The effect of a shoe lift on tensor fasciae latae length during standing with an artificial functional leg length discrepancy: An ultrasonic shear wave elastography study

Abstract

BACKGROUND:

Shortening of tensor fasciae latae is one factor that causes a functional leg length discrepancy. A shoe lift has been used to correct the compensatory posture resulting from the discrepancy. Despite the potential therapeutic benefit of a shoe lift, the mechanism by which it exerts its effect is unclear.

OBJECTIVE:

To investigate the effect of a shoe lift on tensor fasciae latae length during standing with an artificial functional leg length discrepancy using ultrasonic shear wave elastography.

METHODS:

Twenty-two healthy individuals performed static standing under three conditions: drop of the pelvis and flexion of the leg resulting from fixing in the hip abduction position using a hip orthosis (functional leg length discrepancy condition); drop of the pelvis by the orthosis, but no flexion of the leg due to a shoe lift (shoe lift condition); and normal bilateral standing condition. The shear elastic modulus of tensor fasciae latae was calculated using ultrasonic shear wave elastography.

RESULTS:

The shear elastic modulus was significantly lower in the functional leg length discrepancy condition than in the shoe lift and normal conditions ( $p=$ 0.038).

CONCLUSIONS:

Using a shoe lift for the functional leg length discrepancy can result in a functional hip position that elongates tensor fasciae latae.

Keywords

Functional leg length discrepancy tensor fasciae latae shoe lift ultrasonic shear wave elastography

1. Introduction

Total hip arthroplasty (THA) is a valuable procedure for the relief of chronic pain and functional disability and is effective in improving patients’ quality of life and physical function [1]. However, a third of patients after THA have a perceived leg length discrepancy (LLD) and have poorer functional outcomes [2, 3].

Previous studies have found that many patients with a perceived LLD after THA had a physically functional LLD rather than an anatomical LLD [2, 4]. The functional LLD after THA is caused by pelvic obliquity that results from soft tissue tightness in the structures that cross the hip joint [5]. Another previous study reported that most patients with a perceived LLD had both flexion and abduction contractures of the hip joint after THA [6]. In particular, the hip abduction contracture resulted from tight hip abductors that can tilt the pelvis downward on the affected side and lead to apparent lengthening of the ipsilateral leg. The relative lengthening of the affected leg compared to the contralateral leg can cause the perception of leg lengthening on the affected side and a compensatory postural adjustment such as a slightly flexed position of the ipsilateral hip and knee joint on standing.

The discomfort felt due to a functional LLD can be improved using a shoe lift under the unaffected leg. In a recent study of the use of shoe lifts with progressively thinner heights, the functional LLD of the patients who received early postoperative intervention with a shoe lift was significantly improved compared to the control group [7]. The use of shoe lifts that are adjusted to the height of the functional LLD could correct the flexed leg of the compensatory posture and help to passively elongate the length of the hip flexors and abductors.

One study reported that tensor fasciae latae (TFL) of the hip flexors and abductors could be quantitatively evaluated for elongation during stretching using ultrasonic shear wave elastography (SWE) [8]. SWE allows non-invasive and reliable measurement of muscle elasticity [9]. Previous studies confirmed a strong linear relationship between the shear elastic modulus measured by ultrasonic SWE and the referral setting to elongate the muscle length using the simultaneous tensile test [10] or passive ankle joint motion [11]. Therefore, ultrasonic SWE would be useful to measure changes in muscle length of the TFL. In the present study, a functional LLD was created artificially, and the effect of the functional LLD on TFL length and the effectiveness of a shoe lift for changing TFL length were investigated by ultrasound SWE.

2. Methods

2.1 Participants

Twenty-two healthy young adults were recruited at a university between May and December 2018. They had no history of hip pain and no limitation of hip or lumbar trunk motion. They all provided written informed consent prior to the measurement procedures. This study protocol was approved by the Ethics Review Board of the Yamagata Prefectural University of Health Sciences (#1806-08).

The sample size needed for one-way analysis of variance (ANOVA) with repeated measures [effect size $=$ 0.25, described as medium by Cohen [12], $\alpha$ error $=$ 0.05, power $=$ 0.8)] was calculated using G* power 3.1 software (Heinrich Heine University, Duesseldorf, Germany) [13, 14]. The results showed that at least 10 participants were required.

Figure 1.

