Extended Abstract

Introduction
One of the most common injuries among male athletes is an anterior cruciate ligament (ACL) injury.
ACL reconstruction (ACLR) is a common treatment following an ACL injury to restore joint stability and return patients to their pre-injury level of physical activity. ACLR appears to induce changes in the kinematics and kinetics of sagittal plane knee joint motion. Mechanically, ground reaction force in the vertical axis and loading rate are higher in individuals with ACLR compared to healthy individuals. Subtalar joint pronation causes excessive internal rotation of the tibia, resulting in an increased likelihood of knee joint dysfunction. The more pronation an athlete exhibits, the greater the association with ACL injury. Studies have shown that increased internal rotation of the knee joint occurs in individuals with pronated foot. Similarly, it has been reported that with increased internal or external rotation of the knee joint, ACL strength decreases. Regarding the use of insoles to reduce subtalar pronation and consequently reduce tibial internal rotation, researchers have reported varying results. However, it appears that the use of anti-pronation insoles in the knee joint is more beneficial for reducing tibial internal rotation and consequently reducing foot pronation.
Plantar pressure distribution measurement is a common and novel method for quantitatively assessing lower limb function under static and dynamic conditions, particularly during gait. Abnormal plantar pressure distribution can lead to abnormal movements and stress on lower limb structures, affecting muscle dysfunction. Examining the effect of anti-pronation insoles on gait variables using plantar pressure data can provide researchers with valuable information for gait analysis. On the other hand, the high prevalence of ACL injury and ACLR in young and active populations necessitates finding preventive methods to prevent individuals from developing this condition. Therefore, this study aimed to determine the effect of short-term use of anti-pronation insoles on plantar pressure variables after ACLR in pronated foot during gait.
Methods
This quasi-experimental study was conducted on 15 males who had undergone ACLR and exhibited pronated foot, and 15 healthy males recruited using a convenience sampling method.
Inclusion criteria for the ACLR group with pronated foot included the presence of pronated foot, an age range of 18-25 years, a minimum of 6 months post-ACLR surgery with a hamstring graft, a navicular drop greater than 10 mm, a foot posture index between 6 and 10, and a rearfoot inversion angle greater than 4° in a standing position.
The used insole had a 20-mm height differential between the internal and external longitudinal arches. The duration of using this insole was 8 weeks. Participants in the ACLR group with pronated foot were asked to wear the insoles for at least 6 hours daily during their regular activities. Data were collected under two conditions of with and without insole during gait everyday from 9 AM to 2 PM under the supervision of a physiotherapist and recorded by the laboratory technician.
A foot scanner was employed to record plantar pressure data using the RS Scan software at a sampling frequency of 300 Hz. The device was positioned at the midpoint of a 15-meter gait route. Prior to data collection, the foot scanner was calibrated. An initial static trial was first conducted for each participant, during which their weight and foot length were recorded in the device’s software. A correct walking trial involved the foot’s full contact with the central portion of the foot scanner. If the foot scanner was used by the participant to adjust gait or the participant’s balance was disturbed, the gait attempt was repeated. Plantar pressure data were extracted during the stance phase of gait. To ensure participant foot placement on the foot scanner during gait, each participant performed five gait practice trials. The variables of interest included peak plantar pressure in ten regions of the foot: The big toe, second to fifth toes, first metatarsal bone, second metatarsal bone, third metatarsal bone, fourth metatarsal bone, fifth metatarsal bone, midfoot, internal heel, and external heel.
The heel contact to the ground phase was identified by a vertical ground reaction force, exceeding 20 Newtons, and toe-off was determined by the last data exceeding 20 Newtons. The vertical ground reaction force data were filtered using a fourth-order low-pass Butterworth filter with a cutoff frequency of 20 Hz.
Results
There was no significant statistical difference in plantar pressure variables between the insole and no-insole conditions in both the healthy group and the ACLR group with pronated foot.
The effect of insoles on the plantar pressure variable in the first metatarsal (P<0.025) and midfoot (P<0.001) was statistically significant. Additionally, there was a statistically significant decrease in pressure on these areas when using anti-pronation insoles compared to before insole use. The effect of group on the plantar pressure variable of the big toe was statistically significant (P<0.017) so that pairwise comparisons showed a statistically significant increase in pressure in the ACLR group compared to the healthy group.
There was a significant interaction of insole and group on the midfoot pressure variable (P<0.014). Specifically, pressure on the midfoot increased significantly with the use of anti-pronation insole, and this increase was even greater in the ACLR group compared to the healthy group (P<0.05).
Intragroup comparison results revealed statistically significant differences in plantar pressure variables for second to fifth toes (P<0.04), first metatarsal bone (P<0.020), second metatarsal bone (P<0.001), fourth metatarsal bone (P<0.016), and midfoot (P<0.002) in the healthy group so that intragroup pairwise comparison results showed a statistically significant decrease in pressure on the first and second metatarsal bones when using anti-pronation insoles compared to the no-insole condition (P<0.020).
Intragroup comparisons also revealed statistically significant differences in the plantar pressure variable for second to fifth toes (P<0.014), first metatarsal bone (P<0.001), midfoot (P<0.006), internal heel (P<0.035), and external heel (P<0.041) in the ACLR group so that intragroup pairwise comparisons showed a statistically significant decrease in pressure on the second to fifth toes and first metatarsal bone when using anti-pronation insoles compared to the no-insole condition. Additionally, there was a statistically significant increase in pressure on the midfoot, internal heel, and external heel (P<0.041).
Conclusion
The results of this study demonstrated a significant reduction in pressure on the first metatarsal bone in individuals who had undergone ACLR with pronated foot after using anti-pronation insole. The use of anti-pronation insole exhibited a beneficial effect on the forefoot region compared to the condition without insole during gait. Unlike athletes, individuals who have undergone ACLR do not require high levels of athletic ability. However, abnormal physical activity can lead to lower extremity biomechanical abnormalities, often culminating in arthritis.
Ethical Statement
This study was approved by the Research Ethics Committee of the Sport Sciences Research Institute (IR.SSRC.REC.1401.140).
Funding
This research has been extracted from a doctoral dissertation by Ms. Razieh Alizadeh in the field of Sports Biomechanics at the Faculty of Educational Sciences, Islamic Azad University, Tehran Branch.
Conflicts of Interest
No conflict of interest.
Acknowledgment
The authors would like to thank all those who assisted in conducting this study.

Key message: The use of anti-pronation insoles may be effective in reducing plantar pressures following ACLR in individuals with pronated foot during gait. However, further research is needed to definitively confirm this finding.