Michael H. Schwartz

The gait deviation index : A new comprehensive index of gait pathology

This article describes a new multivariate measure of overall gait pathology called the Gait Deviation Index (GDI). The first step in developing the GDI was to use kinematic data from a large number of walking strides to derive a set of mutually independent joint rotation patterns that efficiently describe gait. These patterns are called gait features. Linear combinations of the first 15 gait features produced a 98% faithful reconstruction of both the data from which they were derived and 1000 validation strides not used in the derivation. The GDI was then defined as a scaled distance between the 15 gait feature scores for a subject and the average of the same 15 gait feature scores for a control group of typically developing (TD) children. Concurrent and face validity data for the GDI are presented through comparisons with the Gillette Gait Index (GGI), Gillette Functional Assessment Questionnaire Walking Scale (FAQ), and topographic classifications within the diagnosis of Cerebral Palsy (CP). The GDI and GGI are strongly correlated (r(2)=0.56). The GDI scales with FAQ level, distinguishes levels from one another, and is normally distributed across FAQ levels six to ten and among TD children. The GDI also scales with respect to clinical involvement based on topographic CP classification in Hemiplegia Types I-IV, Diplegia, Triplegia and Quadriplegia. The GDI offers an alternative to the GGI as a comprehensive quantitative gait pathology index, and can be readily computed using the electronic addendum provided with this article.

An index for quantifying deviations from normal gait

A method is derived to calculate the amount by which a subjects gait deviates from an average normal profile, and to represent this deviation as a single number. The method uses principal component analysis to derive a set of 16 independent variables from 16 selected gait variables. The sum of the square of these 16 independent variables is interpreted as the deviation of the subjects gait from normal. Statistical tests of the methods validity and an initial demonstration of its clinical utility are included. It is found that using this index, increasing clinical involvement corresponds to increasing index score.

The Gait Profile Score and Movement Analysis Profile

The Gait Deviation Index (GDI) has been proposed as an index of overall gait pathology. This study proposes an interpretation of the difference measure upon which the GDI is based, which naturally leads to the definition of a similar index, the Gait Profile Score (GPS). The GPS can be calculated independently of the feature analysis upon which the GDI is based. Understanding what the underlying difference measure represents also suggests that reporting a raw score, as the GPS does, may have advantages over the logarithmic transformation and z-scaling incorporated in the GDI. It also leads to the concept of a Movement Analysis Profile (MAP) to summarise much of the information contained within kinematic data. A validation study on all children attending a paediatric gait analysis service over 3 years (407 children) provides evidence to support the use of the GPS through analysis of its frequency distribution across different Gross Motor Function Classification System (GMFCS) and Gillette Functional Assessment Questionnaire (FAQ) categories, investigation of intra-session variability, and correlation with the square root of GGI. Correlation with GDI confirms the strong relationship between the two measures. The study concludes that GDI and GPS are alternative and closely related measures. The GDI has prior art and is particularly useful in applications arising out of feature analysis such as cluster analysis or subject matching. The GPS will be easier to calculate for new models where a large reference dataset is not available and in association with applications using the MAP.

The effect of walking speed on the gait of typically developing children

Many gait studies include subjects walking well below or above typical self-selected comfortable (free) speed. For this reason, a descriptive study examining the effect of walking speed on gait was conducted. The purpose of the study was to create a single-source, readily accessible repository of comprehensive gait data for a large group of children walking at a wide variety of speeds. Three-dimensional lower extremity joint kinematics, joint kinetics, surface electromyographic (EMG), and spatio-temporal data were collected on 83 typically developing children (ages 4-17) walking at speeds ranging from very slow (>3 standard deviations below mean free speed) to very fast (>3 standard deviations above mean free speed). The resulting data show that speed has a significant influence on many measures of interest, such as kinematic parameters in the sagittal, coronal, and transverse planes. The same was true for kinetic data (ground reaction force, moment, and power), normalized EMG signals, and spatio-temporal parameters. Examples of parameters with linear and various nonlinear speed dependencies are provided. The data from this study, including an extensive electronic addendum, can be used as a reference for both basic biomechanical and clinical gait studies.

