INTRODUCTION
Shoulder pain affects up to 67% of the population at some point in their lifetime (17). Although the etiology of shoulder pain is multifactorial, a specific impairment, such as inadequate mobility, has been associated with many of the more common conditions. Posterior shoulder tightness (PST), in particular, has been associated with and implicated in the etiology of numerous shoulder disorders, such as rotator cuff pathology, impingement syndromes, and labral tears (8,18,19,24,25). Research suggests that overhead athletes (4,5,18) and weight-training participants (13,14) have a predilection for PST, thus making them susceptible to the aforementioned shoulder disorders. Interventions designed to mitigate PST “a priori” have been reported as efficacious for reducing injury rates among baseball and tennis players (4). Moreover, efforts to mitigate PST have been associated with symptom resolution among individuals with shoulder disorders from both the athletic and the general population (12,20,23,26). Given the evidence implicating PST as both a causative and a perpetuating factor for shoulder disorders, it is essential for rehabilitation professionals and strength and conditioning specialists to have an understanding of procedures that may be used to quantify PST. The purpose of this column is to present 2 reliable and valid measurement procedures that may be used to quantify PST.
ANATOMICAL AND BIOMECHANICAL CONSIDERATIONS
A brief but necessary discussion of the relevant posterior shoulder anatomy is required to gain an understanding of the structures that may contribute to PST as well as to substantiate the measurement techniques advocated. The shoulder complex comprises the glenohumeral, acromioclavicular, and sternoclavicular joints along with the scapulothoracic articulation. An individual's shoulder mobility is dependent on numerous factors, including joint mobility, flexibility of soft tissues, such as the shoulder capsule and muscles, and synchrony of the shoulder complex musculature. PST primarily affects the glenohumeral joint and is associated with impaired mobility of the posterior glenohumeral joint capsule (1,3,9) (Figure 1), posterior-inferior glenohumeral ligaments (3), and stiffness of the infraspinatus, teres minor, and posterior deltoid musculature (10,20).
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Figure 1: Posterior view of shoulder illustrating the posterior capsule (shaded blue) and scapula 3-dimensional anatomy images (Copyright of Primal Pictures, Ltd,
www.primalpictures.com).
From a biomechanical perspective, PST has been directly linked to altered shoulder biomechanics, such as abnormal humeral head translation. This change in biomechanics may be responsible for ensuing mobility impairments of internal rotation when the arm is abducted to 90° (Figure 2a and 2b) and horizontal adduction (Figure 3) (8). Moreover, altered biomechanics and mobility impairments arising from PST have been associated with shoulder disorders among both the athletic and the general population (4,18,25,26).
Figure 2: Shoulder internal rotation with the arm abducted to approximately 90°. (a) Normal internal rotation and (b) limited internal rotation.
Figure 3: Shoulder horizontal adduction. Arm is brought across chest.
In an investigation of throwing athletes, Myers et al. (18) reported significantly greater PST and internal rotation loss among throwers with impingement syndrome when compared with controls. Tyler et al. (25,26) reported an association between PST and impingement syndrome among individuals receiving rehabilitation for their shoulder. Barlow et al. (2) reported internal rotation limitations among bodybuilders when compared with a control group, suggesting a relationship between bodybuilding and a loss of internal rotation. Moreover, other researchers have reported (13,14) limited internal rotation and PST (using the techniques described in the column) among weight-training participants when compared with a control group, further suggesting an association between PST and weight training. Although internal rotation loss or glenohumeral internal rotation deficit has been directly linked to PST through surgical exploration (23,28) and imaging studies (22,24), its use as a sole measurement may be confounded by joint pathology, such as osteophytes (11) and increased humeral retroversion (7,21), which is often present among overhead athletes. Specifically, in the throwing population, glenohumeral internal rotation deficit may be attributed to both humeral retroversion and PST, with only the latter being amenable to stretching efforts. As a result, measurements have been specifically designed to quantify PST that are not necessarily affected by humeral retroversion.
MEASUREMENT PROCEDURES
The measurement procedures outlined in this column have been found to be reliable and valid for quantifying PST among individuals with and without shoulder disorders (16,15,18,24). The procedures require a treatment table or mat and require either a standard carpenter's square or gravity-based inclinometer (Figure 4), depending on the technique. The equipment used for the measurements may be obtained at a local hardware store at a nominal cost (see Video, Supplemental Digital Content, https://links.lww.com/SCJ/A9, which demonstrates 2 different PST measurement methods).
Figure 4: Gravity-based inclinometer.
