Clinical application research of intelligent monitoring system for knee rehabilitation: a randomized controlled trial

Abstract

Background

This study investigates the effectiveness of a self-developed intelligent monitoring system for home-based knee rehabilitation following total knee arthroplasty (TKA).

Methods

In this randomized controlled trial, 120 patients undergoing TKA were divided using random digit allocation. Preoperative and one-month postoperative assessments of knee function, quality of life, and isometric knee extension strength were conducted with the Intelligent Monitoring System. Patients received group-specific rehabilitation instructions pre-discharge and performed exercises for one month.

Results

Changes in isometric knee extensor strength on the affected side within one month post-surgery for the brace-monitored rehabilitation group showed a significant decrease three days after surgery compared to one day before surgery. Subsequent measurements taken at postoperative days 5, 7, 14, and 21 indicated a gradual increase in strength, although these increases did not reach statistical significance when compared with previous measurements. One month post-surgery, all groups demonstrated significant improvements in knee joint function and mobility compared to pre-surgery levels. Notably, the brace-monitored group showed statistically significant improvements in 36-Item Short-Form Health Survey (SF-36) scores over the conventional rehabilitation group.

Conclusions

The Intelligent Monitoring System provides effective real-time monitoring and guidance for home-based knee rehabilitation post-TKA. It significantly enhances knee joint function, isometric knee extension strength, and quality of life shortly after surgery compared to traditional rehabilitation methods. This system offers a promising approach for improving postoperative recovery in TKA patients.

Trial registration

This study was approved by the Medical Ethics Committee of Xiangya Hospital, Central South University (Ethics Approval Number 202209008-2). It was registered with the China Clinical Trial Registry, a primary registry of the World Health Organization’s International Clinical Trials Registry Platform (Registration Number ChiCTR2300068852).

Supplementary Information

The online version contains supplementary material available at 10.1186/s13018-024-04982-8.

Introduction

Knee replacement surgery began to be widely applied in clinical practice during the 1970s and 1980s and is now considered one of the most common and cost-effective musculoskeletal surgeries [1, 2]. In the United Kingdom, over 100,000 primary knee replacement surgeries are performed annually, and many global joint registries have reported similar patterns of increasing frequency [3]. A study in the United States using the National Inpatient Sample and census data from 2000 to 2014 projected that the annual number of primary TKAs could reach 1.921 million by 2030 and 3.416 million by 2040 [4]. Traditionally, TKA has been used for elderly patients suffering from intolerable knee pain, unacceptable activity limitation with a significant loss of valued activities, and severe end-stage osteoarthritis [5]. However, with advancements in medical technology and improvements in surgical techniques, the indications for TKA are gradually expanding.

Proper rehabilitation exercises post-TKA are crucial for promoting the recovery of physical functions. Failure to perform timely and effective rehabilitation exercises can lead to complications such as joint adhesion, poor muscle strength recovery, and even infections [6]. With the development of medical technology and the widespread application of enhanced recovery after surgery (ERAS) concepts, the length of hospital stay post-TKA has significantly decreased, complications have significantly reduced, and the speed of functional recovery of limbs has significantly increased [7]. After discharge, most patients focus on rehabilitation training within the home or community, while a few opt for outpatient or rehospitalization for rehabilitation treatment. A randomized controlled trial from Canada showed no differences in pain, functional outcomes, or patient satisfaction between groups receiving home-based and in-hospital rehabilitation treatments, suggesting the use of more cost-effective home-based rehabilitation programs after elective primary TKA [8]. A systematic review and meta-analysis involving 752 participants also indicated that clinic-based or inpatient rehabilitation did not significantly differ from home-based rehabilitation in a range of clinical outcomes after TKA [9]. These studies collectively suggest the safety and effectiveness of home-based rehabilitation post-TKA, advocating for its use as a first-line treatment option for postoperative rehabilitation.

The first six weeks post-TKA are critical for rehabilitation training, with 65–75% of patients maintaining their joint function and pain levels at six weeks post-surgery up to six months later, making early rehabilitation crucial [10]. Insufficient rehabilitation can lead to prolonged recovery times, further damage due to improper activities, and increased subsequent costs. Most medical institutions adopt a rehabilitation plan combined with regular follow-up consultations to guide postoperative rehabilitation exercises for TKA patients. However, symptoms such as lower limb swelling, pain, muscle weakness, and joint mobility impairments persist for some time after discharge. Additionally, many patients in rural or remote areas are unable to ensure regular follow-up visits, severely impacting their postoperative rehabilitation [11, 12]. Currently, patients undergoing TKA globally are confronted with simultaneous issues: they strive for satisfactory functional improvement while dealing with concerns about discomfort symptoms, face a difficult balance with the demands of rehabilitation training, and require substantial external support. It is recommended to integrate online remote rehabilitation medical technologies to provide professional support for patients and promote optimal home-based recovery.

