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Abstract
Background Lateral scapular slide test (LSST) quantitatively measures the distance between thoracic spine (T7) and inferior angle of scapula.
Objective In this study, the intra-rater reliability, inter-rater reliability and diagnostic accuracy of LSST were measured using a caliper.
Methods Three measurements of each test position were obtained bilaterally. Intraclass correlation coefficient (ICC) (2.1), 95% CI and 2 SEMs were calculated for intra-rater and inter-rater reliability of the absolute scapular distance. Sensitivity, specificity, positive and negative likelihood ratios were determined.
Results 27 people with and 30 people without shoulder pain participated. The mean age (SD) for the participant was 47.7 (11.6) years and 33.5 (11.7) years, respectively. The ICCs for intra-rater reliability were high. A range of poor to good ICCs was found for inter-rater reliability. The 2 SEMs ranged from 4.6 to 7.9 mm for intra-rater reliability and from 6.8 to 13.4 mm for inter-rater reliability for people with shoulder pain. Positive and negative likelihood ratios from 0.94 to 1.22 and from 0.21 to 2.5, respectively, were demonstrated.
Conclusion SST did not show a consistent high reliability. The diagnostic accuracy of the LSST was low, which questions the clinical importance of the tests outcomes.
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Shoulder joint function may be affected by an alteration in scapular position. Although Devita et al indicated that there is no relationship between the position of the scapula and the muscular force,1 others have shown that scapular position may have a relationship with scapular stability and force generation.2 3 Symmetrical position of the scapula indicates a balance in the stabilising muscles. Any muscle imbalance in shoulder complex may change scapular position and symmetry of shoulder motions.4 5 As a result, shoulder injury and dysfunction pose challenges in sport medicine cases, among others. To assess the asymmetry, a reliable and valid measurement is necessary. The lateral scapular slide test (LSST) developed by Kibler is an indirect method of examining the scapular muscle strength by measuring scapular symmetry in various load positions.6 LSST is a simple, less time-consuming and clinically approved test to evaluate scapular stability in shoulder rehabilitation protocols.7 Kibler initially recognised a 1-cm side-to-side difference in scapular positions as being clinically significant. Then he found that in the injured athlete, the side-to-side differences are greater than 0.63 cm, with a range of 0.83 to 1.75 cm. Therefore, for purposes of clinical evaluation, he has established 1.5 cm of asymmetry as the threshold of abnormality and accepted this in any three positions of the test.6 Some studies6 8 9 used tape measure, but others10 11 used string to measure the reliability of LSST. Previous studies on the reliability and validity of the LSST have shown conflicting results.6 8,–,14 Gibson et al11 and Odom et al10 reported poor inter-rater reliability and low grade of sensitivity and specificity for LSST, but McKenna et al8 showed good inter-rater reliability for LSST. Nijs et al9 determined fair inter-rater reliability for LSST. Koslow et al15 determined the low grade of specificity of LSST in detecting shoulder dysfunction in competitive athletes.
To increase the accuracy and reduce measurement errors due to elastic properties of string or tape, some authors have recommended using a more precise instrumentation such as a caliper.11 15 Therefore, the main goal of the present study was to determine the reliability and diagnostic accuracy of the LSST using the caliper.
Methods
Study design
This was a cross-sectional, prospective, repeated-measure study of 57 subjects by three examiners in one session.
Subjects
Thirty normal subjects and 27 patients, aged between 18 and 65 years old with a variety of shoulder pathology, were referred by an orthopaedic surgeon. All patients were recruited from two private physical therapy clinics and one outpatient physical therapy division of a general hospital. The asymptomatic subjects were recruited into the study by a general announcement in the faculty.
The numbers of subjects with different shoulder dysfunction are shown in table 1. Before participating in this study, all subjects signed an informed consent form.
Patients with different shoulder dysfunctions (n=27)
Inclusion criteria
To be included in this study, subjects had to be diagnosed as having shoulder pathology by an orthopaedic surgeon. Subjects had to be able to actively perform 0°, 45° and 90° of abduction and full internal rotation of the shoulder. All patients had to have pathology in one shoulder.
Exclusion criteria
Patients were excluded if they had the following problems: previous shoulder surgery, a history of systemic disease, neuromuscular dysfunction and obesity (body mass index 29.9 or greater). Obesity would make identification and palpation of bony landmarks difficult.
Instrumentation
A digital Vernier caliper with an accuracy of 0.01 mm (Mitotuyo Company, Kanagawa, Japan) was used in these experiments.
