Sensorimotor function as a predictor of chronic ankle instability

Background

Recurrent ankle injury occurs in 70% of individuals experiencing a lateral ankle sprain. The cause of this high level of recurrence is currently unknown. Researchers have begun to investigate sensorimotor deficits as one possible cause with inconclusive and often conflicting results. The purpose of this study was to further the understanding of the role of sensorimotor deficits in the chronically unstable ankle by establishing which specific measures best distinguish between chronically unstable and healthy ankles.

Methods

Twenty-two participants with chronic ankle instability and 21 healthy matched controls volunteered. Twenty-five variables were measured within four sensorimotor constructs: joint kinesthesia (isokinetic dynamometer), static balance (force plate), dynamic balance (Star Excursion Balance Test) and motoneuron pool excitability (electromyography).

Findings

The above variables were evaluated using a discriminant function analysis [Wilks’ Λ = 0.536 χ²(7, N = 43) = 22.118, P = 0.002; canonical correlation = 0.681]. The variables found to be significant were then used to assess group discrimination. This study revealed that seven separate variables from the static balance (anterior/posterior and medial/lateral displacement and velocity) and motoneuron pool excitability constructs (single-legged recurrent inhibition and single- and double-legged paired reflex depression) accurately classified over 86% of participants with unstable ankles.

Interpretation

These results suggest that a multivariate approach may be necessary to understand the role of sensorimotor function in chronic ankle instability, and to the development of appropriate rehabilitation and prevention programs. Out of the four overall constructs, only two were needed to accurately classify the participants into two groups. This indicates that static balance and motoneuron pool excitability may be more clinically important in treatment and rehabilitation of chronic ankle instability than functional balance or joint kinesthesia.     

Evaluation of static and dynamic postural stability in established rheumatoid arthritis: Exploratory study

Background

It has been proposed that people with rheumatoid arthritis experience difficulties in postural control and activities of daily living such as walking. The aim of the study is to evaluate postural stability in rheumatoid arthritis patients.

Method

A convenience sample of 19 rheumatoid arthritis patients (mean duration 13.1 ± 9.2 years) were aged matched with a non-rheumatoid group (n = 21). Postural stability was measured using a force plate for anterior–posterior and mediolateral centre of pressure excursion for 30 s with eyes closed and open. Patients also performed three walks at a self-selected speed and mean temporal–spatial parameters were recorded.

Findings

Significant differences were observed between the groups in anterior–posterior centre of pressure excursion during the eyes open task and the eyes closed task (P < 0.05). No significant differences were found in the mediolateral centre of pressure excursion during either condition (P > 0.05). The rheumatoid group displayed a significantly slower mean walking velocity, double support, cadence and cycle time than the non-rheumatoid group (P < 0.05).

Interpretation

The results from this study showed that rheumatoid arthritis patients displayed a significantly larger centre of pressure excursion in the anterior–posterior direction during quiet standing, when compared to a non-rheumatoid arthritis control group suggesting that postural control mechanisms such as ankle strategies are impeded by the rheumatoid process.     

Nonlinear analysis of sitting postural sway indicates developmental delay in infants

Background

Upright sitting is one of the first developmental motor milestones achieved by infants, and sitting postural sway provides a window into the developing motor control system. A variety of posture sway measures can be used, but the optimal measures for infant development have not been identified.

Methods

We have collected sitting postural sway data from two groups of infants, one with typical development (n = 33), and one with delayed development and either diagnosed with or at risk for cerebral palsy (n = 26), when the infants had developed to the point where they could just maintain sitting for about 10 s. Postural sway data was collected while infants were sitting on a force platform, and the center of pressure was analyzed using both linear and nonlinear measures.

Findings

Our results showed that a nonlinear measure, the largest Lyapunov exponent, was the only parameter of postural sway that revealed significant differences between infants with typical versus delayed development. The largest Lyapunov exponent was found to be higher for typically developing infants, indicating less repeated patterning in their movement coordination.

Interpretations

A nonlinear measure such as largest Lyapunov exponent may be useful as an identifier of pathology and as a yardstick for the success of therapeutic interventions.     

Postural stability and ankle sprain history in athletes compared to uninjured controls

Background

Diminished postural stability is a risk factor for ankle sprain occurrence and ankle sprains result in impaired postural stability. To date, ankle sprain history has not been taken into account as a determinant of postural stability, while it could possibly specify subgroups of interest.

Methods

Postural stability was compared between 18 field hockey athletes who had recovered from an ankle sprain (mean (SD); 3.6 (1.5) months post-injury), and 16 uninjured controls. Force plate and kinematics parameters were calculated during single-leg standing: mean center of pressure speed, mean absolute horizontal ground reaction force, mean absolute ankle angular velocity, and mean absolute hip angular velocity. Additionally, cluster analysis was applied to the ‘injured’ participants, and the cluster with diminished postural stability was compared to the other participants with respect to ankle sprain history.