The development of remote rehabilitation for patients post-TKA is progressing rapidly, and remote rehabilitation is considered a practical alternative to traditional outpatient physical therapy for TKA patients [13]. Remote rehabilitation includes modes such as real-time interactive video conferencing, applications (Apps) (such as WeChat, QQ, and proprietary medical software), text messaging services, virtual reality technology, and wearable devices [14, 15]. The two most prevalent forms of remote rehabilitation currently involve mobile applications and wearable devices, with some approaches integrating both technologies. Dijk-Huisman HC and colleagues designed and developed a remote rehabilitation monitoring platform that includes a portable inertial measurement unit (IMU) combined with a mobile App and a clinical doctor’s portal backend. A randomized controlled trial confirmed the platform’s potential to improve physical activity levels and functional recovery in home-based rehabilitation for TKA patients [16]. A randomized controlled trial from Shanghai also showed that mobile app-based rehabilitation therapy could have a potential positive impact on patient self-efficacy, patient-reported physical function, health-related quality of life, and levels of anxiety and depression [17]. However, current wearable knee joint supports are mainly based on IMUs with accelerometers and gyroscopes [18, 19], which can only measure the bending movement of the knee joint and are unable to assess muscle strength [20]. Moreover, this is an indirect measurement requiring complex body parameters for subsequent computational modeling to invert the motion state, and periodic adjustments are needed to reduce misalignment errors that increase over time [21]. Therefore, there is an urgent need to develop a new type of wearable technology for long-term monitoring that can simultaneously assess muscle strength and joint mobility.

In the preliminary phase of this study, a wearable knee joint rehabilitation intelligent monitoring system was developed using a triboelectric nanogenerator (TENG) and mechanical sensors [22]. This system is simple, portable, and can be used by patients at home. It collects and measures data on muscle strength of the knee extensor and flexor muscle groups and the mobility of the knee joint, and transmits this data to the doctors via a mobile app. This facilitates remote monitoring and rehabilitation guidance by the physicians, enabling personalized rehabilitation. The primary aim of this study is to evaluate the efficacy of the knee joint rehabilitation intelligent monitoring system in the postoperative recovery of TKA patients. To achieve this, we will compare the outcomes of patients using the intelligent monitoring system with those undergoing conventional rehabilitation and telephone-guided rehabilitation. The aim of this study is to explore whether the system can aid doctors in assessing rehabilitation status and providing effective personalized rehabilitation guidance, and whether it can reduce the frequency of patients traveling back to the hospital for follow-up visits, thus potentially reducing medical costs and saving on family medical expenses. This will provide a reliable data foundation for further clinical promotion, application, and innovative transformation.

Materials and methods

Study design and participants

This study is a clinical randomized controlled trial. From September 2022 to February 2023, based on inclusion and exclusion criteria, a total of 120 patients undergoing TKA at our orthopedic department were enrolled in this study. All patients signed an informed consent form.

Inclusion and exclusion criteria

Inclusion criteria

1. Patients undergoing unilateral total knee arthroplasty for the first time;

2. Individuals with basic literacy skills and no communication barriers;

3. Possessing a smartphone and able to use WeChat and other simple applications;

4. Primarily engaging in home-based rehabilitation post-discharge.

Exclusion criteria

1. Patients with severe organ dysfunction;

2. Individuals with psychiatric disorders or cognitive impairments that prevent learning and active participation in rehabilitation exercises;

3. Patients undergoing simultaneous hip or knee joint replacement or other surgeries;

4. Individuals with a history of joint infection, joint tuberculosis, or osteomyelitis, or those who have undergone other surgical procedures on the lower limbs within the past six months;

5. Residents from other regions who are unable to return to the hospital for follow-up visits one month post-surgery.

Sample size estimation

This randomized controlled trial evaluates the impact of a knee joint rehabilitation intelligent monitoring system on functional recovery after TKA. The primary outcome measure is the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores one month post-surgery. Based on previous literature and pilot study results, the expected mean decreases in WOMAC scores one month post-surgery are 2.690, 4.349, and 4.848, with standard deviations of the differences between groups of 2.039, 2.031, and 2.254, respectively. A two-sided test with an alpha of 0.05 and a power of 90% was specified. Using PASS 15 software, the calculated sample size per group is N = 27. Considering a 20% rate for loss to follow-up and refusals, at least 102 participants are needed. A total of 120 participants were included in this study, divided into three groups of 40 each: the conventional rehabilitation group, the telephone-guided rehabilitation group, and the brace monitoring rehabilitation group.

Randomization and blinding

The randomization scheme was generated using SPSS 21.0 software, which randomly assigned all patients in a 1:1:1 ratio into the brace monitoring rehabilitation group, the telephone-guided rehabilitation group, and the conventional rehabilitation group. This randomization was conducted by an independent physician. The randomization scheme was not blinded to the patients or the attending physicians. However, the personnel responsible for follow-up, data collection, and final statistical analysis were blinded.

