J.E. Robb

Electrophysiological Responses of Human Bone Cells to Mechanical Stimulation: Evidence for Specific Integrin Function in Mechanotransduction†

Bone cells respond to mechanical stimuli, but the transduction mechanisms responsible are not fully understood. Integrins, a family of heterodimeric transmembrane glycoproteins, which link components of the extracellular matrix with the actin cytoskeleton, have been implicated as mechanoreceptors. We have assessed the roles of integrins in the transduction of cyclical mechanical stimuli to human bone cells (HBCs), which results in changes in membrane potential. HBC showed membrane depolarization following 0.104 Hz mechanical stimulation and membrane hyperpolarization following stimulation at 0.33 Hz. The membrane depolarization response involved tetrodotoxin‐sensitive sodium channels and could be inhibited by antibodies against αV, β1, and β5 integrins. In contrast, the hyperpolarization response was inhibited by gadolinium and antibodies to the integrin‐associated protein (CD47), α5 and β1 integrin. Both responses could be abrogated by Arg‐Gly‐Asp (RGD)‐containing peptides, inhibition of tyrosine kinase activity, and disruption of the cytoskeleton. These results demonstrate differential electrophysiological responses of HBC to different frequencies of mechanical strain. Furthermore, they suggest that integrins act as HBC mechanoreceptors with distinct signaling pathways being activated by different frequencies of mechanical stimuli.

Edinburgh visual gait score for use in cerebral palsy

Complex gait analysis systems are not generally available worldwide, and no simple system of assessing gait by observation has been validated specifically for use in patients with cerebral palsy. The authors have developed a visual gait analysis score for use in cerebral palsy. Videotaped sequences of patients were recorded before and after surgery as part of a three-dimensional gait study using a Vicon (Oxford, U.K.) gait analysis system. The score demonstrated good intraobserver and interobserver reliability. The numeric values of the score elements correlated well with the measurements obtained from instrumented gait analysis for the same patients, and the score was able to detect postoperative change.

Kinematic and kinetic gait characteristics of normal children walking at a range of clinically relevant speeds.

Kinematic and kinetic data were obtained from 36 normal children who walked at five different clinically relevant speeds, which were mostly slower than normal speed. Speed groups were normalized for body height. Speed significantly affected most of the stride parameters, joint angles, joint moments, and the ground reaction force in all three planes of motion. The effects of speed were not always the same over the whole range of speeds studied. The clinical relevance of these findings is that when comparing pathologic gait characteristics with those of normal children, these should be derived from the same walking speed. This may help to differentiate between effects caused by speed and underlying pathology.

Gait analysis alters decision-making in cerebral palsy.

This study was designed to assess the impact of gait analysis on the treatment of patients with cerebral palsy. One hundred two ambulant patients with cerebral palsy were assessed clinically and with gait analysis. Separate treatment proposals for each patient were recorded after clinical examination and after gait analysis. The results of the two methods of assessment were compared. After clinical assessment, 71 of the 102 patients evaluated were recommended for a surgical procedure and 31 for nonoperative treatment. After gait analysis, the indications for treatment were confirmed in 91 cases (89%). Clinical assessment by the same orthopedic surgeon was in close agreement with gait analysis in identifying an indication for surgery. There was less agreement in the type or level of operation recommended. Gait analysis altered the decision in 106 of 267 operations (40%). There was good agreement for bone surgery, suggesting that clinical evaluation of torsional problems was fairly reliable. The poorer agreement seen for soft tissue operations probably reflects the difficulties in assessing tone-related problems in these patients clinically. This study confirms the value of gait analysis for decision-making in cerebral palsy.

Sagittal joint kinematics, moments, and powers are predominantly characterized by speed of progression, not age, in normal children.

Twenty-six healthy 7-year-old children were enrolled in a 5-year longitudinal study to examine the importance of age and speed in the characterization of sagittal joint angles, moments, and powers. In 740 gait trials, children walking at self-selected speeds were examined on the basis of age and normalized speed [speed/(height ×g)1/2]. The kinematics and kinetics in these children were characterized predominantly by normalized speed of progression and not age. The clinical relevance of these findings is that normalized speed of walking, rather than age, should be considered when comparing normal with pathologic gait.

