Human balance and posture control during standing and walking

The common denominator in the assessment of human balance and posture is the inverted pendulum model. If we focus on appropriate versions of the model we can use it to identify the gravitational and acceleration perturbations and pinpoint the motor mechanisms that can defend against any perturbation.

We saw that in quiet standing an ankle strategy applies only in the A/P direction and that a separate hip load/unload strategy by the hip abd/adductors is the totally dominant defence in the M/L direction when standing with feet side by side. In other standing positions (tandem, or intermediate) the two mechanisms still work separately, but their roles reverse. In the tandem position M/L balance is an ankle mechanism (invertors/evertors) while in the A/P direction a hip load/unloading mechanism dominates.

During initiation and termination of gait these two separate mechanisms control the trajectory of the COP to ensure the desired acceleration and deceleration of the COM. During initiation the initial acceleration of the COM forward towards the stance limb is achieved by a posterior and lateral movement of the COP towards the swing limb. After this release phase there is a sudden loading of the stance limb which shifts the COP to the stance limb. The COM is now accelerated forward and laterally towards the future position of the swinging foot. Also M/L shifts of the COP were controlled by the hip abductors/adductors and all A/P shifts were under the control of the ankle plantar/dorsiflexors. During termination the trajectory of both COM and COP reverse. As the final weight-bearing on the stance foot takes place the COM is passing forward along the medial border of that foot. Hyperactivity of that foot's plantarflexors takes the COP forward and when the final foot begins to bear weight the COP moves rapidly across and suddenly stops at a position ahead of the future position of the COM. Then the plantarflexors of both feet release and allow the COP to move posteriorly and approach the COM and meet it as quiet stance is achieved. The inverted pendulum model permitted us to understand the separate roles of the two mechanisms during these critical unbalancing and rebalancing periods.

During walking the inverted pendulum model explained the dynamics of the balance of HAT in both the A/P and M/L directions. Here the model includes the couple due to the acceleration of the weight-bearing hip as well as gravitational perturbations. The exclusive control of A/P balance and posture are the hip extensors and flexors, while in the M/L direction the dominant control is with the hip abductors with very minor adductor involvement. At the ankle the inverted pendulum model sees the COM passing forward along the medial border to the weight-bearing foot. The model predicts that during single support the body is falling forward and being accelerated medially towards the future position of the swing foot. The model predicts an insignificant role of the ankle invertors/evertors in the M/L control. Rather, the future position of the swing foot is the critical variable or more specifically the lateral displacement from the COM at the start of single support. The position is actually under the control of the hip abd/adductors during the previous early swing phase.

The critical importance of the hip abductors/adductors in balance during all phases of standing and walking is now evident. This separate mechanism is important from a neural control perspective and clinically it focuses major attention on therapy and potential problems with some surgical procedures. On the other hand the minuscule role of the ankle invertors/evertors is important to note. Except for the tandem standing position these muscles have negligible involvement in balance control.     

Toward Development of Effective Custom Child Restraint Systems in Motor Vehicles

Traveling safely in motor vehicles can be challenging for many families who have young children with physical disabilities. Harnesses, simple adaptations, and special child restraint systems are available, but sometimes these devices do not adequately meet the unique postural support requirements of children with complex seating needs. Faced with no alternative, parents may choose to use the custom seating system from a wheeled mobility device to support their children in the family car. Transporting children in this way can increase the risk of motor vehicle–related injury because custom seating systems are not designed to meet the requirements of federal motor vehicle safety regulations. We studied whether assistive technology suppliers could build custom child restraint systems that met the crashworthiness requirements of a safety standard for production child restraint systems. We provided technical instructions to 10 suppliers from different parts of North America so they could each build a custom restraint system using a transit frame that we designed. This approach allowed suppliers to make custom seats that could be attached to the transit frame using special connection hardware. We crash tested the 10 custom child restraint systems to evaluate the effectiveness of our transit frame design and fabrication instructions. Six custom restraint systems met the dynamic performance requirements of the stringent Canada Motor Vehicle Safety Standard 213.3. The remaining four systems did not meet the compliance criteria due to the failure of postural belt assemblies or seat securement hardware. We recommend that future research include similar effectiveness studies to support the introduction of technical requirements for adaptive seating systems that improve occupant safety and are practical for wheelchair users, their families, and assistive technology professionals to implement.     

