The validity and intra-tester reliability of a clinical measure of humeral head position

Manual Therapy 14 (2009) 397–403

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Manual Therapy journal homepage: www.elsevier.com/math

Original Article

The validity and intra-tester reliability of a clinical measure of humeral head position Leanda McKenna*, Leon Straker, Anne Smith Curtin University of Technology, School of Physiotherapy, G.P.O. Box U1987, Perth, WA 6845, Australia

a r t i c l e i n f o

a b s t r a c t

Article history: Received 18 December 2007 Received in revised form 6 May 2008 Accepted 29 June 2008

The purpose of this study was to determine the degree of criterion validity and intra-tester reliability of humeral head palpation in subjects with shoulder pathology. The study also sought to determine whether there was any effect of arm position on humeral head position in subjects with shoulder pathology. In a same day repeated measures design, 27 subjects had the distance between the most anterior portion of the humeral head and the anterior edge of the acromion measured by a radiologist using MRI (supine), and by a physiotherapist using palpation and photography (supine, sit with arm in neutral and in abduction). The Standard Error of Measurement (SEM) for the difference between MRI and palpation ranged from 3.4 to 4.4 mm and correlated significantly with palpation measures in sit (r ¼ 0.57–0.64, p  0.002). The Intraclass Correlation Coefficients (ICCs) and SEMs for intra-tester reliability were 0.85 and 2.6 mm for supine, 0.86 and 2.2 mm for sit (glenohumeral neutral), and 0.91 and 3.0 mm for sit (glenohumeral abduction). Significant differences between the positions of sit neutral and sit with abduction were found (p < 0.001). Humeral head palpation in sit abduction demonstrates sufficient validity and reliability for clinical use. Ó 2008 Elsevier Ltd. All rights reserved.

Keywords: Shoulder Palpation Validity Reliability

1. Introduction Subacromial impingement is a well recognized, painful and potentially limiting condition. Theoretically, anterior position of the humeral head in relation to the acromion may compromise the subacromial space (Michener et al., 2003), because the humerus is in greater proximity to anterior structures in elevation (Ludewig and Cook, 2002; Werner et al., 2004; Bach and Goldberg, 2006). Measuring the habitual anterior position of the humeral head in relation to the acromion may therefore be important when assessing patients with impingement syndromes. Measurement of in vivo humeral head position usually quantifies the minimal acromiohumeral or coracohumeral interval by imaging or complicated methods. These methods are not practical for repeated clinical use and a simple, palpatory technique may be more appropriate. Published methods have concentrated on evaluating the superior position of the humeral head in relation to the acromion. However, the superior aspect of the humeral head under the acromion is difficult to palpate and assessment of the superior position of the humeral head in relation to the acromion may not be possible in the clinic. Given

* Corresponding author. Tel.: þ61 8 9266 3660; fax: þ61 8 9266 3699. E-mail address: [email protected] (L. McKenna). 1356-689X/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.math.2008.06.004

that anterior and superior migrations of the humeral head (and resultant proximity to subacromial structures) during flexion appear to be closely linked (Harryman et al., 1990a,b; Werner et al., 2004), anterior assessment may also provide insight into acromiohumeral proximity. The anterior portion of the humeral head and acromion are easily located by palpation may provide a useful technique to enhance the therapeutic decision-making process and has been used previously as an assessment tool (Mckenna et al., 2001). 1.1. Validity and reliability of a palpatory method Humeral head palpation has been examined for reliability (Bryde et al., 2005) in a healthy population, but not in a population with pathology. Additionally, there does not appear to be any validity study examining anterior humeral head position assessment that is applicable to impingement. 1.2. Criterion standard X-rays have previously been used as the criterion of gold standard against which palpatory techniques were judged in live subjects, but has possible errors of magnification, projection, patient positioning and identification of landmarks (Vaatainen et al., 1991; Sutherland and Bresina, 1992; Kladny et al., 1996; Duralde and Gauntt, 1999; Graichen et al., 1999b; Burckhardt et al.,

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2000; Schulze and d’Hoedt, 2001). Ultrasound accuracy is highly operator dependent (Tirman et al., 1997; Torriani and Kattapuram, 2003; Roemer et al., 2005) and CT involves high levels of radiation exposure. As a criterion standard, MRI appears to have the advantages of high tissue contrast (Kladny et al., 1996; Eckstein et al., 2001) with high resolution (Torriani and Kattapuram, 2003) and therefore may be theoretically superior in measuring distances.

