Rate of Torque Development in Adolescents With Osgood-Schlatter: A Cross-sectional Case-control Study
Conditions: Osgood-Schlatter Disease
Sponsor: Hvidovre University Hospital

 
 
 
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Rate of Torque Development in adolescents with Osgood-Schlatter: 
Protocol of a cross-sectional case-control study   
Henriette Larsen Strømme¹, Jesper Larsen¹, Amalie Bjerre Jørgensen², Lasse Ishøi²,³, Kasper 
Krommes²  
¹Metropolitan University College, Copenhagen, Denmark.   
 ²Department of Orthopedic Surgery, Copenhagen University Hospital, Amager-Hvidovre, Sports 
Orthopedic Research Center - Copenhagen (SORC-C), Hvidovre, Denmark  
 ³Deparment of Human Performance, FC Nordsjælland A/S – Part of the Right to Dream Group, 
Farum, Denmark  
Background  
Osgood-Schlatter is a growth-related condition involving multiple types of tissue in the tendon-bone 
interface at the tibial tubercle. Osgood-Schlatter affects one in ten adolescents causing persistent 
pain, reduced peak torque during knee extension, and reduced ability to maintain participation in 
sports and physical activity. Rate of torque development is linked to athletic performances, and 
reductions in rate of torque development is associated with decreased neuromuscular functioning and 
pain chronicity.  As peak torque is reduced in Osgood-Schlatter, changes in rate of torque 
development is likely also affected, but this has not yet been investigated. This insight could help 
characterize the condition and guide management.  
  
Aim  
To investigate if early and peak rate of torque development during knee extension is reduced in the 
asymptomatic limbs or during knee flexion in adolescents with Osgood-Schlatter, compared to a 
matched group of asymptomatic adolescents.  
  
Study design  
 A cross-sectional case control study.  
Methods  
The study design and analysis strategy have been published along with a trial registration 
(ClinicalTrials.gov NCT05789095). The study will include 13 adolescent participants with Osgood-
Schlatter and a group of 13 pain free controls matched on sex, age, and sports participation on the 
group level. Testing will include bilateral rate of torque development measurements of knee extension 
and flexion, with a fixated handheld dynamometer, during a single test-session lasting approximately 
two hours. The examiner responsible for strength-testing will be blinded to case-status. Along with 
anthropometric data, participants will perform the anterior knee pain provocation test to assess pain-
response to sustained knee loading, a countermovement jump test to assess power and jump height, 
and provide patient-reported measures of condition severity, pain, disability, and quality of life. Data 
collection will start February 2023 and is expected to be completed by May 2023.  
  
Expected results and implications  
As the condition affects the knee-extensor mechanism, we expect lower levels of rate of torque 
development in the affected knee during extension. The main interest, however, is if the level of rate 
of torque development is also significantly reduced in non-symptomatic limbs or in knee flexion, in 
cases compared to symptom-free healthy controls. This would indicate inhibited neuromuscular 
function on a central level, due to other factors than local tissue pathology, such as pain chronicity, 
central muscle inhibition, or other drivers.  

 
 
 
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Title 
Rate of Torque Development in adolescents with Osgood-Schlatter: Protocol of a cross-sectional 
case-control study.  
Dansk titel 
Rate of Torque Development hos unge med Osgood-Schlatter: protokol på et case-kontrolstudie. 
Trial registration 
Trial identifier and registry name 
Clinicaltrials.gov: NCT05789095 
Protocol version 
1.0, 23-Feb-2023 
Investigating team 
Primary investigators 
Kasper Krommes, 
 Physiotherapist, MSc, PhD Fellow 
Lasse Ishøi, 
 Physiotherapist, MSc, PhD 
Jesper Larsen, Bachelor student, physical therapist 
S Henriette Larsen Strømme, Bachelor student, physical therapist 
Contact information 
Kasper Krommes 
 Mail: Kasper.krommes@regionh.dk 
 Kettegård Alle 30, 2650 Hvidovre   
Funding 
No specific funding was provided for this study. 
Rationale and background 
Osgood-Schlatter is an apophysitis of the tibial tubercle occurring in its primary form during 
adolescence. The condition affects one out of ten, and is even more prevalent in highly active 
adolescents.1 
Adolescents with Osgood-Schlatter experience a reduced ability to participate in sports and physical 
activities.2 A previous study from our group found that maximal strength and pain during isometric 
knee extension strength test on adolescents with Osgood-Schlatter, was moderately correlated to 
self-reported outcomes in terms of knee-related quality of life, sports participation satisfaction, 
mental health and pain beliefs.3 Rate of force development is a measure of explosive strength, or the 
ability to develop force over a short time period and is correlated to explosive actions, such as 
sprinting and jumping.4,5 In patients with prolonged or acute knee pain, rate of force has been found 
to be decreased.6 Several studies have shown that changes in rate of force development is linked to 
decreased neuromuscular function, and thereby is affecting sports function and activities of daily 
living.7 No previous investigations of rate of force development have been published for this group. 

