A Randomized Controlled Trial of the KRONOS Versus Breg T-Scope Post-operative Knee Braces Following Anterior Cruciate Ligament (ACL) Reconstruction
Phase: NA
Conditions: Anterior Cruciate Ligament (ACL) Reconstruction Surgery
Sponsor: Rush University Medical Center

TITLE:  KRONOS Versus Breg T-Scope Post-operative Knee Braces Following Anterior Cruciate Ligament (ACL) 
Reconstruction 
NCT07090616 
DATE:   29 April 2025

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PROTOCOL TITLE:  A Randomized Controlled Trial of the KRONOS Versus Breg T-
Scope Post-operative Knee Braces Following Anterior Cruciate Ligament (ACL) 
Reconstruction 
PRINCIPAL INVESTIGATOR:
Name:   Jorge Chahla, MD, PhD. Jonathan Gustafson, PhD
Telephone Number: :  (312) 432-2818
Email Address:  cartilage.restoration@rushortho.com
VERSION DATE: 04/25/2025
STUDY SUMMARY:
Investigational Agent-s 
-Drugs or Devices
None
IND / IDE / HDE # N/A
Indicate
Special Population-s
Children 
 Children who are wards of the state 
 Adults Unable to Consent  
 Cognitively Impaired Adults 
 Neonates of Uncertain Viability 
 Pregnant Women 
 Prisoners -or other detained/paroled individuals 
 Students/Employees 
Sample Size
40
Funding Source
Department of Orthopedic Surgery
Indicate the type of consent 
to be obtained
Written Main and Assent Form
Verbal/Waiver of Documentation of Informed Consent
Waiver of HIPAA Authorization 
Waiver/Alteration of Consent Process  
Site
 Single Site Research Study
 Data Coordinating Center -DCC
Research Related Radiation 
Exposure
Yes 
 No 
DSMB / DMC / IDMC
Yes 
No
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ACRONYMS & ABBREVIATIONS: 
ACL-  Anterior Cruciate Ligament 
BMI- Body Mass index
IKDC- International Knee Documentation Committee 
KOOS-Knee Injury and Osteoarthritis Outcome Score
MOR – Midwest Orthopedics at Rush
MRI – Magnetic Resonance Imaging 
PRO – patient reported outcome
PROMIS-Patient-Reported Outcomes Measurement Information System
ROM – Range of Motion
RTS- Return to Sport 
RTW-Return to Work 
RUMC – Rush University Medical Center
VAS pain- Visual Analog Pain Scale 
VR/SF 12-Veteran RAND 12-Item Health Survey
Purpose of the study –  
The purpose of this study is to evaluate the clinical efficacy of the KRONOS 
postoperative knee brace compared with the standard Breg T-scope hinged brace 
following anterior cruciate ligament (ACL) reconstruction surgery.
Background & significance –  
Anterior cruciate ligament (ACL) injuries of the knee are prevalent and frequently treated 
with surgical reconstruction of the ligament using a graft to restore knee function and 
stability.1 Postoperatively, early rehabilitation is critical to successful surgical outcomes, 
preventing postoperative complications, and returning to an active lifestyle.2 However, 
care must also be taken to protect the implanted graft against strain that may disrupt 
tendon-to-bone healing, and ultimately cause premature failure of the graft. 
Consequently, over 60% of surgeons who perform ACL reconstruction recommend and 
prescribe rehabilitative postoperative knee braces locked in extension to limit 
extension/flexion motion, varus and valgus (inward and outward) movements at the knee, 
and help patients regain extension range of motion (ROM.2 
Despite widespread clinical use, evidence on the efficacy of current bracing technologies 
remains controversial and inconclusive. Some randomized controlled trials and 
systematic reviews have concluded that rehabilitative bracing provided no clinical benefit 
with respect to knee ROM, knee laxity, pain, or quadriceps (large thigh muscle group) 
strength in the early postoperative period or at mid-term follow-up.2–4 In contrast, 
Melegati et al5 demonstrated improved extension after one week postoperatively among a 
group that used a rehabilitative brace locked in full extension, compared to a group that 
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used the same brace locked from 0-90°. This variability may be in part due to significant 
limitations present across several of the previous studies, including lack of compliance 
data and power calculation to determine necessary sample sizes.2 6
The KRONOS postoperative unloader brace features a new bracing technology that 
combines the capability of hyperextension immobilization with additional benefits of 
offloading up to 60 lbs off the knee joint.  The adjustable tensioning system in the 
KORNOS brace offers promising potential to significantly alleviate patient discomfort 
and pain, facilitate quicker return to a higher level of activity, and ultimately contribute to 
improved surgical outcomes. The primary purpose of this study is to evaluate the clinical 
efficacy of the KRONOS postoperative unloader knee brace compared with standard 
Breg T-scope hinged brace   in improving range of motion and other complications 
following anterior cruciate ligament (ACL)  reconstruction surgery.
