Jonathan S. Akins

Interface shear and pressure characteristics of wheelchair seat cushions

Pressure ulcer incidence rates have remained constant despite advances in support surface technology. Interface shear stress is recognized as a risk factor for pressure ulcer development and is the focus of many shear reduction technologies incorporated into wheelchair cushions; however, shear reduction has not been quantified in the literature. We evaluated 21 commercial wheelchair seat cushions using a new methodology developed to quantify interface shear stress, interface pressure, and horizontal stiffness. Interface shear stress increased significantly with applied horizontal indenter displacement, while no significant difference was found for interface pressure. Material of construction resulted in significant differences in interface shear stress, interface pressure, and horizontal stiffness. This study shows that the existing International Organization for Standardization (ISO) 16840-2 horizontal stiffness measure provides similar information to the new horizontal stiffness measure. The lack of a relationship between interface shear stress and the overall horizontal stiffness measure, however, suggests that a pressure and shear force sensor should be used with the ISO 16840-2 horizontal stiffness measure to fully quantify a cushions ability to reduce interface shear stress at the patients bony prominences.

Test-retest reliability and descriptive statistics of geometric measurements based on plantar pressure measurements in a healthy population during gait.

Previous studies have demonstrated that pressure, force, area, and time measurements can be reliably collected from pedobaragraphic platforms, but no studies have analyzed geometric measurements. The purpose of this study was to establish the test-retest reliability of geometric measurements obtained during gait at a self-selected speed using a two-step approach. Data were collected on both feet for 10 healthy participants using the emed-x platform. Reliability of 15 geometric measurements was assessed using intraclass correlation coefficients (ICC). All 15 measurements were demonstrated to be reliable (ICC>0.8), with 12 measurements ICC>0.90. Collection of geometric measurements at a self-selected pace with the emed-x platform was found to be reliable and can be used for investigation in research settings.

An MRI investigation of the effects of user anatomy and wheelchair cushion type on tissue deformation

AIM OF THE STUDY Tissue deformation is recognized as an important risk factor for pressure injuries. This study investigated the effects of anatomy and wheelchair cushion type on tissue deformation. MATERIALS AND METHODS Direct 3-dimensional tissue deformation response was measured for six participants sitting on six different wheelchair cushions using MR imaging. Two participants had a traumatic spinal cord injury (SCI) within one year of the assessment, two sustained traumatic SCI at least 13 years prior, and two were without SCI. Tissue deformation was quantified using the difference in volume of tissue beneath the ischial tuberosity (IT) between unloaded and loaded (sitting) conditions. RESULTS The participants with SCI tended to have less muscle tissue volume beneath their ITs while sitting compared to participants without SCI. Reductions in muscle and fat volumes in the loaded conditions varied depending on both cushion and participant. Higher interface pressures tended to be associated with lower unloaded tissue thicknesses. CONCLUSION The study showed no single cushion type tested produced the lowest amount of tissue deformation across all participants. Individual anatomy and cushion type affect deformation response of tissue and related pressure injury risk.

Reliability and validity of an accelerometry based measure of static and dynamic postural stability in healthy and active individuals.

Postural stability is an important measure in both research and clinical practice. A portable, easy to use device that can provide higher resolution than current clinical tests may allow for better identification of patients or athletes with postural stability deficits. The purpose of this study was to evaluate the ability of a tri-axial accelerometer to quantify postural stability in a healthy athletic population. Ten subjects were recruited to determine the reliability of the accelerometer to measure dynamic postural stability and thirteen were recruited to compare the accelerometer measures across tasks of varying difficulty. Subjects were asked to complete four static postural stability tasks with eyes open and eyes closed and two dynamic postural stability tasks for a total of ten tasks. During each task postural stability was measured using a tri-axial accelerometer and force platform. Differences between postural stability scores between tasks and the correlation between the two measures were assessed. The accelerometer demonstrated moderate to good test-retest reliability (ICC=0.732 to 0.899). Only the medial-lateral axis of the accelerometer showed significant differences between static tasks but all directions were able to show significant differences between static and dynamic tasks. Additionally, Spearmans ranked correlations showed little to no correlation between the accelerometer and force platform scores. Accelerometers are a reliability tool for postural stability that measure low difficulty tasks best in the medial-lateral direction. Low correlation between the accelerometer and force platform suggest that these two methods are not measuring the same components of postural stability.