 
 
 
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Measuring rate of force development in adolescents with Osgood-Schlatter, might further explain 
the relationship between features of knee function and self-reported outcomes. To account for 
differences in stature and bodyweight, normalizing for these variables will provide the more precise 
measure of rate of torque, often used in biomechanical research.  
It would be interesting to investigate if rate of torque development is affected in this group. If it is, it 
could be explained by the theory that pain in local tissue, is affecting the ability to activate maximal 
muscle contraction in a limited time span.8,9 Furthermore, we suspect that the non-affected leg in 
the Osgood-Schlatter group, also will have a lower rate of torque development. This is based on the 
hypothesis that Osgood-Schlatter, affects the central nervous system due its chronicity, and therefor 
the ability to develop maximum rate of torque.6 
Hypotheses 
The hypotheses being tested are  
1. that adolescents with Osgood-Schlatter, has a lower knee extension RTD in their affected 
knee compared to matched controls 
2. that adolescents with Osgood-Schlatter, has a lower knee extension RTD in their affected 
knee compared to their potential asymptomatic knee 
3. that adolescents with Osgood-Schlatter, has a lower knee extension RTD in their potential 
asymptomatic knee compared to matched controls 
4. that adolescents with Osgood-Schlatter, has a lower knee flexion RTD in their affected knee 
compared to matched control 
5. that adolescents with Osgood-Schlatter, has a lower knee flexion RTD in their affected knee 
compared to their potential asymptomatic knee 
6. that adolescents with Osgood-Schlatter, has a lower knee flexion RTD in their potential 
asymptomatic knee compared to matched controls 
7. That levels of either early or late rate of torque development is negatively correlated with 
pain during rate of torque development-testing, countermovement jump height or power, 
anterior knee pain provocation test score, current pain, pain duration, KOOS child ‘Pain’, 
‘Sport/rec’ or ‘QoL’ subscales,  
Methods 
Study design 
In this study we will include adolescent participants with Osgood-Schlatter, presenting as anterior 
knee pain localized to the tibial tubercle (OSD-group), and a matched group of pain free controls 
(control group), matched on sex, age (<1 year group difference) and type of sports (weightbearing vs 
non-weightbearing). The study will be conducted at the International Olympic Research Center - 
Copenhagen (Sports Orthopaedic Research Centre - Copenhagen), at Hvidovre University Hospital. 
The project will be initiated March 2023, with recruitment of 26 participants: 13 participants in the 
OSD-group, and 13 in control group.  
Approval has been obtained from the ethical review board of the Capital Region of Denmark (H-
20072873), and the Data Management Agency of Capitol Region of Denmark (P-2021-73). 
Recruitment 
Recruitment will happen through social media advertisement, from patients referred to the Osgood-
Schlatter clinic at the orthopedic department, Hvidovre University Hospital, and from local sport 
clubs. Participants from the control group, will be rewarded with a movie ticket after participation. 

