Ankle-foot orthoses: Effect on gait abnormalities in tibial nerve paralysis

212

Ankle-Foot Orthoses: Effect on Gait Abnormalities in Tibia1 Nerve Paralysis Justus

F. Lehmann, Department

MD, Sandra

of Rehabilitation

M, Condon,

Medicine.

MS, Barbara

University

of Washington.

J. de Lateur, Scuttle.

MD, J. Craig

Smith,

BS

WA 081%

ABSTRACT. Lehmann JF, Condon SM, de Lateur BJ, Smith JC: Ankle-foot orthoses: effect on gait abnormalities in tibia1 nerve paralysis. Arch Phys Med Rehabil 66:212-218, 1985. 0 To study the biomechanical effects of gastrocnemius-soleus dysfunction and its potential remediation, the gait patterns of six able-bodied young adults were analyzed before and after induced temporary tibia1 nerve paralysis. Ambulation with the tibia1 nerve block was performed with and without the assistance of an ankle-foot orthosis (AFO) with a rigid anterior stop adjusted to either 5” plantarflexion or 5” dorsitlexion. The gait abnormalities resulting from tibia1 nerve paralysis include delayed advancement of the center of pressure, delayed ipsilateral heeloff and early contralateral heelstrike, decreased steplength, decreased ankle dorsiflexion moment, and increased knee flexion moment. This study provides quantitative information on the degree to which these abnormalities were corrected by appropriately adjusted AFOs. When using an AFO with an anterior stop, subjects with tibia1 nerve paralysis had improved advancement of the center of pressure @
Gait: Nerve bloc~k: Ptrrcl1~si.s

Many common paralyses occurring in stroke, brain injury, cauda equina lesions, and peripheral neuropathies are characterized by gastrocnemius-soleus dysfunction. In this study the gait of able-bodied adults was analyzed before and after induced temporary tibia1 nerve paralysis in order to learn more about this dysfunction and its potential remediation by orthotic devices. Gait abnormalities resulting from tibia1 nerve paralysis have been reported previously. ’ This study provides information on the degree to which these abnormalities were corrected by appropriate ankle-foot orthoses. Double upright metal orthoses’ and plastic orthoses? have been shown to be capable of simulated gastrocnemius-soleus function through application of a dorsiflexion stop and rigid sole plate to the metatarsal heads or the functional equivalent in plastic anklefoot orthoses. A significant bending moment has to be resisted by the orthosis to prevent collapse into dorsiflexion during stance. ‘-4

A---A

Normal

-

Tlblal

o-----o

AFO Anterlar Stop 5” plantarflexlon

-

AFO Anterior 5” dorsiflexlon

2c I

Block

Stop

-

5

SUBJECTS AND METHODS The gait of six young adult volunteers, three men and three women, was analyzed during normal ambulation, ambulation with an induced temporary right tibia1 nerve block, and ambulation with the nerve block and an ankle-foot orthosis (AFO) with an anterior stop adjusted in two positions. Subjects wore unaltered Bliicher shoes when ambulating in the normal and block alone conditions. In the tests of effect of AFOs on gait with a tibia1 block. a rigid sole plate was attached to the right shoe. A stirrup assembly was riveted to the sole plate, which extended to the head of the metatarsals. Two metal uprights. connected by a rigid posterior calf band and a leather closure, were attached to the stirrup at the ankle using Becker joints with adjustable anterior pin stops. Arch Phys Med Rehabll Vol99, April 1985

oz ,?

500 TIME

3co

(ms)

Fig l-Vertical force moment arm with respect to the ankle versus time. Curves represent the mean of six trials of one subject.

In each of six trials. each subject participated in seven ambulation tasks: normal ambulation at 100% normal cadence and at 80% normal cadence; ambulation with a right tibia1 nerve block at 80% normal cadence (after the block, subjects could not safely achieve normal cadence without an AFO); This study wa\ wpportrd in part by research gram GWX31EQ7h tram ihe National Institute of Handicapped Research. Department of Educatwn. Washington. DC 20202. Submitted for publ~cati
213

AFO IN TIBIAL NERVEPARALYSIS,Lehmann Table 1: Steplength and Walking Speed during Four Conditions of Ambulation at 80% Normal Cadence Condition

Right tibia1 block (B)

Block and AFO 5” dorsiflexion (D)

Block and AFO 5 plantarflexion (P)

