Measuring Leg-Length Discrepancy by the Iliac Crest Palpation and Book Correction Method: Reliability and Validity

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1 938 Measuring Leg-Length Discrepancy by the Iliac Crest Palpation and Book Correction Method: Reliability and Validity Edwin Hanada, MD, R. Lee Kirby, MD, Michael Mitchell, MD, Janneke M. Swuste, BSc ABSTRACT. Hanada E, Kirby RL, Mitchell M, Swuste JM. A HIGH PROPORTION of the normal population has at Measuring leg-length discrepancy by the iliac crest palpation least a mild leg-length discrepancy (LLD). 1 A LLD of and book correction method: reliability and validity. Arch sufficient magnitude may lead to a number of problems, including increased energy expenditure in gait, 2 cosmetically Phys Med Rehabil 2001;82: disturbing gait, 3 equinus contracture of the ankle on the shortleg side, 4 late degenerative arthritis of both the long-leg hip and knee (long-leg arthropathy), 5 low back pain, 6 and compensatory scoliosis. 7 The degree of LLD that is clinically significant remains controversial. Although generally assumed to be of little clinical significance, LLD of as little as 5mm has been reported to be associated with low back or hip pain. 6 A simulated LLD of as little as 10mm can lead to a significant shift of the mean center-of-pressure position and an increase in postural sway while standing quietly. 8 In children with a LLD of 5.5% or greater of the longer leg side, more mechanical work is performed by the long extremity and there is a greater vertical displacement of the body s center of mass. 4 One commonly used direct method of clinically assessing LLD is to measure the distance from the anterosuperior iliac spines (ASIS) to the medial malleoli with a tape measure (the Objective: To determine the reliability and validity of a clinical measurement of leg-length discrepancy (LLD), by using the iliac crest palpation and book correction (ICPBC) method. Design: Intra- and interrater reliability and validity determinations. Setting: Rehabilitation center. Participants: Thirty-four healthy subjects, none of whom had an apparent LLD, as determined by iliac crest palpation. Interventions: We induced a simulated LLD (7 53mm) for each subject. To measure the LLD, the examiner performed the ICPBC method by palpating the iliac crests and correcting identified differences with a book opened to the required number of pages. The thickness of the book correction was measured. Main Outcome Measures: Reliability LLD measurement (n 20), by using the ICPBC method to measure the LLD; construct validity (n 34), comparing ICPBC measurement with the extent of the induced LLD; and concurrent validity (n 14), the difference in heights of the superior aspect of the femoral heads from standing radiographs. Results: The intraclass correlation coefficients (ICCs) for the intrarater and interrater reliabilities were.98 and.91, respectively. The ICCs for the construct and concurrent validities were.62 and.76, respectively. The ICPBC method underestimated the induced LLD by a mean difference standard deviation of mm (p.055) and the radiologic measure by mm (p.043). Conclusions: The ICPBC technique for measuring LLD is highly reliable and moderately valid. When there is no history of pelvic deformity and the iliac crests can be readily palpated, we recommend using iliac crest palpation to detect LLD, and the book correction to quantify it. Key Words: Gait; Leg; Palpation; Rehabilitation by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation From the Division of Physical Medicine and Rehabilitation, Departments of Medicine (Hanada, Kirby, Swuste) and Radiology (Mitchell), Dalhousie University, Halifax, NS, Canada. Accepted in revised form August 21, No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the author(s) or upon any organization with which the author(s) is/are associated. Reprint requests to R. Lee Kirby, MD, Rehabilitation Centre Site, Queen Elizabeth II Health Sciences Centre, 1341 Summer St, Halifax, NS B3H 4K4, Canada, kirby@is.dal.ca /01/ $35.00/0 doi: /apmr tape measure method). Nichols and Bailey 9 used the tape measure method to assess LLD, finding it reliable when the LLD was greater than 17.7mm, but unreliable when the LLD was 6.4mm or less. However, Hoyle et al, 10 by using the tape measure method to assess LLD in 25 subjects with mild LLD, found intraclass correlation coefficients (ICCs) of.90 to.95 for intrarater reliability and.98 to.99 for interrater reliability. By using the tape measure method, Clarke 11 found that both observers in his study were within 5mm of the radiograph assessment of LLD in only 20 (40%) of the 50 subjects. In contrast, Beattie et al 12 found an ICC of.77 when the tape measure method was compared with radiologic measurements on 19 subjects. However, palpating the ASIS as a bony landmark for LLD is uncomfortable for some subjects. In addition, measuring to only the medial malleoli disregards the potential for LLD arising from asymmetry in the foot distal to the tibiotalar joints (eg, from calcaneal fracture, developmental abnormalities, degenerative arthritis, Charcot foot, collapsed medial longitudinal arch). Some other potential sources of error of the tape measure method include deviation of the tape measure owing to differences in the circumferences of the legs or unilateral deviations along the long axis of the leg (eg, because of genu valgum). A common alternative method is to palpate the iliac crests of the standing subject and to estimate the extent of the asymmetry. Clarke 11 found that both observers who used the iliac crest palpation (ICP) technique alone were within 5mm of the radiograph measurement of LLD in only 16 (32%) of the 50 cases. Furthermore, of the 21 cases of LLD of at least 10mm, only 9 (43%) were correctly assessed by both observers who used this method. 11 An improvement reported by Jonson and Gross 13 is the iliac crest palpation with blocks (ICPBL) technique, in which 5-mm blocks are used to level the iliac crest heights. The ICCs that they reported for intra- and interrater reliability were.87 and.70, respectively. 13 Lampe et al 14 used

