Migration and Design Characteristics of Functional Knee Braces

7/25/2019 Migration and Design Characteristics of Functional Knee Braces

1/11

Journal

of

Sport Rehabilitation 1998 7

3 43

998 uman

Kinetics Publishers

Inc.

Migration and Design Characteristics of

Functional Knee races

ruce rownstein

Functional braces are often used as part of a comprehensive rehabilitation

protocol following ligamentous injury of the knee. One of the common prob-

lems of a functional knee brace is distal migration. This study was undertaken

to identify the migration tendencies of 14 commonly used functional knee

braces and the design and measurement characteristics that contribute to mi-

gration. Two subjects performed 15 min of exercise

5

min each on a tread-

mill, slide board, and stair machine), and brace position was measured pre-

and postexercise. All 14 braces migrated somewhat. Nine of the braces had

migration of less than mm and were considered superior. The brace design

active or passive) had a significant effect .05) on migration. No differ-

ence

>

05) was noted for brace type custom vs. off the shelf) or fit method

cast vs. measuring tool). Based upon this evaluation, an active brace design is

recommended for functional knee braces.

Functional knee braces have been used as part of a comprehensive rehabili-

tation program after ligamentous injury for 25 years. The first functional brace

was developed by Dr. James Nicholas and Jack Castiglia in the late 1960s. The

original Lenox Hill Brace was designed to restrain anteromedial subluxation and

later redesigned to prevent anterolateral subluxation as well. Since that time, at

least two dozen braces have been marketed as an adjunct treatment of the anterior

cruciate deficient knee

4).

The ideal knee brace accurately and appropriately controls motion about the

knee, does not migrate, and is comfortable, durable, available, easily measured, and

easy to apply 2). Both clinical experience and a review of the literature 1,3) indicate

that the ideal knee brace does not exist. One of the most frequent problems is brace

migration, which results

in

an imbalance between brace and knee joint mechanics 6,

7, 10-15). brace that is not in the correct position may place the user at risk for

injury 6, 10, 13). If a brace migrates during activity, the participant must stop to

readjust the appliance.This reduces patient compliance as well as brace effectiveness.

Bruce Brownstein is with SOAR Research, 51 West 81st St., Suite9J,New York,

IVY

10024.


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6 ro

wnst in

Table 1 Brace Migration Data, Type of Brace Design, and Fitting Method

Braces Listed Alphabetically)

Brace Manufacturer) T Y P ~ Fit method

CE-2000 Donjoy)

CTi-2 Innovation)

Defiance Donjoy)

Elite Omni)

Force Bledsoe)

Goldpoint Donjoy)

GII Generation USA)

Lenox Hill 3M)

MVP Innovation)

Performer OrthoTech)

Proshifter Bledsoe)

Talon Sutter)

TS-7 Ornni)

Townsend

Active

Passive

Active

Active

Active

Active

Passive

Passive

Passive

Passive

Active

Active

Active

Passive

Measure tool

Traceltool

Measure tool

Cast

Off the shelf

Off the shelf

Cast

Cast

Off the shelf

Cast

Off the shelf

Traceltool

Cast

Cast

Average Migration y Brace

Brace

Figure

1

-Data on average migration of each knee brace following exercise protocol.

All measurements are in millimeters.

test to determine which brace models allowed more migration than the others. The

results are ranked according to the amount of average migration. Table 3 shows

that groupings were possible at the p .05 level. There was a significant differ-

ence between braces that migrated less than rn CE-2000, CTi-2, Defiance,

Elite, Goldpoint, Performer, Proshifter, Talon,

TS-7

and those that migrated more

than 5 rnm Force, Generation11 Lenox Hill,MVP Townsend). Among the sec-


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Table

3

Duncan s Multiple Range Comparison Test

Mean

Brace Tal TS7 Pro Perf Ce2 Def Go1 Eli

Tal

TS7

Pro

Perf

Ce2

Def

Go1

Eli

Cti2

M ~ P

Lhb

GI1

Twn

For

Note.

Tal

Talon), TS7 TS-7), Pro Proshifter), Perf Performer), CE2 CE-2000), Def Defiance)

Mvp MVP), Lhb Lenox Hill Brace), GII Generation 11), Twn Townsend), For Force). Asterisk

between brace models

p=

.05). For example, the MVP brace migrated more than Tal and TS7 br

GI1 brace migrated more than the Tal, TS7, Pro, Perf, CE2, Def, Gol, Eli, and Cti2.

