Abstract OBJECTIVE: To analyze the gait of total knee replacement patients by the biomechanical method of three-dimensional gait analysis. METHODS: Fifty-three patients with total knee replacement were selected from Zhongshan Hospital of Dalian University in 2005-11/2006-11, aged 42-82 years, with an average age of 59.2 years. The average height (172±13) cm, body mass (64±11) kg for 33 males and (155±11) cm, body mass (45±1l) kg for 20 females were selected for gait analysis before and 1, 6, and 12 months after surgery. Each measurement should be at least 3 steps in length with a constant stride speed. A total of 16 points in the hip, knee, and ankle joints were set up and connected to form a surface to build a three-dimensional dynamic image. Results: The walking speed, step frequency, step length and standing phase of the affected limb were significantly improved after the replacement (P < 0.01), and the parameters of gait analysis basically reached the normal level one year after the replacement. Before the replacement, the maximum hip flexion was 15°, the maximum back extension was 8°, the maximum knee flexion was 70°, and the maximum ankle flexion was 15°. Six months after the replacement, the maximum hip flexion was 27°, the maximum backward extension was 17°, the maximum knee flexion was 50°, and the maximum ankle flexion was 14°; the differences of the indexes were significant compared with those of the pre-substitution period (P < 0.01). Conclusion: The use of three-dimensional gait analysis to quantitatively evaluate the function of total knee replacement patients can more accurately understand the biomechanical changes of the knee joint, and then explore the best treatment and post-replacement rehabilitation methods. Keywords: three-dimensional gait analysis; total knee replacement; efficacy evaluation Guo Lin, Cui Daping. Three-dimensional gait analysis before and after total knee replacement[J]. Chinese Tissue Engineering Research and Clinical Rehabilitation, 2008, 12(13):2417-2420 [www.zglckf.com/zglckf/ejournal/upfiles/08-13/13k-2417(ps).pdf] Background: This subject is currently applying for the National Natural Fund. The DVMC-8801 three-dimensional motion analysis system is an independently developed three-dimensional gait analysis system for non-invasive detection of patients by infrared system, which is designed to understand the biomechanical changes of gait recovery after joint replacement. Peer evaluation: The authors applied the 3D gait analysis method to the field of joint replacement surgery, and quantitatively evaluated the effect of knee replacement on patients with stage IV osteoarthritis of the knee, and referred to the Tohn.N. Insall score, and concluded that the method can more accurately understand the biomechanical changes of the knee joint, and the topic and design of the research are good. Bias or deficiency: Because it is a new technique, the number of cases is insufficient, the follow-up time is short, and further experience is needed. 0 INTRODUCTION Gait analysis is a special branch of biomechanics, which is the kinematic observation and kinetic analysis of limb and joint activities during human walking, providing a series of temporal, geometric, mechanical and other parameter values and curves [1]. Although the HSS scale [2] is commonly used before and after total knee replacement, the HSS scale does not quantitatively analyze the walking function of patients. The authors used a three-dimensional gait analysis system (Oriental Xinrui DVMC-8801 three-dimensional motion analysis system) to analyze the gait of 53 patients who underwent total knee replacement in our hospital. 1 Subjects and methods Design: observational experiment. Unit: Zhongshan Hospital affiliated to Dalian University. Subjects: 53 cases (53 sides) of total knee replacement patients in Zhongshan Hospital affiliated to Dalian University were selected on 2005-11/2006-11, including 33 cases (33 sides) of men, aged 55-82 years, mean 46.2 years, mean height (171±13) cm, body mass (65±11) kg; 20 cases (20 sides) of women, aged 42-79 years, mean height ( 155±11) cm, body mass (45±11) kg. All of them had stage IV osteoarthritis of the knee. Surgery was performed using the anterolateral patellar approach. The preoperative HSS knee function score ranged from 10 to 74, with a mean of 56.2. The patients gave informed consent to the experiment and treatment, and the experiment was approved and signed by the hospital ethics committee. A Zimmer cemented non-rotating platform type prosthesis was used. Designed, implemented, and evaluated by: the first author for experimental design, the second author for data collection and implementation, and the first author for evaluation, which was assessed using a single-blind method. METHODS: Posterior longitudinal cruciate ligament-preserving artificial total knee arthroplasty. High-dose antibiotic intravenous drip was started 1 day preoperatively. A standard anterior median incision of 10-12 cm was chosen to access the joint capsule through a parapatellar incision approximately 1 cm medial to the edge of the patellar midline. Femoral preparation: ① Rotational positioning of the distal femur. ② Anterolateral