BvN

BvD

BvP

NvD

NvP

PVD

0.69

0.58

0.66

0.66

** *

* **

* * *

ns

ns

ns

0.67 0.71 54.04

0.60 0.55 45.10

0.69 0.63 51.48

0.65 0.66 51.58

Normal (N) Steplength Cm)* Right and left averaged Right (blocked) Left (unblocked) Walking speed** (m/min)

Pairwise comparisons

-

* * *

* * *

* * *

ns

*The analysis of variance indicated a significant condition effect. F (3,15)= 12.9, p
ambulation with the block and an AFO with anterior stop set at 5” dorsiflexion at 100% and at 80% normal cadence; and ambulation with the block and an AFO with anterior stop set at 5” plantafflexion at 100% and at 80% normal cadence. Motions of the right lower extremity, ground reactive forces acting on that extremity, timing of the left and right gait events, and left and right steplength were recorded as each subject walked. Data acquisition, experimental procedures, and data analyses were described in a previous report. ’ Dependent variables measured in the walking conditions at 80% normal cadence were compared using a 4 X 6 Condition by Trial analysis of variance with repeated measures. The dependent variables in walking conditions at 100% normal cadence were compared using a 3 x 6 Condition by Trial analysis of variance with repeated measures. When an analysis of variance showed a significant condition effect, post hoc pairwise Tukey tests were used to determine the significance of the

A---b

100

1

Tibia1 Block

-

AFO Anterior Stop 5” plantarflexron

c-1

TIME

Fig 2-Total

Normal

-

AFO Anterior Stop 5” dorsiflexton

(ms)

ankle moment versus time. Curves represent the mean of six trials of one subject.

“s

ns

by foot interaction.

differences between conditions. In all statistical pcO.05 was required for significance.

F

analyses,

RESULTS Steplength and walking speed. The AFOs with the anterior stop set at either 5” dorsiflexion or 5” plantarflexion proved capable of restoring both steplength and walking speed to levels not significantly different from those observed during normal ambulation at 100% normal cadence (101 +7 steps/min, table 1). The comparison between the conditions at 80% normal cadence showed that condition had a significant effect on steplength and walking speed (~~0.001). The values for steplength and walking speed in the tibia1 block condition were less than those recorded during the following three conditions: normal ambulation, ambulation with the AFO in 5” dorsiflexion and ambulation with the AFO in 5” plantarflexion @
AFO IN TIBIAL NERVEPARALYSIS,Lehmann

214

Table 2: Progression of the Center of Pressure and Ankle Dorsiflexion Moment during Four Conditions of Ambulation at 80% Normal Cadence _ Condition

Normal

(N)

Block and AFO 5 dorsiflexion

tb)

(D)

19

25

Time when the* vertical force moment arm is 5cm anterior to ankle (4 gait cyclel Total ankle** dorsiflexlon moment area (N,m)

Right tibia1 block

28.9

7.1

*The analysis of variance indicated a significant condition F (3.15)=49.8. p
Block and AFO 5’ plantar-

flexion IP)

I

2X

2.

,

:. :. 4

17.4

21.x

i

1

, I

effect.

I IO

20

PERCENT

30

40

BvD

17

F (3. IS) = 24.3. p
Ankle moment. As the center of pressure moves forward on the ankle so does the location of the ground reactive force line. The magnitude of the force times the perpendicular distance from the center of rotation of the talocrural joint to the ground reactive force line equals the moment at the ankle. The dorsiflexion moment at the ankle is normally resisted by gastrocnemius soleus contraction to keep the foot from collapsing forward. This bending moment in the four conditions (fig 2) is consistent with the forward movement of the center of pressure (fig 1). Condition had a significant effect on the magnitude of the dorsiflexion moment as measured by its area (~KO.001). An AFO with an anterior stop partially restores the normal dorsiflexion moment (table 2). While both AFO adjustments produced significant improvements from the block values (~K0.01). they were still significantly less than the normal values (p
0

Pairwise comparisons BvN

*“The

60

70

OF GAIT CYCLE

Fig 4-Mean Stick figures

Fig 3-Mean timing of gait event for six subjects. Gait events are denoted as follows: right heelstrike (RHS), right toestrike (RTS), right heeloff (RHO), right toeoff (RTO), and left heelstrike (LHS). Arch Phys Med Rehabil Vol66, April 1965

NvD

NvP

PVD

n\

f

\ ia

“\

i I

/

of variance

1: >

Indicated

a sigmficant

condition

effect,

this event occurs well before LHS. Use of the AFO set at 5” plantarflexion significantly improved the timing of RHO from that with the block alone (pcO.01). as did use of the AFO set at 5” dorsiflexion Q~0.01). However, the AFO set at 5” plantarflexion restored the timing to normal limits while restoration with the AFO in 5” dorsiflexion was still significantly different from normal (p
”8, /; 50

analv\is

BvP

4-A

NORMAL

-

TIBIAL

-

AFO DORSIFLEXION

-

AFO PLANTARFLEXION

BLOCK

position of right lower limb at the time of LHS. represent the means of six trials of one subject. Circles represent markers placed on the greater trochanters, lateral epicondyle, tibular head, lateral malleolus. and fifth metatarsal head.

