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Research Reports |
PW McClure, PT, PhD, is Associate Professor, Department of Physical Therapy, Arcadia University, 450 S Easton Rd, Glenside, PA 19038 (USA) (mcclure{at}arcadia.edu)
J Bialker, PT, MPT, is Physical Therapist, Penn Therapy and Fitness: University of Pennsylvania Medical Center
N Neff, PT, MPT, is Research Physical Therapist, Department of Physical Therapy, Arcadia University
G Williams, MD, is Orthopaedic Surgeon, Shoulder and Elbow Service, Department of Orthopaedic Surgery, University of Pennsylvania Medical Center
A Karduna, PhD, is Assistant Professor, Department of Exercise and Movement Science, University of Oregon, Eugene, Ore
Address all correspondence to Dr McClure
Submitted December 10, 2003;
Accepted March 23, 2004
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Key Words: Biomechanics • Exercise • Shoulder impingement • Shoulder kinematics
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Multiple factors have been proposed to contribute to the development of impingement syndrome. These factors include abnormal acromial morphology,6,7 aberrant kinematic patterns due to poor rotator cuff or scapular muscle function,8–11 capsular abnormalities,12–14 poor posture,15–17 and overuse secondary to repetitive eccentric loading or sustained use of the arm above 90 degrees of elevation.18–21 The variation in intervention approaches is directly related to various views on the mechanism leading to impingement.22
Researchers have investigated the effects of various rehabilitation protocols on people with impingement syndrome. Brox et al23 compared a supervised exercise program with acromioplasty or placebo laser treatment in 125 patients with shoulder impingement. The exercise program was not standardized or described in detail but apparently consisted of low-resistance, repetitive rotation exercises done daily for 1 hour with twice-a-week supervision for between 3 and 6 months. The primary outcome measure was a Neer impingement test score (possible score of 100 points, with higher scores being better), which is based on pain (35 points), muscle force (30 points), active range of motion (ROM) (25 points), and radiographic assessment (10 points). They found that both the acromioplasty and exercise groups had improved Neer impingement test scores compared with the placebo group. In a follow-up of these patients 2.5 years later, both the exercise and acromioplasty groups had higher Neer impingement test scores than did the placebo group.24
Bang and Deyle25 compared 52 subjects who were randomly assigned to 1 of 2 groups: a group that received supervised exercise with manual therapy and a group that received supervised exercise without manual therapy. Supervised exercise consisted of the following: 2 stretching exercises for the anterior and posterior shoulder performed 3 times for 30 seconds and 6 strengthening exercises performed in 3 sets of 10 repetitions (shoulder elevation, rowing, scapular-plane abduction with the arm medially rotated, horizontal abduction with lateral rotation, seated press-up off a chair, and elbow push-up with shoulder protraction) against elastic tubing of various grades based on a 10-repetition maximum. Manual therapy included individualized joint mobilization, which was not specified but could include passive physiological joint mobilization to the glenohumeral, cervical, or thoracic spine articulations, massage, or muscle stretching techniques. Both groups were treated 2 times per week for 3 weeks with resistive exercise and passive stretching aimed at the anterior and posterior shoulder musculature. The researchers measured pain, isometric force, and function using a shoulder scale that they had developed that had an intraclass correlation coefficient (ICC [3,1]) of .81 for test-retest reliability over a 24-hour period. Although both groups showed improvement, the subjects who received manual therapy showed greater gains than the subjects who did not receive manual therapy for all variables.
Some evidence exists that scapular dysfunction is associated with shoulder impingement. Warner et al,26 using a moiré topography technique, demonstrated a pattern of increased scapular winging with glenohumeral elevation. This winging pattern appears to represent scapular internal rotation and anterior tilting. Recently, 3-dimensional kinematic analysis has demonstrated decreased scapular posterior tilt,10,11 decreased upward rotation,11 and decreased scapular external rotation11 during glenohumeral elevation. Radiographic assessment at multiple joint angles revealed a decrease in scapular posterior tilt and upward rotation at 90 degrees of glenohumeral elevation and a decrease in posterior tilt at 45 degrees of glenohumeral elevation.27 No study to date has assessed the effect of rehabilitation on scapular function in patients.
