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 interrupted due to the following reasons: (1) Superfluous marker points: the movement range of each step of the RTPM is small and complex. When the number of marker points fixed by the operator's hands and the subject’s ankle was excessively large, it tended to cause interference. (2) Inappropriate fixed position of the marker points: the overlap and shelter of some marker points between the operator's hands and patient's ankle resulted in some of them not being captured. (3) Instability of the marker points: marker points were fixed mainly by a magic sticker with firmness that was unstable. In the process of the RTPM, magic stickers collided with each other and caused marker points to drop, which affected the consistency of the motion trail. Therefore, on the basis of the original marker point fixing scheme, we changed and simplified the plan (see Fig. 3d, e, f). The final motion trail was concise and continuous, which could meet the kinematic analysis requirements for the RTPM.
With regard to the quantitative results, the mean maximum force of the thumb, index finger, and middle finger during rotating was 18.89 N, 10.26 N, and 9.51 N, respectively, with a traction force of 18.61 N, 13.25 N, and 8.33 N, respectively, and a poking force of 26.5 N, 8.61 N, and 10.62 N, respectively. Compared with previous studies that included similar kneading and pressing manipulations [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 manipulation of traction and poking puts the ankle in passive varus and valgus, respectively. The displacement and angle of traction manipulation are larger than that of poking. This result is consistent with the physiological characteristics of the range of motion of the ankle, which has greater varus than valgus. The varus and valgus of the ankle are mainly performed by the subtalar joint. Owing to individual differences, studies reporting on this range are inconsistent. Grimston [24] recorded the valgus and valgus motion angles of the subtalar joints in subjects of different ages. The results showed that the valgus and valgus angles were 22.6 and 12.5 degrees, respectively. Guo [25] reported that the subtalar joint was in 10–15 degrees varus and 5–10 degrees valgus. The angle of ankle motion measured in our experiment was larger than other studies, which may be due to the following reasons: the angle measured in our experiment was derived from the whole ankle joint and its subsidiary structure, not the subtalar joint alone. In addition, the motion angle in our study was measured under passive motion, while in other studies it was measured under active motion.
The thumb, index finger, and middle finger exerted the main force in the RTPM. In the rotating operation, the thumb, index finger, and middle finger exerted force in an alternating fashion. The frequency and period of this force were rhythmic, uniform, and at a stable level. After the rotating operation, the traction and poking operation were performed. These three manipulations were in constant motion without a pause. The RTPM technique also reflected the features of rhythmicity and continuity.