Standing postures from the coronal and sagittal planes in the three conditions. FLLD, drop of the right side of the pelvis and flexion of the right leg resulting from fixing the position in 20 ${}^{\circ}$ of abduction by adjustment of the hip orthosis; SL, drop of the right side of the pelvis resulting from fixing the position in 20 ${}^{\circ}$ of abduction by adjustment on the hip orthosis, but no flexion of the right leg resulting from a shoe lift under the left foot; NO, normal bilateral standing with no fixation of the right hip joint on the hip orthosis.

2.2 Experimental protocol

Each participant wore a hip orthosis (Newport 3, Orthomerica Products, Orlando, FL, USA) with a range of motion adjustment on the right hip to artificially create a functional LLD and was then instructed to stand on two force plates. The support base was set at a width of 40 cm, considering the thigh cuff width of the hip orthosis. Trials under three bilateral standing conditions were then conducted as follows (Fig. 1): functional LLD condition, drop of the right side of the pelvis and knee flexion resulting from fixing the position in 20 ${}^{\circ}$ of abduction by adjustment of the hip orthosis (FLLD); shoe lift condition, drop of the right side of the pelvis resulting from fixing the position in 20 ${}^{\circ}$ of abduction by adjustment of the hip orthosis, but no flexion of the right leg due to a shoe lift (LLD Blocks, Atlas International, Irvine, CA, USA) under the left foot (SL); and normal condition, normal bilateral standing with no fixation of the right hip joint on the hip orthosis (NO). The amount of the dropped pelvis in the FLLD condition was measured as the angle between a horizontal line and a line transversely through the two anterior superior iliac spines (ASIS) using a digital goniometer. The angle of the dropped pelvis in the FLLD condition was used as a reference to maintain the posture with an artificial functional LLD in the SL condition. The LLD blocks, made of ethylene vinyl acetate material, which has high-density hardness, come in five different heights (1/8, 1/4, 3/8, 1/2, and 3/4 inches). The desired shoe lift was set by stacking the LLD blocks and customizing the height for each participant. The height of the shoe lift was determined as the minimum height of LLD blocks at which the right knee could be extended without the left heel rising. In order to ensure the postural change, the distance from the umbilicus to the right medial malleolus was measured using a digital tape measure on standing and the amount of change in the distance between the FLLD and SL conditions was calculated. The 40-cm support base was constant during the three standing conditions, so that the hip abduction position fixed by the hip orthosis could effectively create the functional LLD. To maintain symmetrical loading on both legs, the participant received visual and auditory feedback of leg loading from force plates during standing (TWIN GRAVICORDER G-6100, ANIMA Corp, Tokyo, Japan). A stable posture was defined as the posture in which both leg loadings could be controlled between 45% and 55% body weight in the three conditions. TFL stiffness was measured by SWE for 10 s during stable standing.

2.3 Shear-wave elastography

The shear elastic modulus of the right TFL was performed in each of three standing conditions using SWE (Aixplorer, SuperSonic Imagine, Aix-en-Provence, France) with an ultrasound transducer (50-mm-long SL-15-4 linear ultrasound transducer). The SWE mode was selected, and both the SWE image and B-mode image were displayed using a dual screen configuration. The following default SWE settings for the system were used: standard SWE acoustic power, spatial smoothing of 5 and medium persistence. On SWE elastograms, the tissue elastic modulus was displayed in kilopascals (kPa) using a default chromatic scale with progression from blue to red, indicating low to high shear modulus (stiffness).

Figure 2.

A typical example of shear elastic modulus measurement at the tensor fasciae latae (TFL). The lower image shows a B-mode ultrasound image, and the upper image shows a color-coded box. The mean Young’s modulus of the three regions of interest (Q-box: 5.0-mm-diameter), arranged longitudinally in the TFL, is calculated. The shear elastic modulus is obtained by dividing Young’s modulus by three.

The measurement site was defined as the mid-point between the anterior iliac spine and the greater trochanter of the femur. The transducer was placed longitudinally on a hydrogel pad of 7 $\times$ 12 cm ${}^{2}$ (HydroAid, Kikgel, Ujazd Poland). The region of interest (ROI) width was set near the central point of the muscle belly in the image. The ROI depth was different for men and women, considering the limitation of depth that could be measured by the shear elastic modulus: the depth included only the muscle in the image of the male participant, and the depth included both the muscle and the fasciae in the image of the female participant. Three 5-mm-diameters for the measurement of Young’s modulus were drawn longitudinally to cover the entire TFL and their mean was calculated (Fig. 2). All procedures were performed by one of the two investigators (one male and one female). The investigator of the same sex as the participant performed all measurements twice, and the mean shear elastic modulus values for the two trials were used in the analysis. Investigator 1 was a faculty member of the physical therapy department and investigator 2 was a fourth-year physical therapy student. Prior to performing the measurements, both investigators received the same training in using SWE and established the same experimental protocol and SWE method.