PROCEDURE A: CARPENTER'S SQUARE METHOD
This measurement technique requires a 60-cm carpenter's square and is performed with the individual lying on their nontested side (Figure 5) with the tested arm up. The individual should be close to the edge of the table to allow the tested arm to possibly move past the table (although unlikely) during horizontal adduction. The nontested extremity is placed under the individual's head to support a neutral neck position, and the trunk should be directly perpendicular to the plinth with hip and knees flexed to 45°. The tester stands facing the individual at the level of their shoulders and grasps the flexed elbow with one hand while passively abducting the humerus to 90° with the other hand (maintaining 0° of rotation at the humerus) as illustrated in Figure 5. Arm positioning is maintained with the initial contact hand while the other hand manually contacts the participant's lateral scapular border and places it in a fully adducted (retracted) position toward the spine (Figure 5). The retracted scapular position is maintained by the tester throughout the procedure. The next step in the measurement requires the tester to passively lower the arm (toward the table) across the individual's chest (Figure 6). The tester maintains neutral humerus rotation and scapular stabilization in the retracted position for the duration of the measurement. The movement is ceased once the tester determines that the scapula or humerus is unable to be further stabilized and/or movement stops. Once the movement is ceased, another person familiar with the procedure, at the direction of the tester, places the carpenter's square perpendicular to the table in contact with the medial epicondyle of the elbow and records the distance from the bottom of the carpenter's square to the point of the medial epicondyle (Figure 6). The distance is recorded in centimeters and a larger distance implies greater PST (less flexibility). Future measurements may be used for comparison and to document improvement or worsening of PST. A change of 5 cm or more is required to exceed the threshold of error and to be 90% certain that a true change has occurred. This procedure has a reported reliability (reproducibility) coefficient ≥0.80 in both intrarater and interrater investigations and has been found to have both convergent and discriminant validity (27). Essentially, a reliability coefficient of >0.75 is considered to have good reproducibility, thus a tester is likely to record a similar measurement if this procedure was repeated a second time. A limitation of this procedure lies in the absence of normative values. Moreover, the distance measured cannot be compared between individuals due to varied body morphology because chest and shoulder width may affect the measurement (those with wider shoulders may have an increased distance from the table irrespective of PST).
Figure 5: Side lying posterior shoulder tightness measurement procedure. Individual being tested lies on his nontested side. The arm is brought up to a 90° position by the tester, at which point the scapula is retracted toward the spine.
Figure 6: Measurement procedure using carpenter square. Arm is lowered across chest by the tester. The tester is careful to maintain 90° position and to keep forearm perpendicular to the floor. Once end-range horizontal adduction is achieved, the distance between the medial epicondyle of the elbow and table is measured as illustrated.
PROCEDURE B: INCLINOMETER METHOD
This measurement technique requires a gravity-based inclinometer. This procedure is performed similar to the carpenter's square method with the exception being that PST is measured with the gravity-based inclinometer. Once end range is obtained, another person familiar with the procedure places the inclinometer flat on the distal arm (Figure 7) and the measurement angle is recorded in degrees. It should be noted that training an individual to record the measurement angle on the inclinometer requires minimal time beyond reading the dial at eye level because the tester provides specific commands during the procedure. A normal angle for this measurement among asymptomatic individuals who do not participate in overhead sports or weight training is approximately 83° when control group data from 2 investigations were pooled (12,14). A change of 8° or more would be needed to exceed the threshold of measurement error for this measurement technique (16) when the same tester repeats the measurement or 9° when the measurement is obtained by 2 different testers (15). The authors of the aforementioned study recommend using this as a guideline because it represents only 61 participants and cannot be generalized with confidence to the population at large. Similar to the carpenter's square technique, future measurements may be used for comparison and to document change. This procedure has a reported reliability coefficient ≥0.90 in both intrarater and interrater investigations and has been found to have both convergent and discriminant validity (15,27). An advantage to this technique is the availability of reference values and the ability to compare between individuals.
Figure 7: Measurement procedure using gravity-based inclinometer. Once end-range horizontal adduction is achieved, the angle of horizontal adduction is measured by placing the inclinometer flat on the distal arm.
CONCLUSIONS
PST is prevalent among overhead athletes and weight-training participants, thus the measurements described in this column may offer both prescriptive and clinical utility to those individuals involved in the prescription of training regimens and rehabilitation.
Both measurements possess acceptable reliability and have been validated among various populations, including both symptomatic and asymptomatic individuals. Finally, the required equipment is relatively inexpensive and has portability, thus may be used in various settings. Similar to other tests of flexibility, such as the sit and reach measurements, it is not unreasonable for individuals with various levels of training to perform. It should be noted that these measurement methods are by no means designed to diagnose pathology. Efficacious stretching exercises that may be used to mitigate PST are referenced in the article titled “Addressing Posterior Shoulder Tightness in the Athletic Population” found in the December 2009 issue of Strength and Conditioning Journal (6).
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