Muscle contributions to support and progression over a range of walking speeds

Muscles actuate walking by providing vertical support and forward progression of the mass center. To quantify muscle contributions to vertical support and forward progression (i.e., vertical and fore-aft accelerations of the mass center) over a range of walking speeds, three-dimensional muscle-actuated simulations of gait were generated and analyzed for eight subjects walking overground at very slow, slow, free, and fast speeds. We found that gluteus maximus, gluteus medius, vasti, hamstrings, gastrocnemius, and soleus were the primary contributors to support and progression at all speeds. With the exception of gluteus medius, contributions from these muscles generally increased with walking speed. During very slow and slow walking speeds, vertical support in early stance was primarily provided by a straighter limb, such that skeletal alignment, rather than muscles, provided resistance to gravity. When walking speed increased from slow to free, contributions to support from vasti and soleus increased dramatically. Greater stance-phase knee flexion during free and fast walking speeds caused increased vasti force, which provided support but also slowed progression, while contralateral soleus simultaneously provided increased propulsion. This study provides reference data for muscle contributions to support and progression over a wide range of walking speeds and highlights the importance of walking speed when evaluating muscle function.

Comprehensive treatment of ambulatory children with cerebral palsy: an outcome assessment.

A retrospective study was used to evaluate the outcome of treatment of 135 ambulatory children with cerebral palsy. Diplegic subjects were selected from the existing database at the Gillette Childrens Specialty Healthcare Motion Analysis Laboratory. All subjects had undergone gait analysis before and after intervention, which included orthopaedic surgery, selective dorsal rhizotomy, or both treatments. Outcome was based on gait pathology, gait efficiency, functional walking ability, and higher-level functional skills. Gait pathology was assessed using 16 clinically relevant kinematic parameters. Gait efficiency was assessed with steady-state oxygen consumption. Walking ability and higher-level functional skills were based on patient report surveys. Improvements were seen in all outcome measures. A significant majority of subjects (79%) improved on a predominance of outcome measures; only 7% of subjects worsened. Within the restrictions of this study design, the results indicate that surgical intervention, guided by preoperative gait analysis, is effective and safe for children with cerebral palsy.

Compressive Tibiofemoral Force during Crouch Gait

Crouch gait, a common walking pattern in individuals with cerebral palsy, is characterized by excessive flexion of the hip and knee. Many subjects with crouch gait experience knee pain, perhaps because of elevated muscle forces and joint loading. The goal of this study was to examine how muscle forces and compressive tibiofemoral force change with the increasing knee flexion associated with crouch gait. Muscle forces and tibiofemoral force were estimated for three unimpaired children and nine children with cerebral palsy who walked with varying degrees of knee flexion. We scaled a generic musculoskeletal model to each subject and used the model to estimate muscle forces and compressive tibiofemoral forces during walking. Mild crouch gait (minimum knee flexion 20-35°) produced a peak compressive tibiofemoral force similar to unimpaired walking; however, severe crouch gait (minimum knee flexion>50°) increased the peak force to greater than 6 times body-weight, more than double the load experienced during unimpaired gait. This increase in compressive tibiofemoral force was primarily due to increases in quadriceps force during crouch gait, which increased quadratically with average stance phase knee flexion (i.e., crouch severity). Increased quadriceps force contributes to larger tibiofemoral and patellofemoral loading which may contribute to knee pain in individuals with crouch gait.

Distal Femoral Extension Osteotomy and Patellar Tendon Advancement to Treat Persistent Crouch Gait in Cerebral Palsy