Findings

MANCOVA showed no significant difference between groups in postural stability (P = 0.68). A self-reported history of an (partial) ankle ligament rupture was typically present in the cluster with diminished postural stability. Subsequently, a ‘preceding rupture’ was added as a factor in the MANCOVA, which showed a significant association between diminished postural stability and a ‘preceding rupture’ (P = 0.01), for all four individual parameters (P: 0.001–0.029; Cohen's d: 0.96–2.23).

Interpretation

Diminished postural stability is not apparent in all previously injured athletes. However, our analysis suggests that an (mild) ankle sprain with a preceding severe ankle sprain is associated with impaired balance ability. Therefore, sensorimotor training may be emphasized in this particular group and caution is warranted in return to play decisions.     

The effects of sandals on postural stability in patients with rheumatoid arthritis: An exploratory study

Background

Rheumatoid arthritis results in postural instability, pain and functional limitations. As rheumatoid arthritis progresses, localised forefoot deformities such as hallux valgus and clawing of the lesser toes occur, leading to a high proportion of people with rheumatoid arthritis wearing sandals. Sandals may affect postural stability due to poor motion control. The aim was to assess two different open-toe sandals on postural stability in people with rheumatoid arthritis.

Methods

Twenty women with rheumatoid arthritis were assessed in quiet standing under four conditions: (1) open-back sandal; (2) closed-back sandal; (3) own footwear and (4) bare feet. Postural stability was assessed as postural sway in the anterior-posterior and medial-lateral directions, with eyes open and eyes closed, using a pressure mat. Repeated measures analysis of variance tested the interaction effect of the footwear and eye conditions on anterior-posterior and medial-lateral sway.

Findings

In eyes-open, there was no significant difference in anterior–posterior sway (P = .169) and medial-lateral sway (P = .325) for footwear conditions. In eyes-closed testing, compared with barefoot conditions, increased anterior–posterior sway was observed with participants' footwear (P < .0001), the open-back sandal (P = .005), and the closed-back sandal (P = .017). With eyes closed, increased anterior–posterior sway was also observed with the participants' footwear compared with the closed-back sandal (P = .041). Increased medial-lateral sway was observed with the closed-back sandal compared with bare feet (P = .014).

Interpretation

Sandals may be detrimental to older women with well-established rheumatoid arthritis when eyes are closed. Further investigation is needed to evaluate the effect of sandals on dynamic tasks.     

Voluntary sway and rapid orthogonal transitions of voluntary sway in young adults,and low and high fall-risk older adults

Background

Falls amongst older people have been linked to reduced postural stability and slowed movement responses. The objective of this study was to examine differences in postural stability and the speed of response between young adults, low fall-risk older adults, and high fall-risk older adults during voluntary postural sway movements.

Methods

Twenty-five young adults (25 ± 4 years), and 32 low fall-risk (74 ± 5 years), and 16 high fall-risk (79 ± 7 years) older adults performed voluntary sway and rapid orthogonal transitions of voluntary sway between the anterior–posterior and medial–lateral directions. Measures included reaction and movement time and the amplitudes of the centre of pressure, centre of mass, and the separation distance between the centre of pressure and centre of mass.

Findings

Both fall-risk groups compared to the young had slower reaction and movement time, greater centre of pressure and/or centre of mass amplitude in the orthogonal (non-target) direction during voluntary sway, and reduced anterior–posterior and medial–lateral separation between the centre of pressure and centre of mass during voluntary sway and orthogonal transitions. High compared to low fall-risk individuals had slower reaction and movement time, increased non-target centre of mass amplitude during voluntary sway, and reduced medial–lateral centre of pressure and centre of mass separation during voluntary sway and orthogonal transitions.

Interpretation

Age-related deterioration of postural control resulted in slower reactive responses and reduced control of the direction of body movement during voluntary sway and orthogonal transitions. Slower postural reaction and movement time and reduced medial–lateral control of the centre of mass during voluntary sway movements are associated with increased fall-risk in community-living older people.     

Experimental calf muscle pain attenuates the postural stability during quiet stance and perturbation

Background

The purpose of this study was to evaluate how acute pain changes the postural control and stability during quiet standing and after unexpected perturbations.

Methods

Nine subjects stood as quiet as possible on a movable force platform that recorded the centre of pressure position and provided unexpected floor perturbations, before, during and after experimental calf muscle pain. Bilateral surface electromyography from the tibialis anterior and medial gastrocnemius muscles was recorded. The foot pressure distributions were measured using pressure insoles. Intramuscular injections of hypertonic saline were administrated (right leg) to induce acute pain in the tibialis anterior and/or medial gastrocnemius muscles, and an isotonic injection was used as control.