2 LEG-LENGTH DISCREPANCY, Hanada 939 wooden boards of varying thickness to correct for LLD in 159 children and found that 95% of the clinical measurements of LLD were within 15mm of the measurements made with radiographs. In our clinical practice, we have attempted to improve on the sensitivity of the ICPBL technique by using the iliac crest palpation with book correction (ICPBC) method. We screen for LLD by palpating the iliac crests in the standing position. If the extent of the LLD appears to be clinically significant (ie, one for which we would consider intervention), we then measure the extent of the difference by correcting the LLD with a book. The book is opened to the number of pages required and is placed under the foot of the shorter leg until the iliac crests are level by palpation. After removing the book, the pages are firmly compressed and this correction of the LLD is measured. The objective of this study was to determine the reliability and validity of the ICPBC technique for detecting and quantifying LLD. METHODS Subjects Thirty-four subjects were studied with their informed consent. The study had been approved by the Research Ethics Committee of the Queen Elizabeth II Health Sciences Centre. In the reliability part of the study, we examined 20 healthy subjects (13 men, 7 women). Inclusion criteria were that subjects were of adult age ( 19yr); able to tolerate standing upright for 10 minutes without assistance or assistive devices; free of hip, knee, or ankle plantarflexion deformities or contractures; able to follow instructions; and free of significant pain on weight bearing. Subjects were excluded if they had obesity to the extent that their iliac crests were difficult to palpate, if they had greater than 10mm of LLD on screening ICP examination, or if they had a history of pelvic fractures or hip arthroplasty. We chose to use healthy subjects so that, by inducing a simulated LLD, we would know the magnitude of the LLD. Of the 22 subjects originally approached for the reliability study, 1 woman and 1 man were excluded because of preexisting LLD (caused by previous trauma in both cases). In the concurrent validity part of the study, we studied an additional 14 subjects (5 men, 9 women). The inclusion and exclusion criteria were identical to the reliability portion, but each subject must also have had a previously scheduled radiograph of the hip or pelvis, so that the subjects would not be exposed to additional radiation during the study. Fifteen additional subjects were excluded from the concurrent validity study because of preexisting LLD (n 4), obesity (n 5), or previous total hip replacement (n 6). For the construct validity component of the study, all 34 subjects were studied. Simulating LLD The induced LLD, between 7 and 53mm in magnitude, consisted of placing an open book under 1 foot by an assistant who was not an examiner. The side and the magnitude of the induced LLD were randomly balanced to ensure that an almost equal number of small (7 17mm), medium (18 35mm), and large (36 53mm) LLDs were induced to both legs. After each ICPBC measurement, the thickness of the firmly compressed book used to induce the LLD was measured to the nearest millimeter with a metal ruler. The assistant covered both lower legs with modified cardboard boxes so that the examiners could not discern the side or extent of the induced LLD. The subjects were asked to stand as upright as possible, with the feet firmly planted on the book or floor, approximately shoulder-width apart, trying to avoid any compensatory knee flexion or ankle plantarflexion. Clinical Measurement To perform the ICPBC procedure, the examiner crouched in front of the subject to place the eyes at the level of the iliac crests. The examiner held the arms out straight, angling the fingers in from the side, and then palpated firmly on top of the iliac crests in the frontal plane (fig 1). The examiner made an estimate of the side and extent of the LLD by both palpation and visual input. The cardboard box around the shorter leg was removed. The examiner then corrected the induced LLD by placing a second book, open to the required number of pages, under the shorter limb. A square-cut book with a paper cover was found to be most practical. Through trial-and-error of palpating the iliac crests and then making adjustments in the number of open pages in the book on the side being corrected, the examiner arrived at iliac crests that were perceived to be level. This rarely required more than 3 trials. The clinical measurement of the induced LLD consisted of the examiner measuring the thickness of the compressed pages of the book with a metal ruler (to the nearest mm) (fig 2). In a separate time trial in which 2 examiners each evaluated 9 simulated LLDs, the mean standard deviation (SD) time to screen for and quantitate a LLD was seconds, seconds of which was used for screening. Fig 1. The ICP procedure.