 
 
 
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All possible participants will be screened over the phone, before clinical examination and are 
included if criteria is met. 
Patients and guardians' consent 
Before engaging in trial, participants and their parents/guardians will receive a pamphlet with 
written information. During their visit, they will receive verbal information and instructions 
regarding the context and aim of the study. Written consent will be collected from the 
parents/guardians of the participants, and verbal consent from the participants. 
Processing of personal data 
All personal data will be stored on logged secured servers, provided by the Capitol Region of 
Denmark. Journals of the treated cases will be stored electronically as per standard care. 
Participants 
Inclusion criteria  
- 
Patients must be 9-16 years of age 
- 
Presence of pain for 12 weeks or more 
- 
Pain at tibial tubercle during loading activities 
- 
Palpable pain at the tibial tubercle  
Exclusion criteria 
- 
Previous knee or hip surgery  
- 
Other main diagnose of anterior knee pain (patellofemoral pain, Sinding-Larsen Johansson 
disease, Jumpers knee, etc.)  
- 
Hip and/or back pain interfering with activities of daily living or physical activities 
- 
Suspicion of other main diagnose such as meniscal tears and or ligamental tears 
- 
Unable to communicate verbally or orally in Danish  
Clinical examination and treatment  
 
The study procedures will be conducted by two examiners (JL and HS). JL will be aware of the case 
status and conducts the screening and preliminary testing. To avoid bias, examiner HS will be 
blinded for the case status during trial and will not know the Numerical pain Rating Scale-scores 
(NRS, 0-10, ‘no pain’ to ‘worst pain imaginable’) of the participants during testing.10 To strengthen 
the inter-reliability, the examiners will not change roles during the study.  
The session starts with JL examining the potential participant in the OSD-case group, for Osgood-
Schlatter. If the Osgood-Schlatter diagnosis is made, the participant is then enrolled. For the 
potential participant in the control group, JL screens for potential injury or pain in relation to the 
knee joint. In the absence of relevant pathology, the control-participant is enrolled. 
Then, JL measures length of the lever arm and variables for peak hight velocity assessment. 
Participants will then answer the patient-reported outcome measures together with their 
parent/guardian.  
For the rate of force development tests, HS will enter the room and conduct the tests as described 
below. For each attempt the participant will write down their NRS-rating on a piece of paper, out of 
sight from HS.  
Before the rate of force development test is conducted, the participants are told that they can 
always abort the test, if they perceive that pain rises to such a degree that they can´t continue the 

 
 
 
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testing, or they start felling fearful or uncertain of their symptoms. They are ultimately told that 
potential pain felt during testing are not harmful and will subside within 24 hours, as is our 
experience from multiple earlier conducted tests. 
 HS leaves the room, for JL to conduct the Anterior Knee Pain Provocation test and save the NRS 
results.  
HS returns to conduct the Counter Movement Jump Test, again blinded for the participants NRS-
scores, which are written down on a piece of paper. HS leaves the room, and JL either treats the 
patient (case-group) or hands out compensation for participating (control-group).  
Cases and controls will be instructed not to take any pain medication 24 hours prior to any 
assessment to ensure that this does not affect measurements. 
Test protocols 
Rate of Torque Development 
Rate of force development is defined as a change in force over time (Newtons per second). To make 
the measurement more applicable in a group with diversity in gender, age and size, the length of the 
lever arm is considered, by measuring from the lateral joint space in the knee, to two centimetres 
above the lateral malleolus. Rate of torque development is denoted as Newton per meters per 
second per kilograms of bodyweight (Nm/s/kg). 
A reliability study from 2019 showed that a fixated handheld dynamometer, a MicroFet 2 (Hoggan, 
Scientific L.L.C., Salt Lake City, USA) with a sampling rate of 100hz, has a good intra-tester reliability, 
and an acceptable measurement error (SEM ≤15.5%).11 
Knee flexion 
The participant is lying prone, with hip in neutral position, 0°. The knee is flexed about 20°, with the 
leg resting on the testers fist wedged between the examination table and the ankle. The participant 
will be instructed to hold onto the side of the examination table. A strap fixated to the floor, is used 
to fixate the handheld dynamometer. The dynamometer is placed central to the line of lever 
demarcation, approximately 2cm proximal to the lateral malleolus. 
Knee extension 
The participant is sitting with 90° hip flexion, knee flexed approximately 60°, with test leg resting in 
testers hand, and feet free of the floor. They will be instructed to hold onto the back of the 
examination table and keep their upper body upright. A strap fixated to the bottom of the 
examination bed, is used to fixate the handheld dynamometer anteriorly on the shin, corresponding 
to the line of lever demarcation. If the participant feels the metal of the gauge on their shinbone 
through the padding of the dynamometer, extra padding will be placed on the shin. 
The participant will be instructed to press against the dynamometer as fast and hard as possible, and 
to keep pushing until instructed to relax (approximately 3-4sec.). Standardized verbal instruction is 
provided before each trial by the tester: 3-2-1-go-push-push-push and relax. For the knee flexion, 
the participant will be instructed to bend their knee, and for the extension, to straighten the leg.  
Participants will perform two test trials: one at 50% of self-estimated maximal force, and one at 
100%. The assessor will hold the leg in starting position to allow full rest between trials, lasting 1-
minute. Three maximal attempts are recorded. One tester will hold the dynamometer and instruct 
the patient (HS), while one tester (JL) manage data collection software (Hoggan Health Industries 
2000, version 11.0.1, Quest Medical Group, Inc.). The order of the movements is decided by coin 

