Trabecular bone is highly non-uniform throughout the vertebra. This intra-vertebral heterogeneity has often been proposed as a main reason why average measures of bone mineral density (BMD) explain only ~60% of the variance in vertebral strength. The goal of this study was to determine the influence of the intra-vertebral heterogeneity in density on strength predictions. Thirty-one fresh-frozen, human, L1 functional spine units were scanned via quantitative computed tomography (QCT) and then compressed to failure to measure the ultimate force. Heterogeneity was quantified using the inter-quartile range (IQR) of the BMD values for 5mm cubes distributed throughout the centrum. Average BMD (vBMD) and cross-sectional area (CSA) were calculated for the largest elliptical cylinder that fits within the vertebra. The images were also used to calculate areal BMD (aBMD) simulating DXA, and axial rigidity (EA; the resistance to axial loading). Linear regressions were used to determine the dependence of ultimate force on: 1) vBMD*CSA; 2) vBMD*CSA and IQR; 3) aBMD; 4) EA, and to rank the different models. Accounting for intra-vertebral heterogeneity in density in addition to mean density significantly improved strength predictions. Including IQR in addition to vBMD*CSA in the regression model improved the R2 value from 0.43 to 0.58 (p<0.002), resulting in the best regression model. Model 3 was inferior to model 2, and model 4 was not significant. These findings show that non-invasive assessments of the intra-vertebral heterogeneity in density improve predictions of vertebral strength compared to current clinical standards that use only average BMD from QCT or DXA.

Listed In: Biomechanical Engineering, Biomechanics, Mechanical Engineering

INTRODUCTION. “Pitching-fatigue”, considered a primary mechanism for throwing arm injuries, can impact lower body power generation to adopt compensatory stride lengths. The purpose of the study was to investigate stride length compensation impacts on brace-transfer ground reaction forces. Brace-transfer refers to the phase initiated at stride foot contact (SFC) ending at maximal external shoulder rotation (MER). We hypothesize that brace-transfer forces are affected by stride variations without impacting ball velocity. METHODS. Nineteen elite high school and collegiate baseball pitchers were randomly crossed over to throw two, 80-pitch simulated games ; (A) +25% desired stride, and (B) -25% desired stride length. Normalized stride length to body height indicated 76% and 52%, for (A) and (B), respectively. The four highest ball velocity trials per subject (Jugs Sports, Tualatin, OR) recorded by 3D kinematics software (Vicon Nexus, Oxford Metrics, UK) derived normalized propulsion and bracing ground reaction force data (Kistler Instrument Corp., Amherst, NY). Post-processing (Visual 3D, C-Motion Inc, Rockville, MD, USA) indicated SFC, MER, and peak linear throwing hand velocity at ball release (BR). RESULTS. Stride lengthening increased propulsion vertical and anterior shear impulses and posterior shear drive foot forces (p<0.001). Greater stride leg posterior shear forces occurred with increased strides (p=0.002). Ball and throwing hand velocities were not affected. DISCUSSION. Overexertion impacting stride length affects baseball pitchers’ typical propulsion and bracing strategies without impacting ball velocity. CONCLUSION. Radar velocities may not detect high effort pitches thrown consistently with altered ground reaction forces, which may lead to arm injuries.

Listed In: Biomechanics, Sports Science

The purpose of this study was to determine whether performance of a volitional preemptive abdominal bracing maneuver (VPAC) during a drop vertical jumping (DVJ) task alters lower extremity (LE) kinematics, kinetics and muscle electromyography (EMG). Subjects performed DVJs with and without performance of the ABM from a 30 cm and 50 cm height. Differences in EMG values before and after landing were compared with and without VPAC using repeated measures t-tests. Differences between each kinematic and kinetic dependent variable were assessed using 2 (abdominal contractile state) X 2 (landing phase) within design ANOVAs using SPSS. At the 30 cm landing height, VPAC resulted in statistically significant increases in: knee internal rotation angle, knee flexion angle, knee internal abduction moment, knee energy absorption, medial hamstring post contact activity, trunk left rotation, and external oblique activity pre- and post-contact. At the 50 cm landing height, VPAC resulted in statistically significant decreases in ankle inversion angle, hip energy absorption, and external oblique muscle activity post-contact. In addition, increases in knee flexion angle at contact, medial hamstring activity pre-contact, hip flexion angle at contact, trunk left rotation angle post-contact, trunk left rotation angle at contact, and greater external oblique muscle activity pre-contact. The use of VPAC altered LE and trunk biomechanics and neuromuscular control when performing DVJ from 30 and 50 cm heights. The demands of the 50 cm DVJ may have superseded the effectiveness of VPAC. These results suggest an enhanced protective knee response and improved trunk stability with VPAC use.

