Karen Lohmann Siegel

Relative contributions of the lower extremity joint moments to forward progression and support during gait

Abstract A method, which was found to be accurate within 0.54 m/s 2 , was developed to estimate the relative contributions of the net joint moments to forward progression and support in the gait of five normal subjects. Forward progression was produced primarily by the ankle plantar flexors with a significant assist from the knee extensors. Support was produced largely by the plantar flexors during single limb support and by a combination of ankle plantar flexors, knee extensors and hip extensors during double limb support.

Surface movement errors in shank kinematics and knee kinetics during gait

Abstract The movement of surface mounted targets (SMT) on a shell at the mid-shank and of bone mounted targets attached to the distal shank using a Percutaneous Skeletal Tracker (PST) were simultaneously measured during free-speed walking of three adult subjects having different body types. Surface movement errors in shank kinematic estimates were determined by expressing the segmental motion derived from the SMT relative to the PST-based segment coordinate system (SCS) located at the segment center of gravity. The greatest errors were along and around the shank longitudinal axis, with peak magnitudes of 10 mm of translation and 8° of rotation in one subject. Estimates of knee joint center locations differed by less than 11 mm in each SCS direction. Differences in estimates of net knee joint forces and moments were most prominent during stance phase, with magnitudes up to 39 N in the shank mediolateral direction and 9 N.m about the mediolateral axis. The differences in kinetics were primarily related to the effect of segment position and orientation on the expression of joint forces and on the magnitude and expression of joint moments.

Joint moment control of mechanical energy flow during normal gait

The study purpose was to estimate the ability of joint moments to transfer mechanical energy through the leg and trunk during gait. A segmental power analysis of five healthy adult subjects revealed that internal joint extensor moments removed energy from the leg and added energy to the trunk, while flexor moments and gravity produced the opposite effects. The only exception to this pattern was during the push off phase of gait when the ankle plantar flexor moment added energy to both the leg and the trunk. Pairs of joint moments with opposite energetic effects (knee extensor vs gravity, hip flexor vs ankle plantar flexor) worked together to balance energy flows through the segments. This intralimb coordination suggests that moments with contradictory effects are generated simultaneously to control mechanical energy flow within the body during walking.

A technique to evaluate foot function during the stance phase of gait.

A technique to measure foot function during the stance phase of gait is described. Advantages of the method include its three-dimensional approach with anatomically based segment coordinate systems. This allows variables such as ground reaction forces and center of pressure location to be expressed in a local foot coordinate system, which gives more anatomical meaning to the interpretation of results. Application of the measurement technique to case examples of patients with rheumatoid arthritis demonstrated its ability to discriminate normal from various levels of pathological function. Future studies will utilize this technique to study the impact of pathology and treatment on foot function.

Translational and rotational joint power terms in a six degree-of-freedom model of the normal ankle complex

We hypothesized that defining joint power (JP) merely on the basis of joint rotations ignores important translational power terms, and may not adequately represent the energy flow profile for a given muscle group. A novel six degree-of-freedom (6 DOF) model of the ankle complex was implemented, accounting for previously ignored joint translations as well as traditional rotations. Foot and shank kinematic and kinetic data were collected over a stride cycle on five male and five female adults, walking five trials each at 0.69 statures s-1. During intra-subject analyses, ensemble averages were calculated (n = 5) for JP associated with each DOF, and for related velocity and force/moment data. Translational joint velocities typically peaked below 10% of the mean walking velocity. The largest peak in JP occurred for the rotational DOF associated with dorsi/plantar flexion (360 W). The next largest peak in JP was for the vertical translational DOF, and was nearly 10% of the predominant peak. Positive work during push-off was significantly less p < or = 0.05) for the 6 DOF model (27.9 J) than for either 1 or 3 DOF rotational models (30.3 and 29.9 J, respectively). Negative work during early stance was significantly less for the 6 DOF model (-10.3 J) than for either the 1 or 3 DOF models (-13.1 and -12.6 J, respectively). Inter-subject analyses (n = 50) were conducted for JP data only, with similar results. We conclude that translational JP terms are of practical importance in mechanical energy studies, and may be of particular concern when evaluating energy storing prostheses, when summing total power at several joints, and when studying pathologies that disturb joint geometry.

In Vivo Talocrural and Subtalar Kinematics: A non-invasive 3D dynamic MRI study

Background: To improve diagnostic accuracy, prevent injury, and reduce the effect of impairments on hindfoot function, an understanding of the combined in vivo kinematics of the talocrural and subtalar joints is critical. Therefore, the purpose of this study was to test the feasibility of quantifying talocrural and subtalar joint kinematics using fast-phase contrast (fast-PC) MRI, a noninvasive, in-vivo technique for the study of three-dimensional joint motion. Methods: Nine normal ankles and two ankles with a Stieda process were studied. Subjects were each placed supine in a 1.5 T MRI and asked to maintain a repeated dorsiflexion-plantarflexion movement while a full sagittal-oblique fast-PC dataset was acquired. The orientation and position of the calcaneus, talus, and tibia were individually quantified from these data. Results: The precision and accuracy of tracking calcaneal, talar, and tibial movement was excellent. The three-dimensional subtalar kinematics demonstrated that the talus and calcaneus do not move as a single unit. Most calcaneal-tibial supination occurred at the talocrural joint. The ankles with a Stieda process had markedly different kinematics from each other as well as from the normal group. Conclusions: This study demonstrated that fast-PC MRI is a viable, precise, and accurate technique for studying hindfoot kinematics and is potentially a useful clinical diagnostic tool. The findings call into question the earlier anatomical studies on which much of clinical practice on the foot and ankle is based. Since a clear link was found between anatomical variation and altered rearfoot kinematics, future study is warranted.

