John D. Borstad

Measurement of Pectoralis Minor Muscle Length: Validation and Clinical Application

STUDY DESIGN Clinical measurement validity study. OBJECTIVES To validate the measurement of the pectoralis minor muscle length using palpable landmarks and to explore the accuracy of the measurement using a clinical instrument. BACKGROUND The pectoralis minor is believed to adaptively shorten. Individuals with a relatively short pectoralis minor demonstrate scapular kinematic alterations that have been associated with shoulder impingement. METHODS AND MEASURES A 3-dimensional electromagnetic motion capture system was used to calculate the length of the pectoralis minor in 11 cadavers, using 2 measurement techniques. In addition, a measurement with the electromagnetic system using palpable landmarks was compared to a measurement with both a caliper and tape measure in vivo. RESULTS In cadavers, a measurement using palpable landmarks was determined to be a valid measure of the actual muscle length visualized and measured following dissection. There was a high intraclass correlation coefficient and a small root-mean-square error between these 2 measures. High intraclass correlation coefficients were also calculated in vivo when measurements with the clinical instruments were compared with the electromagnetic device measures. CONCLUSION A measurement using palpable landmarks for pectoralis minor length validly represents the muscle length in cadavers. A caliper or tape measure may be used clinically with high accuracy and may help clinicians determine the need for and the effectiveness of interventions for lengthening this muscle.

Scapular muscle activation and co-activation following a fatigue task

Scapular muscles precisely move the scapulothoracic articulation and if fatigued may contribute to pathology. Fatigue of serratus anterior may be a mechanism for shoulder pathology by altering scapula motions and requiring compensation by other shoulder muscles. A total of 28 asymptomatic subjects performed a task to fatigue the serratus anterior, while muscle activity was recorded from three muscles. Mean normalized activation levels and activation ratios were examined before and after the fatigue task during arm elevation and lowering. All muscles demonstrated meaningful declines in the median frequency of the electromyographic signal during the task. Following the task, only the upper trapezius had higher mean activation levels (mean difference 10.79% MVIC), while the serratus anterior/lower trapezius activation ratio was altered (mean difference −0.3). Higher mean upper trapezius activation may be compensatory for fatigue of other shoulder muscles and may reflect fiber type or central control mechanisms. Serratus anterior eccentric endurance training may be beneficial for the prevention of shoulder pathology.

Scapula kinematic alterations following a modified push-up plus task

Scapular kinematic and muscle activity alterations have been identified in individuals with subacromial impingement syndrome of the shoulder, including workers and athletes who regularly perform overhead activities. Serratus anterior fatigue is a proposed mechanism for these kinematic alterations, although no direct evidence supports such a relationship. The purpose of this study was to examine three-dimensional scapula kinematics in asymptomatic participants before and after a task intended to preferentially fatigue serratus anterior. Twenty-eight participants completed the study. The experimental task consisted of five repetitions of scapular plane arm elevation and the fatigue task was the isometric hold of scapular protraction in the push-up position. Electromyography of four shoulder muscles was collected during the task to determine level of muscle fatigue, and the Borg CR10 scale was used to assess subjective fatigue. The fatigue task resulted in decreased median power frequency in all four muscles and significantly increased Borg scores. Scapula posterior tilting and internal rotation were most impacted by muscle fatigue, with decreased posterior tilting and increased internal rotation after the task. There was no effect on scapular upward rotation. Effect sizes were low to moderate (.13-.51) where these kinematic alterations reached statistical significance. Shoulder muscle fatigue contributes to scapular kinematic alterations and is a plausible risk factor for subacromial impingement syndrome.

Quantifying strain on posterior shoulder tissues during 5 simulated clinical tests: A cadaver study

STUDY DESIGN Controlled laboratory study using a repeated-measures approach. OBJECTIVE To quantify the amount of strain on cadaver posterior shoulder tissues during simulated clinical tests across different tissue conditions. BACKGROUND Several clinical tests are used to quantify posterior glenohumeral joint (GHJ) tissue tightness; however, the ability of these tests to directly assess the flexibility or tightness of the posterior capsule has not been evaluated. METHODS The middle and lower regions of the posterior shoulder tissues were instrumented with strain gauges on 8 cadaver shoulder specimens. Strain was quantified on the posterior shoulder muscles, on the native posterior GHJ capsule (baseline condition), and on the posterior GHJ capsule after it was experimentally contracted using thermal energy. Five simulated clinical tests were compared across each of the 3 conditions: humerus cross-body adduction, and GHJ internal rotation with the humerus positioned in 4 combinations of plane and elevation angle. Repeated-measures analyses of variance were used to compare strain measured during the 5 simulated clinical tests across the 3 conditions, and to evaluate the change in strain after contracting the posterior capsule. RESULTS There was a statistically significant interaction between tests and conditions for the middle region of the posterior shoulder. In the experimentally contracted condition, strain was greater when GHJ internal rotation was added to humerus flexion than when GHJ internal rotation was added to humerus abduction. There was a statistically significant main effect of tests at the lower region of the posterior shoulder, with internal rotation in abduction and internal rotation in the GHJ resting position demonstrating greater strain than cross-body adduction. The percent change in strain between the baseline and contracted capsule conditions did not reach statistical significance at either region. CONCLUSION Strain on an experimentally contracted posterior GHJ capsule is highest when tested with a combination of GHJ internal rotation and humerus flexion.

The role of sensitization in musculoskeletal shoulder pain.

