This trial will be carried out at Department of Orthopaedics, Shanghai Guanghua Integrated Chinese and Western Medicine Hospital, Shanghai, China. The hospital is a teaching and tertiary hospital of Shanghai University of Traditional Chinese Medicine, Shanghai, China. KOA patients who will receive unilateral TKA will be recruited through advertisements, mainly from the orthopaedics wards of Shanghai Guanghua Integrated Chinese and Western Medicine Hospital, Shanghai, China. We followed the SPIRIT 2013 Statement  and STRICTA  for the reporting of our trial protocol. This study has been approved by the ethics committee of Guanghua Hospital of Integrated Traditional Chinese Medicine and Western Medicine (Ethics Approval Number: 2019-K-23) and registered at the Chinese Clinical Trial Registry. All participants will be asked to provide their written informed consent.
Inclusion criteria: (1) 60–80 years of age, (2) diagnosed as KOA and willing to receive unilateral TKA, (3) similar surgical approach and normal blood coagulation function is normal, (4) posterior cruciate-stabilizing prostheses (Smith & Nephew, London, UK), (5) the knee prosthesis well placed (as shown by the postoperative X-ray), and (6) post-operative participants having clear consciousness and normal cognitive function.
Exclusion criteria: (1) serious nervous system problems, cardiovascular diseases, osteoporosis and metabolic diseases, (2) suffering from coagulation disorder, hemophilia or tumor, (3) bone fracture, dislocation and structural abnormality during the operation, and (4) skin damage in the acupoint area.
Exit criteria and management
Exit criteria: (1) having such needs, (2) severe postoperative complications (such as pulmonary embolism), and (3) side effects during the treatment.
The sample size will be calculated by using the peak torque of quadriceps femoris from the previous studies . The formula:
An effect size (△) of 2 with a standard deviation (SD) of 3.34 between EA and RT (n = 33*2/0.85 = 82) will be adopted. Based on this data, a two-group trial will be established with 39 participants per group, α = 0.05 (two-sided) and β = 0.2 (80% power) . With a possible sample loss of 15%, the final sample size will be set with 47 participants per group.
Recruitment strategies and enrollment
Participants registration is to begin in January, 2020 and is expected to conclude in June, 2020. Written informed consents will be obtained from all participants. Until then, this cohort of participants will not be included in any other scientific publications. When participants are hospitalized, a trained nurse and some physiotherapists will implement an enhanced recovery after surgery (ERAS) pathways (Fig. 1). Figure 2 is a trial flow diagram, which includes participant recruitment, eligibility, screening, randomization, intervention and outcome assessments. Figure 3 is an overview of the trial design, conduct, review and analysis. SPIRIT 2013 checklist (Word) is has been filled out and presented in Additional file 1.
Randomization and blinding
Using RV.3.5.1 software to generate a randomly-numbered sequence for a complete random grouping. A sequence of numbers will be sealed by an independent assistant in an opaque envelope containing treatment information. Eligible and consenting KOA participants undergone unilateral TKA will be randomly assigned to the EA group and the sham EA group at a ratio of 1: 1, with 47 participants in each group.
The objects of the blind method will include all the participants, physiotherapists, outcome assessors and data statisticians. To help maximize the blindness for the participants, a pragmatic placebo needle will be used and a sham EA design will be applied.
Scheme of Standard Analgesic Use
Postoperatively, patient controlled analgesia (PCA) will be used and removed from the day of surgery to the postoperative day (POD) 3. The analgesic used will be fentanyl (Yichang Renfu Pharmaceutical Co. Ltd., Yichang, China.) at a continuous infusion rate of 0.25 µg/(kg hour) and a bolus of 0.15 µg/kg with a 10-minute lockout time. The locking duration of the projectile will be 10 minutes after administration. Besides, oral celecoxib capsules (Pfizer Pharmaceutica Co. Ltd.,New York State ,USA) will be provided on demand for participants from the POD 4 to POD 14, and additional consumption of analgesia will be recorded.
According to the new standard of "International Acupuncture Nomenclature" , the acupoints to be selected will include LIANGQIU (Stomach 37, ST37), ZUSANLI (Stomach 36, ST36), XUEHAI (Spleen 10, SP10) and YINLINGQUAN (Spleen 9, SP9) on the side of the surgery (Fig. 4). After skin disinfection, adhesive pads (size 8 × 10 mm, Suzhou Medical Supplies Factory, Suzhou, China) will be placed on the acupoints, through which acupuncture needles (size 0.25 × 40 mm, Suzhou Medical Supplies Factory, Suzhou, China) will be inserted approximately by 3 cm into the skin (Fig. 4). After achieving De-qi sensation, the acupuncture points will be stimulated with Huatuo SDZ-II EA apparatus (Suzhou Medical Supplies Factory, Suzhou, China). Intensity of the constant current square wave pulse at a frequency of 40 Hz and a pulse width of 1 ms will be increased gradually until beyond the intolerable intensity of the participants. The treatment of the EA group will consist of 10 sessions of 30 minutes over 2 weeks (5 sessions per week).
Sham EA group
For the sham EA group, sham EA with a pragmatic placebo needle  (size 0.25 × 30 mm) on the sham acupoints will be used for 5 sessions per week. Each sham acupoint is 1 cun (≈ 20 mm) lateral to the acupoints (Fig. 5). The pragmatic placebo needle with a blunt-tip will be inserted into the adhesive pads but without skin penetration (Fig. 4). Huatuo SDZ-II EA apparatus (Suzhou Medical Supplies Factory, Suzhou, China) will connect sham acupoints at the same time that have special electrode wires without electricity output. The sham needles will stay in the adhesive pads for 30 minutes in each session. The sham EA treatment process is similar to the EA treatment process but without skin penetration, needle manipulation and electric output.