Research intervention

Development of the intervention protocol

Preparation of the Knee Joint Rehabilitation Intelligent Assistive Brace: The knee joint rehabilitation intelligent assistive brace comprises two modular components for rehabilitation: an isometric knee extensor strength testing module and an active joint mobility testing module. The structural integration primarily involves assembling the designed components onto a conventional brace. Figure 1 displays the assembly and exploded views of the brace, which includes a TENG angle sensor, angle sensing circuit, force sensor, quick-release, telescopic rod, and force sensing circuit. The isometric knee extensor strength testing module integrates the telescopic rod assembly, tension and compression force sensor, sensor circuit, and its encapsulation into a single unit. Through structural integration, the isometric knee extensor strength testing module can be installed and removed as a whole, facilitating operation by the participants. For the TENG angle sensor, this study primarily employs an embedded integration approach. Given the brace’s ample space, the TENG angle sensor and its circuitry can be well embedded within the knee joint brace without affecting its normal use.

Fig. 1.

Structural diagram of the intelligent assistive brace for knee joint rehabilitation

The development platform for the “Knee Know” app was primarily built using Android Studio to develop the mobile application, named “Knee Know” App for ease of recognition by patients. The app’s user interface primarily includes a selection screen, record screen, statistics screen, connection screen, and testing screen, with the interface language predominantly in Chinese and partially bilingual. As shown in Fig. 2.

Fig. 2.

Interfaces of the “Knee Know” APP. (a) Start interface. (b) The selection screen includes an angle measurement portal and a strength measurement portal. (c) Record interface, taking the angle module as an example, which includes test time, direction, angle speed, the number of times the threshold is exceeded. Besides, the local file open, data export, and data delete buttons are in the upper right corner. (d) Statistics interface including weekly and monthly statistics. (e) Search interface. (f) Strength measurement interface includes portals of searching device, record interface and statics interface. Other functions are illustrated by words. (g) Angle measurement interface also includes interfaces mentioned above and other functions are described by words

The muscle strength measurement module (Figure S1) includes a telescopic rod assembly, column, quick-release, tension and compression force sensor, and digital acquisition circuit. The telescopic rod assembly primarily adjusts the brace’s bending angle, corresponding to isometric strength tests at 30° and 60° knee flexion. The module is fabricated using machining processes, including milling, grinding, electroplating, and welding. The telescopic rod is designed using CAD and SOLIDWORKS software, with materials preferably being 7000 series aluminum alloy and stainless steel. The rod comprises side links and a central sleeve; the side links are equipped with threads and quick-release connecting rings for attachment to the force sensor and fixation on both sides of the brace. The central sleeve is primarily fixed and slides through pre-set pin holes, corresponding exactly to the brace bending at 30° and 60°. By rotating the sleeve to adjust the position, the isometric muscle strength test can be completed once the corresponding fixed position is reached.

The joint mobility measurement module (Figure S2) employs a grid-electrode independent-layer TENG as the angle sensor. The design principle of the TENG angle sensor is based on the relationship between the signals generated by the periodic grid during rotation and the rotation angle, and also on the phase difference between two sets of TENG signals with a quarter-cycle difference related to the rotation direction. Based on these relationships, this work has designed two sets of TENG with phase differences. By analyzing the time sequence of the peaks and troughs of TENG A and TENG B, the sensor’s rotation direction can be determined, and the changing angle values can be iteratively calculated based on the number of occurring peaks and troughs.

The establishment of the knee joint rehabilitation intelligent monitoring system involves a workflow where two testing modules are utilized for conducting two medical tests, while hardware and software facilitate information sharing and rehabilitation guidance between doctors and patients. As shown in Fig. 3, the system supports the patient’s rehabilitation process in three steps: first, using the knee joint rehabilitation intelligent assistive brace module for isometric muscle strength testing and active joint mobility testing; second, using the software platform to display and record; and third, using the network to transmit rehabilitation status information to the doctor. Conversely, doctors can also provide personalized rehabilitation guidance based on the patient’s rehabilitation status. To further test and improve the knee joint rehabilitation intelligent monitoring system, a reference database of brace-based muscle strength and mobility is established. Ten healthy volunteers, comprising 5 males and 5 females aged between 25 and 35 years, participated in a preliminary experiment. All volunteers, who have no history of lower limb functional impairments and possess a Body Mass Index (BMI) ranging from 18.5 to 23.9, meeting the general criteria for healthy adults, provided clinical data, isometric strength, and mobility information. This data was calibrated using professional isometric testing instruments and joint angle rulers, achieving minimum resolutions of 0.01 N and 1°, respectively.

Fig. 3.

Flowchart of the intelligent monitoring system for knee joint rehabilitation assistance

Brace monitoring rehabilitation group

The day before discharge, patients are instructed on how to wear and use the knee joint rehabilitation intelligent assistive brace and the “Knee Know” app. They follow a home rehabilitation exercise plan provided by the “Osteoarthritis Prevention and Treatment” WeChat public account. Daily monitoring is performed using the brace, and routine rehabilitation monitoring data are fed back to the doctor, who then adjusts the rehabilitation plan and provides exercise guidance based on the monitoring data. Patients are advised to seek follow-up consultation if they experience discomfort, with an outpatient review scheduled one month later.

