Li Khim Kwah

In vivo passive mechanical behaviour of muscle fascicles and tendons in human gastrocnemius muscle-tendon units

Non‐Technical Summary  Relaxed skeletal muscles behave like springs that resist joint motion. There have been few in vivo studies of the spring‐like properties of relaxed muscles. In this study, ultrasound was used to image human calf muscles while muscle length was changed by rotating the ankle of relaxed subjects. The muscles of some subjects buckled at short lengths. At short lengths most muscle fascicles (bundles of muscle cells) are slack. As the muscle is lengthened the slack is progressively taken up, first in some fascicles then in others. The increase in muscle length is due partly to increases in the length of muscle fascicles but most of the increase in muscle length occurs in the tendons.

Reliability and validity of ultrasound measurements of muscle fascicle length and pennation in humans : A systematic review

Ultrasound imaging is widely used to measure architectural features of human skeletal muscles in vivo. We systematically reviewed studies of the reliability and validity of two-dimensional ultrasound measurement of muscle fascicle lengths or pennation angles in human skeletal muscles. A comprehensive search was conducted in June 2011. Thirty-six reliability studies and six validity studies met the inclusion criteria. Data from these studies indicate that ultrasound measurements of muscle fascicle lengths are reliable across a broad range of experimental conditions [intraclass correlation coefficient (ICC) and r values were always > 0.6, and coefficient of variation values were always < 10%]. The reliability of measurements of pennation angles is broadly similar (ICC and r values were always > 0.5 and coefficient of variation values were always < 14%). Data on validity are less extensive and probably less robust, but suggest that measurement of fascicle lengths and pennation angles are accurate (ICC > 0.7) under certain conditions, such as when large limb muscles are imaged in a relaxed state and the limb or joint remains stationary. Future studies on validity should consider ways to test for the validity of two-dimensional ultrasound imaging in contracted or moving muscles and the best method of probe alignment.

Passive Mechanical Properties of Gastrocnemius Muscles of People With Ankle Contracture After Stroke

OBJECTIVE To investigate the mechanisms of contracture after stroke by comparing passive mechanical properties of gastrocnemius muscle-tendon units, muscle fascicles, and tendons in people with ankle contracture after stroke with control participants. DESIGN Cross-sectional study. SETTING Laboratory in a research institution. PARTICIPANTS A convenience sample of people with ankle contracture after stroke (n=20) and able-bodied control subjects (n=30). INTERVENTIONS Not applicable. MAIN OUTCOME MEASURES Stiffness and lengths of gastrocnemius muscle-tendon units, lengths of muscle fascicles, and tendons at specific tensions. RESULTS At a tension of 100N, the gastrocnemius muscle-tendon unit was significantly shorter in participants with stroke (mean, 436mm) than in able-bodied control participants (mean, 444mm; difference, 8mm; 95% confidence interval [CI], 0.2-15mm; P=.04). Muscle fascicles were also shorter in the stroke group (mean, 44mm) than in the control group (mean, 50mm; difference, 6mm; 95% CI, 1-12mm; P=.03). There were no significant differences between groups in the mean stiffness or length of the muscle-tendon units and fascicles at low tension, or in the mean length of the tendons at any tension. CONCLUSIONS People with ankle contracture after stroke have shorter gastrocnemius muscle-tendon units and muscle fascicles than control participants at high tension. This difference is not apparent at low tension.

Half of the adults who present to hospital with stroke develop at least one contracture within six months: an observational study

QUESTIONS What is the incidence of contractures six months after stroke? Can factors measured within four weeks of stroke predict the development of elbow, wrist, and ankle contractures six months later? DESIGN Prospective cohort study. PARTICIPANTS Consecutive sample of 200 adults with stroke admitted to a Sydney hospital. OUTCOME MEASURES Loss of range of motion in major joints of the body was measured using a 4-point ordinal contracture scale. In addition, elbow extension, wrist extension, and ankle dorsiflexion range of motion were measured using torque-controlled procedures. Potential predictors of contracture were age, pre-morbid function, severity of stroke, muscle strength, spasticity, motor function, and pain. Measurements were obtained within four weeks of stroke and at six months after stroke. RESULTS 52% of participants developed at least one contracture. Incidence of contracture varied across joints from 12% to 28%; shoulders and hips were most commonly affected. Muscle strength was a significant predictor of elbow, wrist, and ankle joint range. Prediction models explained only 6% to 20% of variance in elbow, wrist, and ankle joint range. CONCLUSION About half of all patients with stroke develop at least one contracture within six months of stroke. Incidence of contractures across all joints ranged from 12% to 28%. Muscle strength is a significant predictor of elbow, wrist, and ankle contractures but cannot be used to accurately predict contractures in these joints.

