A Double-Blinded, Randomized-Controlled-Trial to Investigate the Effect of Pulsed Electromagnetic Field (PEMF) for Patients With Quadriceps Weakness After Anterior Cruciate Ligament Reconstruction (ACLR)
Phase: NA
Conditions: Anterior Cruciate Ligament Injuries, Quadriceps Muscle Atrophy
Sponsor: Chinese University of Hong Kong

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Research Protocol 
Title: A Double-Blinded, Randomized-Controlled-Trial to Investigate the Effect of Pulsed 
Electromagnetic Field (PEMF) for Patients with quadriceps muscle weakness after Anterior 
Cruciate Ligament Reconstruction (ACLR) 
 
Background 
 
In Hong Kong, over 3000 Anterior Cruciate Ligament Reconstructions (ACLR) are performed 
each year in order to restore knee function after an ACL injury. The ultimate goal of ACLR is 
to fulfil the return-to-play (RTP) criteria. Despite successful surgery and a demanding 
rehabilitation process, some athletes still fail to comply to RTP. And for those who achieve 
RTP, 23% of those who return to their sports would suffer a second ACL injury (1). 
After ACL injury, the patients would undergo ACLR and post-operative rehabilitation. The 
rehabilitation gradually helps patients to regain mobility and strength, where most of the 
patients would be expected to RTP by 12 months. Despite comprehensive rehabilitation 
programs, a systematic review showed up to 35% of patients would fail to return to their 
preinjury level of play (2). Additionally, these patients were found to be 6 times more likely to 
sustain a second ACL injury within 24 months after ACLR than the healthy population (3). 
Quadriceps muscle strength is one of the key determinants for a patient’s successful return-to-
play after ACLR, by which muscle size is a crucial factor of muscle strength. Quadriceps 
muscle atrophy is unavoidable after ACLR, while rehabilitation aids in recovering quadriceps 
muscle mass. However, despite good compliance, some patients respond poorly and fail to 
regain muscle mass. Quadriceps muscle atrophy can persist beyond the completion of the 
rehabilitation program in almost half the patients and the reason behind this is still unknown. 
This represents an area requiring significant investigation, as quadriceps muscle atrophy and 
weakness have been shown to be predictive of poor knee function, decreased performance in 
sports and increased risk of reinjury. 
 
Graft-tunnel osteointegration is another key determinant for the successful outcome of ACLR. 
Tunnel widening and bone loss are common after ACLR which affect tendon graft fixation and 
subsequent osteointegration of the tendon graft. Transient loss of 5–10% of bone mineral 
density (BMD) around the knee has been found in our previous clinical study (19). The tunnel 
surface with decreased BMD can become less stable for tendon–bone integration due to 
increased bone resorption. A successful osteointegration of the tendon graft with normal BMD 
is vital for the rehabilitation of ACLR, as early stability of knee joint allows the patients to 
adopt more aggressive rehabilitation therapy and improve the outcomes of surgery. In addition, 
patients having a higher degree of knee pain were found to have a higher degree of bony 
sclerosis and overall subchondral osteopenia and were associated with more quadriceps atrophy. 
Thus, the bone microarchitectural evolution after ACLR is worth monitoring.  
 
PEMF treatment can modulate mitochondrial activities for muscle gain. Molecular processes 
are sensitive to the magnetic flux at extremely low frequency (<300 Hz), which are equivalent 
to the Earth’s natural magnetic resonance (Schumann resonance). Applying magnetic fields at 
these low frequencies in the form of magnetic pulses, like a timely push to swing. The pulsing 
action will enhance the human magnetosensitive processes, which include the electron 
transport chain in mitochondria, calmodulin signaling and ion channels. The affected signal 
transduction pathways further influence the downstream myogenesis (5). Therefore, a pulsed 
electromagnetic field (PEMF) may be a possible intervention to amplify molecular processes 
in favour of myogenesis (6).  