Telephone-guided rehabilitation group

The day before discharge, patients are informed and trained to proficiently follow the rehabilitation and exercise plan from the “Osteoarthritis Prevention and Treatment” WeChat public account. Post-discharge, patients are encouraged to actively engage in home-based rehabilitation exercises according to the plan. Follow-ups via telephone are conducted on days 1, 3, 5, 7, 14, and 21 after discharge to guide the patients through their rehabilitation exercises. Patients are advised to seek follow-up consultation if they experience discomfort, with an outpatient review scheduled one month later.

Conventional rehabilitation group

The day before discharge, patients are informed and trained to proficiently follow the rehabilitation and exercise plan from the “Osteoarthritis Prevention and Treatment” WeChat public account. Post-discharge, patients are encouraged to actively engage in home-based rehabilitation exercises according to the plan. Patients are advised to seek follow-up consultation if they experience discomfort, with an outpatient review scheduled one month later.

Study procedure

All patients who met the inclusion and exclusion criteria were required to sign an informed consent form before participating in the study and were then randomized into groups using random numbers. Upon admission, baseline data were routinely collected for all patients. All surgeries were performed by three chief physicians from our department. All patients underwent knee joint function scoring and quality of life assessments the day before surgery, and isometric muscle strength and joint mobility were measured using the knee joint rehabilitation intelligent monitoring system. The day before discharge, patients were instructed on home rehabilitation exercises according to the intervention plans of their respective groups, as detailed in the “Research Intervention” section. One month post-surgery, knee joint function and quality of life were assessed again, and isometric muscle strength and joint mobility were measured once more using the knee joint rehabilitation intelligent monitoring system.

Outcome measures and tools

General information

General demographic data including gender, age, height, weight, and educational level were collected using a general data survey. Disease-related information such as duration of illness, surgical site, and comorbidities were also recorded.

Knee joint function scoring

The function and therapeutic efficacy of the knee joint were assessed using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and the Hospital for Special Surgery (HSS) scores.

Knee joint mobility

Knee joint mobility was measured using the knee joint rehabilitation intelligent monitoring system. Measurements were conducted by researchers both pre-operatively and during the one-month post-operative follow-up.

Isometric muscle strength of the knee Joint

Isometric muscle strength of the knee joint was measured using the knee joint rehabilitation intelligent monitoring system. Except for the brace monitoring rehabilitation group, measurements for the other two groups were conducted by researchers both pre-operatively and during the one-month post-operative follow-up.

Quality of life

The quality of life of patients post-TKA was assessed using the SF-36 health survey.

Data collection

Researchers explained the purpose, significance, and process of the study to the enrolled patients, informing them that the data collected would be used solely for research purposes. Patients were guided to complete questionnaires and baseline data were collected. At the one-month post-operative follow-up in the orthopedic outpatient clinic, a second set of data was collected. Knee joint mobility and isometric muscle strength were measured using the knee joint rehabilitation intelligent monitoring system by the researchers and averaged. Knee joint function scores (WOMAC and HSS) were completed by researchers, while general data surveys and the SF-36 quality of life questionnaire were filled out by the patients themselves.

Quality control

During the study, dedicated personnel performed supervision and inspection to ensure strict adherence to all aspects of the research protocol and the accuracy of data recorded. Establishing uniform standardized training is a crucial aspect of quality control in the clinical research implementation process, ensuring that each phase meets the standard operating procedures of clinical trial projects. Training participants include data collectors, follow-up personnel, and data entry and statistics staff. Training content covers the trial protocol, brace wearing and app usage, data collection, and entry.

Ethical review and clinical trial registration

This study was approved by the Medical Ethics Committee of Xiangya Hospital, Central South University (Ethics Approval Number 202209008-2). It was registered with the China Clinical Trial Registry, a primary registry of the World Health Organization’s International Clinical Trials Registry Platform (Registration Number ChiCTR2300068852).

Statistical analysis

Statistical analysis was conducted using SPSS 21.0 software. Continuous numerical variables were tested for normality using the Shapiro-Wilk test. Data conforming to a normal distribution were expressed as mean ± standard deviation, while non-normally distributed data were represented by the median and interquartile range. Categorical variables were presented as counts and percentages. Changes in isometric knee extensor strength one month post-surgery in the brace monitoring rehabilitation group were analyzed using repeated measures ANOVA, with variance homogeneity confirmed by Levene’s test. Multiple comparisons between groups were adjusted using the Bonferroni method. Other indices were analyzed as appropriate using one-way ANOVA, paired sample T-tests, Kruskal-Wallis tests, chi-square tests, and Fisher’s exact test. A p-value of < 0.05 was considered statistically significant.