The primary purpose of our study was to identify changes that occur in physical impairments (3-dimensional kinematic patterns, thoracic posture, muscle force, and motion), functional outcome (as measured with the University of Pennsylvania Shoulder Scale), and general health status (as measured with the Medical Outcomes Study 36-Item Short-Form Health Survey [SF-36]) in patients with impingement syndrome following an intensive exercise program. A secondary purpose was to identify relationships between impairments and functional outcome that may help explain mechanisms involved with rehabilitation.
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Subjects
A total of 59 subjects were initially recruited and were judged to meet the criteria for the study. Subjects were recruited from the practices of Penn Therapy and Fitness and the Hospital of the University of Pennsylvania and also through general announcements in local printed media. Twenty subjects did not complete the 6-week exercise program and follow-up testing, leaving a total of 39 subjects. Data regarding the reasons for dropping out of the study were not collected systematically. A retrospective review of records revealed that subjects who did not complete the study cited either scheduling problems (n=4) or personal circumstances that prevented weekly visits (n=4), or they simply did not return and did not give an explanation (n=11). One subject elected to have an injection rather than participate in an exercise program. No subject reported an adverse response to the intervention, and subjects were not charged for intervention. This rate of attrition (33%) was similar to the overall rate of patient attrition (inability to complete a scheduled course of outpatient therapy) for the primary site used in the present study (38%). Descriptive characteristics of the subjects are given in Table 1.
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Instrumentation and Measurement Procedures
Three general types of measurements were collected: (1) 3-dimensional scapular kinematics, (2) impairment measurements of posture, motion, and muscle force, and (3) self-reported measurements of pain, satisfaction, and function.
Three-dimensional scapular kinematics.
The Polhemus 3Space Fastrak* is an electromagnetic-based motion analysis system that we used for collecting 3-dimensional kinematic data of the shoulder complex and resting posture of both the shoulder and thorax. The details of the instrumentation and the error associated with these measurements have been previously described.28–30 The average root-mean-square errors were below 5 degrees for all rotations when compared with sensors mounted directly to the scapula with bone pins.28–30 The majority of the error with this method occurs above 120 degrees of humeral elevation. Subjects stood with their feet a comfortable width apart, their heels against a rigid support, and their elbows extended. The thoracic spine, scapula, and humerus were exposed. This position was maintained throughout the digitization and testing procedures. The following anatomic landmarks were palpated and marked with a dark pen by a physical therapist who was experienced with the test protocol: acromioclavicular (AC) joint line, posterior angle of the acromion, and spinous processes of first, third, and seventh thoracic vertebrae (T1, T3, and T7). These marks were used for subsequent receiver mounting and landmark digitization. The transmitter served as a global reference frame and was fixed to a rigid plastic base and oriented such that it was level and its coordinate axes were aligned with the cardinal planes of the human body. The thoracic sensor was placed on the thorax at T3 using double-sided tape. The humeral receiver was positioned on the distal humerus over a neoprene sleeve using elastic straps. The scapular receiver was positioned on the scapula via a custom-made, adjustable scapular-tracking jig machined from plastic, which was attached to the skin with Velcro adhesive fasteners.
We believe the jig remained well fixed to the scapula from these Velcro attachments during motion.
The arbitrary axis systems defined by the Polhemus 3Space Fastrak were converted to anatomically appropriate axis systems by using a series of standardized axes embedded in each segment.31 These axis systems are derived from a series of points on each segment, which are palpated and individually digitized with a hand-held probe as follows: thorax: T1, T7, and sternal notch; scapula: AC joint, root of the scapula spine, and inferior angle; and humerus: medial epicondyle, lateral epicondyle, and humeral head. All landmarks were palpated and located with a digitizer connected to the Polhemus system except for the center of the humeral head. This landmark was defined as the point on the humerus that moved the least according to a least-squares algorithm when the humerus was moved through short arcs of mid-range glenohumeral motion.32 The location of these points and the resultant embedded axis systems are shown in Figure 1. With these frames established, the raw data from the Polhemus system were converted to anatomically defined rotations and displayed using a custom-made software program written in LabView data acquisition software.
