure ROM and record the measurement at the application software, that is 
facilitate the tele-measurement which the patients are supposed to put on the 
sensors and perform the actions themselves, or with assistance from physical 
therapist. 
 
So this study will be conducted to test the criterion related validity and 
intrarater reliability of the rebee wearable sensor in measuring active knee 
joint ROM compared with digital goniometer measurement. 
 
Statement of the Problem  
1- Is the rebee wearable sensor valid to measure active knee joint ROM 
compared with digital goniometer measurement?  
2- Is the rebee wearable sensor reliable in measuring active knee joint ROM? 
 
Purpose of the Study  
  Purpose of the study to test the criterion related validity and intrarater 
reliability of rebee wearable sensor in measuring active knee joint ROM 
compared with digital goniometer measurement. 
 
Significance of the Study 
            Measurement the joint ROM with the digital goniometer is considered 
time consuming and difficult with respect to repeated measurements. 
(Svensson et al., 2019).  
 
So there is a need to the sensors system which could be considered as a clinical 
measurement for ROM which will reflect in rehabilitation process through 
measuring the patient ROM easily (Hamel et al., 2008). 
 
             Some researchers would prefer taking the ROM of lower limb in a 
more functional way such as standing and walking given that the sensors were 

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developed, which the patients are supposed to put on the sensors where the 
sensor placed on prominent bony landmarks at the level of lateral malleolus. 
It will be stabilized on the testing limbs by elastic bands and perform the 
actions themselves, with or without the supervision from the physical therapist 
(Vohralik et al., 2015). 
 
With the use of rebee wearable sensor, the ROM of knee joint flexion 
and extension can be monitored easily and recorded, that lead to facilitation 
of tele rehabilitation. Which the patients are supposed to put on the sensors 
and perform knee flexion and extension themselves, with or without the 
supervision from the clinicians. 
 
UHypotheses  
It is hypothesized that: 
1. Rebee wearable sensor will not be valid to measure active knee joint 
flexion ROM compared with digital goniometer measurement. 
2. Rebee wearable sensor will not be valid to measure active knee joint 
extension ROM compared with digital goniometer measurement. 
3. Rebee wearable sensor is not reliable to measure active knee joint 
flexion ROM. 
4. Rebee wearable sensor is not reliable to measure active knee joint 
extension ROM. 
 
Basic Assumption  
It is assumed that: 
 The movement applied will be the same for all participants and will be the        
same for each participant repeatedly. 
 All participants will comply with the instructions honestly.  
 All participants will have the same psychophysiological condition during 
the treatment period. 
 
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UDelimitations  
The principles respected in selecting the cases and data recording are: 
1- 40 normal participant will be assigned to group, this number detected by 
G*power 3.1 software (Universities, Dusseldorf, Germany) was used for 
calculation. 
2- The participant's age ranged from 35 to 45 (Miranda et al., 2002). 
3- The participant from both sex (Correll et al., 2018). 
4- Participant Body mass index (BMI) from (19 to 25) normal weight (Weisell 
et al., 2002). 
5- Knee flexion and extension ROM will be measured with the digital 
goniometer. 
6- Knee flexion and extension ROM will be measured with the rebee wearable 
sensor. 
7- The procedures will repeated two times with one week interval between 
measurements. 
 
 
 
 
 
 
 
 
 
 
6 
 
 
 
 
 
 
 
 
 
 
 

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BCHAPTER II  
                                                                                                                                                                                                                                                                                                                                                                                               7BLITERATURE REVIEW 
 
Range of Motion 
          Range of motion of the joint is the arc of motion that occurs at a joint, it 
is one of the factors that determine function of the musculoskeletal system. This 
parameter should be measured and recorded by a reproducible only method 
(Yaikwawongs et al., 2009) 
 
         The assessment of joint range of motion (ROM) is an important 
component of a physical therapy examination. These measurements are critical 
for providing baseline data, determining functional limitations, and monitoring 
changes in joint mobility in response to treatment. Measurement of ROM may 
also be used to detect asymmetry and movement restrictions that may increase 
risk of injury (Clarkson et al., 2005). 
 
           Range of motion of the knee joint is one of the major factors determining 
the outcome after knee injuries. It is also an important measurement required 
by many knee scoring systems to determine the preoperative status and 
postoperative outcome (Anouchi et al., 1996). 
 
Causes of ROM Limitation 
             Reduced range of movement is where there is a limitation of movement 
at a joint.  Types of reduced range of movements are: 
 
 Muscle Injury 
 Ligament injury 
 Pain 
 Swelling 
 Arthritis 
(Konor et al., 2012)  
 
 
 

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 Physical Examination of ROM  
          Each specific joint has a normal range of motion that is expressed in 
degrees. The reference values for the normal ROM in individuals differ slightly 
depending on age and gender. For example, as an individual ages, they typically 
lose a small amount of ROM (Yaikwawongs et al., 2009). 
 