Examiners
Three physical therapists administered the LSST to the patients at the Physical Therapy department of the Faculty of Rehabilitation of Tehran University (Medical Sciences, Tehran, Iran). Before study initiation, the examiners did not receive extensive training on the use of the LSST. The test procedure was explained to the examiners in a 2-h single session.
Three examiners tested the scapular symmetry for inter-rater reliability. For the intra-rater reliability component of the study, one of the examiners repeated the test 30 min later.
Measurements
Each examiner identified and marked the prominent spinous process of C7 in cervical flexion by palpation with the subjects in standing position, and then, the spinous process of other vertebra down to T7 was palpated. The examiners bilaterally measured the distance between the inferior angle of scapula and the spinous process of T7.16 The order of measurements among the three examiners, injured or uninjured side in patients, right or left side in normal subjects and arm positions, were randomised by lottery. Figure 1 shows the position of the subjects during measurements. These experiments followed the Kibler method due to the functional characteristic of this test. The estimation of the shoulder positions was done visually. The first position was of the arm relaxed at the sides (0° of shoulder abduction). The second was the subject's hand around the waist with the web space between the thumb and second finger placed on the lateral iliac crest (45° of shoulder abduction); and the third was with the arm abducted at or below 90° and in full internal rotation. To maintain a consistent posture during the test, subjects were instructed to fix their eyes on an object in the examination area. Subjects were given as much rest time between positions and during measurements as they required, usually not more than 30 s. Interval time between examiners was 2 min.
Three different positions of lateral scapular slide test.
The subject then stood in a relaxed position for 30 s before the same examiner palpated the inferior angle of the scapula. The examiners measured the distance from the T7 spinous process to inferior angle of scapula in all three arm positions; this linear distance was defined as the scapular index. The caliper was set to zero after each measurement. After one examiner obtained a complete set of measurements on a subject in all three test positions, the tags marking the spinous process were cleaned and remarked. The same test procedure was repeated by the other two examiners.
Statistical analysis
Intraclass correlation of coefficient (2 1 two-way random effects model) and 95% confidence interval (CI) for the ICC were used to analyse the reliability of LSST. Standard error of measurements (2 SEMs) were computed.11 The ICCs were classified as follows: ,0.69, poor correlation; 0.70-0.79, fair correlation; 0.80-0.89, good correlation; 0.90-1.00, high correlation.17 We computed both the sensitivity and specificity of the LLST. A sensitive test correctly identifies those individuals with a scapular pathology, whereas a specific test identified healthy individuals. The scapular differences of 1 to 1.5 cm were tested. To determine the diagnostic accuracy of LSST, sensitivity, specificity, positive likelihood ratio (PLR) and negative likelihood ratio (NLR) were computed.18 All data were analysed using SPSS software V.1 1.5.
Results
The ICCs, 95% CI and 2 SEMs for reliability are shown in tables 2 and 3. In all three positions, the ICC scores indicated a high level of reliability for intra-rater and inter-raters for healthy subjects (ICC>0.92). In the patient group, the ICC scores showed a good to high level for intra-rater reliability (ICC>0.87), but a poor to good ICCs scores for inter-rater reliability (0.63 to 0.860).
Level of 2 SEMs (mm), ICCs and 95% CI for intra-rater and inter-rater reliability in healthy subjects
Level of 2 SEMs (mm), ICCs and 95% CI for intra-rater and inter-rater reliability in patients groups (n=27)
The sensitivity was 100%, and the specificity was 4% (tables 4 and 5). The range of PLR was from 0.94 to 1.22 and the range of NLR was from 0.21 to 1.75 (tables 6 and 7).
Sensitivity and specificity of lateral scapular slide test*
Sensitivity and specificity of lateral scapular slide test*
Positive and negative likelihood ratios of lateral scapular slide test*
Positive and negative likelihood ratios of lateral scapular slide test**
Discussion
Intrarater reliability of the absolute scapular distance was between good to high level in both groups. Reliability values were greater for caliper than for tape measure reported by previous studies.6 11 However, inter-rater reliability value was poor in the third position. The results did not demonstrate a consistent pattern of decrement in reliability from the first test position to the third, as was previously noted by Gibson et al.11 The SEMs for reliability of LSST with caliper were lower than that of the tape measure.6 Consistent with pervious studies, our study demonstrated that linear distance between C7 and inferior angle of scapula can be reliable for positions 1 and 2 of the Kibler method.9 14
According to Gibson et al,11 the error in using string or tape existed when on one trial, it is pulled taut to yield the shortest distance between landmarks, and on another trial, it is allowed less tension to follow skin counters. For this reason, Gibson et al suggested an accurate instrument such as a caliper.