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The manufacturer of the Polhemus system has reported an accuracy of 0.8 mm and 0.15 degrees for this device (measured statically), and we have verified this accuracy under controlled laboratory conditions. The error with our protocol using skin-mounted sensors has been tested previously by comparing measurements obtained from sensors mounted directly to the scapula via bone pins with measurements obtained with skin mounted sensors.28 Mean errors associated with the skin-mounted sensors during scapular-plane elevation over the full range of elevation were found to be 1.2 degrees for clavicle protraction, 1.5 degrees for clavicle elevation, 4.7 degrees for scapular posterior tilting, 3.2 degrees for scapular external rotation, and 4.2 degrees for scapular upward rotation. The amount of error was dependent on the range of elevation, with much less error below 120 degrees of elevation and as much as 12.6 and 7.3 degrees of error for posterior tilting and external rotation, respectively, at 150 degrees. Interrater reliability was studied among 3 raters using this protocol on 9 subjects without symptoms of shoulder impingement. Sensors were removed and reattached between raters. Intraclass correlation coefficients (2,1) for scapular motions ranged from .69 to .95 depending on the specific scapular rotation and arc of motion assessed.
Impairments.
Resting thoracic posture was measured using the thoracic sensor of the Polhemus system and was represented by the degree of flexion (anterior inclination from pure vertical) of a vector formed between T7 and T1. Shoulder passive ROM was measured using a standard goniometer. The following measurements were obtained: scapular-plane elevation, external rotation with arm at the side, and external rotation with the arm elevated to 90 degrees in the coronal plane. Composite internal rotation of the glenohumeral and scapulothoracic articulation was measured by noting the highest vertebral level reached with the thumb as the hand was moved behind the back and up the spine as high as possible. This method has been shown to yield measurements that we would consider to have satisfactory reliability (ICCs of .80 and .90).33,34 Isometric shoulder muscle force was measured with the Microfet hand-held dynamometer
using a "make test" technique. Each subject was asked to exert maximal force against the dynamometer, which was held stationary by the tester. Measurements obtained with a hand-held dynamometer such as this instrument have been shown to be reliable (ICC=.84–.97) for shoulder medial rotation, lateral rotation, and abduction force on subjects without symptoms.35 The following force measurements were obtained: (1) external rotation force with the arm by the side in neutral rotation, (2) internal rotation force with the arm by the side in neutral rotation, and (3) shoulder abduction force with the arm in the scapular plane at 45 degrees of elevation. Both force and ROM measurements were obtained such that subjects experienced mild or no pain during testing.
Self-report measures.
We used the University of Pennsylvania Shoulder Scale, which has subscales for pain, satisfaction, and functional activities. The pain subscale asks subjects to rate their symptoms on a 10-point scale at rest, during light activities, and during strenuous activities. These ratings were combined for a possible score of 30, representing "no pain at all." Satisfaction was rated based on a single 10-point scale ranging from "completely unsatisfied" to "completely satisfied" in response to the question: "How satisfied are you with your current level of shoulder function?" Finally, function was assessed based on 20 questions related to functional activities, each rated on a 4-level ordinal scale with 3 representing "no difficulty" and 0 representing "cannot do at all." The highest functional score possible is 60 points. The combined total of the subscale scores may be used to determine a composite score based on 100 points, with higher scores being better. This scale has documented psychometric characteristics, including test-retest reliability (ICC=.94), responsiveness (standardized response mean=8.6, 90% confidence interval [CI]), and a minimal detectable change score of 12.1 (90% CI).36 Subjects also completed the SF-36 questionnaire to describe their general health status.37
Intervention
A standardized intervention regimen was applied based on physical impairments associated with shoulder impingement. Interventions included exercises designed to: (1) strengthen the rotator cuff and scapular stabilizers, (2) enhance flexibility of the glenohumeral posterior capsule, pectoralis minor muscle, and upper thoracic spine, (3) improve upper-quarter postural awareness, and (4) enhance patient understanding of environmental and workplace factors that place high loads on the shoulder and are associated with overuse. Subjects were given color exercise instruction sheets depicting each exercise.
