2025 ISAKOS Congress in Munich, Germany

2025 ISAKOS Biennial Congress Paper


Altered Hip Extensor and Core Muscle Synergy in Symptomatic Cam FAI During the Hurdle Step Task

Etienne Joulin, BEsc, London, ON CANADA
Mohamad El Fateh Shatila, MESc, London, ON CANADA
Ryan M. Degen, MD, FRCSC, London, ON CANADA
Geoffrey Ng, PhD, London, ON CANADA

Western University, London, ON, CANADA

FDA Status Not Applicable

Summary

Individuals with FAI have weaker hip extensors and altered muscle synergy to perform stepping and balance tasks.

Abstract

Cam-type femoroacetabular impingement (FAI) is a morphological deformity of the hip joint characterized by an enlarged femoral head. Although the hurdle step challenges our hips to coordinate and stabilize the joints through stride motions and mechanics, the muscle activity during this task has yet to be investigated to delineate the intricate muscle synergies for balance and postural control. The aim was to examine the lower-limb and core muscle activity in patients with unilateral FAI and compare them with their contralateral, unaffected hip and healthy controls during the hurdle step task.

Seventeen symptomatic unilateral cam FAI patients (n = 17, m:f = 8:9, age = 25 ± 8 years, BMI = 24 ± 5) and seventeen healthy controls (n = 17, m:f = 7:10, age = 25 ± 7 years, BMI = 24 ± 4) were recruited. Twelve surface electromyography (EMG) electrodes were positioned to each subject’s left and right lower-limb muscles and core muscles, including: gluteus maximus (GM), biceps femoris (BF), tensor fasciae latae (TFL), rectus femoris (RF), erector spinae (ES), and rectus abdominus (RA). Each subject was instructed to perform maximum voluntary isometric contractions of their lower-limb and core muscles, with the peak EMG signal captured to normalize task-specific muscle activity. Each subject performed hurdle steps with each leg in the stance position and then through the swing task, stepping over a hurdle bar set at the subject’s knee height. This yielded EMG data for the FAI patient’s symptomatic/affected hip, FAI patient’s asymptomatic/unaffected, and control subject’s hip in both swing and stance. The EMG waveforms were compared using statistical non-parametric mapping between each FAI patient’s affected and unaffected hip (Wilcoxon signed-rank test) and between the control group and each FAI group’s affected and unaffected hips (Mann-Whitney U test).

The FAI patients’ affected side demonstrated reduced gluteus maximus and biceps femoris activity from the initial step to the return step (25–75%) compared to their contralateral, unaffected side and compared to the control group during the swing and stance position. The FAI patients’ affected side had minimal biceps femoris activity during the toe-tap phase (50%), during both the swing and stance positions (p ≤ 0.005). This led FAI patients to increase their muscle activation of their affected sides’ erector spinae and rectus abdominus compared to their contralateral, unaffected side and compared to the control group.

The most important finding was that the FAI patients altered their hip extensor and core muscle activations to help stabilize their symptomatic, affected hip during the hurdle step task. As the gluteus maximus and biceps femoris muscles are the primary hip extensors, the hurdles task challenged our FAI patients and demonstrated that they were unable to activate their hip extensor muscles to effectively control and stabilize the hip. Instead, the FAI group relied on their core muscles (rectus abdominis, erector spinae) to compensate for suboptimal hip extensor muscle activity and to ensure they can maintain their hip-pelvic stability and postural control.