1. Introduction
The anterior cruciate ligament (ACL) is one of the most important structures providing stabilization of the tibiofemoral joint, since it prevents anterior tibial translation and rotation in the knee [
1]. ACL arthroscopic reconstruction is a procedure applied to restore anterior cruciate ligament function in individuals with anterior cruciate ligament deficiency and to reduce the risk of osteoarthritis and degeneration in other soft tissues of the knee joint that may occur in the future [
2,
3]. ACL injuries occur as a result of deterioration in tibiofemoral joint stability provided by the static and dynamic stability mechanisms of the knee [
4]. One of the structures involved in providing static stability is the patellofemoral angle (Q angle) [
5]. The Q angle is defined as the angle between a line drawn from the anterior superior iliac spine (ASIS) to the center of the patella and another line drawn from the center of the patella to the center of the tibial tubercle [
6]. It is thought that when the Q angle exceeds the limit of 15–20°, it causes deterioration in the knee extensor mechanism and patellofemoral pain, with an increasing tendency of the patella to slide laterally [
7]. Abnormally low values have also been associated with various problems [
8]. In addition to causing injuries related to the knee, the Q angle can also be affected by many factors, such as femur length, pelvis width, and postural disorders [
9]. When the gender factor is considered, it can be seen that pelvis width, which is one of the factors that changes the Q angle, is higher in women than in men [
10,
11].
Foot posture differences can lead to postural stability and musculoskeletal problems [
12,
13]. It is thought that the risk of injury is elevated, and sports performance is negatively affected, since structural deviations of the foot (pronation or supination displacement, high or low arch of the foot) may cause biomechanical deviations [
14,
15,
16]. The association between foot morphology and lower extremity injuries is not clear; however, studies in the literature show both weak and strong correlations between arch structure and biomechanical characteristics of the lower extremity [
17,
18].
Single leg hop tests (SLHT) have become a widely adopted assessment tool in the rehabilitation of patients following anterior cruciate ligament (ACL) reconstruction, as well as a key factor in determining their readiness to resume sports participation. Researchers have stated that SLHTs are very important for measuring leg strength on a single joint, and they are commonly used to evaluate the functional states of individuals, identify asymmetries between the operated and non-operated sides, and follow developments in the limb [
19,
20,
21].
Given all of these considerations, this study aimed to examine and evaluate the relationship between patellofemoral angle and foot posture index in patients who had undergone semitendinosus/gracilis (hamstring autograft) anterior cruciate ligament reconstructions (ACLR) and to compare surgically repaired knees with healthy knees.
3. Results
When the lower extremity lengths and quadriceps angles of the operated and non-operated sides were evaluated, no significant differences were found between the Q angle (
p = 0.668, 95% CI = −1.17–1.79), femur length (
p = 0.515, 95% CI = −0.64–0.33), and lower extremity length (
p = 0.904, 95% CI = −0.72–0.64) values (
Table 2,
Figure 1).
When the TFPI scores of the operated and non-operated sides were compared, no significant differences were found between the TH (
p = 0.574, 95% CI = −0.19–0.11), LATM (
p = 0.574, 95% CI = −0.11–0.19), TNJ (
p = 0.425, 95% CI = −0.12–0.29), MA (
p = 0.327, 95% CI = −0.04–0.12), ABD (
p = 0.265, 95% CI = −0.34–0.10), and TFPI (
p = 0.574, 95% CI = −0.56–0.32) values. On the other hand, statistical significance was found for CALC (
p = 0.043, 95% CI = −0.31–−0.01) values (
Table 3,
Figure 2).
When the SLH (single leg hop) and triple hop distance test results of the operated and non-operated sides were evaluated, statistical significance was found for SLH (
p = 0.004, 95% CI = −16.64–−3.60) and THD (
p = 0.022, 95% CI = −41.99–−3.61) (
Table 4,
Figure 3).