2.4 Statistical analysis

The Shapiro-Wilk test was used to assess whether the data were normally distributed. To assess the intra-rater reliability of the shear elastic modulus measurement, the intra-class correlation coefficient (1, 1) (ICC ${}_{1,1}$ ) was used. ICC ${}_{1,1}$ was calculated for the shear elastic modulus of the two measurements in each standing condition. To determine whether TFL stiffness changed in each standing condition, one-way repeated-measures ANOVA was performed with the shear elastic modulus as the dependent variable and with the standing condition as the within-participant factor [15], separately for male and female participants, because the depth of the ROI of the measurements differed between male and female participants. If a significant main effect was found, the post hoc Tukey HSD test was performed. The effect size (ES) was calculated using Cohen’s d coefficient; ES values of 0.2, 0.5 and 0.8 were considered to correspond to small, medium and large differences, respectively [12]. A $P$ value $<$ 0.05 was considered significant. Statistical analysis was performed using SPSS (version 24.0, IBM, Chicago, IL, USA). The ES was performed using G* power 3.1 software (Heinrich Heine University, Duesseldorf, Germany).

3. Results

Twenty-two healthy young individuals participated in this study. Their characteristics are shown in Table 1. The angle of the dropped pelvis in the FLLD was 5.9 ${}^{\circ}$ (SD 3.1). The shoe lifts were used at a mean height of 1.1 inches (SD 0.5). The distance from the umbilicus to the medial malleolus in the SL condition was 0.6 inches (SD 0.4). The reliability of the shear elastic modulus for each standing condition is shown in Table 2. The ICC ${}_{1,1}$ was 0.904–0.983 for all conditions.

Table 1
Participants’ characteristics (mean (SD))

	Male	Female
Age (years)	21.7 (2.6)	21.3 (0.5)
Height (cm)	173.0 (5.0)	159.3 (3.7)
Weight (kg)	63.3 (7.1)	51.3 (5.4)

Table 2

Reliability of shear elastic modulus measurements

Standing posture	ICC	95% CI
FLLD	0.940	0.803–0.983
Shoe lift	0.983	0.943–0.995
Normal	0.987	0.956–0.997

ICC, intraclass correlation coefficient (1, 1); 95% CI, 95% confidence interval; FLLD, functional leg length discrepancy.

One-way repeated-measures ANOVA showed a significant main effect of the standing condition ( $F=$ 9.991, $P<$ 0.01). On the post hoc test, the shear elastic modulus of TFL was significantly lower for the FLLD condition than for the NO condition in both male ( $P=$ 0.004, ES $=$ 1.766) and female ( $P<$ 0.0001, ES $=$ 1.737) participants (Fig. 3). The shear elastic modulus of TFL for the SL condition was not significantly different from the NO condition, but it was significantly higher than for the FLLD condition in both male ( $P=$ 0.038, ES $=$ 0.903) and female ( $P=$ 0.0007, ES $=$ 0.897) participants

Figure 3.

Bar chart showing the shear elastic modulus (kPa) of male and female participants in the post hoc test for standing condition. The shear elastic modulus of male and female participants is significantly lower in the FLLD group than in the NO and SL groups. ${}^{*}P<$ 0.05, ${}^{**}P<$ 0.01, significant difference between conditions. FLLD, functional leg length discrepancy; SL, shoe lift; NO, normal standing.

4. Discussion

The ICC ${}_{1,1}$ of the measurement was 0.904–0.983, which is considered excellent reliability [16], for all conditions. The ICC value of the shear elastic modulus for TFL in this study was also similar to that in a previous study [8]. Therefore, the measurement reliability in the present study can be considered valid.

The present results show that TFL stiffness was lower in the FLLD condition than in the NO and SL conditions. In the FLLD condition, the hip joint on the downward side of the pelvic tilting was abducted because the adjustment on the hip orthosis was fixed at 20 ${}^{\circ}$ of abduction. Additionally, the ipsilateral hip and knee joint were slightly flexed because the leg length of the affected side was apparently longer than the length of the contralateral leg. On the other hand, in the SL condition, the hip joint on the downward side of the pelvic tilting was abducted as in the FLLD condition, but the hip and knee joint extended because the shoe lift compensated for the apparent leg length discrepancy. Therefore, the flexion position of the hip and knee joints in the FLLD condition can be distinguished from other standing conditions. This suggests that the flexion position of the hip and knee joints could be a major factor for the decrease in TFL stiffness in the FLLD condition.