Hypothesis
We hypothesize that subjects randomized to receive the KRONOS postoperative unloader 
knee brace will reach full extension sooner and have reduce extension deficits compared 
to subjects randomized to receive the standard Breg T-scope hinged brace. In addition, it 
is hypothesized that the KRONOS subjects will require fewer additional treatments for 
extensions deficits including, but not limited to, additional therapy, intra-articular 
injections, oral corticosteroids, manipulation under anesthesia, or arthroscopic revision 
surgery.
Selection of Subjects – 
Patients scheduled to undergo primary ACL reconstruction as indicated via CPT 29888 
from the Athena electronic medical record (EMR) will be identified and eligible for 
enrollment in this study. Following the informed consent process outlined below, we will 
prospectively enroll and randomize 20 participants to one of the two study arms 
(KRONOS versus Breg T-scope post-operative knee brace), totaling 40 participants in 
each group.  
Inclusion Criteria: 
•
Subjects > 18 years of age 
•
English-speaking
•
Scheduled to undergo primary anterior cruciate ligament reconstruction surgery
•
No history of prior knee surgery on the operative knee
•
No concomitant ligamentous repair or reconstruction procedures (i.e. ligamentous 
pathology aside from anterior cruciate ligament). 
•
Subjects undergoing concurrent partial meniscectomy or meniscus repair that 
would not alter postoperative weight-bearing status or rehabilitation protocol 
would be eligible for inclusion.
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•
Clinical and radiographic examination (MRI) consistent with an acute full 
thickness ACL tear
Exclusion Criteria: 
•
Age < 18 years of age 
•
Non-English speaking
•
Revision ACL reconstruction
•
Multi-ligamentous injury, including concomitant posterior cruciate ligament, 
medial collateral ligament and fibular collateral ligament injuries
•
Concomitant meniscal or cartilage injury that would alter postoperative weight 
bearing status or rehabilitation protocol
•
Inability to comply with the proposed follow-up clinic visits
•
Subjects lacking decisional capacity
•
Worker’s compensation subjects
•
Requiring a custom-sized brace 
Consent process – 
Potential participants are identified using medical chart and case review.  The study 
eligibility requirements will be  reviewed by the PI and study staff.  The potential 
participant is pre-selected as tentatively meeting the eligibility requirements for the study. 
Research study staff will reach out to eligible patients through a phone call explaining the 
study. Randomization to the treatment (KRONOS postoperative brace) or control group 
(Hinged knee brace) will occur at the time of informed consent
Informed Consent Discussion 
Investigator and/or PI and research study staff will contact the patient in clinic or via 
telephone to discuss the research study with them. Ideally, the informed consent 
discussion should be conducted when the study staff and potential participant has time to 
ask and answer questions.  Information provided to the patient includes the rationale for 
the study procedure or treatment, the number of study visits and the study activities they 
will need to complete, risks involved, expected benefits, and alternatives to treatment. 
The process may occur over a period of several discussions, culminating in the signing of 
a consent form in the office (Ipad or paper) or sent to their verified email address. The 
informed consent discussion will be documented in the patient profile or chart. 
If the patient agrees to participate, their email addressed will be verified. The consent will 
be obtained electronically sent through the secured platform called Patient IQ to their 
email. The potential subject will then be prompted to reply with the appropriate passcode 
in order to access the consent form, and then provide the passcode again with their 
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signature (secured). No research activities will be performed prior to execution of the 
consent. A copy of the time stamped document will be sent to the study team through the 
electronic platform and a copy will be sent to the participant.  
Study Design & Procedures–  
This is a randomized controlled trial.