BACKGROUND Hallmarks of a persistent crouched walking pattern exhibited by individuals with cerebral palsy usually include loss of an adequate plantar flexion/knee extension couple, hamstring and/or psoas tightness, or contracture in conjunction with quadriceps insufficiency. Traditional treatment addresses the muscle-tightness component, but not the contracture or the muscle insufficiency. This study was performed to evaluate the effectiveness of distal femoral extension osteotomy and/or patellar tendon advancement in the treatment of crouch gait in patients with cerebral palsy. METHODS A retrospective, nonrandomized, repeated-measures design was used. Individuals with a diagnosis of cerebral palsy were included if they had had (1) a distal femoral extension osteotomy in combination with a distal patellar tendon advancement (thirty-three patients), (2) a distal femoral extension osteotomy without patellar tendon advancement (sixteen), or (3) a distal patellar tendon advancement only (twenty-four). All subjects were evaluated with preoperative and postoperative gait analysis. Gait, radiographic, strength, and functional measures were included in the analysis to assess changes in knee function. RESULTS Seventy-three individuals met the criteria for inclusion. A single side was chosen for the analysis of each subject. Ninety percent of the subjects had additional, concurrent surgery. Improvements were noted in the index assessing the level of gait pathology and in functional variables across all groups, and pain was consistently decreased. All preoperative stress fractures healed. Strength levels were maintained across all groups. The Koshino index of patellar height improved from 1.4 to -2.3 in the group treated with patellar tendon advancement only and from 1.5 to -2.9 in the group treated with both osteotomy and tendon advancement. The range of knee flexion improved an average of 15 degrees to 20 degrees, and stance-phase knee flexion was restored to the typical range (9 degrees to 10 degrees) in the groups that had advancement of the patellar tendon as part of the procedure. Individuals who underwent a distal femoral osteotomy only were still in a crouch (a mean of 31 degrees of knee flexion in midstance) at the final assessment. CONCLUSIONS Inclusion of patellar tendon advancement is necessary to achieve optimal results in the surgical management of a persistent crouch gait exhibited by adolescents and young adults with cerebral palsy. When this procedure is done alone or in combination with a distal femoral extension osteotomy (for the treatment of a knee flexion contracture), knee function in gait can be restored to values within typical limits, with gains in community function.

Crouched postures reduce the capacity of muscles to extend the hip and knee during the single-limb stance phase of gait.

Many children with cerebral palsy walk in a crouch gait that progressively worsens over time, decreasing walking efficiency and leading to joint degeneration. This study examined the effect of crouched postures on the capacity of muscles to extend the hip and knee joints and the joint flexions induced by gravity during the single-limb stance phase of gait. We first characterized representative mild, moderate, and severe crouch gait kinematics based on a large group of subjects with cerebral palsy (N=316). We then used a three-dimensional model of the musculoskeletal system and its associated equations of motion to determine the effect of these crouched gait postures on (1) the capacity of individual muscles to extend the hip and knee joints, which we defined as the angular accelerations of the joints, towards extension, that resulted from applying a 1N muscle force to the model, and (2) the angular acceleration of the joints induced by gravity. Our analysis showed that the capacities of almost all the major hip and knee extensors were markedly reduced in a crouched gait posture, with the exception of the hamstrings muscle group, whose extension capacity was maintained in a crouched posture. Crouch gait also increased the flexion accelerations induced by gravity at the hip and knee throughout single-limb stance. These findings help explain the increased energy requirements and progressive nature of crouch gait in patients with cerebral palsy.

How robust is human gait to muscle weakness

Humans have a remarkable capacity to perform complex movements requiring agility, timing, and strength. Disuse, aging, and disease can lead to a loss of muscle strength, which frequently limits the performance of motor tasks. It is unknown, however, how much weakness can be tolerated before normal daily activities become impaired. This study examines the extent to which lower limb muscles can be weakened before normal walking is affected. We developed muscle-driven simulations of normal walking and then progressively weakened all major muscle groups, one at the time and simultaneously, to evaluate how much weakness could be tolerated before execution of normal gait became impossible. We further examined the compensations that arose as a result of weakening muscles. Our simulations revealed that normal walking is remarkably robust to weakness of some muscles but sensitive to weakness of others. Gait appears most robust to weakness of hip and knee extensors, which can tolerate weakness well and without a substantial increase in muscle stress. In contrast, gait is most sensitive to weakness of plantarflexors, hip abductors, and hip flexors. Weakness of individual muscles results in increased activation of the weak muscle, and in compensatory activation of other muscles. These compensations are generally inefficient, and generate unbalanced joint moments that require compensatory activation in yet other muscles. As a result, total muscle activation increases with weakness as does the cost of walking. By clarifying which muscles are critical to maintaining normal gait, our results provide important insights for developing therapies to prevent or improve gait pathology.