The change in muscle stiffness during passive joint motion could be attributed to a change in muscle tension. Muscle tension forces with passive motion increase exponentially as the muscle is stretched to its maximal length [17]. The decrease in TFL stiffness in the FLLD condition could indicate passive shortening of TFL length, because the origin and insertion of the TFL come closer together with hip flexion. In contrast, the increase in TFL stiffness in the SL condition from the FLLD condition could indicate passive stretching of TFL length, because the origin and insertion of the TFL move further away from each other with hip extension. These findings would support the previous finding that the shear elastic modulus of the hip extension position was significantly higher than that of the neutral position [8]. However, this interpretation can be acceptable when the TFL activations are equal across the three standing conditions. It has been reported that leg muscle activation patterns varied with weight-bearing load [18, 19]. It can be assumed that the TFL activations could be maintained equally because the participants controlled the leg loadings by visual and auditory feedback across the three standing conditions. Therefore, using the shoe lift to correct the compensatory hip flexion position in the FLLD could lead the hip joint to a functional position which can stretch the TFL because it is thought that positioning a muscle close to its end of range will provide a greater effect on contraction [20].

In contrast, based on the classical kinesiological understanding, it is considered that change of the knee joint into extension passively shortens TFL length. Nevertheless, TFL stiffness increased in the SL condition, indicating that the TFL was stretched. A previous study reported that the stretching position with 90 ${}^{\circ}$ of knee flexion was more effective for stretching the TFL than that with a 0 ${}^{\circ}$ knee angle [21]. In addition, it was reported that TFL stiffness with a knee angle between 0 ${}^{\circ}$ and 45 ${}^{\circ}$ during stretching was not significantly different [8]. These findings could indicate that change of the position of the knee joint to extension from a slightly flexed position is not a significant factor related to shortening or stretching of the TFL. The hip angle in the FLLD condition can contribute to the positioning function, related to the TFL length, more than does the knee angle. Therefore, this seems to suggest that increasing TFL stiffness in the SL condition results not from knee extension, but from hip extension.

These findings showing that the shoe lift for the FLLD condition can result in a functional hip position to improve TFL shortening could support the previous finding indicating the effectiveness of the heel lift in the treatment of FLLD after THA [7]. The shoe lift can be used not only as one of the compensatory approaches for reversible FLLD, but also as one of the remediation approaches to help improve the TFL shortening that causes pelvic obliquity and results in FLLD. Therefore, future studies are required to determine whether the posture change using the shoe lift for the FLLD is the functional position to improve TFL shortening in patients after THA. Clinical intervention studies should be conducted using SWE to investigate the effect of shoe lifts in the treatment of TFL shortening with FLLD after THA.

The present findings show that the effect of the shoe lift for stretching the TFL in FLLD might be useful in rehabilitation after THA. However, the findings also need to be interpreted in the context of the limitations of this study. First, the postural change between the FLLD and SL conditions was defined by extending the distance from the umbilicus to the medial malleolus while maintaining the angle of the dropped pelvis, but postural changes in lower limb joints were not evaluated quantitively. The postural changes in the SL condition could include other factors contributing to the ideal posture in addition to hip and knee extension. Second, the effect of shoe lifts for the FLLD should be applied only to the TFL muscle, because hip abductors include the anterior portion of gluteus maximus, gluteus medialis and gluteus minimus. These other hip abductors also need to be assessed in future studies. Third, lack of TFL activity assessment during the acquisition of SWE is a potential limitation of the study; it is needed to verify the assumption that the TFL activities can be maintained by controlling leg loading across the three conditions. Finally, the FLLD condition was simulated in each participant by fixing the hip angle at 20 ${}^{\circ}$ of abduction by adjustment of the hip orthosis. Additionally, the participants were healthy young adults without contractures of the joint and muscles surrounding their hips. Therefore, if a post-THA patient uses a shoe lift, a similar effect may not always be expected. Finally, myoelectric activity was not evaluated to ensure that the muscle condition was maintained equally among the different conditions. However, each participant certainly maintained symmetrical loading on both legs using the force plates.

5. Conclusions

The present study investigated the effect of an FLLD on TFL length and the effectiveness of the use of a shoe lift to correct the compensatory posture with an FLLD for the TFL elongation using ultrasound SWE. In the FLLD condition, the shear elastic modulus of the TFL decreased. With the shoe lift, the shear elastic modulus of the TFL was restored. These results suggest that using the shoe lift for FLLD can result in a functional hip position, stretching the TFL

Footnotes

Acknowledgments

This work was supported by JSPS KAKENHI Grant Number 18K17755 and the Yamagata Health Support Association.