Feasibility of freehand ultrasound to measure anatomical features associated with deep tissue injury risk

Deep tissue injuries (DTI) are severe forms of pressure ulcers that start internally and are difficult to diagnose. Magnetic resonance imaging (MRI) is the currently preferred imaging modality to measure anatomical features associated with DTI, but is not a clinically feasible risk assessment tool. B-mode ultrasound (US) is proposed as a practical, alternative technology suitable for bedside or outpatient clinic use. The goal of this research was to confirm US as an imaging modality for acquiring measurements of anatomical features associated with DTI. Tissue thickness measurements using US were reliable (ICC=.948) and highly correlated with MRI measurements (muscle r=.988, p ≤ .001; adipose r=.894, p ≤ .001; total r=.919; p ≤ .001). US measures of muscle tissue thickness were 5.4mm (34.1%) higher than MRI, adipose tissue thickness measures were 1.6mm (11.9%) lower, and total tissue thickness measures were 3.8mm (12.8%) higher. Given the reliability and ability to identify high-risk anatomies, as well as the cost effectiveness and availability, US measurements show promise for use in future development of a patient-specific, bedside, biomechanical risk assessment tool to guide clinicians in appropriate interventions to prevent DTI.

Relationship Between Tibial Acceleration and Proximal Anterior Tibia Shear Force Across Increasing Jump Distance

Proximal anterior tibia shear force is a direct loading mechanism of the anterior cruciate ligament (ACL) and is a contributor to ACL strain during injury. Measurement of this force during competition may provide insight into risk factors for ACL injury. Accelerometers may be capable of measuring tibial acceleration during competition. The purpose of this study was to examine the relationship between acceleration measured by a tibia-mounted accelerometer and proximal anterior tibia shear force as measured through inverse dynamics and peak posterior ground reaction forces during two leg stop-jump tasks. Nineteen healthy male subjects performed stop-jump tasks across increasing jump distances. Correlation coefficients were calculated to determine if a relationship exists between accelerometer data and proximal anterior tibia shear force and peak posterior ground reaction force. An analysis of variance was performed to compare these variables across jump distance. Significant correlations were observed between accelerometer data and peak posterior ground reaction force, but none between accelerometer data and proximal anterior tibia shear force. All variables except peak proximal anterior tibia shear force increased significantly as jump distance increased. Overall, results of this study provide initial, positive support for the use of accelerometers as a useful tool for future injury prevention research.

Rehabilitation of People with Lower-Limb Amputations

Rehabilitation of persons with lower-limb amputation is a complex endeavor that requires the consideration of a multitude of factors. This article provides an overview of the current practice of prosthesis prescription, mobility training, and the utilization of wheeled mobility options in the clinical care for this population. Recent technological advancements have helped fit persons with lower-limb amputation with more functional, better fitting, and less activity-limiting artificial limbs and wheelchairs. This is exemplified in modern computer-controlled prosthetic components and biomechanically optimized socket-fitting methods, as well as light weight and versatile wheelchairs to supplement or replace prosthetic devices. In the research setting, technology has enabled new approaches to the kinematic and kinetic assessment of prosthetic interventions, and the development of more accurate fitting and evaluation methods. Despite the noted progress in the field, there is still a considerable gap between the functionality of a sound leg and even the most advanced prosthesis. It can be predicted that continued research efforts will be undertaken to further close this gap.

