Comparison of Active Knee Flexion Angles With and Without Tibiofemoral Joint Rotation Control Between Individuals With and Without Patellofemoral Pain Syndrome

Introduction

Patellofemoral pain syndrome (PFPS) is a frequently diagnosed condition associated with anterior knee pain in adolescents and adults under the age of 60, with an annual prevalence of approximately 22.7% [1,2]. The most frequently reported symptom is retropatellar or diffuse peripatellar pain during activities such as running, stair-climbing, squatting, and prolonged sitting with knees flexed. A frequently cited contributing factor to patellofemoral pain (PFP) is uncontrolled rotational movements of the lower extremities in both the frontal and transverse planes [3,4]. Uncontrolled excessive internal rotation of the femur and external rotation of the tibia can occur in both weight-bearing and non-weight-bearing positions. These abnormal movements increase the Q angle, leading to abnormal tracking of the patella, which elevates stress on the patellofemoral joint, and this may contribute to the development of PFPS [5,6].

Previous studies have attempted to quantify abnormal lower-extremity kinematics in PFPS using imaging techniques such as X-ray, magnetic resonance imaging (MRI), and tropometer [7–9]. Salsich and Perman (2013) reported, using MRI, that a subgroup of individuals with PFP who demonstrated a knee-inward movement pattern during a partial squat exhibited greater tibiofemoral rotation at 0° knee flexion and reduced patellofemoral contact area at 0° and 20° compared with asymptomatic controls [6]. Such reductions in contact area may increase the stress on the patellofemoral joint. Consistent with these findings, other studies have reported that impaired rotational control, such as excessive femoral internal rotation or tibial external rotation, may increase patellofemoral joint stress and contribute to the development and progression of PFPS [10–12]. Collectively, these findings highlight the importance of tibiofemoral mechanics in PFPS. However, these measurement methods may have limitations in practical usage due to their cost and radiation-related risks, making implementation challenging and less accessible in clinical practice [8,9].

A limitation of these methods is that they primarily assess static conditions, making it challenging to evaluate compensatory movements or joint rotation control during functional movements. A previous study suggested that it is important to measure knee motion during dynamic movements, as there is a lack of correlation between knee motion measurements taken in static and dynamic conditions [13]. In clinical practice, dynamic movement tests such as single-leg squats and stair-up-down tests, are commonly used to evaluate PFPS [14–16]. However, because these tasks involve multi-joint movements with a high degree of freedom, it is difficult to isolate the specific contribution of tibiofemoral joint rotation [14,17,18]. As a result, the quantitative assessment of tibiofemoral joint rotation control (TFRC) remains challenging to conduct in a simple and clinically feasible manner.

The evaluation of PFPS in clinical practice often includes the knee flexion range-of-motion (ROM) test, particularly the passive knee flexion method [10,19,20]. This approach is widely accessible and commonly used [20,21]. However, such measurements primarily focus on the maximum ROM of knee flexion without considering the TFRC during active knee flexion. Yazdia et al reported in 2014 that they found no significant differences in the knee flexion angles between individuals with PFPS and those in a control group [21]. Excessive tibial external rotation during knee flexion increases the stress on the patellofemoral joint, and repetition of this impaired lower-extremity movement pattern may ultimately lead to micro- and macro-trauma, thereby increasing the risk of PFPS and other knee injuries [22,23]. Because uncontrolled tibiofemoral rotation can affect patellofemoral joint mechanics, TFRC during knee movements is considered an essential factor in the evaluation and management of PFPS.

However, despite these insights, no study has directly compared knee flexion angles with and without TFRC in individuals with PFPS. Addressing this gap may help improve our understanding of the role of TFRC in PFPS and its potential relevance to clinical assessment and management.

In addition, using the distance between the examination table and the lateral malleolus (DBTL) as an indirect indicator of tibial external rotation may provide clinicians with a simple and clinically feasible means to assess excessive tibial external rotation that is not detected by conventional ROM tests. Therefore, the first purpose of this study was to compare knee flexion angles under conditions with and without TFRC between individuals with and without PFPS. The second purpose was to compare the DBTL during knee flexion without TFRC between the groups. We hypothesized that the PFP group would exhibit a lower knee flexion angle compared with the non-PFP group during knee flexion with TFRC. Further, we hypothesized that the PFP group would exhibit a greater DBTL during knee flexion without TFRC compared with the non-PFP group.

