Orthopedic Research

Gait biomechanics after total hip arthroplasty: using statistical parametric mapping to identify differences between various surgical approaches

Biomechanical studies have tried to assess the impact of the surgical approach on gait characteristics and recovery after total hip arthroplasty (THA). Some studies which used discrete analyses have shown that some surgical approaches provide better hip joint function after one year post-surgery, but several studies did not find any differences. The goal of this study was to compare hip biomechanics during gait using statistical parametric mapping (SPM) in patients who underwent THA with either a lateral (LAT), anterior (ANT), or posterior (POS) approach. Forty-five patients underwent unilateral THA with either a LAT, ANT, or approach, and were compared with 15 healthy controls (CTRL). All patients underwent biomechanical gait analysis approximately 9 months following surgery. Hip biomechanics were compared between groups throughout the entire gait cycle using a One-Way ANOVA SPM. Alpha was set to 0.05 and Bonferroni post hoc comparisons were completed. The POS group had a significantly lower hip flexion moment just prior to toe-off compared to the ANT and CTRL groups. The ANT group had significantly lower hip abduction moment for most of the stance phase compared to the LAT and CTRL groups. The POS group had a significantly lower hip abduction moment compared to the LAT and CTRL groups. These findings tend to contradict existing literature. Future studies should complete both pre- and post-operative assessments with a larger cohort in each group, as well as standardize the implants as much as possible to determine if observed differences are due to the approach and no other factors.
Listed In: Biomechanics, Orthopedic Research


Flexion Angle Dependent Differences in Joint Kinematics and ACL Force In Response to Applied Loads Are Conserved Throughout Skeletal Growth in the Porcine Stifle Joint

The anterior cruciate ligament (ACL) stabilizes the lower limb against translational and rotational loads while the knee is is multiple postures. Surgical reconstruction, the most common treatment for ACL tears, is intended to replicate the biomechanical function of the native ACL in the postures and activities related to daily living and high-impact activities. In order to improve outcomes from ACL reconstructions in patients in pediatric and adolescent age groups, we need to improve our understanding of the knee posture dependent biomechanical function of the ACL. As such, the objective of this study was to quantify flexion angle dependent changes in the response of the ACL and the total knee to applied loads in the anterior-posterior and varus-valgus directions using a skeletally immature porcine model. To do this, we collected stifle (knee) joints from female Yorkshire-cross pigs at ages ranging from 1.5 to 18 months (n=30 total). The joints were tested using a 6 degree-of-freedom universal force sensing robotic system under applied anterior-posterior loads and varus-valgus moments at 40° and 60° of flexion. Studied parameters included anterior-posterior tibial translation (APTT), varus-valgus rotation (VVR), and anterior force carried by the ACL and its anteromedial and posterolateral bundles. We found increased knee laxity (APTT and VVR) was associated with both younger age and increased knee flexion. Greater anterior force carried in the ACL, and specifically in the anteromedial bundle, was associated with increased flexion, regardless of age. These findings have implications in intraoperative graft assessment and biomechanical models.
Listed In: Biomechanical Engineering, Biomechanics, Orthopedic Research, Sports Science


Can We Develop a Biomechanical Functional Score to Quantify the Joint Mechanics of THA Patients?

THA is a reliable method to improve the quality of life in osteoarthritis patients. However, it is still unclear whether it would lead to improved functional mobility. The purpose was to develop a biomechanical functional score to quantify the joint mechanics of THA patients compared to healthy participants (CTRL). Twenty-four THA patients and 12 CTRL (age-, sex-, and BMI-matched) participants were recruited and underwent motion analysis for different ADLs tasks prior and nine months after THA. Three-dimensional joint kinematics and ground reaction forces were collected and five kinematic and six kinetic variables were included in the analysis. The normalized root-mean-square-deviation (nRMSD) was calculated between the THA and the CTRL groups for both pre- and post-op conditions: nRMSD= √((∑_(t=1)^n(x_(1,t)- y_(1,t))^2)/n)⁄(x_max-x_min). Kinematics and kinetics improvement scores (KMIS and KNIS) were calculated to estimate pre/post-op differences: KMIS=∑_(i=1)^n〖〖(KM〗_(pre/ctrl i)-〖KM〗_(post/ctrl i))〗; KNIS=∑_(i=1)^n〖〖(KN〗_(pre/ctrl i)- 〖KN〗_(post/ctrl i))〗. THA patients experienced post-op improvements, with kinetics variables closely resembling the CTRLs, especially on hip and knee power production. Total improvement scores showed that THA experienced greater improvements during a squat task and this can be a practical approach to evaluate the change in biomechanical function and highlight small improvements that may go unnoticed with traditional statistical analysis.
Listed In: Biomechanics, Orthopedic Research