Incidence and predictors of contracture after spinal cord injury-a prospective cohort study

Study design:Prospective cohort study.Objectives:To determine incidence of contracture and develop prediction models to identify patients susceptible to contracture after spinal cord injury.Setting:Two Sydney spinal cord injury units.Methods:A total of 92 consecutive patients with acute spinal cord injury were assessed within 35 days of injury and 1 year later. Incidence of contracture at 1 year was measured in all major appendicular joints by categorizing range of motion on a 4-point scale (0—no contracture to 3—severe contracture), and in the wrist, elbow, hip and ankle by measuring range of motion at standardized torque. Multivariate models were developed to predict contracture at 1 year using age, neurological status, spasticity, pain and limb fracture recorded at the time of injury.Results:At 1 year, 66% of participants developed at least one contracture (defined as ⩾1 point deterioration on the 4-point scale). Incidence of contracture at each joint was: shoulder 43%, elbow and forearm 33%, wrist and hand 41%, hip 32%, knee 11% and ankle 40%. Incidence of contracture determined by standardized torque measures of range (defined as loss of ⩾10 degrees) was: elbow 27%, wrist 26%, hip 23% and ankle 25%. Prediction models were statistically significant but lacked sufficient predictive accuracy to be clinically useful (R2⩽31%).Conclusion:The incidence of contracture in major joints 1 year after spinal cord injury ranges from 11–43%. The ankle, wrist and shoulder are most commonly affected. It is difficult to accurately predict those susceptible to contracture soon after injury.

Models containing age and NIHSS predict recovery of ambulation and upper limb function six months after stroke: an observational study

QUESTIONS What is the incidence of recovery of ambulation and upper limb function six months after stroke? Can measures such as age and the National Institutes of Health Stroke Scale (NIHSS) be used to develop models to predict the recovery of ambulation and upper limb function? DESIGN Prospective cohort study. PARTICIPANTS Consecutive sample of 200 people with stroke admitted to a Sydney Hospital. OUTCOME MEASURES Ambulation was measured with item 5 of the Motor Assessment Scale (MAS); patients scoring ≥3 could ambulate independently. Upper limb function was measured with items 7 and 8 of the MAS; patients scoring ≥5 could move a cup across the table and feed themselves with a spoonful of liquid with the hemiplegic arm. RESULTS Of the 114 stroke survivors who were unable to ambulate initially, 80 (70%) achieved independent ambulation at six months. Of the 51 stroke survivors who could not move a cup across the table initially, 21 (41%) achieved the upper limb task at six months. Of the 56 stroke survivors who were unable to feed themselves initially, 25 (45%) could feed themselves at six months. Models containing age and severity of stroke (measured with NIHSS) predicted recovery of ambulation and ability to move a cup across the table, whilst a model containing severity of stroke predicted ability to feed oneself. All prediction models showed good discrimination (AUC 0.73 to 0.84). CONCLUSION More than two-thirds of people after stroke recovered independent ambulation and less than half recovered upper limb function at six months. Models using age and NIHSS can predict independent ambulation and upper limb function but these prediction models now require external validation before use in clinical practice.

Passive mechanical properties of the gastrocnemius after spinal cord injury

In this study we compared passive mechanical properties of gastrocnemius muscle–tendon units, muscle fascicles, and tendons in control subjects and people with ankle contractures after spinal cord injury.

Mechanisms of increased passive compliance of hamstring muscle-tendon units after spinal cord injury

BACKGROUND People with spinal cord injury sometimes develop abnormally compliant hamstring muscle-tendon units. This study investigated whether the increased muscle-tendon compliance is due to a change in the passive properties of the muscle fascicles or tendons, or to muscle tears. METHODS Semimembranosus muscle fascicle lengths were measured from ultrasound images obtained from 15 spinal cord injured subjects and 20 control subjects while the hip was passively flexed with the knee extended. Semimembranosus muscles of spinal cord injured subjects were inspected for tears using ultrasound imaging. FINDINGS The mean (SD) hip angle at 30 Nm was 97 (SD 24) degrees in spinal cord injured subjects and 70 (SD 11) degrees in control subjects, indicating that spinal cord injured subjects had very compliant hamstring muscle-tendon units. The ratio of change in fascicle length to change in muscle-tendon length was not statistically different between spinal cord injured subjects and control subjects: muscle fascicles lengthened by 0.30 (SD 0.24) mm/mm in spinal cord injured subjects and 0.42 (SD 0.29) mm/mm in control subjects. These data were used to show that there was evidence of increased tendon compliance of spinal cord injured subjects compared to control subjects, but no evidence of increased muscle fascicle compliance. No tears were observed in semimembranosus muscles of spinal cord injured subjects. INTERPRETATION The increased hamstring muscle-tendon compliance apparent in some spinal cord injured subjects is due, at least in part, to increased tendon compliance. There was no evidence that the increased muscle-tendon compliance was due to muscle tears.

Prediction of Walking and Arm Recovery after Stroke: A Critical Review

Clinicians often base their predictions of walking and arm recovery on multiple predictors. Multivariate prediction models may assist clinicians to make accurate predictions. Several reviews have been published on the prediction of motor recovery after stroke, but none have critically appraised development and validation studies of models for predicting walking and arm recovery. In this review, we highlight some common methodological limitations of models that have been developed and validated. Notable models include the proportional recovery model and the PREP algorithm. We also identify five other models based on clinical predictors that might be ready for further validation. It has been suggested that neurophysiological and neuroimaging data may be used to predict arm recovery. Current evidence suggests, but does not show conclusively, that the addition of neurophysiological and neuroimaging data to models containing clinical predictors yields clinically important increases in predictive accuracy.