Findings

Simultaneous pain in tibialis anterior and medial gastrocnemius altered the postural control. During quiet standing: higher medial-lateral centre of pressure speed and increased total sway displacement (P < 0.05), weight moved to the non-painful side, (P < 0.05) and plantar centre of pressure of the left foot was shifted towards the heel’s direction (P < 0.05). During forward perturbation: higher mean displacement in the medial-lateral direction (P < 0.05). After the perturbation: larger sway area (P < 0.05). Pain only in the medial gastrocnemius muscle increased medial-lateral centre of pressure speed (P < 0.05) during the quiet standing. Pain only in the tibialis anterior muscle increased peak pressure on the contralateral foot (P < 0.05).

Interpretation

These findings suggest that large acute painful areas on the calf muscles impair the postural control and potentially increase the risk factors for falls. Further strategies aiming to reduce pain in patients may lead to improvement in balance.     

Dynamic joint stiffness and co-contraction in subjects after total knee arthroplasty

Background

Although total knee arthroplasty reduces pain and improves function, patients continue to walk with asymmetrical movement patterns, that may affect muscle activation and joint loading patterns. The purpose of this study was to evaluate the specific biomechanical abnormalities that persist after total knee arthroplasty and examine the neuromuscular mechanisms that may contribute to these asymmetries.

Methods

Dynamic joint stiffness at the hip, knee and ankle, as well as co-contraction at the knee and ankle, were compared between the operated and non-operated limbs of 32 subjects who underwent total knee arthroplasty and 21 subjects without lower extremity impairment.

Findings

Subjects after total knee arthroplasty demonstrated higher dynamic joint stiffness in the operated knee compared to the non-operated knee (0.056 (0.023) Nm/kg/m/deg vs. 0.043 (0.016) Nm/kg/m/deg, P = 0.003) and the knees from a control group without lower extremity pathology (controls: 0.042 (0.015) Nm/kg/m/deg, P = 0.017). No differences were found between limbs or groups for dynamic joint stiffness at the hip or ankle. There was no relationship between dynamic joint stiffness at the knee and ankle and the amount of co-contraction between antagonistic muscles at those joints.

Interpretation

Patients after total knee arthroplasty walk with less knee joint excursion and greater knee stiffness, although no differences were found between groups for stiffness at the hip or ankle. Mechanisms other than co-contraction are likely the underlying cause of the altered knee mechanics. These findings are clinically relevant because the goal should be to create interventions to reduce these abnormalities and increase function.     

Gastrocnemius tightness on joint angle and work of lower extremity during gait

Background

Muscular tightness is a common clinical musculoskeletal disorder and is regarded as a predisposing factor for muscle injuries. In this study, a two-way mixed design ANOVA was applied to investigate the effects of the gastrocnemius tightness on the joint angle and joint work during walking.

Methods

Twenty-two patients with muscular tightness of gastrocnemius muscle (<12° of ankle dorsiflexion with knee extended) and 22 age- and gender-matched subjects with normal gastrocnemius flexibility (>15° of ankle dorsiflexion with knee extended) participated in this study. The joint angle and work at hip, knee, and ankle joints during the stance phase were analyzed at two preset cadences of 100 steps/min and 140 steps/min.

Findings

Significantly greater flexion angles at hip (P = 0.025) and knee (P = 0.001) were found in the tightness group at the time of maximal ankle dorsiflexion. Significantly less work generation at knee (P = 0.034) and greater work absorption at ankle (P = 0.024) were detected in the tightness group.

Interpretation

The subjects with gastrocnemius tightness revealed a compensatory gait pattern, which included the changes in the joint angles and associated work productions. The potential disturbance of the knee control and strain injuries of plantar flexors might be crucial in the clinical considerations for subjects with gastrocnemius tightness.     

Muscle and fascicle excursion in children with cerebral palsy

Background

Fascicle length and fascicle excursion measurements in children with cerebral palsy have yielded inconsistent results. The purpose of this study was to measure in vivo passive fascicle lengths and fascicle excursions in the Medial Gastrocnemius muscle of children with cerebral palsy and typically developing controls.

Methods

We measured 11 children with spastic cerebral palsy and 14 controls between the ages of 9 and 16 years. Ultrasound imaging was used to measure fascicle lengths while a dynamometer moved the ankle joint through the range of motion. A common range of motion for all subjects was used for analysis of fascicle excursion.

Findings

Fascicle lengths in children with cerebral palsy were 43% smaller than those for control subjects throughout the range of motion. The relative fascicle excursion was 92% greater on average for the cerebral palsy compared to the control group children. The muscle excursion for the control group children was greater than for the cerebral palsy group children.

Interpretation

Since the fascicles in children with spastic cerebral palsy are shorter, but they go through the same excursion as fascicles in typically developing children, sarcomeres within the medial gastrocnemius muscle must be working over a larger range of sarcomere lengths. Combined with findings of overstretched sarcomeres in spastic muscles reported in the literature, our results suggest that the increased passive forces and the weakness found in spastic muscles may be caused by a decrease in contractile filament overlap as sarcomeres are pulled to extreme lengths in children with cerebral palsy.