Kinematic and Mechanical Analysis of the Ankle Rotating-Traction-Poking Manipulation CURRENT STATUS: UNDER REVIEW

Background: In China, the ankle rotating-traction-poking manipulation (RTPM) has been used to increase range of movement and reduce pain in patients with lateral ankle sprains. But no research so far has quantitatively analyzed the kinematic and mechanical data of RTPM therapy. Therefore, the purpose of the present study was to analyze the kinematics and mechanics of RTPM technique. Methods: A total of 60 volunteers who had ankle sprains participated in the study. A single physiotherapist specializing in RTPM worked with each of the subjects. Motion capture technology, self-developed mechanical gloves, and a data synchronization device were used to acquire kinematic and mechanical data during the RTPM. Results: The mean maximum force of the thumb, index finger, and middle finger during the rotating was 18.89 N, 10.26 N, and 9.51 N, respectively, that of the traction force was 18.61 N, 13.25 N, and 8.33 N, respectively, and that of the poking force was 26.5 N, 8.61 N, and 10.62 N, respectively. The average time of rotating for six circles was 11.36 s. The average linear velocity of rotating was 58.28 mm/s, and that of traction-poking was 23.81 mm/s. The average linear acceleration of rotating was 0.43 mm/s2, and that of traction-poking was 0.54 mm/s2. The average displacements of traction and poking were 36.94 mm and 22.44 mm, respectively. The average angle of traction and poking were 23.27° and 22.76°, respectively. Conclusions: The RTPM can be repeatable for clinical application, and also has features of gentleness, rhythmicity, and continuity.

recurrent ankle sprains, decreased neuromuscular control, weakness, an impaired sense of joint position, and diminished performance of functional activities [4]. The most common injury mechanism is a combination of inversion and adduction of the foot in plantarflexion.
This injury mechanism can cause damage to the lateral ankle ligaments. Injury of the anterior talofibular ligament and calcaneofibular ligament leads to anterolateral rotary instability and tilting of the talus [5].
According to severity, ankle ligament sprains are divided into three grades [6]: Grade I (mild) -ligaments stretched mildly without macroscopic rupture or joint instability; Grade II (moderate) -ligaments stretched with a partial rupture -there is moderate pain, swelling, functional limitations, and mild to moderate instability. Typically, patients also present with symptoms of difficulty with weight bearing. Grade III (severe) -ligaments stretched with a complete ligament rupture, which presents with severe pain, swelling, hematoma, and significant functional impairment. Some therapeutic methods have been recommended: surgery, immobilization, cold compresses, and functional treatments with bandages, braces, balance training, and manual therapy. Most authors have suggested non-surgical treatment for LAS [7].
Research has shown that manual therapy following LAS leads to superior early dorsiflexion range compared with a traditional exercise intervention alone [8,9]. In a study, a caudal talocrural joint manipulation led to a significant plantar load distribution change [10].
Mechanical joint alternation and altered postural control may result in this change.
Ankle manipulation has a long history of use in Chinese medicine. At the present, Sun's ankle rotating-traction-poking manipulation (RTPM) is representative [11]. Physical therapists commonly use this kind of passive joint manipulation to increase range of movement and reduce pain in patients with LAS. Rotation manipulation can relax the spastic, curled, twisted muscular ligaments. Traction manipulation can temporarily widen the joint space to reset the position of the joints, such as the tibiotalar and talofibular joints. Poking manipulation can promote absorption of hematoma and rehabilitate the dorsiflexion range of motion. In recent studies, RTPM has been proven by large multicenter randomized controlled clinical trials for the treatment of Grade I and Grade II LAS.
Compared with RICE (rest, ice, compression, elevation) therapy, RTPM can actively adjust the imbalance of joints and ligaments and rapidly improve acute symptoms, and has a stable long-term effect [12,13]. RTPM can relieve pain and improve range of motion by improving the instability of the rotational talus, adjusting torsion of ligaments and other neurophysiological or mechanical mechanisms [14].
This technique pays attention to the operational principles of "gentleness, rhythmicity, and continuity", which requires skill but still lacks uniform clinical standards. Physical therapists only summarize the crucial operation according to abstract description or their own clinical experience, which leads to blindness and randomness. This results in inconsistent efficacy and safety that impedes the generalization of the RTPM technique.
Consequently, it is significant to quantitatively analyze the kinematics and mechanics of RTPM therapy. Motion capture technology is mainly used to analyze foot gait in the ankle field [15], and to quantify cervical and lumbar manipulations [16,17]. No research so far has involved the RTPM technique. The aim of our study was to measure the threedimensional kinematic and mechanical parameters during RTPM and summarize its operating characteristics.  These gloves had built-in mechanical sensors, gyroscopes, and accelerometer modules, which could measure the force, direction, acceleration, and other mechanical parameters of each finger ( Figure 1).

Data Synchronization Acquisition Device.
A kinematic and mechanical data synchronization acquisition device was developed by the Orthopedic Technology Laboratory of CACMS and Beijing Institute of Technology. This system used a Zigbee module with a long transmission distance and a fast sampling speed to communicate, which ensured the synchronous acquisition of mechanical gloves and motion capture system, and avoided the systematic errors caused by asynchronous acquisition.

