Measurement of Static Scapular Positioning
In contrast to visual observation, for all measurements of static and dynamic scapular positioning, the orientation of the scapula depends on the therapists' palpating accuracy. However, previous research has been shown surface palpation of scapular position to be a valid method for determining the actual location of the scapula.
Measurement of the Distance Between the Posterior Border of the Acromion and the Table/Wall
The measurement of the distance between the posterior border of the acromion and the table (AT-distance) was described by Host. Researchers have suggested that forward shoulder posture contributes to head, shoulder and neck pain. This theory is based on the observation of similar scapular kinematics in patients with shoulder impingement syndrome as individuals with short pectoralis minor muscle length. Subsequently, they found that shortening of the pectoralis minor muscle could result in a lack of posterior tilting, and therefore, could reduce subacromial space, which potentially results in shoulder pain.
For the measurement of the AT-distance, the patient is supine, and instructed to relax (figure 2). The assessor measures the distance between the posterior border of the acromion and the table bilaterally (measured vertically with a sliding caliper). The assessor can repeat this procedure with the patient actively retracting both shoulders. The data collected during this measurement are adjusted by dividing by the body length, which results in the so-called AT index. The measurement of the AT-distance displayed excellent intraobserver and interobserver reliability in patients with shoulder pain (Table 2). When comparing the mean values between the symptomatic (72.7 mm relaxed; 48.3 mm retracted) and the asymptomatic side (71.9 mm relaxed; 49.2 mm retracted), no significant difference was found. In an overhead athlete population with shoulder pain more forward shoulder posture was seen: mean AT-distance of 83.6 mm at rest and 53.8 mm during bilateral retraction.
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Figure 2.
The measurement of the distance between the posterior border of the acromion and the examining table.
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Figure 3.
The measurement of the distance between the posterior border of the acromion and the wall in standing.
Baylor Square and Double-square Technique
Forward shoulder posture can also be measured using the Baylor square or double square technique, described by Peterson et al The square consists of a simple carpenter's square having a 24-inch long arm and a 16-inch short arm. During the Baylor square technique, the tester uses this tool to measure (in a sagittal plane) the distance from the anterior tip of the acromion process to the line, perpendicular to the C7 spinous process. During the double square, a 12-inch combination square with a second square is used in an inverted position. This device is used to measure the distance from the wall to the anterior tip of the subject's acromion. Reliability data are presented in Table 2. Besides excellent reliability, they found a strong correlation between the Baylor square (r=0.77) and a moderate correlation between the double-square method (r=0.65) and radiographic measurements.
Although Peterson et al could not support the validity of the double square method, this test could be of clinical value if it is 'accurate in detecting changes in a patients' shoulder posture'. In addition, Kluemper et al demonstrated that by using the double square method, differences in forward shoulder posture can be detected in young competitive swimmers.
Measurement of the Pectoralis Minor Muscle Length
A potential contributing mechanism for forward shoulder posture includes muscle tightness. Another method for measuring forward shoulder posture is the measurement of the pectoralis minor muscle length, which is validated by Borstad and Ludewig using human cadavers. Because of height and muscle length variability among subjects, this measurement is best normalised creating a pectoralis minor index (PMI). The PMI is calculated by dividing the resting muscle length measurement by the subject height and multiplying by 100. The resting muscle length is measured between the caudal edge of the 4th rib to the inferomedial aspect of the coracoid process with a measuring tape or sliding caliper (figure 4). PMI is suggested to reflect a shortened pectoralis minor when 7.65 or lower.
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Figure 4.
Measurement of the pectoralis minor muscle length.
Distance From the Medial Scapular Border to the 4th Thoracic Spinous Process
The measurement of the distance from the medial scapular border to the fourth thoracic spinous processes was also first described by Host. The test is performed while standing. Both the fourth thoracic spinous process (T4) and the medial scapular border are identified through palpation. Palpation of T4 was performed by counting down from the 7th cervical spinous process (C7). Palpation of the C7 has demonstrated acceptable inter-rater reliability. The distance between both anatomical landmarks is measured in the horizontal plane using a tape measure. Again, this procedure is repeated with the patient actively retracting both shoulders. Together with the initial description of the test, Host provided a guideline for the interpretation of the tests' outcome: in normal subjects, the distance from the medial scapular border to T4 should be 5.08 cm. However, the guideline was based on clinical observations rather than on experimental data. Nijs et al found mean values of 6.15±2.07 (symptomatic side) and 6.00±1.62 cm (asymptomatic side). The interobserver reliability for the test was to low (the ICCs varied between 0.50 and 0.79) when performed with the patient relaxed (Table 2). A fair interobserver reliability was found (ICCs between 0.70 and 0.80) for the evaluation of the distance from the medial scapular border to T4 with active bilateral shoulder retraction. Others measured the distance from the medial scapular border to the third (and not the fourth) thoracic spinous processes: evidence supportive of the intraobserver reliability (ICC=0.91) and criterion validity (the clinical tests' outcome correlated with the measurement performed on a radiography: r=0.57) has been provided (Table 2).
Scapular Distance Measurement
Finally, the scapular distance (distance between the acromial angle and third thoracic spinous process) is another test for the assessment of resting scapular positioning. The distance is normalised by dividing it by the scapular length (ie, the distance between the scapular spine, localised at the medial margin and the acromial angle). The measurement of both the scapular distance and the scapular length have been shown to have good to excellent intraobserver and interobserver reliability in asymptomatic subjects (Table 2).