While the focus of most research attention has been limited to the subjective means of scoring tools, the present study identified changes in more objective quantitative metrics utilizing a 3D scanner and wearable gait sensors, i.e. differences in the gait cycle between some of the data sets and the athlete's foot after cutting the anterior half of the peroneus longus tendon. Previous studies have shown that the peroneus longus tendon is one of the optional complementary grafts for ACL reconstruction surgery of the knee when the popliteal tendon is not strong enough and has better results in terms of function and graft survival and is currently available in both total and anterior half cuts [
22,
23]. According to Nazem.K, there is no significant effect on foot and ankle function after total resection of the peroneal longissimus tendon, but this finding lacks support from long-term follow-up [
24]. In the study by Zhao et al. [
25], they concluded that the ACL could be reconstructed by cutting the anterior half of the peroneus longus tendon in combination with the popliteal tendon to minimize the impact on the ankle. The foot and ankle function was evaluated using the foot and ankle AOFAS score and the Foot and Ankle Disability Index (FADI) score, and it was concluded that the anterior half of the peroneus longus tendon did not affect the function of the foot and ankle after resection. Similarly, in our study, the postoperative AOFAS score was evaluated for foot and ankle function and there was no significant difference.
However, both of these scores are more subjective assessment tools and lack objective quantitative indicators of the foot and ankle [
8,
26]. For example, the scoring mentions the gait abnormality grading, with 8 points for none or slight, 4 points for significant, and 0 points for very significant, and the ankle-hindfoot stability grading, with 8 points for stable, and 0 points for significantly unstable. It is not very easy for the assessor to delineate the specific boundaries between each of the grades mentioned above, and there is a wide range of scores between grades, as well as a lack of clarity in the definitions of gait abnormality and ankle-hindfoot stability, which can only be scored by subjective perception by patients with a lack of expertise. The peroneus longus tendon has a role in stabilising the medial column of the foot and preventing excessive pronation of the foot during walking, reacting to sudden pronation of the foot, so the peroneus longus tendon may play an important role in stabilising the arch of the foot. Although the peroneus longus tendon is only one of the structures that stabilise the arch of the foot, it is the only tendon that maintains the arch of the foot by passing through the plantar aspect of the foot. When the joints of the foot become tightly packed together, the foot is better supported and forces are transmitted, and it is the peroneus longus tendon that participates in the maintenance of the arch of the foot by increasing the tension and dependence between the joints of the mid-foot [
27,
28]. In our study, we found that after cutting the anterior portion of the peroneus longus tendon, there was no significant difference in foot length, arch index, and arch volume between the weight-bearing and non-weight-bearing sides of the affected limb compared to the healthy side, and we hypothesised that this might be related to the location of the tendon cut. The plantar terminus of the peroneus longus tendon is located on the plantar side of the medial cuneiform bone and the lateral side of the inferior aspect of the first metatarsal, and the anterior portion of the peroneus longus tendon was dissected at the level of the lateral ankle tip without affecting the plantar portion of the peroneus longus tendon. Therefore, tension could still be transmitted from the origin of the tendon to the plantar aspect of the foot through the residual posterior portion of the tendon, and the maintenance of the arch of the foot by the peroneus longus tendon was not affected [
7]. At the same time, our opinion is in agreement with He et al. [
22] that the peroneus longus tendon is severed at the proximal end of the outer ankle, the plantar portion of the tendon is left intact and the distal portion will be sutured to the peroneus brevis tendon, so there is no effect on the ankle after tendon excision.