AFO IN TIBIAL NERVEPARALYSIS,Lehmann

215

Table 3: Time of RHO and Time of LHS during Four Conditions of Ambulation at SO% Normal Cadence Condition

Time of (% gait Time of (% gait

RHO* cycle) LHS** cycle)

Normal (N)

Right tibia1 block (B)

Block and AFO 5” dorsiflexion (D)

Block and AFO 5 plantarflexion (P)

34.4

49.7

44.6

50.0

46.9

48.8

*The analysis of variance indicated a significant condition F (3,15)= 1 I .7. p-CO.001. ***p
Pairwise comparisons BvD

NvD ***

PVD

t

BvP ***

NvP

39.5

BvN ***

ns

IIS

49.1

***

t

***

ns

ns

ns

effect. F (3.15) = 16.4. p
**The analysis of variance

indicated a significant

condition effect,

done, the knee moments obtained during the four conditions at 80% normal cadence were analyzed as to their origin and then compared. The average knee moments during the time interval from right toestrike (RTS) to LHS were used for comparison because this is the period when the right limb must support body weight. The average total knee flexion moment during the interval from RTS to LHS differed significantly between conditions QKO.01) (table 5, fig 5). The moment was significantly greater with the block than during normal ambulation and during ambulation with AFO set at 5” plantarflexion Q~0.01). The mean value obtained during ambulation with the AFO in 5” dorsiflexion was similar to the mean obtained in the block condition, but it did not differ significantly from normal. The increased knee flexion moment seen during the interval from RTS to LHS in the block condition and its restoration with the AFO set at 5” plantarflexion could be due to changes in the knee extension moment due to posterior shear or to changes in the knee flexion moment due to vertical force. No significant differences in the mean knee extension moment due to shear were found between the conditions. The knee extension moment due to shear force is the product of the shear force and its moment arm with respect to the knee. Figure 6 shows that with the tibia1 nerve block the after shear peak was reduced (~K0.01) (table 6). This was not restored by using an AFO with anterior stop in either the plantarflexed or dorsiflexed position. The shear force moment arm with respect to knee is essentially constant since it is equal to the height of the knee above the ground. The mean knee flexion moment due to vertical force during

fered significantly between conditions @
Table 4: Mean Position of Right Limb at Time of LHS during Four Conditions of Ambulation at 80% Normal Cadence Condition

Horizontal* distance 5th MT to GT (cm) Vertical height of GT (cm) Limb length** 5th MT to GT (cm)

Normal (NJ

Right tibia1 block (B)

Block and AFO 5” dorsitlexion (D)

Block and AFO 5” plantarllexion (P)

21.1

9.9

16.4

19.4

85.0

84.4

83.9

84.6

87.6

85.0

85.6

86.8

*The analysis of variance indicated a significant condition F (3,15)= 10.1, p
Phys Med Rehabil Vol66, April 1995

effect, F (3.15)

Pairwise comparisons BvN ***

BvD ***

BvP ***

NvD ***

NvP

PVD

“S

t

“S

ns

ns

ns

ns

IlS

ns

i

***

ns

ns

***

= 5I .4. p
AFO IN TIBIAL NERVEPARALYSIS,Lehmann

216

Table 5: Components of Knee Movement during Interval from RTS to LHS during Four Conditions of Ambulation at 80% Normal Cadence Condition

Normal (N)

Right tibia1 block (B)

Block and AFO 5’ dorsiflexion tW

Block and AFO 5 plantarflexion (P)

NVD

NVP

PvD

15.0

30.7

2X.1)

15.4

[1\

rl\

n\

n\

20.5

36.9

22 3

1S.h

[1\

n\

[1\

3.1

6.5

5.6

2.7

II\

Total mean* knee flexion moment (N.m) Mean knee flexion** moment due to vertical force (N.rns

Mean length or-**

Pairwise comparisons BvN

BvD

BvP

.:

I,\

vertical force moment arm behind

knee (cm) *The analysis of variance (3,15)=

10.5. p
indicated a sigmficant ***The

condition

analysis of variance

effect. F (3.15) =4.9.

indicated a significant

the interval from RTS to LHS differed significantly between conditions QKO.001) (table 5, fig 7). The mean value of the knee flexion moment due to vertical force in the block condition was significantly greater than the values obtained during normal ambulation and ambulation with the AFO set at 5” plantarflexion QKO.0 I ). The knee flexion moment due to vertical force is the product of the vertical force and its moment arm with respect to the knee. Condition had a significant effect on the magnitude of the second peak of the vertical ground reactive force (~~0.005) (table 6, fig 8). The magnitude of the second peak was less in the block condition than in the normal condition (p
p
condition

**The analysis ot variance indicated a significant conditwn effect. F (2.15) = 17.S.p
Normal

-

Tibia1

a---a

AFO Anterior Stop 5” plantarflexlan

-

TIME

Fig 5-Total

,‘!

1

Normal

-

Tlbiol

-

AFG Anterior Stop 5” planlarflexton

Block

AFO Anterior 5” dorsiflexlon

D------cI

AFO

i?loch

Anterior

Stop

5” dorstflexlon

Stop

(ms)

knee moment versus time. Curves represent the mean of six trials of one subject.

F

block condition did not contribute to the increased knee tlexion moment; rather it acted to reduce it. When the vertical ground reactive force vector is located behind the knee, it produces a tlexion moment. The mean length of the vertical force moment arm behind the knee during the interval from RTS to LHS differed significantly between the conditions ~~0.001) (table 5. fig 9). The length of the moment arm in the block condition was greater than that during normal ambulation or during ambulation with the AFO in 5” plantarflexion (pG.01). The AFO set at 5” plantarflexion restored the moment arm length to within normal limits whereas the AFO set at 5” dorsiflexion did not (~~0.05). Therefore, the increase in magnitude of the

A---A A---A

effect,

Fig 6-Fore/aft shear ground reactive forces versus time. Curves represent the means of six trials of one subject. Arch Phys Med Rehabil

Vol55,

April 1985

AFO IN TIBIAL NERVEPARALYSIS,Lehmann

217

Table 6: Ground Reactions Forces during Four Conditions of Ambulation at 60% Normal Cadence Condition

Block and

Second peak* vertical GRF (% body weight) Peak aft** shear GRF (% body weight)

Normal (N)

Right tibia1 block (B)

AFO 5 dorsiflexion (D)

Block and AFO 5 plantarflexion (P)

BvN

BvD

104

98

100

105

:

ns

BvP ***

17

13

II

I2

ns

ns

*The analysis of variance indicated a significant (3.15)=21.6,p
condition effect, F (3.15) = 8.0. p
vertical force moment arm was the origin of the increased total knee flexion moment in the block condition; the restoration of the total knee flexion moment to normal limits by the AFO with the anterior stop adjusted in 5” plantarflexion was the result of its action minimizing the vertical force moment arm.

DISCUSSION Significant gait abnormalities resulted from gastrocnemius soleus paralysis. The abnormalities included changes in steplength, walking speed, center of pressure advancement, timing of gait events, ground reactive forces, and joint moments. The use of an AFO with an anterior stop set at 5” plantarflexion was most effective in restoring the gait pattern toward normal. In tibia1 paralysis the lag of the forward movement of the hip on the affected side was the result of instability at the ankle. Without the action of the gastrocnemius-soleus, the movement of the center of pressure forward of the ankle joint produces a collapse of the ankle into dorsiflexion. Therefore, the forward movement of the center of the pressure was avoided.

A---A -

Tiblal

AFO Anterior Stop 5” plontarflexion

-

AFO Anterlar Stop 5” dorsiflexron

500 TIME

***

**The analysis of variance

indicated

(ms)

Fig 7-Knee moment due to vertical force versus time. Curves represent the mean of six trials of one subject.

