Jonathan J. Noble

Lower limb muscle volumes in bilateral spastic cerebral palsy.

AIM Muscle weakness is a feature of individuals with spastic cerebral palsy (SCP) but there are few reports in the literature of muscle volume in this group. This study compares muscle volumes in adolescents and young adults with SCP with those of their typically developing (TD) peers. DESIGN Measurements of the volumes of nine major lower limb muscles in 19 independently ambulant subjects with SCP (mean age 14.2 years (sd 2.7), 11 male, GMFCS I (n=5); GMFCS II (n=14)), 19 TD subjects (mean age 16.5 years (sd 3.0), 11 male) were made using magnetic resonance imaging. RESULTS Lower limb muscles were smaller in the SCP group (p≤0.023 in all muscles) than the TD group with the exception of the vastii (lateralis+intermedius; p=0.868) and gluteus maximus (p=0.056). Average muscle volume deficit was 27.9%. Muscle volume deficits were significantly greater for distal muscles than proximal muscles (p<0.001). CONCLUSIONS Reduced muscle size in adolescence and the natural history of sarcopenia in adulthood may contribute to the early loss of mobility of adults with SCP.

In vitro and in vivo comparison of two-, three- and four-point Dixon techniques for clinical intramuscular fat quantification at 3 T.

OBJECTIVE To compare Dixon-based MRI techniques for intramuscular fat quantification at 3 T with MR spectroscopy (MRS) in vitro and in vivo. METHODS In vitro, two- three- and four-point mDixon (Philips Medical Systems, Best, Netherlands) sequences with 10°, 20° and 30° flip angles were acquired from seven test phantoms with sunflower oil-water percentages of 0-60% sunflower oil and calculated fat-water ratios compared with MRS. In vivo, two- three- and four-point mDixon sequences with 10° flip angle were acquired and compared with MRS in the vastus medialis of nine healthy volunteers (aged 30.6 ± 5.3 years; body mass index 22.2 ± 2.6). RESULTS In vitro, all mDixon sequences correlated significantly with MRS (r > 0.97, p < 0.002). The measured phantom percentage fat depended significantly on the flip angle (p ≤ 0.001) and mDixon sequence (p = 0.005). Flip angle was the dominant factor influencing agreement with MRS. Increasing the flip angle significantly increased the overestimation of the mDixon sequences compared with MRS. In vivo, a significant difference was observed between sequences (p < 0.001), with all mDixon sequences overestimating the intramuscular fat content of the vastus medialis muscle compared with MRS. Two-point mDixon agreed best with MRS and had comparable variability with the other mDixon sequences. CONCLUSION This study demonstrates that mDixon techniques have good linearity and low variability for use in intramuscular fat quantification. To avoid significant fat overestimation with short repetition time, a low flip angle should be used to reduce T1 effects. ADVANCES IN KNOWLEDGE This is the first study investigating the optimal mDixon parameters for intramuscular fat quantification compared with MRS in vivo and in vitro.

Bone strength is related to muscle volume in ambulant individuals with bilateral spastic cerebral palsy

OBJECTIVE The aim of this study is to investigate how bone strength in the distal femur and proximal tibia are related to local muscle volume in ambulant individuals with bilateral spastic cerebral palsy (CP). METHODS Twenty-seven participants with CP (mean age: 14.6±2.9years; Gross Motor Function Classification System (GMFCS) levels I-III) and twenty-two typically developing (TD) peers (mean age: 16.7±3.3years) took part in this study. Periosteal and medullary diameter in the distal femur and cortical bone cross-sectional area (CSA) and thickness (CT) in the distal femur and proximal tibia were measured along with nine lower limb muscle volumes using MRI. Additionally, the polar section modulus (Zp) and buckling ratio (BR) were calculated to estimate bone bending strength and compressional bone stability respectively in the distal femur. The relationships of all measured parameters with muscle volume, height, age, body mass, gender, and subject group were investigated using a generalized linear model (GZLM). RESULTS In the distal femur, Zp was significantly positively related to thigh muscle volume (p=0.007), and height (p=0.026) but not significantly related to subject group (p=0.076) or body mass (p=0.098). BR was not significantly different between groups and was not related to any of the variables tested. Cortical bone CSA was significantly lower in the CP group at both the distal femur (p=0.002) and proximal tibia (p=0.009). It was also positively associated with thigh muscle volume (p<0.001) at the distal femur, and with subject height (p=0.005) at the proximal tibia. CONCLUSIONS Bending and compressional strength of the femur, estimated from Zp and cortical bone CSA respectively, is associated with reduced thigh muscle volume. Increasing muscle volume by strength training may have a positive effect on bone mechanics in individuals with CP.