Material and Methods

RESEARCH DESIGN:

This cross-sectional study was conducted at Yonsei University Mirae Campus in Wonju, Republic of Korea. Twenty-four male participants were recruited and classified into either the PFP or non-PFP group based on a questionnaire survey and clinical screening. The experimental protocol was established in accordance with the ethical guidelines of the Helsinki Declaration, and approval was obtained from the Yonsei University Mirae Campus Institutional Review Board (approval no. 1041849-202309-BM-180-02). The study was retrospectively registered with the Clinical Research Information Service (CRIS, KCT0010139) on January 17, 2025. All participants received a detailed explanation of the protocol, including its rationale, objectives, and safety considerations, and provided written informed consent before participation. To ensure confidentiality, all personal data were anonymized before the analysis. A licensed physical therapist with over 4 years of clinical experience in a controlled laboratory setting performed screening and assessments. The primary outcomes were knee flexion ROM and the DBTL.

PARTICIPANTS:

Twenty-four male participants were recruited through a questionnaire survey to confirm their experience with PFP. G*Power v. 3.1.9 (Franz Faul, University of Kiel, Kiel, Germany) was used to estimate the required sample size based on pilot data. For a 2-way mixed analysis of variance (ANOVA) with an effect size of 0.30, statistical power (1-β) of 0.80, and an alpha level of 0.05, this analysis indicated that at least 10 participants per group were required. To account for a potential dropout rate of 20%, we chose to recruit a minimum of 12 participants per group (N=24).

INCLUSION CRITERIA:

The inclusion criteria for the PFPS group were: (1) the presence of anterior or retropatellar knee pain; (2) a pain intensity of at least 3 cm on the Visual Analog Scale (VAS) during the last month; (3) anterior knee pain persisting for at least 8 weeks; (4) pain during activities such as ascending and descending stairs, squatting, kneeling, jumping, prolonged sitting with the knees flexed, isometric knee extension contraction at 60° of knee flexion, and on palpation of the medial and/or lateral facet of the patella (at least 2 of these criteria had to be met if the pain was reported during such activities); and (5) a positive sign in the Clarke’s test.

EXCLUSION CRITERIA:

The exclusion criteria were: (1) previous lower-extremity surgery or significant injury; (2) a history of knee fractures, patellar dislocations, ligament or meniscal injuries, or knee osteoarthritis; (3) inflammatory or swelling conditions in the knee; (4) inability to perform the test due to pain or joint effusion; or (5) knee valgus or varus deformity. Table 1 presents the characteristics of the participants included in the study. There were no missing data. All the participants completed the full protocol.

PROCEDURE:

For each participant with bilateral symptoms in the PFP group, the limb with greater pain intensity was selected for testing, consistent with previous studies [24,25]. The same side limb was assessed in each matched participant in the non-PFP group. Measurements were taken in the following order: (1) active knee flexion in the side-lying position without TFRC (AKWOC) and (2) active knee flexion in the side-lying position with TFRC (AKWC). All measurements were performed 3 times with 20-s intervals and a 5-min rest between each set to minimize muscle fatigue. ROM was measured 3 times at the end range of knee flexion without hip joint flexion or pelvic motion. The average of the 3 measurements was used for analysis. The DBTL was measured simultaneously during the AKWOC condition. This distance was measured 3 times, and the average of these measurements was used for data analysis.

MEASUREMENTS:

The participants were placed in the side-lying position to measure AKWOC. The knee flexion test was performed in the side-lying position, and the tested leg was positioned below the non-tested leg. To minimize the influence of hip movements (such as flexion or rotation), the examiner manually stabilized the femoral epicondyle of the tested leg during knee flexion, ensuring that the patella remained facing forward. Participants were instructed to maintain a neutral ankle position to minimize the influence of gastrocnemius muscle activity. They were then asked to actively bend the knee as much as possible (Figure 1A). To measure knee flexion ROM, a standard universal goniometer (BASELINE® Goniometer, Fabrication Enterprises, Inc., White Plains, NY, USA) was used. The axis was aligned with the medial epicondyle of the femur of the examined leg, the stationary arm along the long axis of the thigh, and the mobile arm along the long axis of the tibia. The universal goniometer has demonstrated high reliability and validity for measuring knee joint ROM, and is widely recognized as a standard tool in musculoskeletal assessments [26,27].

