Patients recruitment
Between 2018–2019, 40 patients underwent ACL reconstruction with a hamstring graft technique were recruited for this study. The study obtained ethical approval from an institutional review board. All the included subjects signed the consent form. The study consisted of 22 male subjects and 18 female subjects, with a mean age of 25 years. All subjects were involved in sports activities (amateurs). The period of time from injury to reconstruction was 3.0 ± 2.4 months. The common rehabilitation program was carried out for all the included patients. Patients who met the following criteria were participated in the study: (1) only one surgery for tear of the ACL that did not include a concomitant tear of the posterior cruciate ligament; (2) no evidence of collateral ligament repair at the time of surgery; (3) no history of surgery or traumatic injury to the contralateral knee; (4) no history of surgery or traumatic injury of the ankle joint; and (5) no history of surgery or traumatic injury to either hip joint. The subjects were clinically evaluated before participating in testing. None of the patients and controls had instability or additional lesions during the study period. All subjects underwent a common rehabilitation program.
Rehabilitation program
For the common rehabilitation program, all patients underwent a standardized rehabilitation protocol [7]. The details of the protocol can be found in Appendix 1. Apart from the common rehabilitation program, the proprioception group accepted proprioception training as well 8 hours after the common program. All the program was conducted by one experienced physiotherapist.
The proprioceptive rehabilitation protocol was consisted of proprioceptive and balance training. The details of the protocol can be found in Appendix 2. The proprioceptive rehabilitation protocol was based on a previous study[8]. Balance training was performed by using an inflated stability wobble cushion, with open and closed eyes in a two-leg stance and then single-leg stance using the involved limb (Fig. 1).
This standard protocol was applied to each patient under the supervision of the physiotherapist. The subjects were asked to come back to the physiotherapist for training guidance once per week from week 1 to week 6; once every two weeks from week 7 to week 12; self-monitoring training after week 12.
Assessment
Lysholm scores were used to assess the patients’ ability to manage in daily activity. The kinematic assessment protocol is described as following:
Before testing, patients were required to complete a 5-min warm-up on a stationary exercise bike. For the kinematic assessment, a portal optical tracking system (Opti_Knee®, Shanghai Innomotion Company) was used to collect kinematics of patients’ involved knees during jump-stop, unanticipated cut maneuver (JSUC). This validated system was used in previous studies [9, 10]. Firstly, spatial orientation was identified for bone landmarks with the assistance of handheld marker (Fig. 2), including the greater trochanter of the femur, lateral and medial femoral condyle, lateral and medial tibial plateau, lateral fibular head, tibial tubercle, and medial and lateral malleolus. Two infrared inductors were fixed on the distal femur and proximal tibia of respondents. Based on the bone landmarks in the system, three-dimensional coordinate systems of femur and tibia were built. The rotation was defined as the tibia’s rotation along with the origin of the coordinate system in the femur. Similarly, displacement was defined as the tibia’s movement relative to the origin of the coordinate system in the femur.
The subjects were shown on JSUC and allowed to practice the maneuver first without observing the visual unanticipated direction cue. This maneuver was selected in order to examine a common sport lover and potentially high ACL injury risk movement that occurs in sports. Incorporation of unanticipated elements into testing protocols may better mimic the demands placed on the lower extremity during sports. Each subject was positioned in an athletic ready position to react to a randomized unanticipated direction cue. The ready position was established before cutting trials. The subject was asked to perform single leg hop before landing; when landing, the subject was instructed simultaneously to perform a sidestep cut at 45 degree and run past a marker 2.5 m away (Fig. 2). The subject was asked to perform a crossover cut immediately when he or she landed on the floor as the knee demonstrated valgus and external tibia rotation with this movement (Fig. 3). It’s well established that this position is a risk factor of ACL injury mechanism. A custom computer program to show signal (left and right) on a digital monitor was used to cue the subject when the subjects were going to land within 0.3 seconds. The subject was instructed to reposition his or her knees to the same flexed position before the start of each JSUC trial. The subjects were asked to try to perform all JSUC trials in consistent postures to minimize the variations of movement.
Totally the subjects were asked to perform six trials with equal ones for each knee. The order of trials was randomly performed to examine the subjects’ performance react to an unanticipated direction movement. After testing, we only exacted the data when subjects performed JSUC. Kinematic data were collected in 15 seconds at a frequency of 60 frames per second. Rotational motions, including abduction and external rotation angles at toe off when cutting, and peak flexion angles during single leg hop test were analyzed. Upon data collection, these parameters were calculated and compared between two groups preoperatively, 6 months after operation, and 12 months after the operation.
Data processing and analysis
Demographic data of included subjects, including age, BMI, and the duration between injury and reconstruction were compared between two groups using independent-t test. Gender, dominant sides, and injured sides were compared using chi-squared test. Lysholmes scores and hop distances measured preoperatively, 6 months, and 12 months after the operation were compared using independent-t test. For kinematics, peak values of knee flexion angles during single leg hop, abduction-adduction angles and tibia external rotations at cutting were compared using paired-t test at different follow-up time points, respectively. The significance level was set at 0.05. Statistical analyses were conducted in SPSS (IBM, Chicago, Ill., USA).