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Biomechanical Mechanisms of Early Gait Training on Knee Cartilage Degeneration After Anterior Cruciate Ligament Reconstruction: a protocol for RCTA
RuiqinDang#1
YiqunLu#1
ZirenZhou1
ZhengZhou Cui1
NaYuanyuan1
YuSisiZhang1
YingfangAo1Emailaoyingfang@163.com
HongjieHuang1
JianquanWang1Emailwjqsportsmed@163.com
ShuangRen1✉Emailhhj@bjmu.edu.cnEmailxixishuang123@126.com
RuiqinDang1Emaildangruiqin0919@163.com
YiqunLu1Email15804081997@163.com
ZhengZhou1Emailzhouzheng1914@163.com
NaCui1Emailzzra12345678@163.comEmailcuina0920@163.comEmail179391494@qq.com
YuanyuanYu1Emailyyy1091012@126.com
SisiZhang1
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Department of Sports Medicine, Beijing Key Laboratory of Sports InjuriesPeking University Third Hospital, Institute of Sports Medicine of Peking University49 North Garden Road, Haidian District100191BeijingPeople’s Republic of ChinaRuiqin Dang# Yiqun Lu# Ziren Zhou Zheng Zhou Cui Na Yuanyuan Yu Sisi Zhang Yingfang Ao Hongjie Huang Jianquan Wang Shuang Ren*
Department of Sports Medicine, Beijing Key Laboratory of Sports Injuries, Peking University Third Hospital, Institute of Sports Medicine of Peking University, 49 North Garden Road, Haidian District, Beijing 100191, People’s Republic of China
Ruiqin Dang, Yiqun Lu, Shuang Ren contributed equally to this article.
* Shuang Ren
xixishuang123@126.com
Ruiqin Dang
dangruiqin0919@163.com
Yiqun Lu
15804081997@163.com
Ziren Zhou
zzra12345678@163.com
Zheng Zhou
zhouzheng1914@163.com
Na Cui
cuina0920@163.com
Yuanyuan Yu
yyy1091012@126.com
Sisi Zhang
179391494@qq.com
Yingfang Ao
aoyingfang@163.com
Hongjie Huang
hhj@bjmu.edu.cn
Jianquan Wang
wjqsportsmed@163.com
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Abstract
Objective
The primary objective of this study is to investigate the effects and biomechanical mechanisms of early gait retraining (GRT) on knee cartilage degeneration following anterior cruciate ligament reconstruction (ACLR).
Methods
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This study is a single-blind randomized controlled trial involving two independent groups. A total of 60 participants scheduled for their first unilateral ACLR surgery will be recruited. Participants will be randomly assigned to either the experimental group (receiving conventional training plus gait training) or the control group (receiving conventional training only). Gait training will commence in the third postoperative week and continue for 6 weeks, with sessions conducted 2–3 times per week, each lasting 15–20 minutes. Data will be collected at baseline, 3 months, 6 months, 1 year, and 2 years postoperatively. Outcome measures include gait analysis, surface electromyography, isokinetic muscle strength testing, functional MRI, Y-balance testing, single-leg hop testing, IKDC subjective knee evaluation score, Lysholm knee score, and Tegner activity level score. Repeated measures multivariate analysis of variance (MANOVA) will be used to assess the treatment effects on outcome measures.Conclusion
Early gait correction training using a body weight support treadmill after ACLR may significantly improve postoperative gait biomechanics. Furthermore, early gait correction can optimize standard rehabilitation protocols, thereby preventing and delaying cartilage degeneration. This approach holds clinical significance for restoring normal gait and preventing secondary injuries in individuals with sports-related injuries.
Trial registration
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All procedures and interventions will comply with the 1964 Declaration of Helsinki and its subsequent amendments or equivalent ethical standards, as well as the ethical standards of the institutional review board. A
Ethical approval was obtained from the Peking Universiy Third Hospital Medical Science Research Ethics Committee (Approval No. M2023816) before the study commenced. Additionally, the study was registered on ClinicalTrials.gov (ID NCT06368544).Keywords:
anterior cruciate ligament reconstruction
gait retraining ༛cartilage degeneration༛gait biomechanics༛weight-loss treadmill
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Introduction
Anterior cruciate ligament (ACL) rupture is a common and severe sports-related knee injury, accounting for approximately 50% of knee sports injuries[1].ACL rupture can lead to joint instability, disrupt the biomechanical homeostasis of the joint, and impair athletic performance[2, 3].
