Computer modeling of movement abnormalities and their surgical corrections

106

Gait & Posture

1995; 3: No 2 prior to going over the obstacle. ARM subjects had their foot further back from the smaller size obstacle. This would allow for greater on-line modulation of the limb trajectory and ensure that the trailing limb encounters little difficulty in clearing the obstacle. ARM subjects also exhibited a safer landing strategy by extending the limb out further and bringing it back for landing. The negative foot contact velocity at landing would minimize chances of slipping. To summarize, loss of control vision has a dramatic effect on obstacle. avoidance strategies.

p~pgzf&myc~ar&xnts

A.E. Patla’, D.B. Elliot?, I. Flanagan*, S. Rietdyk’, S. Spauldir$, ‘Department of Kinesiology, University of Waterloo, Canada “School of Optometry, University of Waterlw, Canada ‘Department of Occupational ‘lbempy, University of Western On&o,

Canada

Introduction A major health issue facing the elderly population is an increase in the incidence of falls. Tripping over obstacles accounts for majority of these falls (P~dham &Evans, 1981). Deterioration in visual function on top of the normal aging process can compound the problem. Over 25% of the older adults suffer from macular degeneration (loss of the fovea). Passini (1979) found that one of the major problems encountered by visually impared individuals was difficulty with small horizontal objects in the awe1 path particularly under low ambient light level. In this study we examined the strategies for going over obstacles of different heights and contrast in subjects with and without agerelated maculopathy (ARM). Methodology Eighteen subjects with ARM and twenty age matched controls were tested while they went over obstacles of three different heights (6.7, 13.4 and 26.8 cm), and two contrasts (hieh-white obstacle on black backmound. and low-black obstacle on black backgmund)~placed in their travel paths. The &esen&ion of obstacles were randomized and included trials with no obstacle: Kinematic, kinetic and muscle activity patterns of the leading limb were recorded and analyzed. A three way between and within subject analysis of variance (subject group, obstacle height and obstacle contrast) ctied out on selected

measures.

Results and Discussion We have identified key kinematics markers that capture. the salient control features of limb trajectory over obstacles (Patla & Rietdyk, 1993). We will focus on these key measnres that showed a significant interaction or main effect with subject group term (controls versus ARM). The results ax summarized in bar graph with icons defining the measure. The most critical parameter is the toe clearance over the obstacle. ARM subjects showed higher toe clearance over the low contrast small and medium size obstacles. This higher toe clearance was not achieved by further hiking the hip joint, but rather by flexing the limb more at the hip and the knee joint. The toe elevation was modulated as a function of obstacle heipht in ARM subjects suggesting they were not adopting a strategy of fixed high toe elevation for all obstacles. The toe clearance data reflects problems in visual judgement of obstacle height under trying conditions and can be attributed to a loss of the foveal region which is responsible for extracting fine details of the environment. Stride length was smaller for the ARM subjects while the swing time 0x1 obstacles was higher (allowing for more on-line modification) with higher values for the low contrast obstacles. Foot location at toe-off before the obstacle represents

COMPUTER AND

MODELING OF MOVEMENT ABNORMALITIES THEIR SURGICAL CORRECTIONS Scott

Assessment

L. Delp

Introduction The outcomes of surgeries performed to correct movement abnormalines are unpredictable and sometimes unsuccessful. This problem exists, in part, because the development and testing of new operative techniques rely almost entirely on chnical t&s in which the means to quantify surgical changes or to predict postoperative results do not exist The use of motion measurement equipment to quantify movement abnormahnes and to assess surgical results is an important step toward providing a rational basis for the treatment of persons wnh movement abnormalities. I believe that the design and developmem of improved treatments for movement disabibties can proceed even more effectively If clinical trials and motion studies are augmented by computer models that help explain the causes of the

abnormalities We

have

and

various surgical tendon

evaluate

developed

procedures

transfers,

the

consequences

a graphics-based

tendon

of

computer

affect muscle function.

lengthenings,

surgrcal

interventions.

model

osteotonxes.

of.the lower extrenuty This model has been and joint replacements

to study how used to analyze Based on these

investigations, we have identified four areas in which musculoskeletal models can be helpful for gaining insight into the causes of movement abnormalnies and the consequences of common altered

treatments. surgeries,

by

(3) characterizina visualizing and other first two

(2)

The four estimating

how sureical

areas are: muscle

alterations

(1) quantifying lengths during

how normal

muscle moment and pathologic

affect muscle force-eeneratine

the &actions-between muscle activity, joint kinematic and kinetic parameters. This abstract areas and suggests dnections for future research.

kine&tics. provides

arms movement,

cauacnies.

are

and (9)

gr&nd’reacwm f&s: examples to illustrate the

Analysis of the Rectus Femoris Transfer The rectus femons transfer is commonly performed to improve swing phase knee flexion in

mdividuals

with

stiff-knee

eat.

Gait

studies

have

shown

that

knee

range

of

motion

frequently improves after tr&fer, but the specific mechanisms respon&e for the improvements are not known. It is possible that transfer converts the rectus femons from a knee swmg

extensor to a knee flexor, thereby However, n is also possible that

allowing transfer

It to generate simply removes

a knee flexmn moment the adverse extension

during moment

generated by the spastic muscle without augmenting knee flenion moment. We have mniated a series of studies that include computer simulations, and measurements on subjects the rectus femoris. The comnuter femoris has a large (3-4 cm)

sermtendmosus This

sugwsts

after

tendon simulations knee flenion

anatomical studies, transfer to explore the postoperanve function of and anatomical studies revealed that the rectum moment arm at the knee after transfer to the

(ST) and a small (~5 mm) moment arm after transfer to the diotibial that

the

rectus

femoris

could

generate

a knee

flexion

moment

References Patla, E.A., et al. Gait & Posture, 1: 45-60, 1993. Passini, R., et al. J. Visual Impairment & Blindness, 80(g): 904.907, 1986. Pnrdham, D., et al. Age and Aging, IO: 141-146, 1981. Acknowledgement: Supported by a grant from NSERC & NHRDP

after

IT band. transfer to

the ST and no knee flexmn moment after transfer to the I T hand To test this hypothesis we snmulated the rectus femoris m four SubJects after transfer surgery. A 60 ms snmuius train (4 pulses at 50 Hz) was delivered to the muscle using mtramuscular electrodes whrle the resukmg momenm were measured with a load cell fixed about the ankle. In a11 tranrfer wbiectr thy maus femons generated a knee extension moment, even after transfer to the semitendmosus where the muscle has a knee flexmn momem arm. This suggests that postoperative scarrine may prevent the rectus femons from generating knee-t&ion after &sfer. The<; complexines need to be mcluded in future musculoskeietal models.

of

Muscle

Lengths

Crouch

During

Gait

Crouch gan. one of the most common movemem abnormahnes among children v,jth cerebral palsy, is characterized by pers,s,ent Rexmn of the knee durmg the stance phase. Short hamstrmgs are thought to be rhe cause of crouch gat: thus. crouch gan is often treated by surgmally lengrhening the hamstrings We have used a graphxs-based model of the lower entrermty m conjunction wth three-dimensional kmematic data obtamed from gan analysis to esflmate the lengths of the hamstrings and psoas muscles during normal and crouch gan Analyst of the model revealed that only 20% of the crouch hmbs had hamstrings that were shorter than normal bv more than one standard dewanon dunne waikmn Sixteen of rhe twenty crouch hmhs a&lyzed had hamstrings that were of normal length or longer. despite subjects’ perswent knee flexian during stance. Th,r occurred because the excesswe knee

flerian

was typxally

contrast normal

to the hamstrings, by more than one

accompamed all of standard

by excessive the

crouch devianon

hip flexion

hmbs had psoas during waikmg

need to consider the geometry and kinematics

of mulnple

throughout muscles These

rhe gait cycle

that were shorter results emphasze

joints before performing

In than the

aurglcai

procedures aimed at correctmg crouch gait. They also suggest that shortness of the hip flexors-not short hamstrings--ls frequently the primary abnormahty in persons wth crouch gait I believe that analysis of mulnJomt muscle lengths may enable B more rational basks to be developed for dewding who should. and should not, haw hamstrmg lengthenings A prospective

cbnical

study

needs

to be conducted

Limitations

to test

of Current

this

Computer

hypothezls.

Models

There are a number of important hmnaoons assocmted wth using computer models IO analyze movement abnormalines and their surgical correcwms. First, the lower-limb modei we use represents an adult male. To gain confidence m computer madeis used to analyze movement disabllines m children, addioonal srudxs are needed to characterize &fferences m musculoskeletal geometry between children and aduks. Second. rhe computer mode, and anatomical specimens we use represents normal musculoskeletai geometry. However, panents

wnh movement dlsabdines

sometimes have bony deformnies

that could affect muscle moment

arms. Future work 1s needed to quannfy how bony deformmes alter muscle lengths and moment arms. Third. the computer model does not account for the effects of muscle-tendon remodeling that can accompany central nervous system (CNS) pathology or Immobilization after surgery. Futher study 1s needed to characterize alteranons I” muscle properties exhIbited by persons wth CNS pathology and to understand how muscle-tendon remodehng alters muscle force-generating characteristics postopera~vely. Finally. even if one knew exactly how the musculoskeletal system changed wirh surgical atteratmns, the funcnonal result of these surgeries would still be unpredictable because of abnormal muscle acfivafron parrems that often accompany CNS pathology. Our studies to date have focused on the lengths, moment arms, and force-generating cspacnies of the murcies because they are affected Future models must account for abnormal muscle activanan patterns dnectly by surgery. and how these are altered by surgery in order to predxt postoperative gait.

Summary Current models of ihe neuromusculoskeletal system have important limitatmns. However, when used appropriately, models are powerful took for analyzing rhe fundamental causes of movement abnormalines and revealing the biomechanical consequences of surgical treatments. I beheve that computer slmularions performed m con~unctmn wnh chmcal studies and quantnatwe motion analysis wdl improve our capacny to prowde effewve treatments for

movement

dliorders