1.3. Influence of testing position One disadvantage of using MRI as a validation tool is that closed MRI machines do not allow shoulder joint elevation and images are generally taken in a neutral position that can be sustained by the patient. Closed MRI is often the standard choice for patients with impingement type symptoms who require imaging. Thus any validity study in patients with impingement that uses closed MRI as the reference comparison should use the same glenohumeral joint position as that utilized within the MRI machine. However, neutral positions may not be provocative enough to elicit a pathological habitual humeral head position. Elevation is recognized as a provocative position for glenohumeral impingement because the subacromial space narrows in elevation (Warner et al., 1994; Allmann et al., 1997; Moffet et al., 1998; Graichen et al., 1999a,b; Hinterwimmer et al., 2003) and may be reduced to 1.0 mm in patients with impingement (Allmann et al., 1997; Graichen et al., 1999b). Measurement of humeral head position in elevation is therefore likely to be used where clinicians wish to elicit symptoms that are difficult to provoke. Validity therefore needs to include both the neutral and the elevation positions to address the dual issues of appropriate validation and clinical need.

1.4. Purpose of this study Firstly, to determine the degree of criterion validity of a palpatory method of humeral head position measurement in subjects who have shoulder pathology. Secondly, to determine the degree of intra-tester reliability of a palpatory method of humeral head position measurement in subjects who have shoulder pathology. Thirdly, to determine the effect of arm position on humeral head position (measured by a palpatory method) in subjects who have shoulder pathology. 2. Methods 2.1. Study design This was a double blind validity and intra-tester reliability study utilizing a qualified physiotherapist (LMcK) and consultant radiologist. Curtin University of Technology Human Research Ethics Committee approved this study and all rights of the individual were protected. 2.2. Subjects Subject recruitment was conducted over one year as shown in Fig. 1. Participating surgeons invited patients undergoing shoulder MRI into the study if they were aged above 18, and had a provisional diagnosis of impingement or rotator cuff disease, as determined by an orthopaedic surgeon. Subjects were excluded from the

Patients referred to Orthopaedic Specialist by General Practitioner

Some patients referred for MRI of the shoulder by Orthopaedic Specialist Patients that met the inclusion no criteria invited to join study

yes

1 patient was unable to allow extra time for testing

32 patients indicated they would like to join the study.

no

3 patients could not be contacted 1 patient could not be tested as the testing room was double booked

yes 25 patients tested immediately yes prior to MRI 27 subjects in study yes

2 patients tested immediately post MRI

Patients underwent MRI Fig. 1. Flowchart of study participants.

L. McKenna et al. / Manual Therapy 14 (2009) 397–403

study if they had a suspected shoulder fracture or grossly unstable glenohumeral joint. Potentially interested patients received written information from the surgeon’s secretary to read in the waiting room. Those interested in participating in the study indicated to the secretary that their phone number could be given to the chief investigator. Inclusion to the study was dependent upon the volunteers’ reading and signing an informed consent immediately prior to measurement at the MRI centre. A priori analysis suggested that a minimum of 24 subjects was needed to achieve 80% power to detect a systematic difference between MRI and palpatory measures of 3.0 mm (5.0 mm) using a 2-tailed t-test (a ¼ 0.05). A sample of 26 subjects has 80% power (a ¼ 0.05) to detect a correlation of 0.52.

399

weighted sagittal and proton density weighted fat saturated axial sequences in patients requiring gadolinium injection (see Fig. 3). Sagittal image resolution matrix was 256  192 pixels (repetition time 500–3250 ms, echo time 14.0–35.4 ms) and 384  224 for the axial views (repetition time 640–3000 ms, echo time 13.5– 28.5 ms). Slice thickness was 3.0 mm (1.0 mm inter-slice gap) and field of view 14.0 cm  14.0 cm. Using digital MRI images, the radiologist identified the anterior margin of the acromion and the anterior margin of the Deltoid where it overlaid the most anterior portion of the humeral head (see Fig. 3). Values drawn from images were made available to the chief investigator at the conclusion of the study. 2.4. Data processing