3 940 LEG-LENGTH DISCREPANCY, Hanada Table 1: Reliability and Validity of the ICPBC Method of Measuring LLD n ICC Mean Difference SD (mm) Reliability Intrarater Interrater Validity Construct Concurrent p Fig 2. Determining the extent of the LLD by measuring the thickness of the book correction needed to level the iliac crests. Reliability Each subject was measured 3 times, twice by the first examiner and once by the second examiner. Although examiner 1 could not be blinded to the results of his first measurement, the approximately 15-minute separation between the first and second measurements was considered to have minimized potential bias. Neither examiner was present during the other examiner s measurement. Validity The ICPBC method was considered to have good content validity in that the segments measured included the feet and, because the technique is performed with the subject bearing weight, the ICPBC takes into consideration any telescoping inherent in the limb (eg, secondary to a Girdlestone procedure). The LLD measured by the ICPBC method was compared with the induced LLD (n 34) as an evaluation of construct validity. To evaluate concurrent validity, the LLD was induced as the subjects stood upright in front of the cassette holder for the radiograph machine. The induced LLDs were measured once for each subject by examiner 1 by using the ICPBC method. While still standing with the induced LLD, anteroposterior radiographs of the hips and pelvis were taken. These radiographs were assessed by a radiologist who was blinded to the side and the extent of the induced LLD. The radiologic measurement of the induced LLD (the criterion measure or gold standard) was determined by drawing horizontal lines perpendicular to the lateral edges of the radiograph film at the levels of the superior margin of each femoral head. The difference in height between these lines was measured with a metal ruler to the nearest millimeter, a method used by Clarke. 11 In a subset of our subjects (n 8), we found a high correlation (r.99) between iliac crest height differences and femoral head height differences as measured on the anteroposterior view of radiographs of the pelvis. Data Analysis Reliability and validity were determined by calculating ICCs and matched-pairs 2-tailed t tests. Statistical significance was defined as p less than.05. RESULTS Table 1 shows the high reliabilities as is reflected by the strong correlations and the minimal differences. The mean differences for validity indicate that the ICPBC tended to underestimate the induced LLD by mm and underestimate the induced LLD that was measured radiologically by mm (table 1). The reliability correlations are shown in the scatter plots (figs 3, 4). In the reliability study, the data collection was incomplete in 2 subjects. In 1 of these subjects, with an induced LLD of 7mm, both examiners incorrectly estimated that the lift was under the contralateral limb, leaving 19 subjects for determining intrarater reliability. In the other subject, with a body mass index (BMI) of 29 (from selfreported height and weight), examiner 2 was unable to determine correctly the side of the induced LLD of 26mm, leaving 18 subjects for determining interrater reliability (fig 4). In both cases, having inadvertently removed the wrong cardboard box, the book correction phase could not be completed. Also, in 3 subjects, the induced LLD was removed from under the foot without it being measured. The loss of these 3 subjects and the single subject mentioned earlier in which both examiners incorrectly identified the side of the lift, left only 30 subjects on which to study construct validity (fig 5). The side of induced LLD was correctly identified in 94% of the 54 ICPBC measurements overall (33 by examiner 1, 18 by examiner 2), in 98% of the 49 ICPBC measurements (31 by examiner 1, 17 by examiner 2) for LLD 10mm or greater, and in 60% of the 5 ICPBC measurements (2 by examiner 1, 1 by examiner 2) for LLD less than 10mm. DISCUSSION The reliability and validity of the ICPBC method of measuring LLD has been documented. Although there was a statistically significant difference between the 2 measurements of examiner 1, the mean difference was only mm, which Fig 3. Intrarater reliability (n 19). The first and second measurements by examiner 1 are plotted.