Results

Baseline characteristics of study participants

A total of 150 patients were assessed for eligibility before enrollment, and after strict adherence to inclusion and exclusion criteria and excluding those unwilling to participate, 120 patients were finally enrolled. All patients were randomly divided into three groups: brace monitoring rehabilitation group, telephone-guided rehabilitation group, and conventional rehabilitation group. During follow-up, all patients completed their one-month post-operative outpatient review or actively attended follow-up visits, with no loss to follow-up. All 120 patients were included in the final statistical analysis. The specific research flowchart is shown in Fig. 4.

Fig. 4.

The study flow chart

General information of the study participants

The general information of the study participants is presented in Table 1. There were no significant statistical differences among the three groups in terms of age, gender, BMI, educational level, marital status, living situation, and average monthly family income (P > 0.05).

Table 1.

General information of the study subjects (N = 120)

Variable	Conventional Rehabilitation Group (N = 40)	Telephone-Guided Rehabilitation Group (N = 40)	Brace Monitoring Rehabilitation Group (N = 40)	Statistic	P
Age (years)	65.49 ± 4.56	66.32 ± 3.98	64.58 ± 3.68	F = 1.822	0.166
Gender (male/female)	32/8	28/12	25/15	χ2 = 2.985	0.225
BMI(kg/m 2 )	24.60 ± 2.68	24.23 ± 3.11	25.54 ± 2.88	F = 2.166	0.119
Educational level (No. and %)				χ2 = 1.512	0.825
Below junior high school	14(35.00%)	16(40.00%)	15(37.50%)
High school and vocational school	11(27.50%)	14(35.00%)	12(30.00%)
Junior college and above	15(37.50%)	10(25.00%)	13(32.50%)
Marital status (No. and %)				χ2 = 0.276	0.871
With spouse	25(62.50%)	23(57.50%)	23(57.50%)
Without spouse	15(37.50%)	17(42.50%)	17(42.50%)
Residential status (No. and %)				χ2 = 2.584	0.859
Living with spouse	20(50.00%)	15(37.50%)	18(45.00%)
Living with children	8(20.00%)	8(20.00%)	10(25.00%)
Living with spouse and children	6(15.00%)	10(25.00%)	6(15.00%)
Other	6(15.00%)	7(17.50%)	6(15.00%)
Average monthly household income per capita(RMB)(No. and %)				χ2 = 4.927	0.295
< 3000	10(25.00%)	8(20.00%)	12(30.00%)
3000–5000	25(62.50%)	20(50.00%)	18(45.00%)
> 5000	5(12.50%)	12(30.00%)	10(25.00%)

Clinical data of the study participants

There were no significant differences among the three groups in terms of duration of illness, comorbidities, surgical site, WOMAC scores the day before surgery, HSS scores the day before surgery, joint mobility the day before surgery, isometric knee extensor strength on the affected side the day before surgery, and quality of life before surgery (P > 0.05), as detailed in Table 2.

Table 2.

Clinical data of the study subjects (N = 120)

Variable	Conventional Rehabilitation Group (N = 40)	Telephone-Guided Rehabilitation Group (N = 40)	Brace Monitoring Rehabilitation Group (N = 40)	Statistic	P
Duration of illness (years)	10.35 ± 3.65	10.26 ± 2.89	9.22 ± 2.54	F = 1.674	0.192
Number of complications				χ2 = 2.790	0.594
None	8(20.00%)	12(30.00%)	6(15.00%)
1–2	23(57.50%)	20(50.00%)	25(62.50%)
3 or more	9(22.50%)	8(20.00%)	9(22.50%)
Surgical site (left/right)	25/15	19/21	23/17	χ2 = 1.892	0.388
Preoperative WOMAC score	65.33 ± 10.56	64.53 ± 11.48	62.38 ± 11.24	F = 0.754	0.473
Preoperative HSS score	39.65 ± 4.36	41.24 ± 3.99	39.24 ± 3.67	F = 2.774	0.067
Preoperative range of motion (°)	90.63 ± 8.03	92.35 ± 6.85	90.86 ± 7.34	F = 0.633	0.533
Preoperative isometric knee extensor strength at 30°(N)	369.54 ± 62.35	372.98 ± 55.48	374.31 ± 52.42	F = 0.075	0.928
Preoperative isometric knee extensor strength at 60°(N)	395.62 ± 60.35	389.46 ± 63.54	391.12 ± 65.52	F = 0.102	0.903
Preoperative SF-36 score	52.36 ± 10.66	53.72 ± 11.24	53.21 ± 12.02	F = 0.147	0.864

Changes in isometric knee extensor strength monitored by the knee joint rehabilitation intelligent monitoring system within one month post-surgery

Given that patients’ knee joint mobility during and three days post-surgery could reach or even exceed pre-surgical levels, this study focuses on describing the changes in isometric knee extensor strength on the affected side, as monitored by the knee joint rehabilitation intelligent monitoring system. Table 3 records the isometric knee extensor strength data for the brace monitoring rehabilitation group on the day before surgery, and on days 3, 5, 7, 14, 21, and 30 post-surgery, specifically at 30° and 60° knee extension. The isometric knee extensor strength on the affected side significantly decreased three days post-surgery compared to the day before surgery, showing a statistically significant difference (P < 0.05). Subsequently, as time progressed, the isometric knee extensor strength on the affected side gradually increased on days 5, 7, 14, and 21 post-surgery, although there were no significant differences compared to the previous measurements (P > 0.05). One month post-surgery, the isometric knee extensor strength on the affected side was significantly higher compared to both 21 days post-surgery and the day before surgery (P < 0.05). The specific trends are illustrated in Fig. 5.