         Analog and traditional devices to measure range of motion in the joints 
of the body include the goniometer and inclinometer which use a stationary 
arm, protractor, fulcrum, and movement arm to measure angle from axis of 
the joint.  
 
           Over the years, the most common instrument used for joint measurement 
in physio-therapy has been the universal goniometer (UG) (Norkin et al., 
1995). Important psychometric characteristics of this instrument, such as 
intratester and intertester reliability, have been examined in many research 
studies. In the clinical setting, these characteristics are important because 
patients are often treated and reassessed, either by the same or by different 
physical therapists (Gogia et al., 1987). 
 
           Many research studies have found the UG to have overall good 
intratester and intertester reliability. However, the majority of these studies 
have found intratester reliability to be greater than intertester reliability (Roach 
et al., 1991) 
 

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          In addition to the goniometer, another device being used by some 
clinicians to measure range of motion is the digital inclinometer. The 
inclinometer is similar to the goniometer in that both are lightweight and 
portable. However, the inclinometer has significantly more associated cost. 
The inclinometer has been demonstrated to possess good to excellent 
reliability and concurrent validity with the universal goniometer (Clarkson 
et al., 2005)  
 
 
The digital goniometer is the most commonly utilized clinical tool for 
measuring joint range of motion, it gives the physiotherapist a useful method 
to diagnose musculoskeletal function in terms of ROM, monitor the progress 
of an intervention (Yaikwawongs et al., 2009). 

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There is high validity, intra rater and interrater reliability of the digital 
goniometer (Svensson et al., 2019).  
 
           To measure joints with the digital goniometer is considered time 
consuming and difficult with respect to repeated measurements. (Svensson et 
al., 2019), so there is a need to a new device that sensors system could be 
considered as a clinical measurement for ROM which will reflect in 
rehabilitation process (Hamel et al., 2008). 
 
     New evolution for measuring ROM called rebee wearable sensor. 
With the use of rebee wearable sensor, the ROM of knee joint flexion and 
extension can be monitored easily, that lead to facilitation of tele 
rehabilitation. Which the patients are supposed to put on the sensors and 
perform knee flexion and extension themselves, with or without the 
supervision from the clinicians. 
 

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The patients are supposed to put on the sensors and perform the actions 
themselves, with or without the supervision from the clinicians/ research. The 
evolution of sensors technology and applications are easy to use, relatively 
inexpensive, and highly accessible (Keogh et al., 2019)  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

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CHAPTER III 
SUBJECTS, MATERIALS AND METHODS 
 
          This study will be conducted at the Outpatient Clinic of Faculty of 
Physical Therapy, Pharos University, Alexandria, Egypt. to test the criterion 
related validity and reliability of rebee wearable sensor in measuring Active 
Knee Joint ROM compared with digital goniometer measurement. 
 
Design of the Study 
The study is Cross Section Study (Observational study). 
 
Participants 
         40 normal participant will be assigned to one group, this number 
detected by G*power 3.1 software (Universities, Dusseldorf, Germany) was 
used for calculation. 
 
Selection of Subjects 
The participant will be recruited from faculty, staff, and students of 
Pharos University, Egypt. Graduate Program in Physical Therapy after 
achieving the inclusion and exclusion criteria.  Each participant will sign an 
informed consent before beginning of the study to insure complete satisfaction 
(Appendix 1) 
 
Inclusion Criteria 
1. 40 normal participant's age ranged from 35 to 45. (Miranda et al.,  
2002) 
2. The participant from both sex. ( Correll et al.,  2018) 
3. Participant Body mass index (BMI) from (19 to 25) normal weight 
(BMI= weight (kg) / [height (m)] 2) (Weisell et al., 2002).  
 
 

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Instrumentations  
1. Digital goniometer. 
The digital goniometer will be used as a valid and reliable ROM 
measurement tool, the type of digital goniometer will be used in the 
study called digital absolute axis goniometer with accuracy about 
0.99(Correll et al., 2018)  
 
2. Rebee wearable sensor and application by XCLR8 Technologies. 
         The package of sensor and application will be used for measure, 
interpret and store participant measurement for test the criterion related 
validity and intrarater reliability of rebee wearable sensor in measuring 
active knee joint ROM 
 
 
3. Health weight scale for weight and height measurement to calculate 
BMI. (BMI= weight (kg) / [height (m)] 2) (Weisell et al., 2002).  
 
 
Procedure for testing Validity 
             The digital goniometer will be used as a valid and reliable ROM 
measurement tool to be compared with rebee wearable sensor in measuring 
active knee joint ROM. 
 
Measure AROM of Knee Flexion with Digital Goniometer 
            The participant will be at supine position with the testing knee 
extended, which allows assessment of the joint ROM without interference 
from tightness in the rectus femoris muscle, axis location at lateral epicondyle 
of the femur, stationary arm will be along the femur to the greater trochanter, 
The movement arm will be along the fibula to lateral malleolus. 
 