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PEMF therapy has been demonstrated to enhance cellular activity related to tissue healing (7), 
and offer beneficial effects such as pain relief, anti-inflammation and oedema resolution (8). 
Numerous variables in the delivery of PEMF signals (i.e., magnetic flux, frequencies, signal 
curve, polarity, etc) may have specific biological implications. Our group (Prof. Alfredo 
Franco-Obregon) showed that brief 10-minute exposure of 1.5mT amplitude of PEMF 
(Quantum Tx) on myoblast in-vitro could activate myogenesis. It is done so by stimulating the 
TRPC-1-mediated calcium entry and downstream factors as well as PGC-1α, this mechanism 
(mentioned above) is similar to the myogenesis in exercise (4). PGC-1α gene expression is 
influenced by every major signaling pathway that is activated in a contracting muscle (9). 
Additionally, it plays an important role in regulating the production and secretion of myokine. 
Therefore, PEMF exposure on top of regular exercise training, may promote the secretion of 
myokine and in turn promote muscle regeneration.  
 
Our study will examine the efficacy of PEMF treatment introduced at the late postoperative 
period. It helps to set up the treatment regime for the PEMF device to impose myogenic effects, 
including exposure time per session, the number of treatment sessions and the duration of 
treatment. To our best knowledge, this proposed study aims to apply PEMF as an intervention 
for patients with myokine-mediated persistent quadriceps muscle atrophy after ACLR. In turn, 
it would be the first study to examine the correlation between PEMF and post-operative 
quadriceps muscle endurance, strength and mass. Apart from the quadriceps muscle, we will 
also examine the bone microarchitecture changes correlating to the PEMF treatment in the 
post-operative period.  
 
Objective 
 
To conduct a double-blinded, randomized controlled trial to investigate the effects of PEMF 
treatment during the late postoperative period on quadriceps muscle strength and muscle 
weakness in ACL injured patients. 
 
Hypothesis 
 
PEMF treatment is effective to reduce muscle weakness and promote a gain in quadriceps 
muscle strength for ACLR patients at the post-operation time points. 
 
Setting 
The study will be carried out in the Department of Orthopaedics and Traumatology at Prince 
of Wales Hospital. 
 
Subject recruitment 
 
The study protocol will comply with the Declaration of Helsinki and ICH-GCP. Subjects will 
be recruited from the Department of Orthopaedics and Traumatology of Prince Wales Hospital 
in Hong Kong and patients who can meet all the inclusion criteria will be invited to participate 
in two sessions of assessments. 
A total of 80 post-ACLR subjects will be recruited and follow up for up to 12 months. They 
will undergo 1:1 randomization into two study arms: 
1. PEMF treatment 
2. Control (Sham treatment) 
 

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Inclusion criteria: 
1. Aged 18-30 with a unilateral ACL injury 
2. Sporting injury with a Tegner score of 7+  
3. LSI for quadriceps strength <70% of the contralateral leg at 4 months post-op 
4. Both knees without a history of injury/prior surgery 
Exclusion criteria: 
1. Ages smaller than 18 years old or greater than 30 years old 
2. Any concomitant bone fracture, major meniscus injury or full-thickness chondral 
injuries requiring altered rehabilitation program post-op  
3. Preoperative radiographic signs of arthritis 
4. Metal implants that would cause interference on MRI  
5. Non-HS graft for ACLR  
6. Patient non-compliance to the rehabilitation program 
7. Pregnancy or possibility of pregnancy 
 
Method  
Intervention 
The intervention will be held at Prince of Wales Hospital twice a week. Participants in the 
intervention group will be exposed to PEMF treatment by a PEMF device (Quantum Tx, 
Singapore). The active pulse electromagnetic field device does not produce heat or cause any 
sensation to the tissue which allows the participants to be blinded to the treatment. Participants 
in the control group will receive a sham exposure with the same PEMF device. The involved 
leg will be exposed to PEMF or sham treatment for 10 minutes per session, and the treatment 
regime will run biweekly for 8 weeks, summing up 16 sessions of PEMF or sham exposure in 
total. According to our pilot study in Singapore, such an arrangement establishes a cross-
feeding scenario whereby muscle recovery is fully supported and systemic myokine release is 
optimized. The procedure of PEMF treatment is shown as follows: 
• 
The subject will be seated at a 90 degrees position on a chair. 
• 
The solenoids of the PEMF device will be adjusted to be over the thigh (quadriceps and 
hamstring).  
• 
The options of the appliance will be adjusted to 1 mT, 15Hz on one leg for 10 minutes.  
 