Table 3.

Isometric knee extensor strength on the affected side at 30 degrees and 60 degrees in patients with brace-assisted rehabilitation

Measurement time	30°(N)	60°(N)	P
1 day before surgery	374.31 ± 52.42	391.12 ± 65.52	0.284
3 days after surgery a	230.52 ± 88.24	126.87 ± 69.78	< 0.001
5 days after surgery a	257.38 ± 81.94	198.38 ± 72.38	0.014
7 days after surgery a	264.43 ± 64.47	205.85 ± 50.53	0.036
14 days after surgery ab	310.26 ± 79.08	261.41 ± 64.00	0.081
21 days after surgery ab	310.52 ± 86.74	265.63 ± 60.20	0.011
1 month after surgery abcdef	477.53 ± 77.25	454.57 ± 68.26	0.109

Note: ‘a’ indicates a statistically significant difference compared to 1 day before surgery; ‘b’ indicates a statistically significant difference compared to 3 days after surgery; ‘c’ indicates a statistically significant difference compared to 5 days after surgery; ‘d’ indicates a statistically significant difference compared to 7 days after surgery; ‘e’ indicates a statistically significant difference compared to 14 days after surgery; ‘f’ indicates a statistically significant difference compared to 21 days after surgery

Fig. 5.

Trend chart of isometric knee extensor strength changes on the affected side within one month before and after surgery in the brace monitoring rehabilitation group. Note: ** indicates a statistically significant difference compared to the previous time point

Comparison of study outcomes among brace monitoring rehabilitation group, telephone-guided rehabilitation group, and conventional rehabilitation group

Comparison of knee joint function scores

One month post-surgery, the functional scores (WOMAC and HSS) for patients in the brace monitoring rehabilitation group, telephone-guided rehabilitation group, and conventional rehabilitation group were all significantly improved compared to the day before surgery (P < 0.05). The differences in the improvements between pre-surgery and one month post-surgery among the three groups were statistically significant (P < 0.05). However, pairwise comparisons showed that only the brace monitoring rehabilitation group was significantly better than the conventional rehabilitation group (P < 0.05), with no significant differences between the brace monitoring rehabilitation group and the telephone-guided rehabilitation group or between the telephone-guided rehabilitation group and the conventional rehabilitation group (P > 0.05). These results are presented in Fig. 6a and b.

Fig. 6.

Comparison of research indicators among the brace monitoring rehabilitation group (BMRG), telephone-guided rehabilitation group (TGRG), and conventional rehabilitation group (CRG). (a) Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores. (b) Hospital for Special Surgery (HSS) scores. (c) Range of motion. (d) 30° Isometric Knee Extensor Strength. (e) 60° Isometric Knee Extensor Strength. (f) 36-Item Short-Form Health Survey (SF-36) scores

Comparison of knee joint mobility

As shown in Fig. 6c, one month post-surgery, knee joint mobility in each of the three groups was significantly higher than the corresponding pre-surgery levels (P < 0.05). The increase in mobility from pre-surgery to one month post-surgery was greater in the brace monitoring rehabilitation group compared to the telephone-guided rehabilitation group, and greater in the telephone-guided rehabilitation group compared to the conventional rehabilitation group, although these differences were not statistically significant (P > 0.05).

Comparison of isometric knee extensor strength

One month post-surgery, the isometric knee extensor strength on the affected side in each group was significantly higher than the corresponding pre-surgery levels (P < 0.05). The differences in isometric knee extensor strength improvements among the three groups were statistically significant, with pairwise comparisons showing: brace monitoring rehabilitation group > telephone-guided rehabilitation group > conventional rehabilitation group (P < 0.05). Details are shown in Fig. 6d and e.

Comparison of quality of life

One month post-surgery, the SF-36 scores for each group were higher than the corresponding pre-surgery scores, although these differences were not statistically significant (P > 0.05). However, the differences in the changes in SF-36 scores among the three groups were statistically significant, with pairwise comparisons revealing that only the brace monitoring rehabilitation group was significantly better than the conventional rehabilitation group (P < 0.05). Details are shown in Fig. 6f.