            The participant will asked to flex the testing knee fully through 
available ROM and the therapist will record the measurement to compare with 
rebee wearable sensor measurement. 
 
 
 

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Measure AROM of Knee Extension with Digital Goniometer 
             The participant will be at supine position with the testing knee flexed, 
which allows assessment of the joint ROM without interference from 
tightness in the rectus femoris muscle, axis location at lateral epicondyle of 
the femur, stationary arm will be along the femur to the greater trochanter, 
The movement arm will be along the fibula to lateral malleolus. 
 
              The participant will asked to extent the testing knee fully through 
available ROM and the therapist will record the measurement to compare with 
rebee wearable sensor measurement. 
 
The following picture illustrate that measurement with the digital goniometer 
will be from the similar supine position of measurement with the conventional 
goniomtere 
 
 
Procedure for testing Reliability 
             Designed according to Guidelines for reporting Reliability and   
Studies, investigating the intrarater reliability of a rebee wearable sensor will 
be conducted. The study will be designed in accordance with the ethical 
guidelines from the Helsinki declaration of ethical principles (World Medical 
Association (Kottner et al., 2011)).  

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Written consent will be retrieved from all subjects before participating in the 
study, the procedures will repeated two times with one week interval between 
measurements. Researcher will records all the measurement.  
 
Knee Active ROM Measurement with Rebee Wearable Sensor  
This process postulated by Kimberlin, 2008 
            
          To detect the joints ROM, the sensors were placed in the most distal 
part of the limbs with prominent bony landmarks at the level of lateral 
malleolus. It will be stabilized on the testing limbs by elastic bands. With the 
sensor light facing Lateral malleolus  
 
Measure AROM of Knee Flexion with Rebee Wearable Sensor 
            The participant will be standing in upright position, the sensor position 
at the level of the Lateral malleolus, participant will be asked to flex the testing 
knee fully while standing supported in one leg. 
 
Measure AROM of Knee Extension with Rebee Wearable Sensor 
            The participant will sitting at the edge of plinth with knee flexed, the 
sensor position at the level of the Lateral malleolus, participant will be asked 
to extent the testing knee through the full ROM. 
 
 

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            The Digital goniometer and rebee wearable sensor will be used for 
comparison of their validity for measuring knee joint flexion and extension 
ROM. 
 
 
            Rebee wearable sensor will be used as mentioned above and this 
procedures will repeated two times with one week interval between 
measurements to test its reliability. Researcher will records all the 
measurement. 
 
Steps for Using Rebee Sensor Package 
 
1- Take the charging end of the charging cable and look for the charging 
port on the sensor. 
 
 
 
 
 
 
 
 
 
 

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2- Making sure the cable aligns with the port then connect the charger. 
 
 
3- The USB end of the charging cable must be connected to a USB port / 
USB charger. 
4- Check the sensor for a red LED light to know that it is successfully 
charging. The red LED will turn off once the device is fully charged. 
 
 
 
 
 
 
 
 

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5- Wearing the devise at the level of the Lateral malleolus with the sensor 
light facing Lateral malleolus. 
 
 
 
6- Connecting the sensor to the device 
 
    Step a: Switch on the sensor device.  
    Step b: Go to phone’s settings and turn on device’s Bluetooth. 

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7-  Look for “HC-06” (Default sensor name) under “Available devices” 
and   tap on it. 
 
8- Identifying the Sensors to Software 
 
 
       Step a: Connect the sensor you are trying to identify  
       Step b: Look for the sensor in the list with the name “HC-06” 
 

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Statistical Analysis 
           Statistical methods will be used to calculate the reliability and validity 
of our measurements will be descriptive statistics for mean and standard 
deviation, also the Pearson product-moment correlation coefficient (r), an 
assessment of covariance. 
 
Ethical Considerations  
1. All participant will sign a consent form to declare that they are not forced 
to participate in this study. (Appendix I) 
2. The study will be conducted after approval of ethical committee of the 
Faculty of physical therapy, Cairo University, Egypt.  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

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Dobkin, B. H. (2013). Wearable motion sensors to continuously measure 
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Hamel, M., Fontaine, R., & Boissy, P. (2008). In-home tele-rehabilitation 
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Vohralik, S. L., Bowen, A. R., Burns, J., Hiller, C. E., & Nightingale, E. J. 
(2015). Reliability and validity of a smartphone app to measure joint 
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Correll, S., Field, J., Hutchinson, H., Mickevicius, G., Fitzsimmons, A., & 
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Appendix I 
Patient Consent Form 
 
 
I am freely and voluntarily consent in this research study under the 
direction of the researcher /Ahmed Mohamed Ahmed Saleh. A thorough 
description of the procedure has been explained to me and I understand 
that I can withdraw my consent and discontinue participation in this 
research at any time without prejudice to me. 
 
 
 
 
 
 
Participant:                                                  Signature: 
 
Researcher:                                                 Signature: 
 
Date: