BACKGROUND

According to the recent mobility device report there are an estimated 36,000 crutch users, including individuals with myelomeningocele (MM), under the age of 18 in the United States (1).  Many of these children develop impairments which may lead to later conditions such as osteoarthrosis and other inflammatory polyarthropathies.  While the number of pediatric and adolescent individuals using crutches is significant, there is only limited information on upper extremity (UE) dynamics and anticipated functional outcomes.

We hypothesize that UE dynamics during Lofstrand crutch-assisted gait are strongly correlated to the Pediatric Outcomes Data Collection Instrument (PODCI) standardized outcomes.  The current study seeks a better understanding of musculoskeletal demands, limb dynamics and functional outcomes of pediatric MM crutch users.  Thus far, results of crutch-assisted gait have not been evaluated methodically, due to the lack of technical ability for quantification and a lack of appropriate outcomes assessment tools.  Many questions exist about the immediate and longer term effects of crutch-assisted gait on joint dynamics and functional outcomes.  New information from measures of impairment, participation, activity, and quality of life, will help achieve a better understanding among clinicians of treatment effects and functional outcomes. Information obtained may improve rehabilitative intervention and design of more appropriate assessment paradigms for Lofstrand crutch users.   

METHODS

Nine subjects, aged 11.1 ± 3.8 years, were recruited and participated in the research study.  Written parental consent and subject assent was obtained in compliance with institutional IRB requirements.  All subjects had an L3 or L4 level myelodysplasia and were ambulatory using Lofstrand crutches in both reciprocal and swing-through gait patterns.  Subjects who had undergone orthopaedic surgery in the past year were excluded from the study.

All subjects were evaluated for clinical outcomes, by means of the PODCI, in order to examine how UE joint stresses affect aspects of each subject’s health and function. The PODCI is a standardized test instrument with summated scales designed to measure patient physical and mental function and symptoms, including pain.  The PODCI is divided into twelve categories of which five functional categories serve as the focus of this study: 1) upper extremity and physical function, 2) transfers and basic mobility, 3) sports and physical function, 4) pain/comfort, 5) global function and symptoms. 

Motion analysis was conducted to evaluate UE dynamics.  The UE model consists of seven rigid body segments (Figure 1) (2).  Twenty-six reflective markers were placed on bony anatomical landmarks and Lofstrand crutches to define seven rigid-body segments and two crutch segments.  Lofstrand crutches were instrumented with 6-axis dynamometers  (AMTI; Watertown, MA) to measure applied reaction forces along the X, Y, and Z axes.  Vicon BodyBuilder was used for the development of the model.  The UE model was previously evaluated for accuracy and precision (3).  Rotations are described using Euler angles (Z-X-Y order).  The rotations of the distal coordinate system are described with respect to the proximal coordinate system.  The thorax and crutch segments are described with reference to the lab coordinate system.

Subjects walked with the instrumented bilateral Lofstrand crutches at a self-selected speed along a six-meter walkway until five successful trials were completed for each gait pattern.  Three-dimensional (3D) motion of the segments was captured using a fourteen-camera Vicon MX motion analysis system.  Data were processed using Vicon Workstation V4.6 software to produce 3D coordinates of each marker.  Further analysis was completed with Matlab software (The MathWorks, Inc.; Natick, MA). 

Temporal-distance parameters including cadence, walking speed, stride length, and stance duration were calculated to examine correlation to clinical results.  Upper extremity and crutch dynamics (temporal-distance parameters, kinematic and kinetic variables) in the sagittal plane (flexion/extension) were determined during reciprocal and swing-through gait and subsequently used to determine correlation with the clinical results (PODCI categories) (2).  The Spearman rank correlation coefficients were computed for the multiple variables and comparisons to identify the strength of the relationships among the variables.

RESULTS

Pediatric Outcomes Data Collection Instrument (PODCI) and Temporal-Distance Parameters

Correlations among the five PODCI categories and the temporal-distance parameters revealed many significant findings (p < 0.05, R > 0.7).  Cadence, walking speed and stride length were correlated with transfers and basic mobility.  Cadence was found to correlate strongly with sports and physical function.  Cadence and walking speed also correlated with global function and symptoms.  Stance duration did not correlate to the PODCI.

Pediatric Outcomes Data Collection Instrument (PODCI) and UE Dynamics

Significant correlations (R > 0.7 and p < 0.05) were seen amongst joint dynamics and functional outcomes (Table 1).