Arthroscopic anterior cruciate ligament reconstruction(ACL reconstruction, ACLR)is the preferred clinical treatment. ACLR effectively restores the structural stability of the ACL. However, the re-rupture rate after ACLR exceeds 10%[4, 5],and the risk of osteoarthritis within 10 years post-ACLR remains as high as 50%[6].Abnormal gait biomechanics is a significant factor contributing to knee osteoarthritis[7–9].ince walking is a repetitive functional movement, long-term abnormal gait can lead to abnormal cartilage loading[10–12]. Over time, abnormal gait can cause cartilage damage, meniscus tears, and other secondary injuries, increasing the risk of the occurrence and development of cartilage degeneration and osteoarthritis[13–15].Therefore, early correction of abnormal gait after ACLR is crucial to reduce the risk of secondary injuries.
Current standardized postoperative rehabilitation protocols primarily focus on range of motion, muscle strength, balance, coordination, and functional exercises. Previous studies have found that even when patients regain muscle strength and range of motion to the level required for returning to sports, their abnormal gait biomechanics often remain uncorrected[16–18].This suggests that current standardized rehabilitation protocols are insufficient to fully restore normal gait biomechanics after ACLR. Therefore, early gait retraining(GRT) is particularly important. GRT involves using various feedback modalities to target specific movement patterns to restore gait pattern before pathology[19–21].However, no studies have yet explored the impact of early GRT on gait biomechanics after ACLR.
Thus, the aim of this study is to investigate the effects and biomechanical mechanisms of early GRT on knee cartilage degeneration after ACLR. This study will conduct a randomized controlled trial to explore the effects of GRT on cartilage biochemical characteristics using functional MRI. Additionally, multimodal biomechanical testing along with model simulations,including motion capture and surface electromyography,will be used to investigate the mechanisms of GRT on gait kinematics, kinetics, and neuromuscular control after ACLR. Regression analysis will be employed to elucidate the relationship between GRT-induced changes in cartilage biochemical characteristics and biomechanical alterations. The study aims to demonstrate the necessity of incorporating GRT into postoperative rehabilitation protocols to prevent and delay cartilage degeneration through musculoskeletal rehabilitation.
Methods
Study Design
This study is a prospective randomized controlled trial. The experimental group will undergo gait training in addition to standard rehabilitation, while the control group will receive only standard rehabilitation. Both groups will be assessed at baseline, 3 months, 6 months, 1 year, and 2 years postoperatively (Fig. 1).
Fig. 1
Technical roadmap for the study protocol
Participants and Recruitment
Sample Size Calculation
The primary outcome measure is the peak knee flexion moment during walking, a key biomechanical indicator of cartilage degeneration. A significant difference in this measure will be considered statistically meaningful. Based on preliminary results, the mean peak knee flexion moment before training in ACLR patients is 0.20 Nm/kg/m, with a standard deviation of 0.09 Nm/kg/m. After training, the mean peak knee flexion moment is 0.28 Nm/kg/m, with a standard deviation of 1.1 Nm/kg/m. Using the formula for sample size estimation for two independent samples,
, with α = 0.05 and β = 0.2, among
,
, the required sample size for each group was calculated to be 25.Accounting for a 20% dropout rate, 30 participants per group will be recruited.
Inclusion and Exclusion Criteria
This study will enroll 60 patients scheduled for ACLR surgery. Participants will be randomized into two groups (30 in the experimental group and 30 in the control group) using the REDCap clinical research and trial database management platform.
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Baseline data will be collected preoperatively, and participants will sign informed consent forms after a thorough explanation of the researcher. All data collection and interventions will take place at the Department of Sports Medicine, Peking University Third Hospital.Inclusion Criteria:
Age 18–35 years;
MRI-confirmed ACL rupture;
First-time unilateral ACL rupture requiring reconstruction at Peking University Third Hospital, with surgery performed by a surgeon with over 10 years of experience using a single-bundle hamstring tendon autograft technique;
Normal BMI: 18.5–23.9 kg/m²;
Time since injury less than 6 months;
Acute symptoms (e.g., swelling, pain, inflammation) have resolved, and joint range of motion has been largely restored.