preliminary osteotomy. ③ Distal femoral osteotomy. ④Femoral measurement. ⑤Anterior, posterior and oblique osteotomies of the femur. Preparation of tibia: ①Localization of tibial force line. ② Positioning of tibial bone marrow external force line: Flex the knee, place the tibial bone marrow external force line guide on the tibial stem, and hold the distal tibia above the ankle joint with a flexible clamp. The tibial prosthesis is placed, the femoral prosthesis is placed, and the incision is sutured. Postoperative treatment: CPM functional exercise was started on the 1st postoperative day, with an initial range of motion of 0~45°, continuous activity for 12 h per day, increasing the range of motion by 10° per day, and reaching at least 95°~110° before discharge. Three-dimensional gait analysis system operation method: three-dimensional gait analysis system (Oriental Xinrui DVMC-8801 three-dimensional motion analysis system) consists of 3 parts. One is in the same space, distributed in different locations of the 8 cameras and pasted in the parts to be measured optical marking points; regulating the above three parts of the device synchronized operation and its measurement data analysis and processing of computers and their peripheral equipment. Firstly, the configuration between the gait analysis mainframe and the infrared camera was adjusted, as well as the measurement range. During the test, the patient wore tight-fitting sports shorts underneath to ensure that the marker points indicate the position of the limbs in motion; to prevent the clothing from obscuring the reflective points. The reflective points of 3D gait analysis were localized as follows: (1) Pelvis to lumbar abdomen: anterior superior iliac spine, posterior superior iliac spine (4 points in total). ② Knee: medial and lateral femoral condyles and tibial tuberosity (3 points). ③Ankle joint: inner and outer ankle tips (2 points in total). ④ Between the first tarsometatarsal joint and the second tarsometatarsal joint (1 point). Gait analysis was performed by a trained and clinically experienced clinician or technician. The patient was asked to walk several times in a natural and accustomed posture and speed, and it was important to note that each of the patient's reflective points should be within the specified infrared area, so as not to affect the results of gait analysis. The main observation indexes: 1 month, half a year and 1 year after the operation, the 3D gait analysis system was applied to observe the changes of step length, step width, step speed, step frequency, gait cycle time, standing phase time, step phase time, and joint movement angle of the patients during walking. The HSS knee function score was also performed. Statistical methods: All data were analyzed by the second author using SPSS 11.5 statistical software, the specific methods were independent samples t-test and correlation analysis, and P < 0.05 was regarded as a significant difference. All data are expressed as x ± s. 2 RESULTS Gait analysis provided the magnitude of motion and degree of stability of the subjects' osteoarthritic joints in the X, Y, and Z axes.The changes in the kinematic data of the 53 patients before and after total knee replacement are shown in Table 1.The series of biomechanical indexes measured showed that the patients' short-legged gait and pain-reducing gait disappeared one year after traveling with the total knee replacements (Figs. 1~3). Three-dimensional gait analysis results: ① walking speed, step frequency and step length were significantly improved after replacement compared with before replacement (P < 0.01), and each parameter of gait analysis basically reached the normal level 1 year after replacement. After replacement, the standing phase of the affected limb was significantly prolonged compared with that before replacement. ③Angle time curve: before replacement, the maximum hip flexion was 15°, the backward extension was 8°, the maximum knee flexion was 70°, and the maximum ankle flexion was 15°. Six months after replacement, the maximum flexion of the hip was 27°, the posterior extension was 17°, the maximum flexion of the knee was 50°, and the maximum flexion of the ankle was 14° after CPM exercise; the differences between the hip and knee and the preplacement were significant (P < 0.01). ④Acceleration time curve: 6 months after replacement, the negative wave and spike wave in the standing phase of the acceleration in the anterior and posterior directions of the affected limb were significantly reduced compared with that before replacement, and the bimodal wave appeared in the swing phase after replacement, and the three positive phase waves before replacement. ⑤ The gluteus medius gait appeared within two months after replacement and disappeared one year after replacement. The HSS knee joint function score improved significantly after replacement, with an average score of 85.8 one year after surgery. 