Kibler3 6 assumed that the injured side should exhibit a longer scapular distance than the uninjured side; however, in this study, the same pattern was frequently observed. In the study by Odom et al,10 the experience of examiners in orthopaedic cases were 4-7 years but in the study by Nijs et al,9 the examiners were all senior physical therapy students. In the present study, three physical therapists administered the LSST to the patients. The examiners were junior physical therapists experienced in outpatient orthopaedics who had received previous training for this project.
Some previous studies have reported poor reliability with greater glenohumeral elevation.6 11 In this study, we found low inter-rater reliability between examiners in the third test position in subjects with shoulder impairment. We believe this position imposed a heavy load on the arms and adversely influenced the accuracy of measurements. On the other hand, the inferior angle of scapula was difficult to identify in the third test position due to muscle contractions of scapular stabiliser. Therefore, the measurements for the third test position might not be accurate.
The LSST is essentially a measurement of a single planar two-dimensional lateral movement of the scapula. Scapular motion, especially as the arm reaches higher levels of abduction, involves three-dimensional motions that are not in the plane of the measurements by caliper. This is probably the major reason for the inconsistency in the findings with progressive arm elevation angles. Moreover, the lack of a distinct reference point on the inferior angle of the scapula contributed to variations in measurements.
Sensitivity of the LSST was high for all the three test positions, but the specificity was low. In contrast to Odome et al,10 our results demonstrated that the caliper could improve sensitivity. Therefore, it appears that LSST can be used to identify individuals with a shoulder dysfunction. Also, these findings clearly suggest that the LSST lacks specificity for subjects without a shoulder dysfunction. The present study supports the notion that asymmetry is not necessarily an indicator of dysfunction. The present study was conducted on non-athletic subjects while the original Kibler study was done on athletic populations. However, because of the low specificity of the LSST, its use in other populations warrants a careful future study. This test will only be of meaning if asymmetry is proven to be associated with shoulder pathology. Additionally, patients in acute phase of shoulder pathology have demonstrated pain and restriction of shoulder movements and are not suitable candidates for this clinical test. Meanwhile, these patients probably do not have any asymmetry in the shoulder joint.
The present study shows that the caliper measurement of the single planar two-dimensional motion is not necessarily an indicator of shoulder dysfunction. The LSST is really a two-dimensional evaluation of a three-dimensional problem, especially as the arm goes into the functional positions of abduction. However, according to the results of positive and negative likelihood ratios, the diagnostic utility of LSST is low, and the clinical importance of the tests outcomes, however, is questionable.
What is already known on this topic
Lateral scapular slide test is used to determine scapular position with the arm abducted 0°, 45°, and 90° in the coronal plane.
Different researches have measured the reliability of LSST by tape or string and reported conflicted results (concerning intra-rater and inter-rater reliability).
What this study adds
The use of a digital Vernier caliper as was applied in the present study appeared to be more accurate than tape and string measurements. Therefore, we recommend the use of such a method in measurement of lateral scapula slide test.
This study demonstrated that the caliper could improve sensitivity of the LSST in identifying subjects with shoulder dysfunction; but positive and negative likelihood ratios showed that the diagnostic utility of LSST was low, and the clinical importance of the tests outcomes, however, is questionable.
Practical applications
To develop a programme for the rehabilitation of scapular dyskinesis, quantitative measurement of the scapular stabilising muscle strength can be made using LSST. This semidynamic test evaluates scapula in three positions on the injured and non-injured sides in reference to a fixed point on the spine, while varying amounts of load are put on the supporting muscles. These positions provide a graded challenge to the scapular stabilising muscles. LSST is a simple, less time-consuming and clinical test to evaluate scapular stability in shoulder rehabilitation protocols.
Acknowledgments
This project was supported by a grant from the Research Program, Tehran University of Medical Sciences, Faculty of Rehabilitation. The authors would like to thank Dr Shohre Jalae for her helpful advice on statistical analysis used in this study. We also appreciate the staff of the Faculty of Rehabilitation, Tehran University of Medical Sciences for their assistance in this project.
References
Footnotes
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Competing interests None.