The measurement procedure for AKWC was similar to that of AKWOC, focusing on restricting tibial rotation. Participants were instructed to execute slow knee flexion, maintaining contact of their lateral malleolus with the table during the knee flexion test to minimize tibial rotation (Figure 1B). The ROM was measured at the end range of knee flexion without hip joint or tibial rotation. DBTL was measured in the knee flexion position during the AKWOC test and expressed in centimeters using a goniometer arm (Figure 2).

STATISTICAL ANALYSIS:

The Shapiro-Wilk test was used to assess the normality of the data. Homogeneity of variance was assessed using Levene’s test. After confirming that the assumptions of normality and homogeneity were met, a 2×2 repeated-measures ANOVA was conducted to evaluate differences in knee flexion angles between the groups and under TFRC conditions (with and without TFRC). The analysis included within-group factors (AKWOC, AKWC) and between-group factors (PFP, non-PFP). When a statistically significant interaction effect was noted, pairwise post hoc comparisons with a Bonferroni correction were performed to adjust for multiple comparisons. The minimal clinically important difference (MCID) was calculated by multiplying the standard deviation by 0.5 [28]. The intraclass correlation coefficient (ICC) was determined using a 2-way mixed-effects model [3,1] based on 3 trials of the AKWOC, AKWC, and DBTL measurements obtained from 24 participants. An independent t-test was conducted to compare the DBTL between the groups. Statistical analyses were performed using SPSS (version 23.0; SPSS Inc., Chicago, IL, USA), with the significance level set at 0.05.

Results

COMPARISON OF KNEE FLEXION ANGLES WITH AND WITHOUT TFRC:

A 2-way repeated-measures ANOVA revealed a significant interaction effect between group and TFRC condition for knee flexion angle (P=0.002). Post hoc analysis showed no significant difference between the PFP and non-PFP groups in the AKWOC condition (P=0.061). However, in the AKWC condition, the PFP group exhibited a significantly lower knee flexion angle compared with the non-PFP group (P=0.001) (Table 2; Figure 3). The measurement reliability was excellent, with ICC values of 0.915 for AKWOC and 0.956 for AKWC, which exceeded the calculated MCID values (4.83° for AKWOC and 11.45° for AKWC).

COMPARISON OF DBTL:

During knee flexion without TFRC, the PFP group exhibited significantly greater DBTL compared with the non-PFP group (P=0.003, Cohen’s d=1.36) (Table 3). The reliability for DBTL measurements was excellent (ICC=0.944).

Discussion

The purpose of this study was to compare the knee flexion angle between the PFP group and the non-PFP group, with and without TFRC. To the best of our knowledge, this is the first study to compare knee flexion angles under conditions of TFRC in individuals with and without PFP. The results of our study indicated no significant differences in knee flexion angle between the groups in the AKWOC condition. However, in the AKWC condition, the PFP group exhibited a significantly lower knee flexion angle than the non-PFP group. This between-group difference exceeded the MCID of 11.45°, indicating that the reduction in knee flexion observed in the PFP group was statistically significant and clinically meaningful. Additionally, the DBTL was greater in the PFP group than the non-PFP group.

In previous studies, various attempts have been made to compare the knee flexion ROM between individuals with PFPS and controls [29–31]. Among several studies using passive knee flexion ROM testing in PFPS and control groups, some studies have reported significant differences, while others found no significant between-group differences. Yazdia et al (2014) investigated active knee flexion ROM between a PFPS group and a control group and reported no significant difference between them [21]. However, in their study, both the hip and knee joints were flexed simultaneously in the supine position. This test position may affect the interpretation of knee flexion ROM results, as the length of the rectus femoris, a 2-joint muscle, becomes relatively relaxed in the hip flexion position. Additionally, the lack of significant differences between groups may be attributed to the failure to control for tibiofemoral joint rotation or account for compensatory movements from other joints during knee flexion.