Multiple Range Tests: Duncan test with significance level .05

Step 2 3 4

6

7 8

Range 3.03 3.17 3.28 3.33 3.37 3.40 3.42 3.44


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Functional Knee Braces 39

Table 4 Tests Comparing Migration Data Between2 Subjects

tests for independent samples of subject

Variable Number of cases Mean

SD

S

of mean

Migrate

Subject 1 14 3.9464 3.117 0.833

Subject 2 14 5.7679 4.604 1.230

Mean difference -1.8214.

t tests for equality of means

Variances value

f

2-tail

sig

S

of diff

96

CI

for diff

Equal -1.23 26

.23 1 1.486 (-4.876, 1.233)

Unequal

-1.23 22.85

.233 1.486 (-4.896, 1.254)

No difference was found between the two subjects based upon migrationdata for llbraces

Distal placement also generated higher anterior-posterior forces on the lateral side.

In general, posterior placement produced the lowest forces. Lew et al. 6) and

Lewis et al. 7) studied the pistoning forces in braces as a function of placement.

Both they and Regalbuto et al. 1 1) determined that inaccurate placement of the

brace hinge was a factor in producing abnormal brace and joint forces. The type

and magnitude of forces were related to the placement of the brace axis rather than

the type of hinge being used. If one accepts this research, then the brace used

should migrate minimally and have a hinge that is posteriorly placed. In this study,

braces which meet that criterion include the Talon, CE-2000, Defiance, TS-7, and

Proshifter.

Functional knee braces use a variety of hinge designs and suspension sys-

tems to mimic the knee joint axis behavior and location

9).According to Walker

et al. 15), the nature of the hinge uniaxial, polyaxial, etc.) does not affect brace

function since the hinge itself is external to the joint. Generally speaking, the brace

design can be identified as either passive o r active

6).

No published studies were

found that determined whether either design is more effective in promoting func-

tional knee joint stability. The data presented here indicate that an active brace

migrates less than a passive brace, perhaps because of the forces present between

Ithe brace and the leg.

All of the braces tested in this study migrated a measurable amount average

migration from 0.25 to 11rnrn .Walker et al. 15) offset the hinge of their braces

by 5 rn to measure abnormal joint mechanics. If one accepts this amount as the

maximum allowable distal migration, then

8

of the braces in this study met this

criterion of acceptability. Of these

8

braces, 7 are considered by the manufacturers

to be of an active design.


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rownstein

Table 5 Tests for Differences in Migration Data Based Upon Fit Method

Custom vs. Off the Shelf)

t

tests for independent samples of fit


S SE

of mean

Migrate

Custom

20 4.6250 4.058 0.907

Off

the shelf 8 5.4375

3.934 1.391

Mean difference

-.8

125.

tests for equality of means

Variances value

f

2-tail sig.

SE

of diff. 96 CI for

diff.

Equal -.48 26

,633 1.684 (-4.274,2.649)

Unequal

-.49 13.34 ,633 1.66

(-4.391,2.766)

No difference in migration noted based upon fitting method.

Two limitations of this study should be examined. Fi st , the use of nonimpaired

subjects rather than ACL-deficient subjects may have affected the results of brace

migration. Second, the small sample size (N 2) made statistical analysis of the

variables in question difficult. The tradeoff in this study was a greater number of

braces versus more subjects with fewer braces.

Nonimpaired subjects were selected for two reasons. First,

all

available people

with chronic ACL-deficient knees were already using one type of functional brace.

The relative level of comfort between a brace style that a subject has used for some

time and a new brace style may affect a subject s performance. Second, the exces-

sive translation of the tibia on the femur was assumed to be minimized by the

functional brace and the weight-bearing exercise conditions imposed by the equip-

ment selected. Wojtys et al. 16), who measured tibia1 translation and rotation in

braced, ACL-deficient cadaver knees, found that anterior translation and external

rotation were reduced in all cases (14

braces), although there was a great deal of

variability. They also noted that strap tension and brace application are important

variables of brace performance.

Little evidence exists to indicate that ACL deficiency affects brace migra-

tion. Previously published studies on motion between the tibia and femur follow-

ing sectioning of the ACL do not indicate an increase in distraction and compres-

sion of the tibia on the femur (translation along the longitudinal axis). Gerber and

Matter

(5)

noted a downward and forward shift of the centrode defined by instant

center of rotation analysis in the ACL-deficient knee. There are technical problems


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Functional Knee Braces 41

Table

6

t Tests

for

Migration Data BasedUpon Design (Active vs. Passive)

tests for independent samples

of type


SD SE

of

mean

Migrate

Active

16 3.4688

3.468 0.867

Passive 12 6.7083 3.963 1.144

Mean difference= -3.2396.

t tests for equality of means

Variances value

df

2-tail sig.

SE

of diff. 96

CI

for cliff.

Equal -2.30 26

.030* 1.407 (-6.132, -.347)

Unequal -2.26

21.95 .034* 1.435 (-6.217, -.263)

Significantdifference .05) noted between means based upon hinge design

type.

with this type of analysis. Marans et al. (8) did not find a change

in

superiorlinferior

tibial motion during gait in ACL-deficient knees. Moreover, the exercise techniques

used in our investigation were all weight bearing. Relative distraction of the tibia

with

respect to the femur should be minimized, if not eliminated. Therefore, the use of

nonirnpaired subjects should not affect the distal migration of the functional braces

used in this study. It was assumed that a brace which migrates on a nonimpaired knee

would not migrate less on nACL-deficient knee.A brace that migrates excessively

>5 mm on a nonimpaired knee should not be recommended for nACL-deficient

knee, particularly during high-level, high-performance athletics or dance.

A second limitation of this study was the number of subjects N=2)used for

the evaluation of distal migration. The cost of braces precluded a full examination

(N> 10) of each brace, although a larger sample size would have allowed more

powerful statistical analysis. The choice was made to examine as many braces as

possible N

=

14). The braces chosen were nationally marketed brands. Follow-up

study on subjects with ACL-deficient knees to confirm the assumptions made in

this investigation would be beneficial.

o difference was found in brace migration based upon fit method or type

(custom/off-the-shelf) characteristics. There has been some debate as to whether

custom braces fit better or are more comfortable. The data from this investigation

indicate that the fit obtained with a custom brace versus an off-the-shelf brace does

not affect brace migration. The same can be said about the brace fitting method.

There was no difference between braces that were casted or measured via a tool.

For the clinician and the patient, fitting a brace with a measurement tool takes less


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Functional Knee Braces

43

6. Lew, W.D., C.M. Patrnchuk, J.L. Lewis, and J. Schmidt. A comparison of pistoning

forces in orthotic knee joints.

Orthot. Prosthet.

36:85-95, 1984.

7. Lewis, J.L., W.D. Lew, C.M. Patrnchuk, and

G.T.

Shybut. A new concept in orthotics

design.

Orthot. Prosthet.

37: 15-23, 1984.

8. Marans,

H.J.,

R.W. Jackson, N.D. Glossop, and M.C. Young. Anterior cruciate liga-

ment insufficiency: A dynamic three-dimensional motion analysis.

Am.

J

Sports Med.

17:325-332,1989.

9. Millet, C.W., and D.J. Drez. Principles of bracing for the anterior cruciate ligament

deficient knee.

Clin. Sports Med .

7:827-833, 1988.

10. Regalbuto, M.A., J.S. Rovick, and P.S. Walker. The forces in a knee brace as a function

of hinge design and placement. Am.

J

Sports Med. 17535-543, 1989.

11. Regalbuto, M.A. R. Schrager, J.S. Rovick, and P.S. Walker. The effectiveness of knee

braces as a function of hinge design and placement. Proceedings of the Orthopedic

Research Society, San Francisco,

p.

246, 1987.

12. Scott, E.R., and H H Mita.

Comparing the paths of orthotic knee joints and normal

human knee s.Unpublished master s thesis, Division of Physical Therapy, Stanford Uni-

versity, 1985.

13. Walker, P.S. Engineering principles of knee prostheses. In Disorders of the Knee A.J.

Helfet (Ed.). Philadelphia: Lippincott, 1974, pp. 261-274.

14. Walker, P.S., M.D. Kurosawa, J.S. Rovick, and R.A. Zirnrnerman. External knee joint

design based on normal motion. J

Rehabil. Res. Dev.

22:9-22, 1985.

15. Walker, P.S., J.S. Rovick, and D.D. Robertson. The effects of knee brace hinge design

and placement on joint mechanics.

J Biomech.

21:965-974, 1988.

16. Wojtys, E.M., P.V. Loubert, S.Y. Samson, and D.M. Viviano. Use of a knee brace for

control of tibial translation and rotation.

J Bone Joint Surg.

72-A: 1323-1329, 1990.

cknowledgment

This research project was funded in part by a grant from Sutter Corporation, San

Diego, California.

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Migration and Design Characteristics of Functional Knee Braces