INFLUENCE OF AGE AND GENDER ON INTERLIMB ASYMMETRY IN RECREATIONAL RUNNERS

INTRODUCTION:Previous studies have reported that men and women demonstrate distinctly different biomechanics during running and that older runners use a variety of biomechanical adaptations compared with younger runners. It is hypothesized that excessive asymmetry due to biomechanical and anatomical abnormalities contributes to increased risk of injuries, however it is still unclear how age and gender might impact this.METHODS: A cross sectional study was employed and healthy recreational runners were categorized into four groups based on age and gender.Two-way multivariate analysis of variance was performed with age and gender as factors and Symmetry Angle values for peak hip adduction angle (HA), peak knee adduction moment (KAM), peak knee flexion angle (KF), and peak vertical ground reaction force (VGRF) were used as the dependent variables. RESULTS: Overall, gender had a significant effect on HA asymmetry (p=0.02) and both gender and age showed a significant interaction effect on KAM asymmetry (p=0.04).CONCLUSIONS:This study suggests that interlimb asymmetry in running gait for KAM and HA also differs with aging and gender.Understanding age and gender related adaptations in interlimb asymmetry will help improve running performance and develop programs aimed at reducing injury rates.
Listed In: Biomechanics, Gait, Orthopedic Research


QUADRICEPS IMPAIRMENT IS ASSOCIATED WITH KNEE MECHANICS DURING GAIT IN OBESE YOUNG ADULTS

Background: Approximately 33% of the adult population in the United States is considered obese (28), which increases the risk of comorbidities such as osteoarthritis (OA) (34). The most notable feature of OA is the loss of articular cartilage within a joint, resulting in pain and physical disability (3). The association between obesity and OA is due to a combination of mechanical and metabolic factors (3). Greater weight from obesity adds stress to articular cartilage in weight-bearing joints, and contributes to cartilage breakdown (21). Previous studies have demonstrated an association between gait biomechanics and OA in older populations (15, 25), but data are lacking in young obese individuals without OA. Young obese compared to normal weight adults have lesser knee flexion excursion (KFE) (31), and greater vertical loading rates (vLR) during gait (30, 31). However, the source of aberrant gait mechanics in obese adults is unclear, and could be related to impaired shock attenuation from weakened musculature in the lower extremity. Obese young adults have deficits in quadriceps function after normalizing to fat-free mass, and walk slower compared to normal weight young adults. RTD was moderately associated with KEM at habitual gait speed, and KEM was also lesser in obese compared to normal weight adults. The lesser KEM in the obese group suggests that obese young adults walk with a quadriceps avoidance gait, which may contribute to knee OA development. Exercise interventions targeting RTD may be useful for improving walking mechanics in obese adults.
Listed In: Biomechanics, Gait, Orthopedic Research


Increased Role of the Secondary Passive Stabilizers Following Complete but Not Partial Loss of Anterior Cruciate Ligament Function During Post-Natal Growth

Robotic testing was performed with a 6-degree of freedom load cell in order to analyze functional contributions of the soft tissues in the knee under physiologically relevant loading conditions. Age groups ranging from 1.5 months to 18 months, porcine equivalent to early youth through late adolescent human ages, were studied. Complete ACL transection resulted in increased APTT and VVR across all ages (p<0.05), while injury to the AM bundle did not affect APTT or VVR. Additionally, increasing age resulted in decreased APTT normalized to the tibial plateau (p<0.05) and an average 19° decrease in VVR across states from 0 to 18 months of age (p<0.05). The ACL was the primary restraint against anterior drawer in the intact knee state [75-111%]. Following AM bundle dissection, the PL bundle carried the vast majority of the anterior load regardless of age [66-112%]. Following complete ACL transection, the MCL and medial meniscus carried most of the force across ages under anterior drawer. The LCL contributed increasing resistance to varus torque across states with age, as did the MCL under valgus torque.
Listed In: Biomechanical Engineering, Biomechanics, Orthopedic Research, Sports Science


Static Foot Structure May Predict Midfoot Mechanics

INTRODUCTION: Clinical interventions for foot injury prevention are often prescribed based on static measures of foot structure. However, this convention merits further investigation as the static-dynamic relationship has only been explored in walking and running. The primary aim of this study was to explore the relationship between static foot structure and dynamic midfoot kinematics and kinetics during a barefoot single-leg landing. METHODS: 48 females (age=20.4±1.8 yr, height=1.6±0.06 m, weight=57.3±5.5 kg) completed the study. Standing arch height index (AHI) was measured using the Arch Height Index Measurement System. Skin markers were attached using a multi-segment foot model by Bruening et al.1 A14-camera motion capture system (Vicon) was used to sample kinematic data at 250Hz while two force platforms (AMTI) sampled kinetic data at 1000Hz. A static trial was captured then subjects hung from wooden rings and performed barefoot single-leg drop landings from a height of 0.4m. Metrics were calculated in Visual 3D (C-motion, Inc.) to obtain static midfoot angle (MA), midtarsal range of motion (ROM), and midtarsal work. PCCs were calculated for static and dynamic variables using paired t-tests in SAS. RESULTS: AHI was correlated negatively with sagittal plane midtarsal ROM (r=-0.32032, p=0.0264) and positively with midtarsal work (r=0.33180, p=0.0212). MA was correlated positively with sagittal plane midtarsal ROM (r=0.48336, p=0.0005) and negatively with midtarsal work (r=-0.32321, p=0.0250). DISCUSSION/CONCLUSION: Static foot structure may be a valuable clinical tool in assessing midfoot function relating to injury risk in athletes, who participate in high-impact loading activities, as well as in pathological populations.
Listed In: Biomechanics, Orthopedic Research, Physical Therapy, Sports Science