We addressed these limitations by measuring the knee flexion ROM in the side-lying position with the hip fixed at a neutral position. Although we used a different measurement position from previous studies, no significant difference was observed in knee flexion ROM between the groups without TFRC, which is consistent with the results of Yazdia et al (2014). However, in our study, a significant difference was observed in knee flexion ROM between the groups when TFRC was applied. Such differences may reflect biomechanical mechanisms associated with rotational control during knee flexion. Knee joint motion is influenced by both passive anatomical structures, such as bony morphology and ligament tension, and dynamic factors, including muscle activation [32]. However, during open kinetic chain (OKC) knee flexion, tibial movement relies primarily on active muscle contraction [33]. Previous studies have demonstrated that individuals with greater tibial external rotation during OKC knee flexion tend to exhibit increased activation of the lateral hamstring [33]. In the present study, the application of TFRC likely resulted in a reduction in excessive tibial external rotation in the PFP group, thereby limiting reliance on compensatory strategies involving the lateral hamstrings. The altered movement pattern under the TFRC may help explain, at least in part, the reduced knee flexion ROM observed in the PFP group, which may be attributed to the limited ability to complete motion without relying on rotational compensation. These findings suggest that impaired TFRC may be observed as a characteristic movement pattern in individuals with PFPS and, from a clinical perspective, that its assessment may help clinicians identify impairments in rotational control that are not apparent during standard passive ROM measurements. Furthermore, incorporating the TFRC test into PFPS evaluation could guide the development of targeted interventions aimed at improving rotational control during knee flexion. Finally, because muscle activation was not directly measured, future studies should investigate medial and lateral hamstring activities under both TFRC and non-TFRC conditions to clarify the mechanisms underlying these kinematic differences.

Additionally, when the knee was flexed without TFRC, the DBTL was significantly greater in the PFP group than in the non-PFP group. A greater DBTL value indicates increased tibial external rotation relative to a fixed femur, thereby providing an indirect measure of uncontrolled tibiofemoral rotation when TFRC is not applied. This interpretation is consistent with previous studies that reported increased tibial external rotation during knee movements in individuals with PFPS. Willson and Davis (2008) observed that individuals with PFPS demonstrated approximately 4.3° greater tibial external rotation during tasks such as single-leg squats, running, and repetitive single-leg jumps, whereas Paoloni et al (2010) found greater tibial external rotation in individuals with PFPS than in healthy subjects during the loading response phase of gait [34,35].

Excessive tibial external rotation may contribute to PFPS by increasing patellofemoral joint stress. Lee et al (2001) reported that tibial external rotation significantly increased both average and maximum patellofemoral contact pressures across different flexion angles, whereas tibial internal rotation had no such effect [36]. Similarly, Csintalan et al (2002) demonstrated that peak pressures were higher when the tibia was fixed at 15° of external rotation compared with neutral or internal rotation [37]. In addition, Salsich and Perman (2007) reported that tibial external rotation reduced the patellofemoral contact area, which they suggested could increase joint stress and potentially exacerbate PFP [12]. Collectively, these findings underscore the clinical significance of assessing uncontrolled tibiofemoral joint rotation in individuals with PFPS. However, causality could not be determined in the current study; further longitudinal research is needed to clarify whether impaired TFRC contributes to the development of PFPS or arises as a consequence of this condition.

Our study has several limitations. First, since only male participants were included, it is not possible to generalize the results to a broader population. Second, a novel method for measuring the DBTL during knee flexion, without using TFRC, was explicitly developed to quantify tibial external rotation. Therefore, the results involving DBTL should be interpreted with caution owing to the potential measurement errors and methodological limitations of the newly developed approach. Third, despite efforts to minimize tibial rotation by stabilizing the femur and instructing participants to maintain contact between the lateral malleolus and the examination table, a minimal degree of measurement error cannot be entirely excluded. Future studies should employ advanced motion analysis techniques to validate these findings. Fourth, the examiner was not blinded to the treatment. However, to minimize the potential measurement bias, all assessments were performed by a single experienced physical therapist using a standardized protocol and repeated trials. Fifth, information on the participants’ activity levels was not collected, which may have influenced both TFRC and knee flexion patterns. Future studies should incorporate these factors to improve the external validity of our findings. Finally, the causal relationship between impaired TFRC and PFPS remains unclear. Prospective longitudinal studies are needed to determine whether deficits in TFRC contribute to the development of PFPS or are a consequence of the condition.

Conclusions

This study demonstrated that individuals with PFP exhibited significantly reduced knee flexion ROM under the TFRC condition compared with the non-PFP group, whereas no difference was observed without TFRC. In addition, the greater DBTL values in the PFPS group reflected increased tibial external rotation, suggesting a tendency toward uncontrolled tibiofemoral rotation during knee flexion. These findings suggest that tibiofemoral rotational control impairments, revealed under the TFRC condition, may represent a characteristic movement pattern in PFPS. From a clinical perspective, incorporating a TFRC test into PFPS evaluation could provide information on rotational control that is not apparent through conventional ROM assessments, enabling clinicians to identify impairments in rotational control during knee flexion and to inform the development of targeted interventions.