Effects of a Mobility Assistance Dog on the Performance of Functional Mobility Tests Among Ambulatory Individuals with Physical Impairments and Functional Disabilities

This study aims to verify whether individuals with physical impairments and ambulatory disabilities perform functional mobility tests faster using an assistance dog for mobility (AD_Mob). Thirty-four individuals with various physical impairments and functional disabilities performed at least one of the four functional mobility tests within their natural environment during an in-home assessment. Participants randomly performed the 10-meter walk test, the timed up-and-go (TUG) test, and the stair ascent and descent tests with and without an AD_Mob during an in-home assessment. The main outcome measure was the time needed to complete all tests with and without an AD_Mob. When using an AD_Mob, many participants (≥70.4%) were faster when performing the 10-meter walk test (15.7 ± 8.5s vs. 19.1 ± 11.2s), TUG test (23.6 ± 14.2s vs. 27.3 ± 16.5s), and stair ascent test (18.6 ± 13.5s vs. 22.4 ± 17.5s) compared to doing the tests without an AD_Mob. As for the stair descent test, the use of the AD_Mob had no significant effect on performance (20.7 ± 15.9s vs. 24.0 ± 17.1s). When using an AD_Mob, the majority of individuals with physical impairments and functional disabilities significantly improved their performance (i.e., reduced their time) during the 10-meter walk test, the TUG test and the stair ascent test.     

Socioeconomic Status and Injury in a Cohort of Saskatchewan Farmers

Purpose: To estimate the strength of relationships between socioeconomic status and injury in a large Canadian farm population. Methods: We conducted a prospective cohort study of 4,769 people from 2,043 farms in Saskatchewan, Canada. Participants reported socioeconomic exposures in 2007 and were followed for the occurrence of injury through 2009 (27 months). The relative hazards of time to first injury according to baseline socioeconomic status were estimated via Cox proportional hazards models. Findings: Risks for injury were not consistent with inverse socioeconomic gradients (adjusted HR 1.07; 95% CI: 0.76 to 1.51 for high vs low economic worry; adjusted HR 1.72; 95% CI: 1.23 to 2.42 for completed university education vs less than high school). Strong increases in the relative hazard for time to first injury were identified for longer work hours on the farm. Conclusions: Socioeconomic factors have been cited as important risk factors for injury on farms. However, our findings suggest that interventions aimed at the prevention of farm injury are better focused on operational factors that increase risk, rather than economic factors per se.     

Stereotactic ablative radiotherapy before resection to avoid delay for early-stage lung cancer or oligometastases during the COVID-19 pandemic: Pathologic outcomes from the SABR-BRIDGE protocol

Background

During coronavirus disease 2019 (COVID-19)–related operating room closures, some multidisciplinary thoracic oncology teams adopted a paradigm of stereotactic ablative radiotherapy (SABR) as a bridge to surgery, an approach called SABR-BRIDGE. This study presents the preliminary surgical and pathological results.

Methods

Eligible participants from four institutions (three in Canada and one in the United States) had early-stage presumed or biopsy-proven lung malignancy that would normally be surgically resected. SABR was delivered using standard institutional guidelines, with surgery >3 months following SABR with standardized pathologic assessment. Pathological complete response (pCR) was defined as absence of viable cancer. Major pathologic response (MPR) was defined as ≤10% viable tissue.

Results

Seventy-two patients underwent SABR. Most common SABR regimens were 34 Gy/1 (29%, n = 21), 48 Gy/3–4 (26%, n = 19), and 50/55 Gy/5 (22%, n = 16). SABR was well-tolerated, with one grade 5 toxicity (death 10 days after SABR with COVID-19) and five grade 2–3 toxicities. Following SABR, 26 patients underwent resection thus far (13 pending surgery). Median time-to-surgery was 4.5 months post-SABR (range, 2–17.5 months). Surgery was reported as being more difficult because of SABR in 38% (n = 10) of cases. Thirteen patients (50%) had pCR and 19 (73%) had MPR. Rates of pCR trended higher in patients operated on at earlier time points (75% if within 3 months, 50% if 3–6 months, and 33% if ≥6 months; p = .069). In the exploratory best-case scenario analysis, pCR rate does not exceed 82%.

Conclusions

The SABR-BRIDGE approach allowed for delivery of treatment during a period of operating room closure and was well-tolerated. Even in the best-case scenario, pCR rate does not exceed 82%.     