We estimate 40 particpants (20 Kronos: 20 T-Scope) will be enrolled in the study.
Primary outcome variable
•
Rates of extension deficit (as measured by the fraction of patients with reduced 
extension compared to the contralateral knee, determined by heel height and 
goniometric measurements of knee extension) 
Bracing Protocol
Both treatment groups will progress according to a standard of care postoperative 
rehabilitation program regardless of the group to which the patient is randomized.
KRONOS  Bracing Group
Subjects randomized to the treatment group will be measured and fitted with the 
KRONOS knee brace at their initial clinic visit after study enrollment. The patient will be 
instructed to use the brace preoperatively and bring it to their surgery, after which the 
brace will be placed again on the patient postoperatively at the conclusion of their 
procedure.  Subjects will be instructed to wear the brace until symmetric terminal 
extension is achieved as indicated by side-to-side comparison with the non-surgical limb. 
This will be under the supervision and approval of the providing physician. Subjects will 
be instructed to use the brace (locked in extension and under high tension) at night during 
sleep and ambulation, though removal for therapy and rehabilitation exercises will be 
permitted.
Control Group – Standard Breg T-Scope Postoperative Bracing
Subjects will be placed in a standard postoperative hinged knee brace in the operating 
room that will be locked in full extension. Subjects will be instructed to use the brace 
locked in extension while sleeping for 6 weeks and when ambulating until the patient is 
able to perform a straight leg raise with no extension lag outside of the brace, at which 
point the brace may be worn unlocked during ambulation.
Table 1. Study timeline.
Preop
Surgery
2 
6 weeks
12 
6 months
12 
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weeks
weeks
months
Patient Recruitment 
●
Informed Consent and 
Randomization
●
Physical Exam (i.e. 
Heel height and 
goniometer 
measurement of active 
extension, passive 
flexion, passive 
extension)
●
●*
●
●
●
●
Circumferential thigh 
measurement 
(including healthy 
knee at pre-op)
●
●
●
●
 ●
Brace Placement 
●**
●
PROMs
●
●
●
●
Brace compliance 
survey
●**
●
●
*Passive flexion and extension ROM only under anesthesia prior to beginning 
surgery
** Only for patients randomized to the KRONOS brace treatment group 
       PROMs will include: IKDC, KOOS, VR-12, PROMIS Depression, PROMIS Physical 
Function, PROMIS Pain Interference, Return to Sport (RTS) and Return to Work 
(RTW), Resilience scale and brace compliance survey.
Study Interventions – 
Prospective Data Collection
Timeline of Events
1.
Once subjects are indicated for ACL surgery, a review of inclusion criteria will be 
undertaken, and subjects will be offered the opportunity to participate in the study. 
2. Pre-operative physical exam findings including Pivot-shift, Lachman, and range of 
motion data will be recorded. 
3.
Range of motion measurements (ROM), including heel height7,8 and goniometric 
measurements of 3 types of ROM (active extension, passive flexion, and passive 
extension) will be done at the initial visit, preoperatively on the day of surgery, 
intraoperatively under anesthesia before the initiation of the surgery (passive flexion 
and passive extension only), and at the designated postoperative timepoints indicated 
in Table 1 (1 week, 2 week, 6 week, 12 weeks, 6 months, and 12 months). 
4. Thigh circumference will also be measured with tape measure at the mid-thigh and 
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suprapatellar levels on the operative knee as a surrogate for quadriceps atrophy, as 
previously done10–12, pre-operatively and at the designated postoperative visits in 
Table 1 (1 week, 2 week, 6 week, 12 weeks, 6 months, and 12 months). Thigh 
circumference of the nonoperative healthy knee will also be measured pre-operatively 
for baseline comparison
5. Informed consent will be obtained. Prior to surgery (preoperative) subjects will be 
asked to complete standard of care patient reported outcomes questionnaires 
including IKDC, KOOS, PROMIS (Depression, Pain Interference, Physical function) 
, VAS pain, VR/SF 12, RTS, RTW and brief resilience scale.
6. Brace compliance survey  A survey assessing patient compliance with bracing 
instructions will be administered at the designated postoperative timepoints indicated 
in Table 1.
7. Subjects will proceed with operative management of their ACL tear, including 
appropriate treatment and documentation of concomitant injuries.
