Giulia Mantovani

How Different Marker Sets Affect Joint Angles in Inverse Kinematics Framework.

The choice of marker set is a source of variability in motion analysis. Studies exist which assess the performance of marker sets when direct kinematics is used, but these results cannot be extrapolated to the inverse kinematic framework. Therefore, the purpose of this study was to examine the sensitivity of kinematic outcomes to inter-marker set variability in an inverse kinematic framework. The compared marker sets were plug-in-gait, University of Ottawa motion analysis model and a three-marker-cluster marker set. Walking trials of 12 participants were processed in opensim. The coefficient of multiple correlations was very good for sagittal (>0.99) and transverse (>0.92) plane angles, but worsened for the transverse plane (0.72). Absolute reliability indices are also provided for comparison among studies: minimum detectable change values ranged from 3 deg for the hip sagittal range of motion to 16.6 deg of the hip transverse range of motion. Ranges of motion of hip and knee abduction/adduction angles and hip and ankle rotations were significantly different among the three marker configurations (P < 0.001), with plug-in-gait producing larger ranges of motion. Although the same model was used for all the marker sets, the resulting minimum detectable changes were high and clinically relevant, which warns for caution when comparing studies that use different marker configurations, especially if they differ in the joint-defining markers.

Comparison of total hip arthroplasty surgical approaches by Principal Component Analysis

Gait adaptations are persistent after total hip arthroplasty and can depend on the type of surgery. This study focused on two surgical approaches: anterior and lateral. To analyze gait adaptations, biomechanical analyses usually employ an a priori selection of the parameters that leads to incomplete or redundant information. In contrast, Principal Component Analysis (PCA) provides an efficient transformation of the dataset by automatically identifying the major sources of variability. The purpose of this study was to investigate differences in level-walking among three groups of participants using PCA: patients undergoing an anterior surgical approach, patients undergoing a lateral surgical approach, and healthy controls. Biomechanical descriptions of the extracted principal components aided in the interpretation of the statistically significant results obtained from multivariate analysis of covariance (MANCOVA) tests. A point system was introduced to summarize the results and guide the interpretation. PCA captured reduced magnitude in sagittal and frontal moments in the anterior approach group, and reduced sagittal peaks angle in the lateral group, as previously found with traditional analyses. PCA also identified significant pattern delays in the anterior group, unnoticed in previous studies. In conclusion, neither surgical approach restored normal gait functionality because lower extremity kinetics and kinematics alterations persisted at 300-day follow-up after the surgery, regardless of the technique.

Increased Hip Stresses Resulting From a Cam Deformity and Decreased Femoral Neck-Shaft Angle During Level Walking

BackgroundIt is still unclear why many individuals with a cam morphology of the hip do not experience pain. It was recently reported that a decreased femoral neck-shaft angle may also be associated with hip symptoms. However, the effects that different femoral neck-shaft angles have on hip stresses in symptomatic and asymptomatic individuals with cam morphology remain unclear.Questions/purposesWe examined the effects of the cam morphology and femoral neck-shaft angle on hip stresses during walking by asking: (1) Are there differences in hip stress characteristics among symptomatic patients with cam morphology, asymptomatic individuals with cam morphology, and individuals without cam morphology? (2) What are the effects of high and low femoral neck-shaft angles on hip stresses?MethodsSix participants were selected, from a larger cohort, and their cam morphology and femoral neck-shaft angle parameters were measured from CT data. Two participants were included in one of three groups: (1) symptomatic with cam morphology; (2) asymptomatic with a cam morphology; and (3) asymptomatic control with no cam morphology with one participant having the highest femoral neck-shaft angle and the other participant having the lowest in each subgroup. Subject-specific finite element models were reconstructed and simulated during the stance phase, near pushoff, to examine maximum shear stresses on the acetabular cartilage and labrum.ResultsThe symptomatic group with cam morphology indicated high peak stresses (6.3–9.5 MPa) compared with the asymptomatic (5.9–7.0 MPa) and control groups (3.8–4.0 MPa). Differences in femoral neck-shaft angle influenced both symptomatic and asymptomatic groups; participants with the lowest femoral neck-shaft angles had higher peak stresses in their respective subgroups. There were no differences among control models.ConclusionsOur study suggests that the hips of individuals with a cam morphology and varus femoral neck angle may be subjected to higher mechanical stresses than those with a normal femoral neck angle.Clinical RelevanceIndividuals with a cam morphology and decreased femoral neck-shaft angle are likely to experience severe hip stresses. Although asymptomatic participants with cam morphology had elevated stresses, a higher femoral neck-shaft angle was associated with lower stresses. Future research should examine larger amplitudes of motion to assess adverse subchondral bone stresses.