Discussion

TKA is a crucial therapeutic intervention for alleviating joint pain and mobility limitations, aiding patients in regaining joint function and mobility [23]. Patients scheduled for TKA often exhibit a decline in periarticular muscle strength due to joint pain and restricted mobility [24]. In the early postoperative period, factors such as soft tissue dissection, surgical incision pain, and inflammatory responses prevent the recovery of periarticular muscle strength to normal levels. This study monitored the changes in isometric knee extensor strength on the affected side from the day before surgery up to 30 days post-surgery using the knee joint rehabilitation intelligent monitoring system. Three days post-surgery, the isometric knee extensor strength measured at knee flexion angles of 30 degrees and 60 degrees was significantly lower than that measured pre-surgery at corresponding angles (P < 0.05), but muscle strength exceeded pre-surgical levels by one month post-surgery (P < 0.05). A follow-up study from the United States also observed a significant decline in knee joint range of motion (ROM) and quadriceps muscle strength post-TKA, with quadriceps strength showing the most substantial decrease among all assessed parameters, although there was an observed increase in quadriceps muscle strength in knee joint function tests one month post-surgery [25]. Jennifer E. Stevens et al. [26] also noted a decrease in quadriceps muscle strength post-TKA. The decline in muscle strength post-TKA is common, not only due to surgical incision pain leading to voluntary knee extension limitations, but also due to intra-articular inflammatory responses and quadriceps arthrogenic muscle inhibition caused by intraoperative soft tissue dissection [27]. In this study, the knee joint rehabilitation intelligent monitoring system facilitated convenient and precise measurements of isometric knee strength, allowing for more frequent measurements compared to other similar studies [25], which supports dynamic monitoring of early postoperative rehabilitation quality and personalized adjustment of rehabilitation plans. Studies on the biomechanics of knee flexion-extension under different conditions show that under normal physiological conditions, the knee joint exhibits maximum isometric knee extensor strength at a 75-degree angle, increasing from 30 degrees to 90 degrees before decreasing. In this study, post-TKA patients demonstrated greater isometric knee extensor strength at a 30-degree flexion angle compared to a 60-degree angle. Early post-TKA, when the surgical wound is in the recovery phase, increased flexion angles can enhance tension around the incision, leading to restricted voluntary movement and a temporary decline in muscle strength.

The focus of this study is to assess the clinical efficacy of the knee joint rehabilitation intelligent monitoring system in enhancing recovery post-TKA, by comparing it with conventional and telephone-guided rehabilitation modalities. The results indicated that one month post-surgery, the knee joint function scores (both HSS and WOMAC) for patients in the brace monitoring rehabilitation group, telephone-guided rehabilitation group, and conventional rehabilitation group were all higher than the scores on the day before surgery (P < 0.05). Additionally, the WOMAC scores for all three groups were lower than the pre-surgery scores. This demonstrates that TKA significantly improves knee joint function one month post-surgery. Notably, only the difference in the pre- and post-surgery knee joint HSS and WOMAC scores between the brace monitoring rehabilitation group and the conventional rehabilitation group was statistically significant (P < 0.05), indicating that the improvement in scores in the brace monitoring rehabilitation group was superior to that in the conventional rehabilitation group. There were no significant differences in the changes in scores between the brace monitoring rehabilitation group and the telephone-guided rehabilitation group, or between the telephone-guided rehabilitation group and the conventional rehabilitation group (P > 0.05). The efficacy of the telephone-guided rehabilitation group depended on the interaction and cooperation between doctors and patients. However, due to the lack of real-time health data during this process, it is difficult to provide targeted advice on actual deficiencies in the rehabilitation plan, which might be the main reason for the lack of expected efficacy in the telephone-guided rehabilitation group.

Measurement of joint mobility is a crucial basis for assessing joint health status. During the rehabilitation training period following TKA, achieving satisfactory measurements of joint mobility, and improving the efficiency and accuracy of these measurements, are essential for monitoring the progress of rehabilitation training and evaluating its effectiveness [28, 29]. In this study, the knee joint mobility on the affected side one month post-surgery was significantly higher than the pre-surgery levels for all groups: the brace monitoring rehabilitation group, the telephone-guided rehabilitation group, and the conventional rehabilitation group (P < 0.05). This suggests that even without any interventions, simply undergoing one month of rehabilitation exercises can improve knee joint mobility post-TKA. Other researchers have also studied the rehabilitation efficacy of different interventions. A systematic review conducted by the University of Madrid in Spain also indicated that there are no statistical differences in improving knee joint mobility post-TKA between home-based rehabilitation exercises and supervised rehabilitation exercises [30]. From these results, it can be inferred that regular home-based rehabilitation exercises also significantly improve joint mobility. Among the various indicators for assessing knee joint function, joint mobility is the most visually observable indicator for patients and their families. Patients can roughly assess the effectiveness of joint mobility rehabilitation without relying on other measurement devices. Furthermore, the further popularization of postoperative rehabilitation education also plays a promotive role in the recovery of postoperative joint mobility.