Multigenerational growth approach to incorporate residual stress in an intervertebral disc finite element model with validation in multi-axial loading

Residual stresses are known to exist in human intervertebral discs but have not been incorporated in finite element models. A multigeneration model was applied to the annulus fibrosus of the intervertebral disc to simulate residual stresses arising from growth and remodeling. The intervertebral disc shape and compressive creep were used to verify that the multigeneration approach generates realistic values of residual stress. The model was then validated by comparing its 6 degree-of-freedom mechanical response to experimental data. Human intervertebral discs were tested in a custom-built hexapod in all 6 degrees-of-freedom (lateral shear, anterior-posterior shear, torsion, bending, flexion, and compression). Incorporating residual stresses resulted in a finite element model which can predict 4 degrees-of-freedom while excluding residual stresses produces a finite element model that can only predict 2 degrees-of-freedom.
Listed In: Biomechanical Engineering, Biomechanics, Orthopedic Research


Measuring Soft Tissue Contributions to Elbow Joint Motion and Virtual Ligament Modelling An In-Vitro Study

Knowledge of ligamentous contributions to joint stability is essential to restore normal joint range of motion and functionality through reconstruction procedures. Although, there has been numerous studies on the pathomechanics of the elbow joint, there have been very few rigorous and systematic attempts to characterize the roles of soft tissues during clinically relevant motions. Five fresh frozen cadaveric elbows from three male subjects were used for this study. In-vitro simulations were performed using a VIVO six degree-of-freedom (6-DOF) joint motion simulator (AMTI, Watertown, MA) capable of virtually simulating the effects of soft tissue constraints (virtual ligaments). This study introduces a unique, hybrid experimental-computational technique for measuring and simulating the biomechanical contributions of ligaments to elbow joint kinematics and stability. In vitro testing of cadaveric joints is enhanced by the incorporation of fully parametric virtual ligaments, which are used in place of the native joint stabilizers to characterize the contribution of elbow ligaments during simple flexion-extension motions using the principle of superposition. our results demonstrate the importance of AMCL and RCL structures as primary stabilizers under valgus and varus loading respectively. Virtual ligaments demonstrate the ability to restore the VV stability of the joint in the absence of any soft tissues attached to the osseous structures. This demonstrates the effectiveness of “virtual” ligaments for in vitro testing of elbow joint biomechanics, with applications in pre-clinical assessment of elbow implants.
Listed In: Biomechanical Engineering, Biomechanics, Mechanical Engineering, Orthopedic Research


Examining Postural Control With and Without Visual Feedback in Individuals with history of Ankle Sprain

Lateral ankle sprains are common orthopedic injuries and often result in chronic ankle instability (CAI). Studies have shown that the CAI population typically has decreased ankle proprioception and possibly a greater reliance on visual feedback when compared to healthy controls. However, little is known about how the postural control characteristics change in those with and without CAI when external visual feedback is manipulated. Purpose: To compare postural control characteristics of persons with CAI, Copers and healthy adults when performing a single leg balance test with and without external feedback. Method: The definition for CAI used for this study includes persons who have experienced recurrent ankle sprains, in addition to self-reported “feelings of instability” and “giving way,” and a score on the Identification of Functional Ankle Instability (IdFAI) of 11 or greater. 18 participants with CAI, 15 Copers, and 18 healthy controls (mean age of all groups: 22 years) performed the Athlete Single Leg Test on the Biodex Balance System (BBS) at Level 4 which involved a high degree of platform instability. All participants completed 2 trials without and with feedback in that order. Center of pressure position was recorded and the two trial mean was used for further analysis. Overall stability index (OSI) defined as the mean distance of the center of pressure from the center of the platform was obtained from the system. Sway area was calculated using custom Matlab script. Separate 3 (Group) x 2 (Feedback) mixed ANOVAs were run using overall stability index (OSI), and sway area as dependent variables. Results: Significant feedback main effect showed participants had significantly lower (better) OSI value with feedback (1.4±0.1) compared to without feedback (2.6±0.2; P < 0.001) but sway area with feedback (8.61±2.33cm2) was similar to without feedback (10.94±2.43 cm2). There was no significant group main effect or interaction observed for either of the variables. Conclusion: Results suggest that external visual feedback may not play a significant role in helping persons with CAI improve their postural control.
Listed In: Orthopedic Research, Physical Therapy