Artificially induced leg length inequality and its effect on sway

Por: Deloss Brubaker, Jeffrey Lander, Matthew Goldman, Rodney Rutland e Scott Paton.

Athens 2004: Pre-olympic Congress

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Introduction

Some studies have suggested that a person without a leg length inequality (LLI) has a physiologic advantage over one with a LLI (1, 7).  These studies have stated that subjects without a LLI require less postural muscle usage in order to maintain steady balance.  Some studies have used force platforms to analyze balance differences in subjects with a known LLI that was determined a tape measure analysis.  Some authors have suggested that this is an unreliable method of LLI detection (2, 5, 6, 8).  There is little research involving balance relating to a LLI when the LLI was based on a radiograph. The purpose of this study was to determine if an induced LLI caused greater sway, which would result in more postural muscle usage.  Additionally, the tape measure method of LLI was tested against the radiographic method.

Methods

Thirty subjects (15 males and 15 females) of various weights and ages participated in the study.  Determination of leg lengths occurred by placing each patient in parallelogram posture (2, 3, 4, 5, 6, 8) and exposing a radiograph from 182.9 cm source image distance.  Tape measurements of leg lengths were also taken at the time of the radiograph.  An AMTI force plate, along with Biosoft 2.0, was used to analyze 19 different dependant variables relating to center of balance.  Four different cork foot inserts of varying thickness (3.175 mm to 12.7 mm) were utilized under each foot (chosen at random) to artificially induce a LLI.  A factor analysis was utilized to condense the 19 dependant variables into common groups, which reduced the amount to six.  An analysis of variance (ANOVA) with repeated measures was performed.  Selected planned comparisons (HSD) were utilized to further analyze the data as well as intraclass correlation (R) regarding tape measurement as it related to radiographic measurement of LLI.

Results

One significant difference, F=12.75 (p<0.02) was identified between males and females in total travel.  Significant differences (p<0.05) in average COP(x) were also identified in the female group who had no LLI initially (based on radiograph) between the 9.5mm (0.31+0.61) right lift and the 12.7 mm (0.30+0.75) right lift condition.  The intraclass correlation (R) was 0.54 for tape measurement of LLI.  Additional data shown in table 1.

 

Table 1.  Mean (sd) of planned comparisons (HSD) comparing tape measurement to x-ray measurement in determination of LLI. Any measurement less than 3mm was considered clinically insignificant and deemed balanced.

 

 

 

                 Method

 

 

X-ray (cm)

Tape Measure (cm)

Leg Length

Left Short

7.4 (3.8) a,b

1.1 (6.5)

Inequality

Balanced

0.0 (1.7) c

1.9 (4.7)

(LLI)

Right Short

6.9 (2.3) d

3. 9 (8.1)

a = significant (p<.05) between x-ray and tape measurement for given LLI.

b = significant (p<.05) between left short and right short for given method

c = significant (p<.05) between left short and balanced for given method

d = significant (p<.05) between right short and balanced for given method

 

Discussion

Males sway significantly less (p<0.02) than females.  This may be in part due to the fact that females are proportioned differently than males, including having a smaller base of support.  Based on planned comparisons, only two differences were identified and appear to have occurred by chance due to an outlier.  It appears that the human body has the ability to adapt to induced LLIs without any increase in sway.  Additionally, as suggested by other authors, the tape measurement of LLI does not appear to be a valid method of LLI detection (2, 5, 6, 8).

 

References

[1]. Bailey, H. (1978). J Am Osteopath Assoc, 77, 65-68.

[2]. Beal, M. (1977). J Am Osteopath Assoc, 76, 745-751.

[3]. Denslow, J., Chace, J., Gutensohn, O., Kumm, M. (1955). J Am Osteopath Assoc, 54(11), 633-670.

[4]. Friberg, O., Koivisto, E., Wegelius. (1985). Diagn Imaging Clin Med, 54, 78-81.

[5]. McCaw, S. (1992). Sports Med, 14(6), 422-429.

[6]. McCaw, S., Bates, B. (1991). Br J Sp Med, 25(1), 10-12.

[7]. Subotnick, S. (1981). J Orthop Sports Phys Ther, 3(1), 11-16.

[8]. Vincent, W. (1999). Statistics in Kinesiology. Northridge, Human Kinetics.

 

 

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