Outcome measures 
Isokinetic muscle strength  
The dynamometer (Biodex System 4, Biodex Medical Systems Inc., New York, USA) will be 
used. Subjects will perform a standardized warm-up exercise (5 min cycling) followed by the 
fatigue test. 5 repetitions at speed of 180°/s will be done first to familiarize the patient. 
Concentric/concentric contractions of knee extension/flexion will be tested at 180°/s for 30 
repetitions. Subjects will be seated on the dynamometer chair with the hip flexed to 85°. The 
re-test reliability has been proven for this protocol (11). The relatively fast speed is chosen to 
perform the fatigue test since the fast-twitch muscle fibres are expected to fatigue faster at high 
speeds (12). Peak torque will be the single highest repetition value within the 30 repetitions 
(13). Muscle endurance could be reflected by fatigue test, where the trends for peak torque, 
work, and power will be examined. Fatigue Index (F.I.) will be used to calculate the percent 
decrease for each variable (13). Percent decrease = 100 – [(last 5 repetitions/ first 5 repetitions) 
x 100]. For individuals that did not achieve their peak torque within the first 3 repetitions, a 

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second F.T. will be calculated as follows. Percent decrease = [100 – [(last 5 repetitions/ highest 
consecutive 5 repetitions) x 100], where the highest consecutive five repetitions will be 
determined by values attained from the repetitions immediately before and following, the single 
highest repetition value (13).  
 
Self-reported knee functions 
The subjective functional outcome will be evaluated by the Lysholm knee scoring system, the 
International Knee Documentation Committee (IKDC) subjective scoring system, Tegner 
activity score and International Physical Activity Questionnaire (IPAQ) will be used.  
1) Lysholm knee scoring system: Consists of eight items, total score ranging from 0 to 100 
where higher scores indicate a better outcome with fewer symptoms or disability (14).  
2) International Knee Documentation Committee (IKDC): Consisted of 10 questions on 
symptoms and activity ranging from 0 to 100 where 100 implies perfect knee function (15).  
3) Tegner activity score: This is an activity level scaled from 1 (low activity) to 10 (high activity) 
(16).  
4) International Physical Activity Questionnaire (IPAQ): The level of physical activities during 
the past 7 days will be evaluated with a validated Chinese version of the quantitative physical 
activity questionnaire (17). 
Muscle thickness 
1. Ultrasound Imaging 
The Aixplorer® ultrasound system (SuperSonic Imagine, Aix-en-Provence, France) 
and a linear transducer probe with a bandwidth of 2-10 MHz (SuperLinear™ SL10-2, 
Vermon, Tours, France) were used to measure the muscle thickness of Vastus Medialis 
(VM), Vastus Lateralis (VL), and Rectus Femoris (RF) on both the injured and 
uninjured leg. Participants laid supine on a treatment table for the assessment. A 
measuring tape was used to locate VM, VL, RF and the patella by palpation, 
consequently marked with a pen for reference. For consistency and ease of comparison 
across patients, the locations measured and labelled as the three muscle groups follow 
the guidelines below. RF was marked at 1/2 of the distance from the anterior superior 
iliac spine (ASIS) to the superior pole of the patella, VM was located at 1/5 of the 
distance away from the midpoint of the medial patella border to the ASIS, and VL was 
noted at 1/3 of the distance from the midpoint of the lateral patella border to the ASIS. 
After locating the anatomical points, excess contact gel was applied on these points. 
The transducer probe was aligned in the transverse plane and moved along the entire 
muscle bundle to capture a view of the VM, VL and RF. The operator would position 
the probe into the sagittal plane to measure muscle thickness upon the marked 
anatomical points. Minimal pressure was applied on the limb to prevent the deformation 
of the muscle and the results would be derived from the average of three measurements. 
2. Magnetic Resonance Imaging (MRI) 
Muscle volumes of quadriceps muscle are measured using a 1.5 or 3.0 Tesla MRI 
Scanner. Axial (3mm thick cut) T1W images are obtained from the anterior superior 
iliac spine (ASIS) to the patella. Quadriceps muscles were manually outlined in each 
axial slice. Muscle volume was calculated by summing all of the slice-multiplied by 
slice thickness. The quality of the muscle is assessed by analyzing the fat content of the 
muscle mass using a technique that has been reported by Reeder et al (15). Scans will 
be performed on both legs before the start of the PEMF treatment (4 months post-op) 
and only on the injured side repeated after the completion of the 8 weeks PEMF 