Strengthening exercises were performed using 0.9-m (3-ft) lengths of color-coded elastic bands (Thera-Band#). All subjects began with 3 strengthening exercises using the lightest grade (yellow). These exercises were:
The subjects were instructed to start with the band under very mild tension. When they were able to do 3 sets of 10 repetitions without feeling substantial pain or fatigue, the next strongest elastic band was used. Once they had progressed to using green (moderate resistance), new exercises were added, as follows:
The subjects were instructed to do 2 or 3 sets of 10 repetitions for each exercise, once per day.
Flexibility exercises were done throughout the 6-week period and consisted of the following:
All subjects were instructed to do the internal rotation towel stretch, the cross-body stretch, and the upper thoracic extension stretch. The remaining 3 flexibility exercises were shown based on the therapists' judgment, after taking goniometric measurements, as to whether a subject lacked normal flexibility for those motions. Subjects were instructed to hold an individual stretch for 30 seconds and to repeat each stretch 3 times. They were instructed to perform flexibility exercises at least once per day and twice if able.
To address upper-quarter posture, all subjects were instructed in a chin-tuck exercise, which was supposed to be performed at least 3 times every hour. Subjects were instructed to apply pressure to the chin with the fingers as the head was pulled back, holding it for 3 seconds. Emphasis was placed on keeping the motion horizontal and avoiding tilting the head back or looking at the ceiling.
Subjects were given an exercise adherence log and were required to make a least one visit per week to the treating physical therapist over the 6-week intervention period. Many subjects did not bring their adherence log on return appointments despite what we believed was apparent adherence to exercise. Therefore, adherence was monitored based on verbal reports, ability to demonstrate exercises, and weekly attendance where the exercise program was checked and modified appropriately. Subjects' muscle force and motion were tested weekly, primarily for motivational purposes. No subject who finished missed more than one weekly visit.
In addition to exercise, all subjects were given basic instruction regarding the anatomy and basic biomechanical issues related to shoulder impingement. This instruction included an explanation of arm and trunk positions that may promote impingement such as shoulder elevation with internal rotation or elevation with a flexed thoracic spine. Simple strategies to reduce loads on the shoulder were reviewed such as working with the arms below 60 degrees of elevation, keeping loads close to the body, use of armrests, and use of ergonomic aids or assistance from other people for heavy lifts. The concept of avoiding undue repetition and prolonged static work postures also was reviewed.
Data Analysis
Descriptive statistics were calculated for all dependent variables (kinematics, posture, muscle force, motion, shoulder function, and overall health status). For analysis of kinematic variables, plots based on group means before and after exercise were generated for each scapular and clavicular rotation (y-axis) versus humerothoracic motion (x-axis). To determine differences between pretest and posttest kinematics, a 2-way (time x humeral angle) analysis of variance was performed for each scapular and clavicular rotation. For the flexion and scapular-plane abduction tests, we included only the humeral angles of 60, 90, and 120 degrees during raising and lowering in the analysis because not all subjects were able to achieve 150 degrees and the arc between 60 and 120 degrees is believed to be the range where maximal impingement typically occurs.38,39 For humeral rotation testing, we analyzed the data between 0 and 60 degrees of external rotation because this was the range all subjects were able to achieve. For posture, muscle force, and motion, paired t tests were used to determine differences before and after 6 weeks of intervention. Shoulder pain and function were compared before intervention and 6 weeks and 6 months after intervention using repeated-measures analysis of variance. Pearson product moment correlation coefficients were computed to determine the relationship between change in various impairments and change in overall shoulder function as measured by the University of Pennsylvania Shoulder Scale.