Table 1.  Summary of correlations (ROM: range of motion, FTI: force-time integral, MIF: maximum inferior force, MFM: maximum flexion moment, MEM: maximum extension moment).

PODCI Category	ROM	FTI	MIF	MFM	when MFM occurred	MEM	when MEM occurred
UE and Physical Function	S, E, W	E, W	W
Transfers and Basic Mobility		S		E, W	W		S
Sports and Physical Function				S, E
Pain and Comfort			W			S	S
Global Function and Symptoms		S, E, W		S, E
S: shoulder, E: elbow, W: wrist

Correlations among gait variables and the PODCI were numerous.  A major correlation occurred between the threshold index of the inferior force and UE function during reciprocal gait at the right crutch, right wrist, right shoulder, and right elbow.  Other correlations were also discovered.  Range of motion during reciprocal and swing-through gait was correlated with UE function at the right and left crutches.  The maximum inferior force during reciprocal and swing-through gait was correlated with UE function at the left wrist.  The force time integral correlated with UE function during reciprocal gait at the right wrist and left elbow.  The maximum inferior force rate of loading during swing-through gait correlated to UE function at the right crutch.  Also, the percent in the swing-through gait cycle was correlated to UE function at the left crutch. 

The key correlation among transfers and basic mobility and gait metrics, occurred with the threshold index of the inferior force during reciprocal gait at the left crutch, left wrist and left elbow.  Transfers and basic mobility also correlated with the maximum flexion moment during reciprocal gait at the right wrist and right elbow.  A correlation was also discovered between the force time integral during swing-through gait and transfers and basic mobility at the right shoulder.  The percent in the swing-through gait cycle where the maximum flexion moment occurred was found to correlate to transfers and basic mobility at the left wrist.  The left crutch maximum extension moment during swing-through gait correlated to transfers and basic mobility.  Also correlated was the percent in gait cycle where the maximum extension moment occurred during swing-through gait with transfers and basic mobility at the left shoulder.

The maximum flexion moment correlated to sports and physical function during reciprocal gait at the right elbow and during swing-through gait at the left shoulder.  The maximum extension moment during reciprocal gait was also found to correlate to sports and physical function at the right crutch.

Pain and comfort correlated to the maximum inferior force during reciprocal and swing-through gait at the left wrist.  The force-time integral also correlated to pain and comfort during reciprocal gait at the left wrist.  At the left shoulder, pain and comfort were correlated to the maximum extension moment during swing-through gait and the percent in the gait cycle where the maximum extension moment occurred during reciprocal gait.

Strong correlations occurred between global function and symptoms and the force-time integral during swing-through gait at the right crutch, right elbow, right shoulder, and left shoulder.  Global function and symptoms were correlated with the maximum flexion moment during reciprocal and swing-through gait, at the right elbow, right wrist, and left wrist and the left crutch and left shoulder, respectively.  Correlations between the maximum extension moment during swing-through gait and global function and symptoms at the left crutch and right crutch were found.  Another correlation was found between the percent in the swing-through gait cycle where the maximum flexion moment occurred and global function and symptoms at the left wrist.

DISCUSSION

The PODCI provides a quantitative measure of the subject’s activity, participation, and quality of life.  Calculations of temporal-distance parameters, kinematic and kinetic parameters provide a way to investigate significant relationships among clinical and biomechanical measures.  Currently, there are no reports in the literature that quantify the relationships among clinical measures and UE dynamics during Lofstrand crutch-assisted gait in children with MM. 
           
Important clinical findings were revealed from the current study, which may prove useful during continued, longer-term applications.  Cadence, walking speed and stride length were correlated to global function, transfers and basic mobility in children with MM during swing-through gait.  Crutch range of motion during reciprocal and swing-through gait was directly correlated to UE and physical function in children with MM.  The measured mechanical impulse during both reciprocal and swing-through gait patterns was strongly correlated to the outcomes measures of UE function, physical function, and global function and symptoms in children with MM.  During the reciprocal gait cycle, greater than 90% of the maximum force was correlated to outcomes measures of UE and physical function, transfers, and basic mobility.  The maximum extension moment during swing-through crutch-assisted gait was correlated to outcomes measures of global function and symptoms of children with MM. 

Further work is now being directed towards an analysis of the reciprocal gait pattern to determine if higher levels of activity, participation, and quality of life can be achieved.  Knowledge from this study may ultimately support less frequent rehabilitative treatment intervention through improved planning and better monitoring of walking strategies.