Conflict of interest

The authors have no conflicts of interest associated with this study.

References

Nilsdotter

Petersson

Roos

Lohmander

. Predictors of patient relevant outcome after total hip replacement for osteoarthritis: a prospective study. Ann Rheum Dis. 2003; 62(10): 923-30.

Wylde

Whitehouse

Taylor

Pattison

Bannister

Blom

. Prevalence and functional impact of patient-perceived leg length discrepancy after hip replacement. Int Orthop. 2009; 33(4): 905-9.

Iversen

Chudasama

Losina

Katz

. Influence of self-reported limb length discrepancy on function and satisfaction 6 years after total hip replacement. J Geriatr Phys Ther. 2011; 34(3): 148-52.

Nakanowatari

Suzukamo

Suga

Okii

Fujii

Izumi

. True or apparent leg length discrepancy: which is a better predictor of short-term functional outcomes after total hip arthroplasty? J Geriatr Phys Ther. 2013; 36(4): 169-74.

Gurney

. Leg length discrepancy. Gait & posture. 2002; 15(2): 195-206.

Sobiech

Jabłoński

Gorzelak

Turżańska

Posturzyńska

Drelich

. Postoperative limb lengthening following total hip arthroplasty (THA) through a posterior approach – a challenge for the orthopaedist or physiotherapist? Ortop Traumatol Rehabil. 2010; 12(5): 420-9.

Nakanowatari

Suzukamo

Izumi

. The effectiveness of specific exercise approach or modifiable heel lift in the treatment of functional leg length discrepancy in early post-surgery inpatients after total hip arthroplasty: a randomized controlled trial with a PROBE design. Phys Ther Res. 2016; 19(1): 39-49.

Umehara

Ikezoe

Nishishita

Nakamura

Umegaki

Kobayashi

, et al. Effect of hip and knee position on tensor fasciae latae elongation during stretching: an ultrasonic shear wave elastography study. Clin Biomech. 2015; 30(10): 1056-9.

Bercoff

Tanter

Fink

. Supersonic shear imaging: a new technique for soft tissue elasticity mapping. IEEE Trans Ultrason Ferroelectr Freq Control. 2004; 51(4): 396-409.

10.

Eby

Song

Chen

Greenleaf

. Validation of shear wave elastography in skeletal muscle. J Biomech. 2013; 46(14): 2381-7.

11.

Koo

Guo

Cohen

Parker

. Quantifying the passive stretching response of human tibialis anterior muscle using shear wave elastography. Clin Biomech. 2014; 29(1): 33-9.

12.

Cohen

. Statistical Power Analysis for the Behavioral Sciences. 2nd ed. New York: Psychology Press Taylor & Francis Group; 1988.

13.

Faul

Erdfelder

Lang

Buchner

. G*Power 3: a flexible statistical power analysis program for the social, behavioral, and biomedical sciences. Behav Res Methods. 2007; 39(2): 175-91.

14.

Faul

Erdfelder

Buchner

Lang

. Statistical power analyses using G*Power 3.1: tests for correlation and regression analyses. Behav Res Methods. 2009; 41(4): 1149-60.

15.

Jekel

Katz

Elmore

. Multivariable Analysis. Epidemiology, Biostatistics, and Preventive Medicine. 2nd ed. Philadelphia: W. B. SAOUNDERS COMPANY; 2001: 209-19.

16.

Leong

Leung

. Quantitative estimation of muscle shear elastic modulus of the upper trapezius with supersonic shear imaging during arm positioning. PLoS One. 2013; 8(6): e67199.

17.

Magid

Law

. Myofibrils bear most of the resting tension in frog skeletal muscle. Science. 1985; 230(4731): 1280-2.

18.

Clark

Manini

Ordway

Ploutz-Snyder

. Leg muscle activity during walking with assistive devices at varying levels of weight bearing. Arch Phys Med Rehabil. 2004; 85(9): 1555-60.

19.

Asami

. Muscle activity of the lower and upper extremities in partial weight-bearing exercise. Rigakuryoho Kagaku. 2009; 24(2): 273-9.

20.

Ada

Goddard

McCully

Stavrinos

Bampton

. Thirty minutes of positioning reduces the development of shoulder external rotation contracture after stroke: a randomized controlled trial. Arch Phys Med Rehabil. 2005; 86(2): 230-4.

21.

Gajdosik

Sandler

Marr

. Influence of knee positions and gender on the Ober test for length of the iliotibial band. Clin Biomech. 2003; 18(1): 77-9.