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through 5. During both shoulder flexion (Fig. 3) and scapular-plane abduction (also known as "scaption") (Fig. 4), a general pattern of scapular upward rotation, posterior tilting, and external rotation with clavicular elevation and retraction was observed. The pattern of motion found during raising of the arm was, in our view, very similar to that found during lowering of the arm. During both flexion and scapular-plane elevation, there were no increases in scapular posterior tilting, external rotation, or clavicular retraction after intervention. During humeral rotation with the arm abducted 90 degrees in the coronal plane, a general pattern of scapular posterior tilting, upward rotation, scapular external rotation, and clavicular retraction was found as the arm moved from internal to external rotation with very little change in clavicular elevation angle.
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| Discussion |
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The natural history of shoulder impingement without intervention has not been well documented. Table 4 compares the results of our study with those of previous shoulder impingement studies where placebo or no intervention was compared with other interventions and pain and function were measured.23,40,42 Although different measures of pain were used in each study, collectively they suggest that pain associated with impingement does not spontaneously resolve and may even worsen slightly with no intervention or placebo. Without active intervention, shoulder function showed a decline in 2 studies23,40 and did not improve in another study.42 In comparing our results with the results of these studies, we believe it is unlikely that natural history accounted for the positive changes in pain and function.
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We expected to find more substantial changes in kinematic patterns after exercise based on previous studies suggesting deficits in patients with impingement10,11,26,43 as well as previous work suggesting that exercise in individuals with common postural deficits alters scapulohumeral rhythm.44 Wang et al44 found an increased relative contribution of the glenohumeral joint compared with the scapulothoracic joint during shoulder elevation after a 6-week exercise program that focused on the posterior scapular stabilizers and glenohumeral external rotators. They used a static technique that required digitization of multiple bony landmarks while the subjects held their arm in various positions statically, whereas our method tracked motion continuously. They also used planar projections to represent scapular motion, whereas we used a Euler angle system with axes embedded in each bony segment.
We believe another potential explanation for the lack of change in scapular kinematics is that not all patients with impingement have abnormal scapular motion. It may be that only a subset of patients with shoulder impingement may have scapular motion abnormalities. However, at present, there is no accepted or validated operational definition of "abnormal kinematics." Graichen et al45 used 3-dimensional reconstruction of magnetic resonance images in subjects with and without impingement syndrome. They found that a subset of 5 out of 20 subjects with impingement syndrome showed a pattern that was abnormal, defined as greater than 2.5 standard deviations of the mean, yet these differences were obscured in the group data. The abnormality they identified was increased upward rotation of the scapula. Ludewig and Cook11 found that subjects with impingement symptoms anteriorly tilted their scapulae about 2 degrees during humeral elevation (60°–120°) in the scapular plane, in contrast to the posteriorly titled scapulae seen in the subjects without impingement symptoms. In contrast to Graichen and colleagues' findings, Ludewig and Cook found subjects with impingement symptoms had less scapular upward rotation compared with subjects without impingement symptoms. Our subjects, as a group, anteriorly tilted their scapulae by about 1 degree between 60 and 90 degrees of elevation and then posteriorly tilted their scapulae about 1 degree between 90 and 120 degrees of scapular-plane elevation. These motions are small and within the range of measurement error. During flexion, our subjects anteriorly tilted their scapulae about 3 degrees between 60 and 120 degrees of humeral elevation. A defensible operational definition of "abnormal" kinematics remains to be determined.
There is also no standard method for determining which patients have abnormal scapular motion. Kibler46 has described a simple test based on linear measures of the distance between the scapula and the vertebral column with the arm in defined positions. The reliability and validity of data obtained with this method, however, have been challenged.47,48 We believe a method of reliably identifying patients with scapular motion abnormalities that is suitable for routine clinical use would be of great value because it would allow intervention to be directed toward improving scapular muscle force and control in those patients. Shoulder impingement secondary to poor scapular control may require different intervention than impingement due to other causes.
Our intervention was focused primarily on changing physical impairments related to impingement in order to produce changes in pain and function. We found an association between shoulder function and 2 specific impairments, external rotation force and internal rotation ROM. In the absence of a control group, we could not determine whether improved motion and force caused an improvement in pain and function. It is possible that a decrease in pain allowed greater ROM and force generation.