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treatment (6 months post-op). The uninjured side will be used as a reference for ‘normal 
volume’. 
High-Resolution Peripheral Quantitative Computed Tomography Scans (HR-pQCT)  
High-resolution peripheral quantitative computed tomography scans (HR-pQCT) using 
XtremeCT II (Scanco Medical AG®, Brüttisellen, Switzerland) provides an analysis of bone 
microarchitecture at human peripheral sites with high spatial resolution and low exposure to 
radiation. Bone mineral density (BMD, calibrated with hydroxyapatite standards) and finite 
element analysis of subchondral bone over the knee joint will be performed using the Scanco 
software. Scans will be performed on both legs before the start of the PEMF treatment (4 
months post-op), and on the injured side after the completion of the PEMF treatment (6- and 
12-months post-op). The uninjured side will be used as a reference for ‘normal’ bone condition. 
Biomechanical analysis 
The kinematics will be assessed by the skin marker-based motion analysis system (Vicon MX, 
Oxford, UK) with the lower-body marker setup followed the OSTRC standard protocol using 
16-camera and 16 reflective skin markers. The kinetic variables including vertical and 
horizontal ground reaction force (GRF) and joint moments will be evaluated by a synchronized 
force plate (0.60 × 0.40 m, model OR6-7, AMTI, Watertown, Massachusetts) at the centre of 
the capture volume at 1000 Hz. From the SLH task, the knee kinematics in the landing phase 
is the key measurements including knee flexion angle at initial contact and the range of knee 
motions (flexion-extension, valgus-varus, external-internal rotation). The hip and ankle flexion 
angle at initial contact will also be recorded. The GRF will be normalized to body weight and 
moments will be normalized for body weight ×limb length to make the comparison between 
subjects possible. All analyses for moments and angles were performed in the anatomical 
sagittal (XY) plane and are counted as positive for flexion angles and extension moments. The 
start of the rise in the vertical GRF will be used to determine initial ground contact. From the 
SLS task, the knee kinematics are the key measurements including the range of motions 
(flexion-extension, valgus-varus, external-internal rotation) and the frequency of the relative 
tibiofemoral angular displacements from the kinematics curve, which will be quantified by the 
number of peak appearance. The kinematic and kinetic variables were imported and calculated 
in the Matlab (The Mathworks Inc., Natick, Massachusetts, USA). A biomechanical analysis 
will be performed on all patients. At the same time, the motion will be videotaped by high-
speed cameras. 
Serum myokine evaluation  
Phlebotomy (5ml) will be performed at pre-op,  before PEMF treatment, at 4- and 8- weeks 
after commencement of treatment, and at post-op 12 months. The serum will be prepared by 
centrifugation and kept in a -80o freezer until use. Quantitative analysis for myokines and 
proteins related to muscle metabolism will be performed by Human Myokine Magnetic Bead 
Panel (Millipore) with Bioplex-200 bead-based suspension assay system (LKSIHS core 
facilities), or enzyme-linked immunosorbent assay (ELISA). These include Brain-derived 
neurotrophic factor (BDNF), Fibroblast growth factor-21 (FGF-21), Interleukin-6 (IL-6), IL-
15, Irisin, Myostatin (MSTN)/GDF8, Insulin-like growth factor 1 (IGF-1), FGF-2, IL-8, 
Follistatin, Musclin, Myonectin, Decorin, Meteorinlike, Osteopontin, Secreted protein acidic 
and rich in cysteine (SPARC), Klotho, Procollagen type III N-terminal peptide (P3NP), and C- 
terminal of troponin T1 (TNNT1). 
Passive Knee laxity 