RTPM Operation
The subjects were manipulated in a supine position (Figure 2), The specific methods were performed as follows: 1.
Rotating manipulation: the operator rotated the injured ankle in six circles with a mild traction force with the help of an assistant.

2.
Traction manipulation: the operator and assistant applied moderate traction force with a varus ankle position.

3.
Poking manipulation: the operator's thumb poked and pressed the injured lateral ligaments with a valgus ankle position under a moderate traction force.

Procedures
This study was carried out at the Orthopedic Technology Laboratory of CACMS. The operator wore mechanical gloves and adjusted the position of the sensor and the tightness of the gloves, and then fixed the marker points on the glove surface. To avoid the interference of marker points and ensure the conciseness and continuity of the motion trail during manipulation procedures, after repeated attempts, we removed the marker points on the participant's ankles (see Figure 3a, b, c), and simplified the marker points on the operator's hands (see Figure 3d, e, f). Finally, a total of six marker points were placed on the mechanical gloves worn by the operator. The specific placement was as follows (see Figure 3d, e, f): one point was on the radial side of the first metacarpophalangeal joint. One point was on the radial side of the second metacarpophalangeal joint, and one point was on the radial side of the second proximal interphalangeal joint. The placement of marker points on the left and right hands was symmetrical.
A bed was placed in the center of the test site. The participant was placed in position on the uninjured side with the lower third of the shin out of the bed. Then we performed a calibration of the apparatus and initialization of the software. The doctor operated the RTPM. The digital motion capture system and mechanical gloves tracked and saved the data of the whole process.

Experimental Observation Parameters
The observation parameters were as follows: (1)

Mechanical Data Analysis
As shown in Table 1, the thumb exerts the maximum force during the whole process of the RTPM. The force of the index finger is similar to the middle finger. The data of the ring finger and little finger are negligible due to being extremely small.  The displacement and angle of the traction-poking manipulation are shown in Table 3

Discussion
Manual therapeutic methods are a major feature and advantage of orthopaedics in traditional Chinese medicine. It is particularly important to inherit and develop these clinically effective methods. The development trend for manipulation is gradually changing from a simple empirical mode to a quantitative, objective, digital, and precise mode. In this way, physical therapists can refer to the strength, frequency, time, displacement, angle, and other parameters during manipulation [18]. Therefore, by quantifying the manipulation technique, summarizing the mechanical and kinematic parameters, and forming the operational criteria, not only can the physical therapists have evidence to follow, but this has great significance for teaching and popularization of clinical manipulation.
At the present, the quantification of manipulation procedures is mostly limited to single analysis of mechanics or kinematics, or a phased study of both [19]. Although this method can also achieve the purpose of manipulation quantification, it takes more time and increases the subjective errors of researchers during both operations. In this study, the kinematic and mechanical data synchronization acquisition system was developed to ensure the synchronous acquisition of mechanical gloves and motion capture system data, which improved the efficiency of the experiment. To our knowledge, no similar synchronous data acquisition device has been used in previous studies. In addition, the self-developed mechanical gloves were more suitable for the clinical practice of the RTPM.
These innovative instruments also add new contents and provide new ideas for the quantitative measurement technology of manipulation.

Motion capture technology was proposed by psychologist Johansson in a Moving Light
Display experiment in the late 1970s [20]. This technology is a commonly used tool in biomechanical research that has been proven to be helpful in understanding complex human motion [21]. The accurate fixed scheme of marker points is the key to the success of the experiment. The initial marker points sticking scheme in this study was more complex (see Fig. 3a, b, c), including the patient's ankle and the operator's hands.
However, the motion trail obtained in the pre-experiment process was disordered and  [22], the force of the fingers in the manipulation process obtained in our experiment was smaller. The reason for this difference may be: previous studies measured the mechanical data directly on the force platform. In our study, the object of manipulation was patients with an ankle sprain, which meant that the operator's finger force could not be large. This also indicated that the RTPM is based on the operational principle of "gentleness and softness".
The standardization of manipulation should be based on safety. According to the biomechanical study of the ankle ligament in cadavers, it is found that the ultimate damage load of the ankle ligaments is greater than 100 N [23]. The maximum force of the finger in this study was 34.72 N, which was much less than the load that causes damage to the ankle ligaments. Therefore, the RTPM technique is safe from this perspective. The

Conclusions
The self-developed mechanical gloves and data synchronization acquisition device are beneficial for the biomechanical study of manipulation. The RTPM skill has features of gentleness, rhythmicity, and continuity after obtaining and analyzing the kinematic and mechanical data. This quantitative parameters and characteristics will help beginners to quickly master the skill of RTPM. Participants were consented using the approved informed consent document before their enrollment into the study.

Consent for publication
Not applicable.

Availability of data and materials
The data sets analysed during the current study are available from the corresponding author on reasonable request.

Competing Interests
The authors declare that they have no conflicts of interest.

Funding
This work was supported by the National Natural Science Foundation of China (Grant no. 81473694). The funders had no role in the design of the study, data collection, analysis, interpretation of data, in writing the manuscript, or decision to publish.

Authors'contributions
GJH and ZLG was involved in obtaining the grant, designing the study. GCY and WBJ was involved in the data collection and writing the protocols. LJ and LJG was involved in designing kinematic and mechanical instrumentations. FMS supervised all the phases of this research project. All authors participated throughout the writing process and have read and approved the final version.      Force-time curve of the fingers