Improved agreement of foot segmental power and rate of energy change during gait: Inclusion of distal power terms and use of three-dimensional models

Traditional models used to calculate foot segmental power have yielded poor agreement between foot power and the rate of energy change during the stance phase of gait and limited the applicability of foot segmental power analyses to swing phase only. The purpose of this study was to improve the agreement of foot segmental power and rate of energy change by using more inclusive models to calculate foot segmental power and energy. The gait of 15 adult subjects was studied and models were used to calculate foot segmental power that included either the proximal terms only (Model P, the most common method in the literature) or both proximal and distal terms (Model PD, a mathematically complete model). Power and energy terms were computed in two ways, from sagittal plane vector components only (two-dimensional condition) and from complete three-dimensional components (three-dimensional condition). Results revealed that the more inclusive the model, the higher the agreement of foot power and rate of energy change. During stance phase, Model P produced poor agreement (r(c) = 0.108) for both two-dimensional and three-dimensional conditions, Model PD-2D yielded higher agreement (r(c) = 0.645), and Model PD-3D exhibited nearly perfect agreement (r(c) = 0.956). The advantages of a segmental power analysis include the ability to identify the mechanisms of energy transfer into and out of the foot during movement. The results of this study suggest that foot power analyses are valid when using Model PD-3D to describe foot function during locomotion.

Evaluating interventions to improve gait in cerebral palsy: a meta‐analysis of spatiotemporal measures

A number of interventions to improve gait in individuals with cerebral palsy (CP) have been reported in the literature. The aim of this study was to perform a meta‐analysis of these studies to determine the overall efficacy of these interventions. Effect sizes (Hedges g) for spatiotemporal measures of gait (velocity, cadence, stride length) pre‐ and postintervention were analyzed. Sixty‐three studies were included, and the overall effect size was statistically significant for both fixed effects and random models. Types of interventions were grouped into spasticity treatments, orthopedic (bony and soft tissue) surgery, lower extremity orthoses, or ‘other’. When the data were analyzed in subgroups by type of intervention, each intervention had a statistically significant effect size with the exception of the ‘other’. More importantly, the present study indicates the need to address participant inclusion criteria and power analysis more adequately in future research studies of interventions to improve gait in CP.

Rehabilitation Management of Friedreich Ataxia : Lower Extremity Force-Control Variability and Gait Performance

We describe the rehabilitation management during a 12-month period of a 14-year-old female with Friedreich ataxia. Interventions included task-oriented bimanual reaching activities, functional strengthening, and gait training using a walker featuring tension-controlled wheels and a reverse-braking system. Her physical status was assessed with the Nine-Hole Peg Test, single limb stance time, manual muscle testing, self-reported falls, isometric force control testing, and 3-dimensional gait analysis in a motion-capture laboratory. Although measures of the patient’s Nine-Hole Peg Test, single limb stance time, and manual muscle testing reflected minimal changes, her gait speed decreased by 69.4%. However, the force-control targeting of her dominant knee extensors showed a 43.7% increase in force variability that was concomitant with her decline in gait performance. The decrement of her initial gait speed was reduced to 42.9% on replacing the wheeled walker with the U-Step Walking Stabilizer at the end of the intervention period. Although the patient’s gait remained significantly impaired, extended use of the U-Step Walking Stabilizer modestly improved her gait performance, and her rate of falls decreased from 10 to 3 per month. Our observations suggest that use of force-control testing as proxy measures of ataxia and tension-controlled gait aids show promise in the management of Friedreich ataxia and merit further investigation.

Effects of withdrawal of bracing in matched pairs of children with osteogenesis imperfecta

OBJECTIVES To evaluate the effects of withdrawal of long-leg braces (hip-knee-ankle-foot orthoses [HKAFO]) on activity and ambulation in children with osteogenesis imperfecta. DESIGN A prospective, randomized cross-over trial, that describes the effects of withdrawing HKAFO. PATIENTS Ten children who were ambulatory with the assistance of braces. All had type III or IV osteogenesis imperfecta. Children were paired for age and clinical severity. Strength testing, fractures, and independence in daily activity were monitored at 4-month intervals for 32 months (16 months each of braced and unbraced periods). Gait was analyzed during braced and unbraced conditions. RESULTS Muscle strength declined .35 grade during unbraced and .1 grade during braced intervals. Children spent more time in upright activity during braced intervals than during unbraced intervals (p = .17). Children were more independent in daily activities during braced than during unbraced periods (p = .14). Seventeen fractures of lower extremities occurred during all the unbraced periods, and 8 occurred during the braced intervals (p = .08); the fracture rate was higher during unbraced intervals. (p = .06) Bracing was associated with increased hip flexion and stride length and decreased transverse plane pelvic rotation. CONCLUSION Withdrawal of HKAFO in children with osteogenesis imperfecta who had achieved upright activity was not associated with significant decrease in muscle strength or independence, but there was an associated increase in fracture rate that nearly reached significance.