2.3. Data collection 2.3.1. Palpatory method Subjects completed a questionnaire, immediately prior to palpation testing at the MRI centre, which enquired about date of birth, hand dominance and shoulder pathology. Height and weight were measured. The shoulder was prepared with the application of a patch of clear adhesive plastic dressing (Tegaderm, 3M Health Care, St. Paul, Minnesota, USA). Subjects were tested using a random order for position: (1) supine with arm by side and slight external rotation, (2) sitting, neutral glenohumeral joint, and (3) sitting, arm supported in abduction. The arm was supported in abduction using a removable wooden platform set at axillary height and attached to the camera tripod. The anterior acromion was palpated and marked with a line. The examiner placed a mark on their index finger that corresponded with the point of maximal palpatory pressure. The most anterior aspect of the subject’s humeral head was palpated and the examiner placed their marked finger on this point. A photograph (see Fig. 2) was taken using a digital camera (Kodak DC4800, Eastman Kodak Company, NY) mounted 20.0 cm superiorly above the shoulder. All subject marks were removed and the procedure was repeated twice for each position.

Digital photographic images were corrected for lens pincushion distortion using a 32% correction from Colour Science Image factory Home Edition program (http://www.colour-science.com/if/ registration.htm). A custom program (High-Tech Laboratories, Perth, Western Australia) was used to calculate the humeral head distance following correction for scaling and parallax error using the formulas shown in Appendix 1. The scaling factor was taken from a rule included in the field of view. Calculation of parallax error required the vertical distance (dv in Appendix 1) between the acromion and most anterior portion of the anterior humeral head as measured from MRI by the chief investigator. Using the computer software, the investigator placed digital points on either end of the marked anterior margin of the acromion and at the marked investigator’s finger (placed against the anterior point of the humeral head). The software calculated the line of best fit along the acromion and the perpendicular distance from the line to the most anterior point of the humeral head (see Appendix 1 and Fig. 2). 2.5. Statistical analysis Statistical processing was performed using SPSS (Statistical Packages for the Social Sciences) version 13 for Macintosh. A trial

2.3.2. MRI The subject underwent MRI in supine with arm by side and in slight external rotation. A closed MRI system (General Electric Sigma 1.5T, Milwaukee, USA) with dedicated phased array shoulder coil was used. Two image sequences were used – either proton density weighted sagittal and fat saturated axial sequences or T1

Fig. 2. Photograph showing palpation technique for measurement of anterior humeral head to acromion distance (viewed from the superior aspect of the shoulder). Dashed line indicates the extrapolated acromion line. The continuous line (points 1–2) indicates the perpendicular distance between the examiner’s finger overlaying the anterior humeral head and the dashed acromial line.

Fig. 3. MRI showing measurement of anterior humeral head to acromion distance. Dashed line extrapolates the most anterior portion of the humeral head to level with the acromion. Continuous line (points 1–2) indicates the distance between anterior acromion and the dashed line.

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order effect was examined with a Repeated measures Analysis of Variance (RANOVA), with posthoc examination of individual trial comparisons. Validity was examined for agreement between the two methods of measuring humeral head position by calculating a mean difference between methods (Bland and Altman, 1986), Pearson’s correlation coefficient (r) and Standard Error of Measurement (SEM). SEM ¼ OMSE, where MSE is the square root of the RANOVA Mean Square Error (Stratford and Goldsmith, 1997). Intra-tester reliability of the palpatory method was examined using Intraclass Correlation Coefficient (ICC) for consistency and for absolute agreement (McGraw and Wong, 1996), and SEM. Comparison between positions was analysed using a one factor RANOVA. Posthoc analysis of contrasts between individual positions was performed to identify significant differences in position. Bivariate correlations between arm positions were also performed.

Table 2 Anterior humeral head to acromion distances (mm) as measured by palpatory and MRI methods (mean (sd)). Palpation

Supine Sit neutral Sit abduction

MRI

Trial 1

Trial 2

Trial 3

Mean of 3 trials

18.7 (6.5) 17.0 (6.4) 22.9 (7.8)

18.3 (6.4) 17.0 (6.6) 21.5 (7.8)

17.8 (5.5) 16.0 (6.1) 20.7 (8.0)

18.2 (5.8) 16.7 (6.1) 21.7 (7.5)

14.0 (5.3) NA NA

Larger values indicate a more anterior humeral head, in comparison to the acromion.