Comparison between a dorsal and a belt tactile display prototype for decoding physiological events in the operating room

Objective. Vibrotactile display technology represents an innovative method to communicate vital information on patients from physiological monitoring devices to clinicians. The increasing number of sensors used in clinical practice has increased the amount of information required to be communicated, overwhelming the capacity of visual and auditory displays. The capacity to communicate could be increased with the use of a tactile display. In this study, we have compared a dorsal (DTD) and belt tactile (TB) display prototype in terms of learnability, error rate, and efficiency. Methods. We conducted a prospective randomized preclinical study with non-clinicians in a simulated clinical setting to compare the two tactile display prototypes. Information encoded in the tactile message included the type of physiological parameter monitored, the direction of change, and the magnitude of change. Following a period of training, 24 alerts were repeated three times for each display in random order. Each subject evaluated each display. Experiments were repeated with the addition of a distraction task. Results. DTD stimuli were easier to learn (52 trials compared to 101 trials; P = 0.0003), but the accuracy in decoding following training did not differ between the two prototypes. The DTD took longer to display the information, resulting in a faster TB response time (start of stimulus to response; 9.3 ± 1.4 s [mean ± SD] vs. DTD, 10.0 ± 1.4 s; F[1,27] = 4.66; P = 0.04). However, the DTD had a faster response interval (end of stimulus to response) compared to the TB (5.6 ± 1.4 s vs. 8.0 ± 1.4 s; F[1,27] = 47.91; P < 0.0001). Compared to the TB, performance was affected less by distraction with the DTD. Conclusions. The communication of information on physiological parameters by tactile displays was easy to learn and accurate for both prototypes. The DTD was easier to learn and affected less by distraction. Further evaluation is required in a clinical setting with expert users to determine the clinical applicability of these prototypes. Barralon P, Dumont G, Schwarz SKW, Magruder W, Ansermino JM. Comparison between a dorsal and a belt tactile display prototype for decoding physiological events in the operating room.     

Kinematic I and Oxford knee arthroplasty: A 5–8-year follow-up study

Sixty-seven consecutive Oxford Meniscal total knee arthroplasties (TKAs) were compared prospectively with 66 Kinematic I TKAs. At follow-up examination an average of 5.5 (range, 5-8) years later, 20 (30%) of the Oxford Meniscal TKAs had been revised (nine due to aseptic loosenings, seven to aseptic loosening and patellofemoral syndrome, two to patellofemoral syndrome, one to meniscal bearing dislocation, and one to sepsis) and in 16% one or more of the remaining tibial components was radiographically at risk. Three (5%) Kinematic I TKAs had been reoperated upon (one for anterior dislocation, one for a loose patellar component, and one for sepsis) and no component was considered radiographically at risk. The remaining cases demonstrated good and excellent knee ratings (Oxford, 82 +/- 11; Kinematic I, 88 +/- 6; P less than .01; Hospital for Special Surgery). This study suggests that the results of Kinematic I TKA are superior to those of Oxford Meniscal TKA; that patellofemoral resurfacing is advisable; and that Kinematic I TKA yields 5-year data comparable to those of total hip arthroplasty.     

Performance analysis of the T‐DOC® air‐charged catheters: An alternate technology for urodynamics

Aims

Urodynamics (UDS) is widely used for the diagnosis of lower urinary tract dysfunction. Air‐Charged catheters (ACC), one of the newer technologies for UDS pressure recording, has been adopted in growing numbers around the world for the past 15 years. Currently, there is a lack of published studies characterizing specific performance of the ACC. Since linearity, hysteresis, pressure drift, and frequency response are important components in characterizing accuracy for catheter‐manometer systems; this study aimed to assess these four aspects in ACC.

Methods

A total of 180 T‐DOC® ACC were used in three different laboratory settings to assess pressure linearity and hysteresis (15 dual‐sensor vesical and urethral and 30 single‐sensor abdominal), pressure drift over 2 h (115 single‐sensor), and frequency response (20 single‐sensor). Data are presented as mean ± standard deviation.

Results

ACC showed linearity of 0.99 ± 0.01, 0.99 ± 0.01, and 1.01 ± 0.01; and hysteresis of 0.57 ± 0.3%, 0.76 ± 0.48%, and 1 ± 0.89% for the abdominal, vesical, and urethral sensors, respectively. A pressure drift of 2.2 ± 1.4% at 1 h and 4.4 ± 2.5% at 2 h were observed when compared to baseline pressures. The catheters did not show any amplification factor during the sweep from 1 to 30 Hz, and recorded signals up to 5 Hz attenuating higher frequency signals.

Conclusions

In this study the T‐DOC® ACC showed a linear performance with minimal hysteresis associated with acceptable pressure drift, and adequate frequency response to capture clinically relevant pressures. The accurate results observed in this study suggest that these catheters are technically suitable to be used as a measuring instrument for UDS.