Monitoring changes in isometric muscle strength post-surgery is crucial for guiding personalized postoperative rehabilitation training, and this metric has increasingly attracted the attention of scholars. In this study, the isometric knee extensor strength measured at knee flexion angles of 30 degrees and 60 degrees one month post-surgery was higher than the strength measured at corresponding angles the day before surgery in the brace monitoring rehabilitation group, the telephone-guided rehabilitation group, and the conventional rehabilitation group (P < 0.05). This suggests that with the further refinement of post-TKA rehabilitation plans, regular home-based rehabilitation exercises can effectively mitigate the decline in periarticular muscle strength observed post-surgery. To date, research on wearable devices for measuring isometric muscle strength in the knee joint is still not mature. Matthew G. Liptak and colleagues registered a clinical application of a wearable lower limb rehabilitation device in 2019, but the primary function of this device was to measure joint mobility, and it did not involve the measurement of isometric muscle strength in the knee joint, nor did it address its clinical efficacy evaluation [31].

Assessing patients’ quality of life before and after surgery is an important tool for evaluating the effectiveness of TKA and rehabilitation training. In this study, the quality of life one month post-surgery for patients in the brace monitoring rehabilitation group, the telephone-guided rehabilitation group, and the conventional rehabilitation group was higher than on the day before surgery, although the differences were not statistically significant (P > 0.05). Post-TKA, factors such as surgical incision pain, periarticular pain caused by rehabilitation training, and anxiety can hinder the recovery of quality of life scores to pre-surgery levels within one month. Nihal Büker and colleagues conducted a study on the prognosis and cost-effectiveness of supervised rehabilitation training versus standard home-based rehabilitation training, finding no statistical difference in the improvement of SF-36 scores between the two modalities within three months post-surgery, with standard home-based rehabilitation training offering a higher cost-benefit value [32]. Researchers at the Jyväskylä Hospital Rehabilitation Medicine Center in France also compared the efficacy of personalized guided rehabilitation training versus standard home-based rehabilitation training, and their findings showed no statistical difference in the SF-36 score differences between the two groups within twelve months post-surgery [33]. Current research indicates that telephone/WeChat/supervised rehabilitation training does not significantly enhance postoperative rehabilitation outcomes or quality of life. This may be due to a lack of real-time interaction between patients and healthcare providers during the process. Healthcare providers often rely on patients’ subjective perceptions rather than data-driven information about their rehabilitation, and patient compliance also varies. These factors directly affect the effectiveness of such rehabilitation training models.

Limitations

This study has several limitations. Firstly, it only measured and analyzed the isometric knee extensor strength and knee joint mobility on the affected side, without assessing the healthy side. Consequently, no comparative study was conducted between the affected and healthy sides regarding isometric knee extensor strength and knee joint mobility. Secondly, this study is a single-center randomized controlled trial, which limits the generalizability of the findings. Future studies will aim to conduct nationwide, multicenter, randomized, controlled, double-blind clinical research to validate these findings. Lastly, this study did not consider pre-admission levels of physical activity or nutritional status as confounding factors, which may introduce bias into the results.

Conclusion

This study was designed and developed in response to the needs of rehabilitation medicine, creating a knee joint rehabilitation intelligent monitoring system for monitoring and guiding home-based rehabilitation exercises in patients following TKA. Clinical research conducted within this study has validated that the system is capable of real-time monitoring of postoperative isometric knee extensor strength and joint mobility. Compared to other home-based rehabilitation plans, the knee joint rehabilitation intelligent monitoring system can enhance knee joint function, joint mobility, and isometric knee extensor strength in the short term post-surgery, significantly improving patients’ quality of life.

Electronic supplementary material

Below is the link to the electronic supplementary material.

Abbreviations

TKA

Total Knee Arthroplasty

APP

Application

TENG

Triboelectric Nanogenerator

WOMAC

Western Ontario and McMaster Universities Osteoarthritis Index

HSS

Hospital for Special Surgery Knee Score

SF-36

36-Item Short-Form Health Survey

Author contributions

Data collection and analysis were performed by HZL. The first draft of the manuscript was written by WQX and MH. HFJ, BZJ and GY made meaningful corrections to the structure and research design of the article and guided statistical methods and data processing. WQX and SYZ contributed to the revision process. YSL contributed to the concept and design of the study and participated in the revision of the manuscript. All authors reviewed the manuscript.

Funding

This work was supported by the National Natural Science Foundation of China (82072506,92268115), National Key R&D Program of China (2019YFA0111900), Hunan Young Talents of Science and Technology (2021RC3025), Provincial Natural Science Foundation of Hunan (20203060), Provincial Clinical Medical Technology Innovation Project of Hunan (2020SK53709), Wu Jieping Medical Foundation (320.6750.2020-03-14), the Hunan Key Laboratory for Bio-analysis of Complex Matrix Samples (2017TP1037) and National Clinical Research Center for Geriatric Disorders (Xiangya Hospital, 2021KF02).

Data availability

No datasets were generated or analysed during the current study.

Declarations

Ethics approval and consent to participate

This study was approved by the Ethics Committee of Xiangya Hospital of Central South University (Ethical Code: 202209008-2) and in accordance with the ethical standards formulated in the Declaration of Helsinki. The participants themselves gave their written informed consent to participate in the study and were informed that they could refuse to participate at any stage.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.