Our exercise program emphasized rotator cuff strengthening and avoided elevation exercises until the glenohumeral rotators demonstrated enough force to use green Thera-Band. This approach was based on our belief that the glenohumeral rotators perform an important depressor function that keeps the humeral head centered on the glenoid fossa during elevation. Paletta et al9 have documented that patients with rotator cuff tears demonstrate abnormal superior translation of the humeral head during elevation, which is abolished after rotator cuff repair. Therefore, our protocol was based on the belief that premature use of elevation exercises (flexion or abduction) with rotator cuff weakness may encourage the impingement process by allowing humeral head superior translation from the deltoid muscle and should not be used until adequate force and activation of the glenohumeral rotators has been achieved.
We found that the ability to move the thumb up the back, as a measure of internal rotation, improved by almost 2 vertebral levels. Internal rotation is believed to reflect the length of the glenohumeral joint posterior capsule, and tightness of this structure has been shown to promote anterior-superior translation of the humeral head consistent with subacromial impingement.12 Measuring internal rotation by vertebral level has been criticized for poor intertester reliability by one group of researchers,49 although they used ratings obtained for only 3 subjects, whereas other researchers33,34 have found reasonable reliability (ICC>.80). Other researchers50 also have pointed out that measuring medial rotation by vertebral level incorporates elbow motion and substantial scapulothoracic motion. We chose to use this measure primarily because patients with impingement are often unable to tolerate internal rotation with the arm elevated to 90 degrees. In addition, placing the hand behind the back appears to be important for several functional activities such as fastening a bra, tucking in a shirt, or toileting functions. Determining the optimal way to document tightness of the posterior capsular as well as the optimal way to improve it with stretching, we believe, are worthy of further study.
Despite exercises directed at encouraging upper thoracic extension, we did not find altered resting posture in the upper thoracic area, nor did we find increased thoracic extension during shoulder flexion. Upper thoracic extension is believed to be an essential component of arm elevation, and the exercise program may have facilitated subtle increases in upper thoracic motion that were not detected with our measurement system.
The relatively high attrition rate (33%) was disappointing and potentially biased the results. The subjects who dropped out, however, were very similar to those who completed the study in terms of age, size, duration of symptoms, pain intensity, and shoulder function. A greater percentage of male subjects than female subjects dropped out of the study. The majority of the subjects who dropped out (11/20) did not return after the first session, which consisted of initial testing and exercise training; 6 subject completed 2 visits, 1 subject completed 3 visits, and 3 subjects dropped out after 4 visits. We believe it is unlikely that an adverse response led to dropping out of the study, because no subject reported such a response and the exercise program was designed to avoid pain. We believe the urban location combined with stressful personal schedules prevented many subjects from completing the 6-week program, which may explain why our attrition rate was similar to that for all other patients seen at the same clinic (38%). The fact that patients were not paying for intervention may have been an incentive; however, the majority of patients in the primary clinic pay little or nothing out of pocket for intervention, and "free" intervention that emphasized a home exercise program may have been perceived as less valuable. Another possibility is that once patients realized the intervention consisted of a home exercise program, weekly clinic attendance may have been perceived as unimportant.
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| Footnotes |
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This study was approved by the institutional review boards of Arcadia University and the University of Pennsylvania.
An earlier version of this work was presented at the Combined Sections Meeting of the American Physical Therapy Association, February 20–24, 2002, Boston, Mass, and published in abstract form in the Journal of Orthopaedic and Sports Physical Therapy (2002;32:A-8).
This work was supported by a grant from the Foundation for Physical Therapy.
* Polhemus Inc, 40 Hercules Dr, Colchester, VT 05446. 
Velcro USA Inc, 406 Brown Ave, Manchester, NH 03103.
National Instruments Corp, 11500 N Mopac Expressway, Austin, TX 78759-3504.
Hoggan Health Industries Inc, PO Box 957, Draper, UT 84020-0957.
# The Hygenic Corporation, 1245 Home Ave, Akron, OH 44310.
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-year follow-up.
J Shoulder Elbow Surg.1999; 8:102–111.[Web of Science][Medline]
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