Exclusion Criteria:
History of musculoskeletal injury or surgery in the contralateral lower limb;
ACL injury more than 6 months prior;
Outerbridge grade III or IV cartilage damage;
Concurrent meniscus tear requiring repair during ACLR;
Severe injury to the posterior cruciate ligament, medial collateral ligament, or lateral collateral ligament;
Metabolic syndrome (e.g., obesity, dyslipidemia, diabetes), immune system diseases affecting joint cartilage, or severe cardiovascular or cerebrovascular diseases;
Unwillingness to undergo the proposed treatment.
Outcome Measures
Measurement Procedures
Participants will complete baseline information and subjective functional scoring scales (including basic information, IKDC2000 subjective knee function score, Tegner activity level score, Lysholm knee score, pain VAS score, and dominant side questionnaire). Subsequently, bilateral knee MRI (including functional MRI), three-dimensional gait biomechanics, isokinetic muscle strength, and lower limb balance tests will be conducted. All tests will be performed at baseline, 3 months, 6 months, 1 year, and 2 years postoperatively.Two-dimensional gait videos were collected at the time points before and after training in the intervention group to evaluate the symmetry.
Gait Analysis
A 10-camera three-dimensional motion capture system (Vicon) will be used to collect three-dimensional motion data during walking at a sampling rate of 100 Hz. Ground reaction forces will be simultaneously collected using force plates at a sampling rate of 1000 Hz. Surface electromyography will be used to assess the activation of the quadriceps, hamstrings, tibialis anterior, and gastrocnemius muscles during walking, with a sampling rate of 2000 Hz. Gait biomechanics analysis will be performed using Visual 3D software (C-Motion, USA) to calculate three-dimensional kinematics and kinetics of the hip, knee, and ankle joints. The AnyBody musculoskeletal model (18 rigid bodies and 92 muscles) will be used for inverse dynamics analysis to determine knee joint contact forces, anterior-posterior and lateral shear forces, and muscle forces.
Basic Motor Function Tests
Isokinetic Muscle Strength Test:
Conducted using the Con-Trex MJ system (Fitzmann, Germany). Using an isokinetic dynamometer, the subject's trunk and thigh were bound and extended from 90° to 20° knee flexion position at 60°/s, 180°/s, 300°/s, centrimetricallyand 60°/s centrifugally, and then returned to the initial position at the same angular velocity.
The subject stood on the test platform with one foot, the hallux aligned to the red starting line on the test platform, and both hands pinched at the waist. The other foot pushed the test board forward, posteromedial, and posterolateral as far as possible, and then returned to the starting line. The maximum distance (accurate to 0.5cm) of pushing the test board in different directions was recorded, and this was repeated three times. The foot support was changed, and the above tests were repeated and the results were recorded.
Y-Balance Test
The subject stood on the test platform with one foot, the hallux aligned to the red starting line on the test platform, and both hands pinched at the waist. The other foot pushed the test board forward, posteromedial, and posterolateral as far as possible, and then returned to the starting line. The maximum distance (accurate to 0.5cm) of pushing the test board in different directions was recorded, and this was repeated three times. The foot support was changed, and the above tests were repeated and the results were recorded.
Single-Leg Hop Test(Conducted at 6 months, 1 year, and 2 years)
Including single leg jump, single leg triple jump, single leg diagonal triple jump, 6 m time jump, etc.
Lysholm Knee Score
Lysholm is a quantitative score for daily symptoms and exercise capacity of the knee joint. This scoring system contains eight questions. The total score ranges from 0 to 100, with higher scores indicating better knee function. According to the score results, the functional status of the knee joint of the patient can be evaluated. More than 95 points are excellent, 94 − 85 points are good, 84 − 65 points are fair, and less than 65 points are poor[22].
IKDC 2000 Subjective Knee Score
IKDC 2000 knee subjective rating scale is a widely used tool to evaluate knee function and symptoms, especially for patients after knee injury or surgery [23].The scale assesses the performance of the knee joint in daily activities through patient self-report. The overall score ranges from 0 to 100, with higher scores indicating better knee function.
Tegner Activity Level Score
The Tegner rating scale is a tool commonly used to assess the degree of athletic injury and functional recovery to assess the ability to perform athletic activities after knee injury. The Tegner rating scale is graded on a scale from 0 to 10 based on the level of motor activity participants engage in and the gradual increase in demands[24].