NvP

PVD

ns

ns

i

***

***

a significant

condition

A----A

Normal

M

Tlbiol

a--+

AFO Anterior Stop 5” plantarflexlon

-

AFO Anterior Stop 5“ dorsiflexlon

Block

900

NvD

ns effect, F

As a result. ipsilateral heeloff occurred later and contralateral heelstrike occurred earlier. The contralateral heel struck in a less forward position, thus reducing steplength and walking speed. When the ankle and foot of a subject with tibia1 nerve paralysis were braced using a rigid anterior stop and a rigid sole plate to the metatarsal heads, forward movement of the center of pressure was again possible. The body’s center of gravity and ground reactive force line moved forward more normally, pivoting over the metatarsal head area and raising the heel earlier than when observed with uncorrected tibia1 paralysis, thus approximating normal timing of the gait events, normal advancement of the hip, and normal steplength. The AFO with the anterior stop set at 5” plantarflexion was more effective in restoring the values to normal than was the AFO with the anterior stop set at 5” dorsiflexion. However, the forward movement of the center of pressure and the values of the parameters dependent on it, that is, ankle dorsiflexion moment,

Normol

-

0

Pairwise comparisons

,

400 TIME

“l

Block

000

(ms)

Fig g-Vertical ground reactive forces versus time. Curves represent the means of six trials of one subject. Arch Phys Med Rehabll Vol66, April 1966

218

20 2 2

I

A---A

Normal

-

Tlbial

o---o

AFO Anterior Stop 5” plontorflexion

-

AFO Anterror 5” dorsiflexion

Block

Stop

This study shows that gait deviations resulting from tibia1 nerve paralysis are minimized by use of an AFO with a rigid anterior stop. The adjustment of the anterior stop influences the extent to which the abnormalities are corrected. The normal advancement of the center of pressure was better approximated using the AFO with the anterior stop set at 5” plantarflexion than with the stop set at 5” dorsitlexion. As a result. the AFO set at 5” plantarflexion also was better in restoring the timing of the gait events. the advancement of the hip of the affected limb at the time of opposite heelstrike. the ankle dorsitlexion moment and the knee flexion moment. None of the factors measured during ambulation with the tibia1 block and use of the AFO set at 5” plantarflexion were significantly different from normal with the exception shear and the ankle dorsiflexion moment.

0

500 TIME

900

(ms)

Fig !)-Vertical force moment arm with respect to the knee versus time. Curves represent the means of six trials of one subject.

timing of heeloff, hip advancement and steplength, were delayed or decreased during ambulation with the tibia1 block using the AFO in 5” plantarflexion as compared with normal ambulation. The forward movement of the center of pressure accelerates more quickly via active plantarflexion than when the ankle is passively fixed and the total movement of the center of pressure is dependent upon the movement of the center of gravity forward. Knee stability also was affected by the tibia1 nerve paralysis. The lack of forward movement of the center of pressure on the ankle, and thus the forward movement of the vertical component of the ground reaction force line with respect to the knee, produced a markedly increased knee flexion moment in midstance when body weight was supported by the paralyzed limb. The contribution of the aft shear force to the total knee flexion moment was not significant. Use of the AFO with the anterior stop set at 5” plantarflexion during ambulation with tibia1 nerve paralysis reduced the knee flexion moment to normal levels. This was largely due to the change of the relative position of the knee center to the vertical component of the ground reactive force.

Arch Phys Mod Rehabil

Vol99,

April 1995

of the peak

after

The resu!ts suggest that it would be advantageous to adjust the anterior stop of an AFO substituting for loss of gastrocnemius-soleus function in some degree of plantarflexion. Adjustment of the anterior stop in excessive plantarflexion would be expected to result in insufficient toe clearance during swing for persons with combined plantarflexion-dorsiflexion dysfunction. Setting the anterior stop in too much plantarflexion also may produce an extension moment at the knee sufficient to result in genu recurvatum. It appears that approximately 5” plantarflexion provides the maximum benefit while avoiding potential problems. ADDRESS REPRINT REQUESTS TO: Justu, F. Lehmann, MD Department uf Rehabilitation University of Washington Seattle. WA 9X195

Medicine

RJ-30

References

Lehmann JF. Condon SM. de Lateur BJ. Smith JC: Gait abnormalities in tibia1 nerve paralysis:

a biomechanical

study. Arch

Phys Med Rehabil (Chicago) (in press) Lehmann JF. Esselman PC. Ko MJ. Smith JC. de Lateur BJ. Dralle AJ: Plastic ankle-foot orthoses: evaluation of function. Arch Phys Med Rehabil 64:402407. 1983 Lehmann JF. Ko MJ. de Lateur BJ: Double stopped ankle-foot orthosis in flaccid peroneal and tibia1 paralysis: evaluation of function. Arch Phys Med Rehabil 61536541. 1980 Lehmann JF. Warren CG. de Lateur BJ: Biomechanical evaluation of knee stability in below-knee braces. Arch Phys Med Rehabil 51:688-695, 1970