Postural stability and isokinetic strength do not predict knee valgus angle during single-leg drop-landing or single-leg squat in elite male rugby union players

BACKGROUND: Knee injuries have been identified as the most common injury in rugby. Knee valgus has been identified as a risk factor for ligament injuries in athletes and predictors of knee valgus may assist in the design of knee injury prevention programs. PURPOSE: The purposes of this study were to use postural stability (PS) and strength measures to predict knee valgus angle during dynamic tasks, identify relationships between PS and strength, and compare measures between positions. METHODS: Participants presenting positive during a gluteal dysfunction screening exam were enrolled. Participants performed PS, isokinetic strength, and biomechanical assessments. Stepwise multiple linear regression analyses were performed to identify predictors of knee valgus. Correlation coefficients identified relationships between PS and strength, and independent t-tests compared forwards and backs. RESULTS: Backs had significantly ( p< 0.05) better PS and greater strength as compared to forwards. Hip abduction strength was correlated (r = �0.52–�0.71, p< 0.05) withall eyes open staticPSmeasures. Regression analysis failed toidentify predictors of knee valgus angle. CONCLUSION: Although PS and strength were not multivariate predictors of knee valgus in male rugby players, bivariate correlations suggest that hip abduction strength training may be beneficial for enhancing PS.

Reliability and measurement precision of concentric-to-isometric and eccentric-to-isometric knee active joint position sense tests in uninjured physically active adults

OBJECTIVES Proprioception is important because it is used by the central nervous system to mediate muscle control of joint stability, posture, and movement. Knee active joint position sense (AJPS) is one representation of knee proprioception. The purpose of this study was to establish the intra-tester, inter-session, test-retest reliability of concentric-to-isometric (seated knee extension; prone knee flexion) and eccentric-to-isometric (seated knee flexion; prone knee extension) knee AJPS tests in uninjured adults. DESIGN Descriptive. SETTING University laboratory. PARTICIPANTS Six males, six females (age 26.2 ± 5.7 years; height 171.1 ± 9.6 cm; mass 71.1 ± 16.6 kg). MAIN OUTCOME MEASURES Mean absolute error (AE; °); intraclass correlation coefficient (ICC) (2,1); standard error of measurement (SEM; °). RESULTS Mean AE ranged from 3.18° to 5.97° across tests. The ICCs and SEMs were: seated knee extension 0.13, 1.3°; prone knee flexion 0.51, 1.2°; seated knee flexion 0.31, 1.7°; prone knee extension 0.87, 1.4°. CONCLUSIONS The prone knee flexion and prone knee extension tests demonstrated moderate to good reliability. Prone knee flexion and prone knee extension AJPS tests may be useful in cross-sectional studies estimating how proprioception contributes to knee functional joint stability or prospective studies estimating the role of proprioception in the onset of knee injury.

Reliability and Validity of Instrumented Soccer Equipment

Ankle ligament sprains are the most common injury in soccer. The high rate of these injuries demonstrates a need for novel data collection methodologies. Therefore, soccer shoes and shin guards were instrumented with inertial sensors to measure ankle joint kinematics in the field. The purpose of this study was to assess test-retest reliability and concurrent criterion validity of a kinematic assessment using the instrumented soccer equipment. Twelve soccer athletes performed athletic maneuvers in the laboratory and field during 2 sessions. In the laboratory, ankle joint kinematics were simultaneously measured with the instrumented equipment and a conventional motion analysis system. Reliability was assessed using ICC and validity was assessed using correlation coefficients and RMSE. While our design criteria of good test-retest reliability was not supported (ICC > .80), sagittal plane ICCs were mostly fair to good and similar to motion analysis results; and sagittal plane data were valid (r = .90-98; RMSE < 5°). Frontal and transverse plane data were not valid (r < .562; RMSE > 3°). Our results indicate that the instrumented soccer equipment can be used to measure sagittal plane ankle joint kinematics. Biomechanical studies support the utility of sagittal plane measures for lower extremity injury prevention.