8. Subjects will be appropriately fitted for the brace corresponding to randomization on 
the day of surgery. All braces will be placed on the subject in the operating room at 
the conclusion of the procedure. All subjects will begin a standard of care physical 
therapy protocol on postoperative day 1-14. 
9.
Subjects will undergo standard of care follow up at 1-week, 2-week, 6-weeks, 12-
weeks, 6-months, and 12 months. At these standard of care visits, range of motion, 
including goniometric angle and heel-height measurements, will be made at all 
postoperative time points.                                    
 
Time-to-achievement of full symmetric extension relative to the non-surgical knee 
will be monitor and recorded. Additional physical exam of the knee will be performed 
at all follow-up time points. 
10. At 12 weeks, 6 months, and 12 months, subjects will also be asked to complete 
standard of care patient reported outcomes questionnaires including IKDC, KOOS, 
PROMIS, VAS pain, VR/SF 12, and brief resilience scale. Subjects will also be asked 
to answer standard of care questions regarding return to work and return to sport 
throughout the 1-year postoperative period.
Retrospective Data Collection
The following data will be abstracted from secured electronic medical record databases 
(Epic, Athena, Opal, Patient IQ) and electronically recorded on coded data collection tool 
for this study: 
•
Demographic information (age, sex, body mass indes (BMI), laterality) 
•
Chief Complaint
•
History of present illness
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•
Physical Exam 
Opal and Joints will be used to capture the following:
Surgical approach 
Arthroscopic diagnoses
Techniques used 
Fixation device / technique 
Preoperative imaging including but not limited to MRI
The following outcome variables will be taken from Athena and Patient IQ:
•
Postoperative complications
•
Failure of primary reconstruction
•
Need for a revision or subsequent procedure 
•
Preoperative / postoperative patient reported outcomes (PRO) including:
IKDC, KOOS, VR-12, PROMIS Depression, PROMIS Physical Function, PROMIS 
Pain Interference, Return to Sport (RTS) and Return to Work (RTW), Resilience scale
Other outcomes variables of interest:
•
Time-to-achievement of full extension
•
Degree of extension loss
•
Time to walking without a limp
•
Quad circumference difference 
•
Frequency of brace use
•
Number of postoperative physical therapy visits up to one year post-op
•
Standard of care Breg T-scope group: time to unlocking the brace
•
Kronos group: time to no quad assist (no dial engaged)
Rehabilitation Protocol
The rehabilitation program will be started on the day after surgery according to the 
providing physician’s standard protocol. 
Risk/benefit assessment – 
There is no direct benefit to the patient for his/her participation in this study. 
The results will contribute to the optimization postoperative bracing and rehabilitation 
protocols following ACL surgery. This study will help determine if the KRONOS 
postoperative knee brace is an efficacious and safe methodology to improve range of 
motion and reduce extension deficits following ACL reconstruction.
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Potential risk may include having the participant’s privacy or confidentiality 
compromised. The participant’s identities will not be identifiable in publications resulting 
from this investigation.  Every reasonable effort will be made to protect the participant’s 
information while their data is used as part of this study.
The alternative to participation in this study is not to participate. 
Costs to the subject– 
A brace will be provided to each study participant free of cost regardless of what group 
they are in– a standard of care Breg T-Scope brace or a Kronos brace.
No insurance coverage will be offered for regularly scheduled standard of care 
postoperative visits. However, any additional visits scheduled solely for the purpose of 
this study will be covered at no cost to the patient. 
Compensation of subjects– 
No compensation will be offered to study participants.
Data Analysis and Statistical Considerations –  
Power analysis was based on data published by Mikkelsen et al.6 as part of an ACLR 
randomized controlled trial of a hyperextension brace. A priori power analysis was 
conducted to determine the sample size required to detect a significant difference in the 
proportion of patients experiencing a loss of full knee extension of ≥2° between the 
straight brace and hyperextension brace groups. Using the observed proportions from the 
study (	 for the extension group and 

), the following parameters were used in G*Power for the calculation: Statistical 
test: Fisher's exact test (two independent groups); Effect size: Significance 
level (): 0.05; Power (−β): 0.8. The analysis indicated that a total sample size of 32 
participants (16 per group) would be required to achieve 80% power to detect a 
statistically significant difference in the proportions of patients experiencing knee 
extension loss at α=0.05. To account for potential loss of subjects to follow-up, a total 
of 40 subjects will be eligible to be enrolled.