Gait analysis is currently one of the most common ways to dynamically detect foot and ankle motion data, and wearable gait sensors have the advantage of being easier, more accurate, and more comprehensive [
29‐
31]. We used a gait analysis device wearable gait sensor to collect dynamic data from patients. In terms of dynamic function, the peroneus longus tendon has a role in plantar flexion and external rotation of the ankle joint, and the gait cycle may be affected by tendon excision [
6]. The gait cycle is the process from the landing of one side of the foot to the landing of that side of the foot again, which is divided into the stance phase and the swing phase [
32‐
34]. The stance phase is divided into the touchdown phase, the mid-stance phase, and the propulsion phase, of which the stance phase is the phase in which the foot and ankle play a role [
35,
36]. In our study, we also did not find any significant difference in the proportion of time spent in the swing phase between the operative side and the healthy side. During the touchdown phase, the heel just touches the ground with dorsiflexion of the ankle joint and simultaneous valgus due to the synergistic action of the peroneus longus tendon, which if insufficiently valgus will result in a reduction of the dorsiflexion moment [
6]. In our study, we found that the average touchdown elevation angle of the affected foot during the gait cycle was reduced by approximately 2° compared to the healthy foot with a statistically significant difference (
P < 0.05), which may be due to the weakening of the foot's eversion force after the anterior half of the peroneus longus tendon is cut, which is also following the study findings of Shao and Angthong et al. [
26,
37]. During the transition from the mid-stance to the propulsive phase, the talonavicular joints remain rotated anteriorly for most of the time, and when the ground reaction forces diminish in the latter part of the mid-stance, the talonavicular joints begin to rotate posteriorly, thus performing a phase transition: i.e. from an active adaptive function required in the touchdown phase to a strong leverage function in the propulsive phase [
38]. Contraction of the peroneus longus tendon causes dorsiflexion and valgus of the dice bone, thus locking the lateral aspect of the foot, maintaining the stable state of the lateral longitudinal arch of the foot, and guaranteeing effective power transmission [
39]. We detected a statistically significant difference by gait cycle timeshare test, which showed that the mean touchdown period timeshare of the affected side was 0.92% shorter than that of the healthy side, while the mid-stance timeshare was 0.82% longer. We hypothesise that the foot takes longer to adapt during the transition from the mid-stance to the propulsive phase and less time to complete the propulsive manoeuvre, both of which may be related to the weakened muscle force contraction of the peroneus longus tendon after the anterior half of the tendon is cut [
40]. After the onset of the propulsion phase, the peroneus longus tendon completes the propulsion by plantarflexing the first metatarsophalangeal joint and the lateral column of the pronator teres [
41]. This is because the first metatarsal is shorter than the other metatarsals and must be plantarflexed to maintain contact with the ground. In plantarflexion, the transverse axis of the first metatarsophalangeal joint moves backward and upward, so that the lesser phalanx can reach the optimal dorsiflexion angle without hindrance [
38]. In our study, we found that the average propulsive pitch angle on the operated side decreased by 4.2° (
P < 0.001), the propulsive period time percentage decreased by 1.24% (
P < 0.001) compared with that on the healthy side, and we hypothesised that this may also be related to the weakening of the foot's metatarsal flexion force after the peroneus longus tendon was cut in half. As the metatarsal flexion angle of the metatarsal bone decreased, the dorsal extension angle of the lesser toes also became smaller, and the vertical stress on the ground during foot propulsion also decreased accordingly, which affected walking efficiency [
42,
43]. On the other hand, in our study, it was shown that there was no significant difference in gait parameters such as mean step frequency and stride length between the healthy side and the affected side, which is the same as most of the scholars have concluded [
43,
44]. At the same time, the results of this gait analysis may have included changes in gait from the knee surgery itself, and although most studies have shown no difference in postoperative Lysholm scores, few comparisons of quantitative metrics have been made to rule out the effect of ligament surgery on gait. The study by Kaur et al. [
45] reported that they compared the lower extremity mechanics of the affected limb and the healthy limb after ACL reconstruction and found no significant differences in kinematics at 5 years postoperatively, but there was not yet a complete recovery of the lower extremity abduction and adduction moments. Finally, there are limitations in this study, such as the small number of subjects and the short follow-up period. Our next step is to need a large amount of data and long-term follow-up to further evaluate the effect of cutting the anterior half of the peroneus longus tendon on foot and ankle function.