 
 
 
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toss. The affected leg is tested first in each movement. In the control group the affected leg will be 
decided by coin toss before tester HS enters the room.  
Anterior knee pain provocation test 
The anterior knee pain provocation test is a unilateral self-performed and self-rated test, designed to 
provoke known anterior knee pain. Only the affected or most affected knee is tested. In the control 
group, the “affected leg” is decided by coin toss.  
The participant will be instructed to stand on the affected leg, with the non-affected side against the 
wall, and their back straight. The back of the hand is held against the wall as support. They will then 
be instructed to stand in a static single-legged squat position, with knee flexion about 60°, while the 
other leg is extended forward above the ground. The position is held for 45 sec and timed with a 
stopwatch. Standardized verbal instruction is provided before each trial by the tester: are you ready 
to start the test? Start... and stop. 
Participants will provide their perceived pain intensity immediately before and after completing the 
45s. hold.  
Counter Movement Jump Test 
The counter movement jump test measures jump height(cm), power(watt), and pain during trial 
(NRS 0-10). Increased countermovement jump height is associated with increased sprint 
performance, lower body power and enhanced force-velocity.12–14 Likewise, the test is found feasible 
for adolescents.12 
The participant is standing with their legs shoulder width apart, and with their hands placed on their 
hips. They will be instructed to jump straight up and down, and as high as possible. One test trial is 
conducted, and three trials where measurements are made.   
Standardized verbal instruction is provided before each trial by the tester: are you ready to jump? 
Go. There will be a 30second rest between each attempt. After each test jump a written NRS is made 
by the participant, hidden from tester HS. 
The attempts are recorded using the slow-motion function (>240frames per second) on a fixated 
iPhone. To analyse the recordings, the smartphone application MyJump 2 is used for a highly reliable 
slow-motion video analysis.15–18  
Data will be normalized per MyJump 2 procedures to push-off distance (distance from the floor to 
trochanter major in a 90˚ squat position) combined with leg length (measured prone from the 
superior anterior iliac spine to the tiptoes in full plantar flexion). The mean of three trials will be 
used. 
Patient Reported Outcome Measures 
Participants will fill out a questionnaire, containing some basic information about their pain 
experience, such as: duration of pain, previously received treatment, current pain, worst pain during 
past 24 hours and week. Furthermore, there are questions about activity level, as well as questions 
from Knee Injury and Osteoarthritis Outcome Score (KOOS-child) and Tampa Scale of Kinesiophobia 
(TSK-17). 
KOOS 
KOOS is used for patients with knee pain and injuries. The questionnaire contains questions within 
five categories: symptoms, pain, physical function in daily life, physical function during sports and 
activities, and life quality. In this study, participants will fill out questions from the ‘Sport/rec’ and 

 
 
 
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‘Quality of Life’ subscales, and questions P1, P4, P6a, and P6b from the ‘Pain’ subscale. Questions are 
answered on a 1-4likert scale in normalized to a 0-100 score for each subscale with 100 being the 
optimal score19,20. 
TSK-17 
 The Tampa scale is a 17-item questionnaire to evaluate fear avoidance behaviour in patients 
experiencing pain. It consists of two subscales, activity avoidance and somatic focus. The questions 
are rated on a 1-4 likert scale by the patient. The sum of the points are ranged from 17-68points, 
with above 37 being defined as “high levels of kinesiophobia”21,22. All questions are used in the 
questionnaire.  
Outcome measures 
The outcome measures are rate of torque development and NRS-values in relation to the force-
measurements. To calculate the rate of torque (Nm/s/kg), the rate of force development-variables 
(N/s) is multiplied with length of the lever (m) and divided with the participant's bodyweight (kg).  
 