3 DISCUSSION The gait cycle refers to the time from the grounding of one foot to the re-grounding of the heel of that foot. In a gait cycle, each limb passes through two phases of weight-bearing on the ground and swinging away from the ground, which are called the stance and swing phases of the gait cycle, respectively. The stance phase is categorized into single-limb weight-bearing phase and double-limb weight-bearing phase according to whether it is single-footed or double-footed [3-8]. Step length, step frequency and step speed are the three major elements of gait, and gait analysis should firstly find out the values and curves of normal parameters such as time, geometry and mechanics in the gait cycle of normal people, and then analyze the abnormal parameters and curves of various pathological states on this basis, so as to provide objective and real basis for the evaluation of surgical efficacy and function. The gait of patients undergoing total knee replacement surgery for stage IV osteoarthritis of the knee has the following characteristics. 3.1 Pain-reducing gait When pain occurs in one side of the lower limb, a pain-reducing gait is often presented, which is manifested in the image of three-dimensional gait analysis as a shortening of the time of the affected side's stance phase, in order to minimize the weight-bearing of the affected limb, and shortening of the stride length. In patients with knee pain, the shoulder of the affected limb drops when the affected limb is loaded, the trunk is slightly tilted, the lower limb of the affected side is externally rotated and flexed, and heel strike on the ground is avoided as much as possible. In patients with knee pain, the knee was slightly flexed, and the patient walked with the toes on the ground. Images at 1 year after surgery showed that the stride length of the affected limb became larger and closer to the healthy side, while the flexion and extension angles of the hip, knee, and ankle, the maximum flexion of the hip joint before surgery was 15 °, and the posterior extension was 8 °, the maximum flexion of the knee joint was 70 °, and the maximum flexion of the ankle joint was 15 °; half a year after the operation, the maximum flexion of the hip joint was 27 °, and the posterior extension was 17 °, the maximum flexion of the knee was 50 °, and the maximum flexion of the ankle joint was 14 °; the hip, knee were significant compared with preoperative (P < 0.01).The pain level score of the HSS score is completely subjective and is divided into mild to moderate severity, compared to the 3D gait which is more objective, but the two should be viewed in combination. 3.2 Short-legged gait[9-14] The preoperative shortening of the affected limb was more than 2.5 cm in 6 cases, and the pelvis of the affected side could be seen to fall during the support period, leading to the fall of the ipsilateral shoulder, and during the swing period there was a sinking of the affected foot, and the healthy side of the step leg had excessive flexion of the hip-knee and dorsiflexion of the ankle joint; 1 year after the operation, it was shown that the fall of the pelvis to the affected side had disappeared, and the angle of the affected side of hip-knee-ankle joint dorsiflexion and extension compared with that of the healthy side was parallel. 3.3 Flexor-knee muscle weakness gait[15-20] Flexor-knee muscle is the main accelerating muscle in the swing phase, and its reduced muscle strength causes lack of power in swing phase limb travel. The patient's preoperative step length was 0.49 m, 0.51 m at 6 months postoperatively, and 0.54 m at 1 year postoperatively. This was due to the flexor-soleus muscle weakness that caused the trunk to swing backward at the end of the support phase and to swing forward suddenly at the early stage of the swing phase to compensate for this, and finally, the affected side's step length was significantly shortened, and the patient's step length was returned to normal after the muscle strength was restored after surgery. The mean preoperative HSS score was 56.2, and the mean score at 1 year postoperatively was 85.8; the results of this score were close to those observed in our tests, confirming the efficacy of the surgery in both subjective and objective terms, respectively. The lack of long-term follow-up in this study is a drawback, and follow-up observations will have to be continued in future studies. Gait analysis is an indispensable means of overall analysis and evaluation for extracting information on life activities related to human walking, and bioengineering technology for imitating human walking function devices, etc. It has a broad prospect. With the continuous development of optical and electrical measurement technology and information processing technology, this method will be developed in the direction of multi-indicator, integration and comprehensive system of expert analysis, diagnosis and evaluation. Using three-dimensional gait analysis to quantitatively evaluate the function of patients with stage IV osteoarthritis of the knee, we can more accurately understand the biomechanical changes of the knee joint, and then explore the optimal treatment and post-surgical rehabilitation methods. 4 References 1 Kyriazis V, Rigas C. Temporal gait analysis of hip osteoarthritic patients operated with cementless hip replacement. Clin Biomech (Bristol, Avon) 2002;17(4). 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