Selective motor control correlates with gait abnormality in children with cerebral palsy

Children with bilateral cerebral palsy (CP) commonly have limited selective motor control (SMC). This affects their ability to complete functional tasks. The impact of impaired SMC on walking has yet to be fully understood. Measures of SMC have been shown to correlate with specific characteristics of gait, however the impact of SMC on overall gait pattern has not been reported. This study explored SMC data collected as part of routine gait analysis in children with bilateral CP. As part of their clinical assessment, SMC was measured with the Selective Control Assessment of the Lower Extremities (SCALE) in 194 patients with bilateral cerebral palsy attending for clinical gait analysis at a single centre. Their summed SCALE score was compared with overall gait impairment, as measured by Gait Profile Score (GPS). Score on SCALE showed a significant negative correlation with GPS (rs=-0.603, p<0.001). Cerebral injuries in CP result in damage to the motor tracts responsible for SMC. Our results indicate that this damage is also associated with changes in the development of walking pattern in children with CP.

Selective motor control and gross motor function in bilateral spastic cerebral palsy

To investigate the relationship between selective motor control (SMC), muscle volume, and spasticity with gross motor function in adolescents and young adults with bilateral spastic cerebral palsy (CP).

Lower limb muscle volume estimation from maximum cross-sectional area and muscle length in cerebral palsy and typically developing individuals

Background: Deficits in muscle volume may be a significant contributor to physical disability in young people with cerebral palsy. However, 3D measurements of muscle volume using MRI or 3D ultrasound may be difficult to make routinely in the clinic. We wished to establish whether accurate estimates of muscle volume could be made from a combination of anatomical cross‐sectional area and length measurements in samples of typically developing young people and young people with bilateral cerebral palsy. Methods: Lower limb MRI scans were obtained from the lower limbs of 21 individuals with cerebral palsy (14.7 ± 3 years, 17 male) and 23 typically developing individuals (16.8 ± 3.3 years, 16 male). The volume, length and anatomical cross‐sectional area were estimated from six muscles of the left lower limb. Findings: Analysis of Covariance demonstrated that the relationship between the length*cross‐sectional area and volume was not significantly different depending on the subject group. Linear regression analysis demonstrated that the product of anatomical cross‐sectional area and length bore a strong and significant relationship to the measured muscle volume (R2 values between 0.955 and 0.988) with low standard error of the estimates of 4.8 to 8.9%. Interpretation: This study demonstrates that muscle volume may be estimated accurately in typically developing individuals and individuals with cerebral palsy by a combination of anatomical cross‐sectional area and muscle length. 2D ultrasound may be a convenient method of making these measurements routinely in the clinic. HighlightsMuscle volume can be estimated by muscle length and maximal cross‐sectional area.The relationship between these variables is not dependent on subject group.Demonstrates the potential of utilizing quick 2D measurements to estimate volumeSuggests volume may be estimated utilizing clinically‐feasible 2D ultrasound

A practical clinical kinematic model for the upper limbs

A novel clinically practical upper limb model is introduced that has been developed through clinical use in children and adults with neurological conditions to guide surgery to the elbow and wrist. This model has a minimal marker set, minimal virtual markers, and no functional joint centres to minimise the demands on the patient and duration of data collection. The model calculates forearm supination independently from the humerus segment, eliminating any errors introduced by poor modelling of the shoulder joint centre. Supination is calculated by defining the forearm segment twice, from the distal and proximal ends: first, using the ulna and radial wrist markers as a segment defining line and second using the medial and lateral elbow markers as a segment defining line. This is comparable to the clinical measurement of supination utilising a goniometer and enables a reduced marker set, with only the elbow, wrist, and hand markers to be applied when only the wrist and forearm angles are of interest. A sensitivity analysis of the calculated elbow flexion–extension angles to the position of the glenohumeral joint centre is performed on one healthy female subject, aged 20 years, during elbow flexion and a forward reaching task. A comparison of the supination angles calculated utilising the novel technique compared to the rotation between the humeral and forearm segments is also given. All angles are compared to a published kinematic model that follows the recommendations of the International Society of Biomechanics.

P 110 – Lower limb muscle volume estimation from maximum cross-sectional area and muscle length in cerebral palsy and typically developing individuals

BACKGROUND Deficits in muscle volume may be a significant contributor to physical disability in young people with cerebral palsy. However, 3D measurements of muscle volume using MRI or 3D ultrasound may be difficult to make routinely in the clinic. We wished to establish whether accurate estimates of muscle volume could be made from a combination of anatomical cross-sectional area and length measurements in samples of typically developing young people and young people with bilateral cerebral palsy. METHODS Lower limb MRI scans were obtained from the lower limbs of 21 individuals with cerebral palsy(14.7 ± 3 years, 17 male) and 23 typically developing individuals (16.8 ± 3.3 years, 16 male). The volume, length and anatomical cross-sectional area were estimated from six muscles of the left lower limb. FINDINGS Analysis of Covariance demonstrated that the relationship between the length*cross-sectional area and volume was not significantly different depending on the subject group. Linear regression analysis demonstrated that the product of anatomical cross-sectional area and length bore a strong and significant relationship to the measured muscle volume (R2 values between 0.955 and 0.988) with low standard error of the estimates of 4.8 to 8.9%. INTERPRETATION This study demonstrates that muscle volume may be estimated accurately in typically developing individuals and individuals with cerebral palsy by a combination of anatomical cross-sectional area and muscle length. 2D ultrasound may be a convenient method of making these measurements routinely in the clinic.