Listed In: Biomechanics, Physical Therapy, Sports Science

Purpose: Total Hip Replacements (THR) are a common procedure for older people who suffer from degenerative joint disease. Golf is a very popular leisure sport played by many older Americans including those with THR. Hip torques encountered in a golf swing after THR has not been reported. The purpose of this study is to describe three- dimensional (3D) hip joint torques generated during a golf swinging by those with THR. Methods: Three male amateur golfers who were at least 1 year post THR (ages 59-71 year old and right hand dominant, (2 were left THR) participated. Golf handicap ranged from 16-18. All participants completed the Hip Harris Score. Passive reflective markers were placed on key boney anatomical landmarks. Participants were allowed to warm up prior to testing by performing golf swings. During data collection, participants completed ten swings using a standardized driver. Kinetics and kinematics were captured using a 10 camera Motion Analysis system (Motion Analysis Corp, Santa Rose, CA) and two AMTI (Advanced Medical Technology, Inc., Watertown, MA) forceplates. Inverse dynamics procedure was used to calculate peak hip torques in all three planes. Hip torques were normalized to body weight x height (BW x Ht) and presented as internal torques. Comparisons were made to previously collected similarly aged healthy male golfers (senior group). Results: Average Club head velocity was slower than senior group. Like the senior group, THR golfers exhibited the greatest torque in the sagittal plane .In the frontal plane, all THR golfers demonstrated a lower hip adductor torque on the lead leg compared to the trail leg and compared to senior group. In the transverse plane, those with THR exhibited higher hip external rotation torques compared to the internal rotation torques and compared to the senior group. Conclusion: Three dimensional peak hip torques generated during the golf swing by persons with a THR are greatest in the sagittal plane. THR golfers demonstrated slower club head speed but generated higher hip torques in the transverse plane as compared to those without a THR. Hip external rotation torque was higher in all of the THR compared to the senior group. Clinical Significance: Subjects with a THR may be prone to abnormal forces in the transverse plane during the golf swing. Future studies are needed to determine impact on return to golf decisions following a THR.

Listed In: Biomechanics, Physical Therapy, Sports Science

Purpose: Total Hip Replacements (THR) are common procedures for older people who suffer from degenerative joint disease. Golf is a popular leisure sport played by older Americans including those with THR. Hip torques encountered in a golf swing after THR has not been reported. The purpose of this study is to describe 3D hip joint torques generated during a golf swinging by those with THR. Methods: Three male amateur golfers who were at least 1 year post THR (ages 59-71 year old and right hand dominant, (2 were left THR) participated. Golf handicap ranged from 16-18. All participants completed the Hip Harris Score. Passive reflective markers were placed on key boney anatomical landmarks. During data collection, participants completed ten swings using a standardized driver, after a warm up. Kinetics and kinematics were captured using a 10 camera Motion Analysis system and two AMTI forceplates. Inverse dynamics procedure was used to calculate peak hip torques in all three planes. Hip torques were normalized and presented as internal torques. Comparisons were made to previously collected similarly aged senior group. Results: Average Club head velocity was slower than senior group. Sagittal Plane: THR golfers exhibited the greatest torque similar to senior group. Frontal plane: THR golfers demonstrated a lower hip adductor torque on the lead leg compared to the trail leg and senior group. Transverse plane: THR exhibited higher hip external rotation torques compared to the internal rotation torques and the senior group. Conclusion: 3-D peak hip torques generated during the golf swing by persons with a THR are greatest in the sagittal plane. THR golfers demonstrated slower club head speed but generated higher hip torques in the transverse plane as compared to those without a THR. Hip external rotation torque was higher in all of the THR compared to the senior group. Clinical Significance: Subjects with a THR may be prone to abnormal forces in the transverse plane during the golf swing. Future studies are needed to determine impact on return to golf decisions following a THR.
Listed In: Biomechanics, Physical Therapy, Sports Science