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To measure anterior-posterior knee laxity, the KT-1000 knee ligament arthrometer 
(MEDmetric Corp, San Diego, CA, USA) will be used. A manual force test will be applied 
until a 30lb sound signal is activated. Three trials will be performed. A side difference of 3 mm 
above is considered clinically relevant. 
Visual Analogue Scale 
The subjective measurement for chronic and acute pain will be recorded by the Visual 
Analogue Scale (VAS). VAS consists of a 10-cm line which represents the continuum between 
“painless” and “worst pain from 0 cm to 10 cm. The subject will be asked to draw a mark of it 
before and after each PEMF treatment session. 
 
Study design 
Randomization and blinding 
Participants will be randomized into 1:1 allocation. Blocked randomization will be undertaken 
based on the computer-generated allocation sequence, whereby 80 participants would be 
divided into blocks of 10 for 2 groups, Thereafter, the participants will use their key card to 
complete the assigned treatment regime, without knowing if the machine is delivering active 
or sham PEMF. Outcome assessors and trial administrators are blinded for the group 
allocation.  
 
Follow up time points 
Subjects with a Tenger Score 7+ and with ≥ 7% of the deficit in total quadricep volume on the 
involved leg compared with the uninvolved leg will be recruited into a randomized controlled 
trial. Baseline assessments including isokinetic quadriceps muscle strength, quadricep muscle 
thickness, blood sampling for myokines measurement (5ml), biomechanical analysis, knee 
laxity and self-reported outcome with a questionnaire will be taken before commencement of 
treatment, and the same set of measurement will be monitored at 4- and 8- weeks after 
commencement of PEMF or sham treatment. MRI will be performed before PEMF and 8- 
weeks after the commencement of PEMF if possible. And at post-op 12 months, isokinetic 
quadriceps muscle strength, quadricep muscle thickness, biomechanical analysis and 
questionnaire will be taken again. (Appendix 10) 
Sample size calculation 
Quadriceps muscle endurance and strength will be employed as the primary outcome for 
sample size estimation. Based on our recent pilot result, the difference in extension strength 
between atrophy and non-atrophy group was 30 Nm (SD 60 Nm), providing an effect size 0.42 
Hence, with effective size set at 0.42, the estimated sample size will be 64 (32 for each arm) 
will be able to achieve 90% confidence to detect the difference between the two groups with a 
significance level (alpha) of 0.05 using a two-sided sample test. With an inclusion of 25% 
dropout rate, we have modified the total sample size to be 80 (40 for each arm). Thus, 80 
subjects will be recruited in total.  
Data processing and analysis 
The data obtained in the tests will be analyzed using Statistical Package for Social Science 
(SPSS) (IBM SPSS ver.26). For parametric data, a paired-sample t-test will be used. Wilcoxon 
signed-rank test will be used to analyze the data sets if they are non-parametric. The alpha level 
will be set at 0.05 for all statistical tests.  

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Potential pitfall and contingency plan 
Patients that are potentially intolerable for magnetic low-field magnetic stimulation or trigger 
discomfort will not be included in our study during screening. If the patient record did not 
indicate any potential adverse reaction to the PEMF treatment and experience such a situation 
during the intervention, the patient would be immediately removed from the study in their best 
interest to safeguard their health. All staff operating the PEMF would have thorough training 
on the operation of the machine and familiarize themselves with the troubleshooting scheme. 
Study personnel would indicate and explain to patients during recruitment about the 
intervention duration and frequency to stress the importance of compliance, accompanied with 
frequent reminders to participants. In the case of patient non-compliance, study personnel 
would remove the patient from the study only when multiple failed attempts to contact and 
convince the patient occurs. 
 
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