When the correlations between pelvis diameter, Q angle, FPI, lower extremity length, and SLHT on the operated side were examined, positive correlations were found between TFAPI and ABD (r = 0.554), TFFPI and TNJ (r = 0.444), ABD and CALC (r = 0.520), TFAPI and TH (r = 0.646), TFAPI and LATM (r = 0.730), TFAPI and CALC (r = 0.713), and THD and SLH (r = 0.917). Negative and significant correlations were found between SLH and CALC (r = −0.475) and THD and CALC (r = −0.441) (
Table 5).
When the correlations between pelvis diameter, Q angle, foot posture index, lower extremity length, and SLH tests on the non-operated side were examined, positive correlations were found between LATM and TH (r = 0.492), ABD and CALC (r = 0.485), CALC and TH (r = 0.517), CALC and LATM (r = 0.600), ABD and LATM (r = 0.510), TFAPI and TH (r = 0.729), TFAPI and LATM (r = 0.667), TFAPI and CALC (r = 0.794), TFAPI and ABD (r = 0.567), and THD and SLH (r = 0.867). Negative and significant correlations were found between TNJ and Pelvis D. (r = −0.403), SLH and CALC (r= −0.413), and THD and CALC (r = −0.427) (
Table 6).
4. Discussion
The results of our study did not show any significant differences between the operated and non-operated sides in the 6th month post-operative Q angle, lower extremity length, or total FPI scores of patients who had undergone ST/G ACLR surgery. These results indicated that the operated side reached the healthy side in Q angle, lower extremity length, and FPI over a period of approximately 6 months. It was found that the operated sides showed lower results than the non-operated sides for SLHTs. However, when these results were evaluated in terms of the limb symmetry index (LSI), they were found to be within the normal range. Although significant differences were not found in the total FPI scores, significance was found only in the inversion/eversion of the calcaneus score between the operated and non-operated sides. The most important results in the correlation analyses evaluated on both the operated and non-operated sides was the negative and significant correlations between the CALC parameter in FPI and SLHTs.
Studies have been found in the literature that examined Q angles, SLHTs, and some physical characteristics in subjects after different ACL autograft methods. Dhillon et al. [
26] did not find any significant differences in patients who had undergone ACLR with the patellar tendon graft method when compared with the control group in terms of pre-operative and post-operative Q angle (preop −13.86°, postop −12°). A Q angle of 8–15° is considered normal in men, while a Q angle of 12–19° is considered normal in women [
27,
28,
29,
30,
31]. When Hertel et al. [
32] compared the Q angles of 20 healthy subjects (11.84°) and 20 patients who had undergone ACLR (11.16°), they did not find any significant differences. An increase in this angle leads to uneven distribution of weight on the knee joint, exposing the medial or lateral knee joint compartments to more stress and joint disorders. Moreover, it may cause collapse in the medial arch of the foot because it creates an increase in joint pronation [
7,
33]. Increasing the subtalar will cause traction in the medial knee joint, lateral compression tension, supination in the transverse tarsal joint, and increased internal rotation-flexion-adduction angles in the hip joint. On the contrary, following an increased subtalar joint supination angle, there will be medial compression in the knee joint, lateral traction tension, pronation in the transverse tarsal joint, and increased external rotation-extension-abduction angles in the hip joint. In addition, an increase in the Q angle may cause a collapse in the medial arch of the foot [
34]. In a study conducted in 2009, Barrios et al. showed that the subtalar joint supination angles were directly proportional to the Q angle and that the subtalar joint supination and tibial mechanical axis measurements were important in the estimation of varus stresses on the knee joint [
35]. Although researchers have studied the norm values of the Q angle, there are also studies reporting that there may be differences in these angular values depending on certain factors, such as gender, age, and measurement position [
29,
36,
37,
38]. While some researchers have reported that the measurements on knee flexion according to knee extension position were not reliable [
10,
39], others have stated that there were no differences between Q angle measurements in extension and flexion of the knee and that the differences could be due to errors in determining measurement points or because the measurements were taken by different researchers [
40]. When evaluated with all this information in the literature, the findings of our study that there were similar results on the operated and non-operated sides in terms of the 6th month Q angle indicate that the subjects had a good rehabilitation process after their ACLR, especially for the operated sides. It should also be considered that the 6-month process may lead to similar results in Q angles, depending on foot domination. Indeed, these results also show the main limitations of our study. The fact that no measurements were taken before ACLR has caused us not to show pre-operative and post-operative differences and to make interpretations based only on the literature. However, in the literature-supported findings, as in our study, the absence of any difference in Q angles after ACLR is thought to be due to the fact that ACLR does not include any procedure that would affect the patellofemoral angle. However, changes in the Q angle may occur when there are additional injuries that accompany the ACL tear. This situation may arise with detailed studies being carried out with a prospective design.