Functional MRI
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Early cartilage degeneration may not be detectable by conventional MRI. Functional MRI, including T1ρ and T2 mapping sequences, can assess cartilage biochemical characteristics (collagen and proteoglycan content). Increased T1ρ and T2 values indicate a decline in collagen and proteoglycan content, reflecting early cartilage degeneration[25–27].Bilateral knee MRI (including functional MRI) will be performed preoperatively and at 3 months, 6 months, 1 year, and 2 years postoperatively. A GE 750W scanner will be used for T2 mapping and T1ρ sequences (TR/TE: 9.3/3.7 ms, field of view: 16 cm, slice thickness: 1 mm).The T2 mapping and T1rho values of different regions of knee cartilage, including femoral cartilage (medial condyle, lateral condyle, trochlea), tibial cartilage (medial and lateral), patellar cartilage, and femoral trochlea cartilage, were analyzed to reflect the biochemical characteristics such as collagen and protein content of the cartilage. As shown in Fig. 2, the division of tibiofaminal joint and patellofemoral joint is shown.
AI segmentation + manual fine tuning in 21 zones of knee cartilage and VR segmentation effect
Figure 2 Schematic representation of cartilage partitions in the knee joint
Postoperative Gait Intervention
The experimental group will undergo GRT using a combination of body weight support and visual feedback. The intervention will focus on correcting knee flexion moment, adduction moment, and flexion angle during the terminal stance phase of gait to restore normal gait patterns.The gait intervention was performed with the use of a weight-loss treadmill consisting of a lower-limb positive pressure system and a visual feedback screen. Using air pressure to reduce body weight during walking or running, using a weight-loss treadmill can stimulate weight loss and reduce knee pain, and studies have shown that weight-loss treadmill can reduce knee pain in patients with knee OA[28]. Weight-loss treadmill provides a relatively safe walking condition and environment for patients, which has great advantages over traditional treatment in terms of the recovery of walking ability, gait correction and balance function improvement [28–30].It combines the three elements of loading, stepping and balance in the process of walking, so as to promote the formation of the normal gait pattern of the affected limb. At the same time, the upper limb can move freely in this process, and the balance and the cooperative movement of the upper and lower limbs can be trained while the posture is controlled, which is more conducive to the recovery of walking stability[28, 31].
From the second week after surgery, the subjects in the experimental group used the lower limb positive pressure system to perform GRT 3 times a week, 15–30 minutes each time (3 groups *5–10 minutes/day, rest interval 90s), under the condition of controlled lower limb weight-bearing, for a period of 6 weeks. Before GRT, warm up for 5 minutes, and stretch and ice for 5–10 minutes after the test. During GRT, the lower limb brace should be removed, and the weight bearing of the lower limb should be quantified and individually adjusted according to the different weeks after surgery and the subject's own condition (Table 1). In the process of GRT, GRT was carried out through the interactive screen of the lower limb positive pressure system, and the real-time feedback of bilateral lower limb weight bearing and walking posture images was provided. The subjects made self-adjustment of bilateral lower limb weight bearing and walking posture to achieve the balance of bilateral lower limb weight bearing during gait (Fig. 3). VAS scores were performed before GRT, during GRT, at rest intervals, and immediately after GRT to evaluate knee pain before, during, and after GRT. The degree of knee swelling was assessed before and immediately after GRT.
Content | The first week | The second week | The third week | The fourth week | The fifth week | The sixth week |
|---|---|---|---|---|---|---|
Loading degree | 30%body weight | 50%body weight | 65%body weight | 80%body weight | 100%body weight | 100%body weight |
Time/ time | 15min(3*5min) | 15min (3*5min) | 15min (3*5min) | 15min (3*5min) | 15min (3*5min) | 15min (3*5min) |
Rest/min | 90s | 90s | 90s | 90s | 90s | 90s |
Trequen-cy | 3times/ week | 3times/ week | 3times/ week | 3times/ week | 3times/ week | 3times/ week |
Speed | Optional comfort speed(does not cause or aggravate pain) | |||||
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Fig. 3
Gait training combined with weight loss and visual feedback
Both groups used the same routine rehabilitation training protocol, and the routine rehabilitation training lasted for 30min, 4–5 times per week. The routine rehabilitation training program is shown in Table 2.