Estimating muscle volume from two‐dimensional measurements: a promising method for assessment

Lower limb muscle volume is greatly reduced in individuals with cerebral palsy (CP). Muscle volume is directly related to the force generating capabilities of muscle and will therefore have an impact on an individual’s functional ability. Despite this, the interaction between intervention and muscle volume is poorly understood. Estimates of muscle volume from three-dimensional (3D) imaging techniques such as magnetic resonance imaging (MRI) or 3D ultrasound are costly, require specialist expertise, and take a long time to perform and process. These limitations may explain, in part, why the measurement of muscle volume has not yet transitioned into clinical practice or been included in large-scale clinical trials. To date, research studies of muscle volume in CP have low numbers of participants or are restricted to one or two muscles. Therefore, for larger research studies to be performed, and for muscle volume to become a routine clinical assessment, a new clinically feasible approach for measuring muscle volume is required. The work of Schless et al. suggests that muscle volume may be estimated from measurements made using a standard two-dimensional (2D) ultrasound scanner. Schless et al. reported a strong linear relationship between muscle volume and the product of muscle length and cross-sectional area in the medial gastrocnemius. This strong relationship has implications for the clinical feasibility of assessing muscle volume in this group. However, the work described is not a complete test of the utility and accuracy of estimating muscle volume by 2D ultrasound. The measurements of muscle length and anatomical cross-sectional area were made using a 3D ultrasound system. It cannot be assumed that by using a 2D method in isolation the relationship would be as strong as Schless et al. report. The authors identified the muscle insertion and musculo-tendinous junction from within a reconstructed 3D data set postdata collection. This has the advantage of allowing longitudinal reconstructions of the whole muscle length to be viewed, which greatly aids in identifying muscle end points. In practice, a 2D assessment would involve measurement of muscle length by tape measure guided by live 2D ultrasound imaging, and the identification of an optimal ultrasound image from which to estimate the anatomical cross-sectional area. Variation in probe location, orientation, and surface pressure are all likely to increase variability in the data set. Therefore, this 2D technique for estimating muscle volume is likely to have lower repeatability compared to MRI and 3D ultrasound techniques. However, accepting a suboptimal 2D technique that is simple, realistic, and feasible may be the way forward to enable large scale research studies to be performed and ultimately for a routine clinical assessment technique to be developed. The authors use an unconventional definition of the proximal origin of the medial gastrocnemius at the tibia, rather than utilising the real anatomical origin at the formal condyle. Although this limitation is unlikely to have a significant impact on the strength of the relationship between muscle volume and the product of muscle length and cross-sectional area, the regression equation developed by the authors is only valid for measurements made following the same definition. Furthermore, the findings of Schless et al. may not be generalisable to other muscles. Further investigation of the reliability of muscle volume estimated by the product of muscle length and cross-sectional area utilising a 2D data collection technique across different muscles is required. Despite these limitations, the findings of Schless et al. represent a significant stepping-stone towards the validation of a simple, low cost, clinically feasible method for estimating muscle volume that could potentially become a valuable clinic tool for assessing treatment outcome and aiding treatment selection in the future.

A device for testing the dynamic performance of in situ force plates

Force plates are often incorporated into motion capture systems for the calculation of joint kinetic variables and other data. This project aimed to create a system that could be used to check the dynamic performance of force plate in situ. The proposed solution involved the design and development of an eccentrically loaded wheel mounted on a weighted frame. The frame was designed to hold a wheel mounted in two orthogonal positions. The wheel was placed on the force plate and spun. A VICON™ motion analysis system captured the positional data of the markers placed around the rim of the wheel which was used to create a simulated force profile, and the force profile was dependent on spin speed. The root mean square error between the simulated force profile and the force plate measurement was calculated. For nine trials conducted, the root mean square error between the two simultaneous measures of force was calculated. The difference between the force profiles in the x- and y-directions is approximately 2%. The difference in the z-direction was under 0.5%. The eccentrically loaded wheel produced a predictable centripetal force in the plane of the wheel which varied in direction as the wheel was spun and magnitude dependent on the spin speed. There are three important advantages to the eccentrically loaded wheel: (1) it does not rely on force measurements made from other devices, (2) the tests require only 15 min to complete per force plate and (3) the forces exerted on the plate are similar to those of paediatric gait.