Muscle and Hip Contact Forces in Asymptomatic Men With Cam Morphology During Deep Squat

Abstract

Cam morphology is defined as an aspherical femoral head-neck junction that causes abnormal contact of the acetabular rim with the anterior hip. Imaging confirmation of the cam morphology, associated with clinical signs and pain in the hip or groin, is characterized as femoroacetabular impingement (FAI) syndrome. Although some individuals with cam morphology do not experience any symptoms, sparse studies have been done on these individuals. Understanding the way asymptomatic individuals generate muscle forces may help us to better explain the progression of the degenerative FAI process and discover better ways in preventing the onset or worsening of symptoms. The purpose of this study was to compare the muscle and hip contact forces of asymptomatic cam morphology (ACM) and FAI syndrome men compared to cam-free healthy controls during a deep squat task. This prospective study compared 39 participants, with 13 in each group (ACM, FAI, and control). Five deep squatting trials were performed at a self-selected pace while joint trajectories and ground reaction forces were recorded. A generic model was scaled for each participant, and inverse kinematics and inverse dynamics calculated joint angles and moments, respectively. Muscle and hip contact forces were estimated using static optimization. All variables were time normalized in percentage by the total squat cycle and both muscle forces and hip contact forces were normalized by body weight. Statistical non-parametric mapping analyses were used to compare the groups. The ACM group showed increased pelvic tilt and hip flexion angles compared to the FAI group during the descent and ascent phases of the squat cycle. Muscle forces were greater in the ACM and control groups, compared to the FAI group for the psoas and semimembranosus muscles. Biceps femoris muscle force was lower in the ACM group compared to the FAI group. The FAI group had lower posterior hip contact force compared to both the control and ACM groups. Muscle contraction strategy was different in the FAI group compared to the ACM and control groups, which caused different muscle force applications during hip extension. These results rebut the concept that mobility restrictions are solely caused by the presence of the cam morphology and propose evidence that symptoms and muscle contraction strategy can be the origin of the mobility restriction in male patients with FAI.

Hip Contact Force Magnitude and Regional Loading Patterns Are Altered in Those with Femoroacetabular Impingement Syndrome

“…Consistent with our hypothesis, participants with FAI syndrome generated smaller-magnitude hip contact forces during walking compared with controls. Our findings are consonant with previous modeling studies reporting that those with FAI syndrome generated lower-magnitude hip contact forces during walking (7) and squatting (20), compared with controls. We did find between-group differences in anteroposterior and mediolateral components of hip contact force (expressed in the pelvic coordinate system), but these differences did not coincide temporally with the peak anteroposterior and mediolateral forces, as was reported by Ng and colleagues (7).…”

“…Neuromuscular control seems to be the primary factor producing altered external biomechanics and regional loading at the hip in those with FAI syndrome. A cam morphology alone does not determine whether an individual will experience symptoms of FAI syndrome or altered movement patterns (2,20). Furthermore, hip motions produced during walking are likely insufficient to elicit contact between cam morphology and the acetabulum (3,53).…”

“…Separately, finite element analyses report higher contact pressure (16,23) and more concentrated cartilage stresses during walking (16,23,24) and higher subchondral stresses, but only during squatting (25). Overall, the literature suggests regional loading patterns of the hip’s articular surfaces, and not just magnitude of contact force, may be altered in individuals with FAI syndrome compared with controls (3–8,16,19–24).…”

“…Neuromusculoskeletal (NMS) models present a computationally tractable approach to studying regional articular loading. Their use to understand hip biomechanics in individuals with FAI syndrome has, so far, not incorporated personalized muscle activation patterns and has been limited to assessing the magnitude of hip contact forces (7,20), rather than regional loading patterns. Therefore, the purpose of this study was to evaluate hip regional loading during walking, using an NMS model, in those with FAI syndrome and controls.…”

What the papers say

“…In this study, the authors from Ottawa, Canada [ 2 ], note that cam morphology is defined as an aspherical femoral head–neck junction that causes abnormal contact of the acetabular rim with the anterior hip. Imaging confirmation of the cam morphology, associated with clinical signs and pain in the hip or groin, is characterized as femoroacetabular impingement syndrome (FAIS).…”