Besides knee injuries, the Q angle can be affected by many other factors, such as femur length, pelvis width, and posture disorders [
9]. In their study, Murat et al. [
41] found a negative weak correlation between Q angle and femur length, regardless of gender.
In addition, while it is claimed that high Q angle values are directly proportional to the width of the pelvis, some studies have not been able to confirm this result [
27,
28,
42,
43,
44]. No significant correlation was found between pelvis width and Q angle in our study. This result also supports the literature information above, and it is thought that this may be due to the fact that our subjects were all male. As a matter of fact, it is known that women have higher pelvis widths and diameters than men due to their anatomical structures; therefore, studies on anthropometry have shown different levels of correlation in women compared with men. In a study conducted by Hertel et al. [
32], the Q angle was found to be 12.7° in women and 10.2° in men, regardless of injury history, which showed that women had significantly higher Q angle results than men.
Another factor affecting the Q angle is ankle deformities [
45]. Any injury or deformity in the foot or ankle disrupts the body’s biomechanics, starting from the knee, and if no precautions are taken, the problems in the body worsen [
46]. Researchers have reported that with an increased Q angle, the foot tends toward pronation, and the amount of load carried on the medial side increases. Conversely, decreased Q angle causes supination of the foot and more load on the lateral side [
33]. Considering that foot posture differences between the operated and non-operated sides may cause musculoskeletal problems, such as problems in the Q angle in FPI values after ST/G ACLR, no difference was found between the operated and non-operated sides in terms of total FPI scores. However, although both the operated and non-operated sides showed significant differences in the CALC parameter, both revealed findings close to pronation, but no significant correlation was found between the CALC results and the Q angles of the subjects. It is known that high-level athletes have flexible pronation in the calcaneum, and the deviation of the forefoot varies in almost all normal individuals. In addition, directions for palpation and curvature of the talus head are variable in almost all normal individuals. For this reason, it is important to evaluate kinematic analyses that will provide clearer findings instead of FPI in future studies.
The SLHT is commonly used after ACLR to assess functional performance [
47,
48,
49,
50,
51]. SLHTs are frequently utilized in clinical practice to assess limb asymmetries between the operated and non-operated sides and to monitor the progress of lower extremity development following ACL reconstruction [
19,
20,
21]. Studies on healthy individuals have reported that the difference between the limbs for SLH and THD tests between conventional SLHTs is, at most, 10–15% [
52,
53]. While one study found >90% similarity between the limbs in all of the participants that were tested with conventional SLHTs, another study conducted on healthy and athletic groups with a history of ACLR did not find limb asymmetry in conventional SLHTs [
54,
55]. In our study, it was found that although the operated sides showed much lower results than the non-operated sides, the results were still within the normal ranges in terms of LSI. Other important results of our study are the negative and significant correlations between the CALC parameter, which is an FPI score, and the SLH and THD tests. This shows that increased pronation in foot posture negatively affects performance in SLHTs. Indeed, since it is known that high Q angles correlate with feet that have high pronation [
33], especially in high LSI rates that may occur in SLHTs after ACLR, the Q angle and FPI indices should be evaluated.
All our results show that the main limitation of our study is the lack of evaluation of healthy subjects as a control group. The fact that we did not have healthy subjects in our study made us unable to clearly explain the relationship between operated and non-operated sides in terms of all parameters.