The statistical software R will be used for analyses and calculation of relevant p-values, 
standard deviation, correlation coefficients, and confidence intervals. Categorical 
variables will be analyzed via Chi-squared test, while quantitative variables will be 
analyzed via students’ t-test for parametric data and Wilcoxon Mann-Whitney test for 
nonparametric data. 
Data & Safety monitoring 
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There is minimal risk to the subjects except the potential for loss of privacy and 
confidentiality, but every reasonable effort will be made to protect the patient’s 
information while their data is used as part of this study. 
Data storage & confidentiality – 
Participant information will be collected and maintained in a excel data sheet housed on 
the Midwest Orthopedics at Rush (MOR) server, which is dual-factor authentication 
protected and accessible only to research staff. Subjects identity will be coded via the use 
of a separate document key (electronic excel spreadsheet) correlating subjects’ Rush 
medical record numbers with a study ID assigned for the sole purpose of this study.  
This key electronic document will be maintained as a separate electronic file (excel 
spreadsheet) from data collection tool and will be housed in the Midwest Orthopaedics at 
Rush server, which is dual-factor authentication protected and accessible only to research 
staff. 
 Files will not be shared with non-study personnel. 
According to  (Rush policy OP-0432 and CC-G04) and study data must be maintained for 
10 years in accordance with Illinois State Law.  After this time the data will be destroyed 
by permanently and securely deleting electronic files on the Master key document (PHI) 
and the coded data collection tool.
References:
1.
Marois B, Tan XW, Pauyo T, Dodin P, Ballaz L, Nault ML. Can a Knee Brace 
Prevent ACL Reinjury: A Systematic Review. Int J Environ Res Public Health. 
2021;18(14):7611. doi:10.3390/ijerph18147611
2.
Wright RW, Fetzer GB. Bracing after ACL Reconstruction: A Systematic 
Review. Clin Orthop Relat Res. 2007;455:162. doi:10.1097/BLO.0b013e31802c9360
3.
Kruse LM, Gray B, Wright RW. Rehabilitation After Anterior Cruciate 
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4.
Yang X gang, Feng J tao, He X, Wang F, Hu Y cheng. The effect of knee bracing 
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5.
Melegati G, Tornese D, Bandi M, Volpi P, Schonhuber H, Denti M. The role of 
the rehabilitation brace in restoring knee extension after anterior cruciate ligament 
reconstruction: a prospective controlled study. Knee Surg Sports Traumatol 
Arthrosc. 2003;11(5):322-326. doi:10.1007/s00167-003-0386-3
6.
Mikkelsen C, Cerulli G, Lorenzini M, Bergstrand G, Werner S. Can a post-
operative brace in slight hyperextension prevent extension deficit after anterior 
cruciate ligament reconstruction? Knee Surg Sports Traumatol Arthrosc. 
2003;11(5):318-321. doi:10.1007/s00167-003-0406-3
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7.
Sachs RA, Daniel DM, Stone ML, Garfein RF. Patellofemoral problems after 
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8.
Schlegel TF, Boublik M, Hawkins RJ, Steadman JR. Reliability of Heel-Height 
Measurement for Documenting Knee Extension Deficits. Am J Sports Med. 
2002;30(4):479-482. doi:10.1177/03635465020300040501
10.
Doxey GE. Assessing Quadriceps Femoris Muscle Bulk With Girth 
Measurements in Subjects With Patellofemoral Pain. J Orthop Sports Phys Ther. 
1987;9(5):177-183. doi:10.2519/jospt.1987.9.5.177
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Giles LS, Webster KE, McClelland JA, Cook J. Does Quadriceps Atrophy Exist in 
Individuals With Patellofemoral Pain? A Systematic Literature Review With Meta-
analysis. J Orthop Sports Phys Ther. 2013;43(11):766-776. 
doi:10.2519/jospt.2013.4833
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Douciette SA, Goble EM. The effect of exercise on patellar tracking in lateral 
patellar compression syndrome. Am J Sports Med. 1992;20(4):434-440. 
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