(F ¼ 49.43, p < 0.001). These two positions were also highly correlated to each other (r ¼ 0.89, p < 0.001), whereas there appeared to be no correlation with supine measures (sit neutral–supine r ¼ 0.26, p ¼ 0.200; sit abduction–supine r ¼ 0.12, p ¼ 0.555).

4. Discussion

3. Results One subject’s data were excluded from analysis as the MRI showed evidence of previous anterior dislocation (marrow oedema was evident within the posterosuperior aspect of the humeral head, with slight flattening) and therefore possible instability, despite fulfilling initial inclusion criteria. Patient demographic data are presented in Table 1. There were 21 males and 5 females. 54% of subjects had dominant arm symptoms. Pathology found at MRI included calcification, atrophy, thickening, fraying and tears of the rotator cuff tendons, bursal thickening and effusion, mild subluxation, tearing and rupture of the biceps tendon, acromioclavicular joint degeneration, glenohumeral joint synovitis, SLAP lesions, and paralabral cysts. 7 Subjects had been injected with gadolinium to enhance diagnostic findings. Mean anterior humeral head distance from the anterior acromion measured between 14.0 and 21.7 mm, depending on position and method of assessment (see Table 2). There was a trial effect within the palpatory method for sit abduction (F ¼ 3.49, p ¼ 0.039) due to a difference between trial 1 and trial 3 (F ¼ 5.31, p ¼ 0.030). Other positions did not demonstrate a significant trial effect. The mean of three trials was used for further analysis. Soft tissue overlay measured between the anterior humeral head and skin on MRI was on average 17.7 mm thick (Standard deviation (sd) ¼ 0.5 mm, range ¼ 8.0–32.0 mm). MRI measured the average anterior difference between the humeral head and acromion as 4.2, 2.7 (see Fig. 5) and 7.7 mm smaller than the palpatory measurement of the humeral head in supine, sit neutral and sit abduction, respectively (see Table 3). A pattern of higher validity for palpation in sit positions compared to supine positions was demonstrated by lower SEMs and greater correlations between palpation in sit and MRI (see Table 3 and Fig. 4). Intra-tester reliability revealed ICCs (repeated measures in each position) that were all above 0.85. The SEMs were all below 3.0 mm (see Table 4). There was a significant difference between positions (F ¼ 7.07, p ¼ 0.009) with sit abduction demonstrating the most anterior humeral head position (see Table 2). This overall difference was due to the significant difference between sit abduction and sit neutral

Table 1 Subject attributes. Attribute (unit)

Mean (standard deviation)

Range

Age (years) Weight (kg) Height (cm) Chronicity of pain (months)

52.0 87.2 175.3 30.5

22.4–76.3 60.0–146.0 157.0–188.5 2.0–120.0

(13.6) (15.8) (8.6) (32.3)

4.1. Validity Previous criterion validity studies of palpation assessment techniques of the humeral head were confined to assessment of inferior subluxation. These studies reported slightly higher correlation coefficients (rho ¼ 0.70–0.76) than that found in this study (r ¼ 0.64), which may be a result of the differences in recording (fingerbreadths versus mm) and the type of correlation coefficients used (Spearman versus Pearson). Despite finding similar correlations to each other, these authors have concluded the technique to be both valid (Prevost et al., 1987; Boyd et al., 1993) and invalid (Hall et al., 1995). These conclusions were based only on correlations and demonstrate the subjective nature of using an association to decide whether to use a technique or not. This demonstrates the need for reporting additional statistical analyses such as SEM and mean difference to allow adequate assessment of validity. Comparison of MRI to anterior palpation in the present study demonstrated that MRI values were consistently smaller than palpation values, which is to be expected as palpation included overlying soft tissue. This systematic mean difference was greatest in sit abduction (see Table 3), possibly due to the superior migration of deltoid during abduction. The systematic differences between MRI and palpation in upright positions were also expected, given the changing orientation of structures in the different body and glenohumeral positions. Systematic differences between MRI and palpation in supine measures may also have been caused by the longer measurement period for MRI, which may have allowed greater soft tissue creep. Random error factors that may have affected validity in all positions include soft tissue creep, the use of gadolinium contrast injection in 7 patients, phasic muscle firing, examiner line of vision difficulties and MRI accuracy. Patients may have different rates of creep (e.g. patients with occult glenohumeral laxity versus those with rotator cuff thickening) and this may have contributed to random error. Contrast injection was rejected as a contribution to