Regression models to predict hip joint centers in pathological hip population

The purpose was to investigate the validity of Harringtons and Daviss hip joint center (HJC) regression equations on a population affected by a hip deformity, (i.e., femoroacetabular impingement). Sixty-seven participants (21 healthy controls, 46 with a cam-type deformity) underwent pelvic CT imaging. Relevant bony landmarks and geometric HJCs were digitized from the images, and skin thickness was measured for the anterior and posterior superior iliac spines. Non-parametric statistical and Bland-Altman tests analyzed differences between the predicted HJC (from regression equations) and the actual HJC (from CT images). The error from Daviss model (25.0 ± 6.7 mm) was larger than Harringtons (12.3 ± 5.9 mm, p<0.001). There were no differences between groups, thus, studies on femoroacetabular impingement can implement conventional regression models. Measured skin thickness was 9.7 ± 7.0mm and 19.6 ± 10.9 mm for the anterior and posterior bony landmarks, respectively, and correlated with body mass index. Skin thickness estimates can be considered to reduce the systematic error introduced by surface markers. New adult-specific regression equations were developed from the CT dataset, with the hypothesis that they could provide better estimates when tuned to a larger adult-specific dataset. The linear models were validated on external datasets and using leave-one-out cross-validation techniques; Prediction errors were comparable to those of Harringtons model, despite the adult-specific population and the larger sample size, thus, prediction accuracy obtained from these parameters could not be improved.

Altered Walking and Muscle Patterns Reduce Hip Contact Forces in Individuals With Symptomatic Cam Femoroacetabular Impingement

Background: Cam-type femoroacetabular impingement (FAI) is a causative factor for hip pain and early hip osteoarthritis. Although cam FAI can alter hip joint biomechanics, it is unclear what role muscle forces play and how they affect the hip joint loading. Purpose/Hypothesis: The purpose was to examine the muscle contributions and hip contact forces in individuals with symptomatic cam FAI during level walking. Patients with symptomatic cam FAI would demonstrate different muscle and hip contact forces during gait. Study Design: Controlled laboratory study. Methods: Eighteen patients with symptomatic cam FAI were matched for age and body mass index with 18 control participants. Each participant’s walking kinematics and kinetics were recorded throughout a gait cycle (ipsilateral foot-strike to ipsilateral foot-off) by use of a motion capture system and force plates. Muscle and hip contact forces were subsequently computed by use of a musculoskeletal modeling program and static optimization methods. Results: The FAI group walked slower and with shorter steps, demonstrating reduced joint motions and moments during contralateral foot-strike, compared with the control group. The FAI group showed reduced psoas major (median, 1.1 newtons per bodyweight [N/BW]; interquartile range [IQR], 1.0-1.5 N/BW) and iliacus forces (median, 1.2 N/BW; IQR, 1.0-1.6 N/BW), during contralateral foot-strike, compared with the control group (median, 1.6 N/BW; IQR, 1.3-1.6 N/BW, P = .004; and median, 1.5 N/BW; IQR, 1.3-1.6 N/BW, P = .03, respectively), which resulted in lower hip contact forces in the anterior (P = .026), superior (P = .02), and medial directions (P = .038). The 3 vectors produced a resultant peak force at the anterosuperior aspect of the acetabulum for both groups, with the FAI group demonstrating a substantially lower magnitude. Conclusion: FAI participants altered their walking kinematics and kinetics, especially during contralateral foot-strike, as a protective mechanism, which resulted in reduced psoas major and iliacus muscle force and anterosuperior hip contact force estimations. Clinical Relevance: Limited hip mobility not only is attributed to bone-on-bone impingement, caused by cam morphology, but could be attributed to musculature as well. Not only would the psoas major and iliacus be able to protect the hip joint during flexion-extension, athletic conditioning could further strengthen core muscles for improved hip mobility and pelvic balance.

Identification of Femoral-Acetabular Symptoms using sEMG Signals during Dynamic Contraction.

This paper focuses on development of an algorithm that automatically differentiates a Femoro-Acetabular Impingement (FAI) patient from a healthy control person by comparing their surface electromyography (sEMG) signal recorded from Gluteus Maximus (GMax), Tensor Fasciae Latae (TFL), and Rectus Femoris (RF) muscles in the hip area. A discrete wavelet transform (DWT) method was used to analyse sEMG signals by thirty-eight different wavelet functions (WFs) with 5 decomposition levels of dynamic contractions during the three phases (descending, stationary, and ascending) of a squat task. The Bior3.9 WF was selected as it provided higher amount of energy for most of the subjects and then the wavelet power spectrum was computed for healthy control and FAI groups. The results show that the RF muscle is more active in the ascending phase than the descending phase for FAI subjects, whereas it is more active in the descending phase for healthy control. An independent sample t-test was used to check the activities of muscle in both groups. The results demonstrate no significant difference for GMax (p=0.7477) and TFL (p=0.4997) muscles, while there is a significant difference for RF muscle (p=0.0670).