4 LEG-LENGTH DISCREPANCY, Hanada 941 Fig 4. Interrater reliability (n 18). The measurements of the 2 examiners are plotted. is not clinically significant (table 1). In comparison with the extent of the induced LLD and the radiologic measure, the examiner using the ICPBC method underestimated the LLD by mm and mm, respectively (table 1). Although the latter was statistically significant, the magnitude of the mean difference was of minimal clinical significance. In comparison to the ICP method alone, that has been reported not to be highly reliable, 15 the ICPBC technique fared well. Some difficulties encountered by the examiners in this study included having uncertainty in determining the side and extent of the LLD in subjects with increased adipose tissue over the iliac crests. This uncertainty was more frequent in, but not exclusive to, patients with a higher BMI. For patients in whom the adipose tissue prevents a clear identification of the iliac crests and in whom clinically significant LLD is suspected, we recommend that the radiologic method be used. Similarly, it was difficult for the observers to palpate the iliac crests in subjects who wore loose, bulky clothing. We recommend that the clothing over the iliac crests be removed or displaced when performing this clinical test. Also, both examiners experienced some difficulty in determining the correct side for induced LLD less than 10mm though the small number of subjects in this group warrants further study of the validity of the ICPBC technique for small LLDs. Furthermore, the examiners found it challenging to ensure that subjects were weight bearing equally on both feet, while keeping their knees straight, especially with Fig 6. Concurrent validity (n 14). The extent of the LLD measured by the ICPBC method is plotted against the radiologic measurement of the LLD. larger induced LLDs. Although having the subjects stand on scales could have decreased the magnitude of this problem, we chose to use the more clinically realistic situation without scales. Examiner 1 performed 2 measurements within a short interval, which might have lead to an overestimation of intrarater reliability. However, the high interrater reliability suggests that any such overestimation was minimal. In the validity part of the study, any magnification error on the radiograph would be a source of error in the validity of the radiologic measurement of the LLD (fig 6). Finally, because ICP was a key component in the ICPBC technique, pelvic or sacroiliac joint asymmetry may have been another source of error. We recommend the radiologic technique in patients with a history of pelvic deformity or fracture. Despite the occasional patient for whom the ICPBC technique is inappropriate (ie, owing to obesity or pelvic deformity), we believe that the ICPBC method of measuring LLD is the best of the clinical techniques reported to date. It is quick and simple to administer. In comparison with the tape measure method, there is only minimal discomfort experienced by the participants and, unlike the tape measure method, the ICPBC method will identify any asymmetry in the foot distal to the tibiotalar joints. With the subjects upright and weight bearing, the ICPBC takes into consideration any telescoping inherent in the limb (eg, secondary to a Girdlestone procedure). In comparison with the ICPBL method, the ICPBC method allows greater sensitivity (it can be measured to the nearest 1mm rather than 5mm) and is a more portable method (books are more readily available on wards and in offices than blocks). The reliability and validity of the ICPBC method is as good or better than other published methods. CONCLUSIONS The ICPBC technique for measuring LLD is highly reliable and moderately valid. When there is no history of pelvic deformity and the iliac crests can be readily palpated, we recommend using the ICP component of the test to detect LLD, and the book correction component to quantify it. Fig 5. Construct validity (n 30). The extent of the LLD measured by the ICPBC method is plotted against the extent of the induced LLD. Acknowledgments: The authors thank Jeannine Romard for radiographic assistance; Alison McDonald, Jeff Pike, and Don MacLeod for participating in pilot work; and the staff of the Orthotics and Prosthetics Department at the Nova Scotia Rehabilitation Centre for their participation as subjects.

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