Table 3 Differences and relationships of palpatory and MRI measures for anterior humeral head to acromion distance. Position

Mean difference (mm) (LOA)

SEM (mm)

r (p)

MRI – supine MRI – sit neutral MRI – sit abduction

4.2 (7.3 to 1.2) 2.7 (4.6 to 0.7) 7.7 (10.2 to 5.2)

5.3 3.4 4.4

0.10 (0.630) 0.64 (<0.001) 0.57 (0.002)

Mean difference ¼ mean difference between MRI and palpation (mean of 3 trials); SEM ¼ Standard Error of Measurement; r ¼ Pearson’s correlation coefficient. LOA ¼ Limits of Agreement.

L. McKenna et al. / Manual Therapy 14 (2009) 397–403

Average difference between MRI + Palpation in Sit neutral (mm)

Palpation measures (mm)

35 30 25 20 15 10 5 0

0

5

10

15

20

25

30

35

MRI (mm)

401

15 10

7.1

5 0

0

5

10

15

20

25

30

-2.6

-5 -10

-12.4

-15

Average by MRI + Palpation in Sit neutral (mm) Fig. 5. Bland and Altman plot of the differences between MRI and palpation in sit neutral position measures of anterior humeral head position.

Fig. 4. Scattergram of anterior humeral head to acromion distance measured by MRI versus palpation in supine, sit neutral and sit abduction (mean of 3 trials). Dotted line ¼ MRI – supine trendline. MRI – supine data point. Dashed line ¼ MRI – sit neutral trendline. ¼ MRI – sit neutral data point. Solid line ¼ MRI – sit abduction trendline. ¼ MRI – sit abduction data point.

random error after posthoc examination showed no difference between those injected and not injected. Intermittent inhibition or phasic muscle guarding by the rotator cuff may have intermittently affected humeral head position during the test procedure. Supine palpation appeared to have greater random error, as palpation in this position correlated poorly with MRI and had the largest SEM (see Table 3) compared to other positions. The line of vision for estimating the position of landmarks varied between supine and the sit positions. In supine, posterior palpation of the acromion and humeral head was more difficult, diminishing 3D appreciation of anatomical geometry. Accuracy of MRI measures may be dependent on a number of issues including the anatomical structure being imaged, the equipment used (Eckstein et al., 2001) and the specific MRI sequence (Sittek et al., 1996). Linear error for MRI can be as high as 3.0 mm (Chandnani et al., 1991), therefore some of the random ‘error’ may have been error in the ‘gold standard’ rather than the palpatory method. In summary, systematic and random errors found in this study favour palpation in sit positions rather than the supine for measurement of the habitual humeral head position. 4.2. Reliability Previous research (Bryde et al., 2005) on anterior humeral head palpation reliability in subjects without shoulder pathology demonstrated similar results (intra-tester SEM 2.3 mm and ICC 0.86 for the arm at side position) to the present study. The arm at side position described by these authors (Bryde et al., 2005) was directly comparable to the sit neutral position used in the present study. Little difference between the ICCs for consistency and agreement was evident in the present study, demonstrating a minimal effect of systematic error for intra-tester reliability. There was

Table 4 Intra-tester reliability for palpatory measures of anterior humeral head to acromion distance. Position

ICCa (CI)

ICCc (CI)

SEM (mm)

Supine Sit neutral Sit abduction

0.85 (0.74–0.92) 0.85 (0.73–0.92) 0.91 (0.82–0.95)

0.85 (0.73–0.92) 0.86 (0.75–0.93) 0.91 (0.83–0.96)

2.6 2.2 3.0

ICCa (CI) ¼ Intraclass Correlation Coefficient for absolute agreement (confidence interval); ICCc (CI) ¼ Intraclass Correlation Coefficient for consistency (confidence interval); SEM ¼ Standard Error of Measurement.

a slight systematic trend across all arm positions for a reduction in values over time that may be a slight posterior ‘‘settling’’ of the humeral head. This was most evident in the most provocative position of sit abduction. This may be due to anterior relaxation of muscle after active abduction or guarding, or increasing posterior muscle spasm due to growing discomfort during the provocative abduction position.