Outcome variables related to the specified hypotheses are rate of torque development during 0-100 
ms, 0-200 ms, peak RTD, and time to peak force during knee extension and knee flexion for both 
cases and controls. 
Descriptive variables 
Variables collected for descriptive purposes are data on examination findings, pain intensity and 
duration, Peak Heigh Velocity, level of sports participation and anthropometrics  
 
 
Statistical considerations 
Sample size 
No previous investigations of rate of torque have been published for adolescents with Osgood-
Schlatter. One previous study using the same clinical test setup, equipment, and time-epochs (Early 
RTD: 0-100 ms, Late RTD: 0-200 ms, and peak RTD) for testing RTD over the hip in young (Under-19) 
professional soccer players found a mean of 9.57 Nm/kg/s and a standard deviation of 2.6 Nm/s/kg 
at 0-100 ms23. 
Considering that peak torque is around 30-50% lower for adolescents (U13 and U14) compared to 
U19 players24, a similar difference might be expected for RTD, and thus we expect a group mean RTD 
of around 5 or 6 Nm/kg/s at 0-100 ms for asymptomatic adolescents. In adults with non-traumatic 
knee pain, investigations of RTD during maximal isometric hip extension, has shown differences 
between symptomatic participants and controls of >50 % during early RTD.25  
As this study includes RTD of the knee, which is the affected joint, we expect at least similar 
differences for our primary measure, early RTD at 0-100 ms, this would correspond for example to a 
between-group difference of 6 vs. 3 Nm/kg/s. We will assume 2.6 Nm/kg/s as an asymptomatic 
population standard deviation for 0-100 ms. Based on a two-sided two-sample t-test at 80% power 
and 5% alpha level, 13 participants in each group would thus be needed to detect a 50% between-
group difference (R 4.0.2, Foundation for Statistical Computing, Vienna, Austria; RStudio 1.0.153, 
power.t.test package). 

 
 
 
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Statistical methods  
The outcome variables (rate of torque development 0-100 ms, 0-200 ms, peak RTD, time to peak 
RTD, time to peak torque for both knee extension and knee flexion, respectively) will be compared 
between groups using an unpaired two-sided students t-test, assuming the residuals will be normally 
distributed, otherwise the non-parametric alternative, the Wilcoxon rank sum test, will be used. The 
alfa and beta-1 level will be set for 5% and 80%, respectively.  
As outcome variables have been a priori specified and prioritized, and also analyzed and reported in 
the pre-specified order, no corrections for multiple testing will be applied26,27. Data will be reported 
with between-group differences, standardized effect sizes based on Cohens d, exact p-values, and 
95% confidence intervals. All data inspection, analysis, and visualizations will be conducted using R 
(R Foundation for Statistical Computing, Vienna, Austria), in the jamovi interface (The jamovi project 
2023, version 2.4.1). All r-code and full data set will be shared with journal publication or in an open-
access repository. 
Risks and adverse events 
In this context, adverse events will be any unintended symptoms or findings during examination, or 
severe increase in pain intensity during testing, to such extend that testing can't continue. In the 
case of adverse events, the data relevant to the participant will be excluded, and a new participant 
enrolled. A participant that can´t continue due to pain intensity will be treated with caution and 
observed for potential pain increase. If needed, they will be set in contact with a medical doctor 
from the orthopedic department, at Hvidovre University Hospital and still receive 
treatment/compensation. 48 hours after testing, a phone consultation will be made, to make sure 
that the pain intensity has decreased. 
 If problems with equipment or testing should occur to such an extent that test protocol can´t 
continue, a new date will, if possible, be set. Or else a new participant will be enrolled, and 
treatment/compensation is provided to the former participant. 
In the case of unintended unblinding during testing (if allocation is revealed to HS), the data will be 
excluded from the collection due to risk of bias. If possible, a new set of participants (case and 
control) will be included, otherwise, subgroup analysis with participants with breach of blinding 
omitted will be performed.  
An expected result from the test protocol is temporary pain and muscle soreness from the muscle 
force tests, in both cases and controls. Furthermore, an increase in symptoms from Osgood-
Schlatter may be present after testing, in the case group. To our knowledge, this presents no safety 
hazard to the participants.  
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