Management of completely displaced metaphyseal fractures of the distal radius in children: A PROSPECTIVE, RANDOMISED CONTROLLED TRIAL

In a prospective, randomised controlled trial, 68 children who had a completely displaced metaphyseal fracture of the distal radius were treated either by manipulation (MUA) and application of an above-elbow cast alone or by the additional insertion of a percutaneous Kirschner (K-) wire. Full radiological follow-up to union was obtained in 65 children and 56 returned for clinical evaluation three months after injury. Maintenance of reduction was significantly better in the K-wire group and fewer follow-up radiographs were required. There was no significant difference in the clinical outcome measured three months after injury. Seven of 33 patients in the MUA group had to undergo a second procedure because of an unacceptable position compared with none of the 35 in the K-wire group (chi-squared test, p < 0.01). One patient in the K-wire group required exploration for recovery of a migrated wire. We conclude that the use of a percutaneous K-wire to augment the reduction of the fracture in children who have a completely displaced metaphyseal fracture of the distal radius is a safe and reliable way of maintaining alignment of the fracture.

Normalisation of gait data in children

The comparative effect of semi-dimensional (SD) and non-dimensional (ND) normalisation on the results of a longitudinal study of gait in 5-12-year old children was investigated. The use of both height and leg length in the normalisation was examined. Only ND analysis could be used to identify subjects with the same accelerations. ND analysis of the childrens gait indicated that there was little change in the combination of step length and cadence used to achieve a particular velocity between 5 and 12. The first peak and mid-stance trough values of the vertical component of ground reaction force did not change with age. We recommend the use of ND normalisation rather that SD to allow comparisons between individuals of differing size and mass.

Delay increases the need for open reduction of type-III supracondylar fractures of the humerus

Recent reports have suggested that a delay in the management of type-III supracondylar fractures of the humerus does not affect the outcome. In this retrospective study we examined whether the timing of surgery affected peri-operative complications, or the need for open reduction. There were 171 children with a closed type-III supracondylar fracture of the humerus and no vascular compromise in our study. They were divided into two groups: those treated less than eight hours from presentation to the Accident and Emergency Department (126 children), and those treated more than eight hours from presentation (45 children). There were no differences in the rate of complications between the groups, but children waiting more than eight hours for reduction were more likely to undergo an open reduction (33.3% vs 11.2%, p < 0.05) and there was a weak correlation (p = 0.062) between delay in surgery and length of operating time. Consequently, we would still recommend treating these injuries at the earliest opportunity.

Gait patterns in children with hemiplegic spastic cerebral palsy.

Twenty-six nonoperated spastic hemiplegic children underwent three-dimensional kinetic gait analysis. We identified five patterns based on sagittal plane kinetics. Group I had a minimal gait disturbance, a drop foot pattern, and normal kinetics, Group II had a flexed knee but normal hip extension, Group III a flexed knee and hip, Group IV knee hyperextension and tibial arrest, and Group V knee hyperextension and persistent ankle dorsiflexion. We concluded that Group I had weak anterior tibial muscles, and in stance Group II a functionally tight gastrocnemius, Group III a functionally tight gastrocnemius and hip flexors, and Group IV a functionally tight soleus, and in Group V the patients generated an abnormally large fore-aft shear force and the gastrocnemius and soleus were not tight. Kinetics help in the understanding of gait aberrations in spastic hemiplegia.

Normalized speed, not age, characterizes ground reaction force patterns in 5-to 12-year-old children walking at self-selected speeds.

Twenty-six healthy 5-year-old children were enrolled in a 7-year longitudinal study to examine the importance of age and speed in the characterization of ground reaction forces. One thousand forty gait trials of children walking at self-selected speeds were examined on the basis of age and normalized speed [speed/(height ×g)½]. Results, presented as discrete peak and trough values and as continuous trace plots over the stance phase, indicated that there was little change in ground reaction forces with age, but there were significant changes in vertical force and anterior-posterior force values with normalized speed. The ground reaction force patterns in these children were characterized predominantly by normalized speed of progression and not age. The clinical relevance of these findings is that normalized speed of walking, rather than age, should be considered when comparing normal with pathological gait.