4.3. Arm position It appears that glenohumeral abduction has a significant effect on humeral head position, causing an anterior shift of 5.0 mm compared to the acromion in patients with shoulder pain. This may demonstrate the provocative nature of glenohumeral abduction or alternatively the influence of a larger bulk of deltoid in the abduction position. Previous literature demonstrates that the humeral head glides an average 1.0 mm anteriorly (range 0.5– 1.5 mm) with abduction in healthy live shoulders (Graichen et al., 2000; von Eisenhart-Rothe et al., 2002; von Eisenhart-Rothe et al., 2005; Hallstrom and Karrholm, 2006; Ogston and Ludewig, 2007). One study demonstrated that shoulders with impingement lose this usual anterior glide during 10–60 abduction (Hallstrom and Karrholm, 2006). It is possible that shoulders with pathology have early or late anterior translation of the humeral head, which may explain the discrepancy between the findings from those authors and this research. Other factors such as an increase in deltoid thickness with abduction may also account for differences between results.

4.4. Clinical implications A clinical measurement of anterior/posterior humeral head position may be required to accurately and reliably detect differences of at least 5 mm, as this appears to be a possible pathological threshold, calculated from anatomical distances near glenohumeral neutral in the sagittal plane given in the literature (see Appendix 2). The literature did not provide a single linear measurement of anterior humeral head position in relation to the anterior acromion in normal or pathological shoulders and the proposed threshold is based on the calculations outlined in Appendix 2 and Fig. 6. Comparison of the pathological threshold value of 5.0 mm to SEM found in the present study demonstrates acceptable validity. The SEMs in sit (3.4 and 4.4 mm) were lower than the pathological value. However, palpation in supine should be avoided as the error (5.3 mm) was higher than the pathological threshold and neutral positions in supine do not normally elicit symptoms.

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5. Conclusion The findings of this study indicate that palpatory measurement of anterior humeral head position has sufficient validity and reliability for clinical use in a sit position. The errors associated with the measurement performed in sit are lower than the pathological threshold (average difference between pathology and normal). The pathological threshold was derived theoretically and the true value needs to be determined in further research. In glenohumeral abduction the humeral head occupied a position 5.0 mm more anterior than when in the neutral position, in shoulders with impingement type pathology, and clinicians may need to expect this change. Acknowledgements We thank Klaus Sussenbach for technical assistance; Dr. Ritu Gupta for statistical advice, Perth Radiological Centre and surgeon Mr. Kon Kozak for examining rooms, orthopaedic surgeons Mr. Greg Janes, and Mr. Hari Goonatillake for subject recruitment. In particular, the help of radiologist Dr. Bill Breidahl made this study possible. Appendix. Supplementary material

Fig. 6. Theoretical pathological threshold for anterior humeral head distance. D (theoretical horizontal distance from acromion to anterior humeral head) ¼ A  B þ C where A ¼ anterior margin of the acromion to the centre of the glenoid fossa distance; B ¼ the centre of the glenoid fossa to the centre of the humeral head distance; C ¼ the humeral head radius; D ¼ the anterior humeral head to anterior acromion distance. Small circle ¼ centre of humeral head. Star ¼ centre of glenoid fossa. Large circle ¼ humeral head.

Intra-tester reliability demonstrated errors (2.2–3.0 mm) lower than the critical pathological threshold of 5.0 mm in all positions. Together with good ICCs, this indicates that the method has good intra-tester reliability for clinical use. Clinicians can be 68% confident that changes of greater than 3 mm in sit positions are a result of any treatment and not measurement error. As both sit positions demonstrated adequate validity and intratester reliability, clinicians may wish to use the sit neutral position for patients who have severe or irritable pain and use the sit abduction position in those whose pain is more difficult to provoke.

4.5. Limitations The samples of subjects used in this study were not necessarily representative of the broader community that develop arm pain and impingement as these were all cases that had severe enough symptoms to warrant referral to an orthopaedic surgeon. A variety of impingement pathologies were included in this study, which prevents focus on one particular discrete syndrome. Pathologies such as traumatic acute dislocations or atraumatic multidirectional instability were not included in the study and may be subject to greater errors in reliability and validity due to the influence of greater, inconsistent and changeable rate of tissue creep. This study was limited to examining intra-tester reliability in subjects with pathology. Intra-tester reliability is an important first step in establishing reliability. The reliability results are therefore limited to one clinician reexamining a patient. Further research is required to examine inter-tester reliability and has been completed in a separate study.

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