Postoperation time | rehabilitation protocol |
|---|---|
2–3 week | 1) Ankle pump exercise: use maximum strength to hook the toe up for 5 seconds and then step down for 5 seconds. The pain can be tolerated for a total of 500 times a day, if the pain is significantly reduced 2) Quadriceps femoris contraction: immediately after surgery. Forcefully contract the anterior thigh muscles for 5 seconds and then relax for 2 seconds, 500 times a day 3) Hamstring contraction: after the knee joint is fully extended, press down on the pillow under the foot, for 5 seconds, and relax for 2 seconds. The total number of times per day is 500 4) Straight leg raise: the knee joint was lifted straight 15° from the bed surface until exhaustion, twice a day, and each group until exhaustion. 5) Knee extension exercise: the heel pad pillow, the knee joint is empty, the muscle is completely relaxed, the acid swelling feeling on the back of the knee joint is normal, twice a day, for 30 minutes. 6) Range of motion exercise (0-100°) : perform knee flexion exercise once a day in the morning, against the wall in a sitting position, bend the knee to the target Angle and maintain it for 10 minutes, then wear a brace and apply ice for 20 minutes 7) Gradually transition to full weight-bearing walking |
3–4 week | 1) -5) As above 6) Range of motion exercise (0-120°) : perform knee flexion exercise once a day in the morning, Knee Flexion Training, Supine Leg Hang, knees bent to the target Angle and maintained for 10 minutes, and then wear braces and apply ice for 20 minutes 7) Weight-bearing walking |
5–12 week | 1) -4) The same as before 5) Range of motion exercise (0-130°) : knee flexion exercise was performed once every morning, kneel sitting, knees bent to the target angle and maintaining it for 10 minutes, then wearing braces and applying ice for 20 minutes 6) Static squat: the horse step, in the painless Angle of practice, pay attention to the knee joint does not exceed the tip of the foot, each time for 1–2 minutes |
Statistical analysis
Repeated measures multivariate analysis of variance was used to evaluate the longitudinal changes in the biochemical characteristics of cartilage in each region over time. Repeated measures two-way ANOVA was used to evaluate the differences in the biochemical characteristics of cartilage between the experimental group and the control group at different time points. Repeated measures analysis of variance was used to evaluate the difference of EMG signals before and after GRT, and to analyze the neuromuscular control mechanism of the effect of GRT on gait biomechanics.
Statement of Ethics and consent to participate
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The National Bioethics Committee's Review Board granted ethical approval for this research with human participants. A
Written informed consent will be obtained from all study participants.Discussion
At present, the standardized rehabilitation training for ACLR mainly includes muscle strength, range of motion, coordination, etc. However, even if these indicators return to normal, abnormal gait biomechanical characteristics still cannot be completely corrected, and specific GRT should be added to restore gait. Therefore, this study aims to fill the imperfection of GRT in the postoperative rehabilitation program of ACLR, optimize the standard rehabilitation program, so as to prevent and delay the occurrence and development of cartilage degeneration, which has certain clinical significance for the sports injury population to restore normal gait and prevent secondary injury.
List of Abbreviations
ACL
Anterior cruciate ligament
ACLR
anterior cruciate ligament reconstruction
GRT
gait retraining
Declarations
Ethical Approval
All procedures and interventions will comply with the 1964 Declaration of Helsinki and its subsequent amendments or equivalent ethical standards, as well as the ethical standards of the institutional review board. Ethical approval was obtained from the Peking Universiy Third Hospital Medical Science Research Ethics Committee (Approval No. M2023816) before the study commenced. Additionally, the study was registered on ClinicalTrials.gov (ID: NCT06368544).
Consent to participate
participants will sign informed consent forms after a thorough explanation of the researcher.
Consent for publication
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Written informed consent was obtained from all participants (or their legal guardians) for the publication of any potentially identifiable data or images included in this manuscript.A
Data Availability
The datasets generated during and analysed during the current study are available from the corresponding author on reasonable request.
Conflict of interest
There are no any relevant conficts of interest. The authors declare they have no fnancial interests. The au thors have no relevant fnancial or non-fnancial interests to disclose.
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Funding
This work was supported by grants from Beijing Natural Science Foundation grant(L241073)and Clinical Key Projects of Peking University Third Hospital(BYSY2022058).
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Author Contribution
Ruiqin Dang, Yiqun Lu, Shuang Ren contributed equally to this article.
Acknowledgements
This work was supported by grants from Beijing Natural Science Foundation grant(L241073)and Clinical Key Projects of Peking University Third Hospital(BYSY2022058).
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