Indexes for primary outcomes evaluations include muscle strength and the Hospital for Special Surgery (HSS) score. Those for secondary outcomes evaluations include a 6-minute walking test (6MWT), numerical rating scale (NRS), the Hamilton Anxiety Scale (HAM-A). An additional use of analgesia is also categorized as a secondary outcome. The additional outcome indexes include incidence of analgesia-related side effects and participant satisfaction rate.
NRS, additional use of analgesia, incidence of EA-related and analgesia-related side effects will be recorded daily. Evaluation of the discomfort and acceptance of EA will be conducted after the first day of EA intervention. Muscle strength, HSS, 6 MW, HAM-A will be evaluated at four time points, viz, before the surgery, before EA intervention (at POD 3), one week after EA intervention, and two weeks after EA intervention.
Demographic / medical variables
These variables include sex, age, marital status, occupation, ethnicity information, education level, blood pressure, temperature, respiration, pulse, height, weight, body mass index (BMI), combination of disease and medication, Kellgren-Lawrence classification, course of KOA and history of major operations.
Knee muscle strength will be evaluated as the peak torque (PT) of knee flexion and extension by using Biodex 4 isokinetic muscle strength tester (IST, Biodex Medical Systems, New York, USA). Prior to the test, the physiotherapist will stabilize the participant on a dynamometric chair in a 90° sitting position, with the participant’s torso and thighs fixed. The machine’s power axis will be aligned with the center of the rotation of the knee, and the participant will be asked to move the knee to measure the range of motion. The participant's knee will be tested within the range of previous tests. The physiotherapist will set the angular velocity at 60° per second and ask the participant to do five constant flexion and extension activities. During the test, the participant will be asked to use his/her maximum strength in each flexion and extension activity to measure the PT of knee flexion and extension. The test will be conducted independently by the physiotherapist.
Hospital for Special Surgery (HSS) Score
HSS score, developed by John N. Insall, the father of the modern artificial knee joint, was first used in 1976 for preoperative and postoperative evaluation of four different types of knee arthroplasty prostheses, and has since been proved to be reliable and effective for such evaluation . HSS score mainly includes 10 items to evaluate the comprehensive condition of participants in terms of pain, daily activity, range of motion of knee, muscle strength, deformity and instability. In this trial, the score will be used to evaluate the knee joint function of participants before and after TKA to evaluate the effect of EA on early rehabilitation. In addition, the components will be further analyzed to find out the factors that can promote the rehabilitation of participants.
Walking capacity will be evaluated by a 6-minute walking test (6MWT). Participants will be required to walk as fast as they normally would (with walking aids, if necessary) along a 30-m corridor several times. 6MWT is employed because it has been used as a performance metric in a variety of other conditions with minimal adaptations . Participants will be allowed to use assistive devices to walk, and the test is reliable in participants after TKA [34, 35, 36].
Numerical rating scale (NRS) consists of a horizontal line segment similar to the VAS segment, with "painless" and "extreme pain" or "the most severe pain experienced" as the anchor for the starting and ending points of the scale, and are marked with "0" and "10", respectively. Participants will mark the scale to assess their knee pain (pain recorded at rest, pain recorded at movement). NRS is employed because it is easy to understand and allows wide adaptation and offers minimal difficulty with operation [37, 38].
Psychic and somatic symptoms of perioperative anxiety will be assessed using the Hamilton Anxiety Scale (HAM-A), which consists of 14 items evaluated on a five-point scale ranging from 0 (not present) to 4 (very severe) . The scores of 0–7, 8–14, 15–19, 20–29 and 30–56 indicate that the subject has no anxiety, questionable anxiety disorder, mild anxiety disorder, moderate anxiety disorder and severe anxiety disorder, respectively.
Analgesia-related side effects mainly include postoperative nausea and vomiting (PONV). The participants will be asked to choose their satisfaction rate in a scale  (Fig. 6).
Adverse events of EA
In this trial, EA-related complications mainly refer to broken needles, halo acupuncture, stagnation acupuncture, acupuncture site hematoma, continuous post-needling pain lasting > 2 h, bleeding and so on.
Assessment of the blinding
Blinding of participants will also be assessed via analyzing questionnaire response (Fig. 7). The questionnaire will be completed by participants within 5 min after the latest intervention. Regardless of whether participants received a true EA treatment or sham EA treatment, the percentage of subjects from each group who believe that they are given a true EA treatment will be recorded. The difference in the participant blinding success rates between the EA group and the sham EA group will be analyzed.
Epidata V3.1 will be used to input the data and IBM SPSS Statistics V21 will be used for statistical analysis. A complete follow-up study of the participants will be performed using the per-protocol sets and intent-to-treat population. Statistical analysis consists of four aspects. Firstly, if the measurement data will be subjected to a normal distribution, the mean ± standard deviation (SD) will be used for statistical description of the degree of concentration trend and dispersion. Differences between the two groups will be compared using two independent sample T-tests. If the normal distribution will not be followed. The median will be used for statistical description of the degree of concentration trend and dispersion. The difference between the two groups will be compared using the Mann-Whitney U test. Secondly, the participants’ gender composition ratio is continuous in data, using the Fourfold Table Chi-Square Test. Thirdly, the difference in the ranked data between the two groups will be compared using the Mann-Whitney U test. Lastly, the repeated measurement data will be compared using the generalized linear mixed models (GLMMs). Statistical significance will be considered as p value < 0.05 (two-side).