Poster 219: The Double-Leg Squat: A Potential Diagnostic Biomarker for Femoroacetabular Impingement Syndrome
Authors: Malloy Philip , Mell Steven P. , Yuh Catherine , Wright-Chisem Joshua , Wichman Daniel M. , Chahla Jorge , Nho Shane J. 
Published: August 2024

Objectives:

Femoroacetabular impingement syndrome (FAIS) commonly reproduces hip pain and symptoms during movement tasks that require near end range hip motion, such as a double-leg squat.  A double-leg squat (DLS) can be easily assessed in the clinical setting and is able be performed by most FAIS patients— therefore, it has potential to be developed as a ‘diagnostic biomechanical marker’ for this motion related hip disorder. However, the contributing literature presents conflicting results, most likely due to small sample sizes. Moreover, several recent studies utilize data from the same cohort of subjects. Thus, larger studies that expand on and validate previous findings are needed to better understand DLS biomechanics within the context of FAIS. Additionally, a study with a larger sample size provides the statistical power to simultaneously evaluate mechanical variables of the knee and ankle, in addition to the hip. Since the lower extremity joints are kinematically linked, other joints may demonstrate equal or greater magnitude of change than the hip alone. Therefore, the purpose of this study is to compare DLS lower extremity joint kinematics and squat performance in patients with FAIS versus healthy controls. We hypothesize that compared to healthy controls, patients with FAIS will squat to a lesser depth at a lower velocity, and demonstrate decreased hip, ankle, and knee joint sagittal plane motion.

Methods:

Sixty subjects, including thirty FAIS patients and thirty healthy controls were enrolled in this institutional review board approved study. Subjects underwent marker based three-dimensional motion capture while performing three trials of a DLS (Figure 1) where kinematic and kinetic data was sampled at 100 and 1000 Hz, respectively. The subjects to “squat as low as possible”. All data were processed using Visual3D software, and a custom MATLAB script was used to define the squat cycle, and calculate squat depth, maximum descent and ascent velocities, and joint range of motion (ROM) at the hip, knee, and ankle. Squat depth and velocities were normalized to height. Joint ROM at the hip, knee, and ankle were defined as the difference between the maximum and minimum angles during the squat cycle. Independent sample t-tests (α = 0.05) were performed in SPSS to compare means in patients with FAIS and healthy controls. Bonferroni adjustments for multiple comparisons were applied to all comparisons. Cohen’s d (effect sizes) was also calculated for all variables.

Results:

Patients with FAIS and controls were matched with no between group differences in age, sex, height, and weight (p > 0.05). Patients with FAIS demonstrate significantly less squat depth (p=0.0002), and both slower ascent (p=0.0022) and descent (p=0.0015) velocity, when compared to healthy controls (n=30, Figure 2). Total sagittal plane hip, knee, and ankle ROM were significantly less in patients with FAIS than controls (Hip p=0.0059; Knee p=0.0001; Ankle p=0.0029). Interestingly, the largest effect size for total joint ROM was observed at the knee (d=-1.0936), followed by the ankle (d=-0.7882), and then the hip, which showed the lowest effect size (d=-0.7295). All effect sizes and p-values are listed in Table 1.

Conclusions:

Our findings demonstrate key differences in DLS biomechanics between patients with FAIS and healthy controls for all variables studied, confirming our hypotheses that FAIS patients squat lower and slower than healthy controls, and that the differences in squat depth would be reflected across the entirety of the lower extremity in the sagittal plane. Our results also further support and validate the findings of several studies that show decreased DLS performance in FAIS patients.  However, the existing literature on DLS biomechanics in the FAIS population is inconsistent, with studies often limited by low sample sizes and underpowered comparisons. Our study is unique in that our large FAIS and healthy control cohorts enabled highly powered comparisons, allowing a large number of biomechanical variables to be assessed. Our findings indicate that FAIS patients demonstrate altered squat movement strategies in several ways: 1) FAIS patients perform DLSs more slowly during both the ascent and descent phases, 2) FAIS patients squat to a lower depth, and 3) this lower squat depth is reflected in a lower total ROM at all joints of the lower extremity in the sagittal plane. This last point is critical, as it indicates that squat modification strategies in FAIS patients are not limited to the hip alone. In fact, the largest effect size was observed at the knee, while the hip had the smallest effect size. Similarly, Lamontagne et al. showed that knee and ankle joint ROM changed significantly after hip arthroscopic surgery for FAIS, whereas hip joint ROM did not. Together, these findings suggest that motion at the knee and ankle may be equally as important to study as motion at the hip in patients with FAIS. A limitation to the current study is that differences may exist in the other anatomical planes, which we will investigate in future work. DLS biomechanics clearly differ between FAIS patients and matched controls, both in magnitude and significance. We demonstrate DLS movement alterations across the lower extremity kinematic chain, indicating the need to understand the contributions of other joints above and below the hip to compensatory movement strategies in these patients. Since the DLS is easy to assess in a clinical setting, this task is therefore an exciting potential diagnostic biomechanical marker of FAIS, that could have implications on clinical diagnosis, athletic performance, and return to sport.