Introduction: Peripheral and central sensitization are neurophysiological processes that can prolong painful conditions. Painful shoulder conditions are often persistent, perhaps due to the presence of sensitization. Method: This manuscript summarizes six studies that have evaluated those with musculoskeletal shoulder pain for the presence of sensitization. Results: All six manuscripts report evidence of peripheral sensitization, while central sensitization was described in five of the studies. The chronicity of symptoms in subjects who were included in the studies is probably influencing this finding. The primary somatosensory test used to assess sensitization in these studies was Pressure Pain Threshold, a test for lowered nociceptive thresholds. Discussion: It appears that peripheral sensitization manifests consistently in those with musculoskeletal shoulder pathology, probably due to the inflammatory processes related to tissue injury. Central sensitization, while not universally present, was reported in a majority of the manuscripts. Because central sensitization is thought to be a key step on the pathway to chronic pain, evidence for its presence in those with shoulder pain is significant. Clinicians should expect the presence of sensitization with shoulder pathology and make appropriate choices about interventions so as not to exacerbate pain.

Three-dimensional scapula kinematics and shoulder function examined before and after surgical treatment for breast cancer

Shoulder motion loss following surgical treatment of breast cancer is common and may be associated with surgery-related soft tissue changes and altered shoulder kinematics. Knowledge of short term biomechanical changes at the shoulder will inform treatment decisions and may help prevent the development of shoulder pathology. Shoulder motion loss following surgery also impacts quality of life and shoulder function, and measuring function with a shoulder-specific tool may direct rehabilitation. This study examined the short term effects of surgery on scapula kinematics and function in breast cancer survivors. Bilateral three-dimensional scapular kinematics were quantified before and after surgery for unilateral breast cancer and analyzed with repeated measures ANOVA. Shoulder function was assessed with the Shoulder Rating Questionnaire (SRQ) and analyzed with ANOVA. Subjects (n = 11) demonstrated statistically significant increases in scapula internal rotation on their involved side following surgery. An intention to treat analysis on all enrolled subjects supported this finding. The findings suggest that soft tissues restrictions impact short-term scapula motion following surgery for breast cancer. Significantly poorer shoulder function was reported for pain, recreation/athletic activities and total SRQ score after surgery. The SRQ appears sensitive enough to identify areas of life affected by changes in shoulder function following surgical intervention for breast cancer.

A longitudinal analysis of the effects of a preventive exercise programme on the factors that predict shoulder pain in construction apprentices

Construction apprentices are at risk for developing shoulder pain with increasing exposure to repetitive overhead work. Risk may decrease if shoulder biomechanics are optimised and if risk factors that contribute to shoulder pain onset are identified. This prospective cohort study examined demographic and work-related factors and shoulder pain onset over 2 years in a cohort of 240 construction apprentices. Approximately 50% of the sample (n = 117) performed a home exercise programme intended to have a protective effect, while the other 50% served as controls. The proportion of new-onset shoulder pain in the control group was higher than in the exercise group. Regression analysis identified four factors related to new-onset shoulder pain: previous neck pain; working in hot, cold or humid conditions; subject height; and bending and twisting the back. This information may assist employers and workers in preventing shoulder pain. By knowing factors predictive of shoulder pain development in construction workers, employers can take measures to protect workers and may secondarily decrease medical expenses and maintain productivity. Previous neck pain, working in extreme environmental conditions and being shorter all increased a workers risk of developing shoulder pain. Exercises to optimise shoulder biomechanics have a small effect on preventing shoulder pain development.

Reliability of measuring pectoralis minor muscle resting length in subjects with and without signs of shoulder impingement

Background: Pectoralis minor adaptive shortening may change scapula resting position and scapular kinematics during arm elevation. A reliable and clinically feasible method for measuring pectoralis minor length will be useful for clinical decision making when evaluating and treating individuals with shoulder pain and dysfunction. Objectives: To evaluate intrarater, interrater, and between-day reliability of a pectoralis minor (PM) muscle length measurement in subjects with and without signs of shoulder impingement. Method: A convenience sample of 100 individuals (50 asymptomatic and 50 symptomatic) participated in this study. Intra- and interrater reliability of the measurement was estimated in 50 individuals (25 asymptomatic and 25 symptomatic), and between-day reliability of the measurement repeated over an interval of 7 days was estimated in an independent sample of 50 additional participants. Pectoralis minor length was measured using a flexible tape measure with subjects standing. Results: Intraclass correlation coefficients (ICC3,k) for intrarater and interrater reliability ranged from 0.86-0.97 and 0.95 for between-day reliability in both groups. Standard error of measurements (SEM) ranged from 0.30-0.42 cm, 0.70-0.84 cm, and 0.40-0.41 cm for intrarater, interrater, and between-day reliability, respectively, across the sample. The minimal detectable change (MDC) for between-day measurements ranged from 1.13-1.14 cm for both groups. Conclusions: In asymptomatic individuals and in those with signs of shoulder impingement, a single rater or pair of raters can measure pectoralis minor muscle length using a tape measure with very good reliability. This measurement can also be reliably used by the same rater over a seven day interval.

Critical and Theoretical Perspective on Scapular Stabilization: What Does It Really Mean, and Are We on the Right Track?

Stabilization exercises have been a focus and mainstay of many therapeutic and performance training programs in the past decade. Whether the focus is core stabilization for the spine or scapular stabilization, clinicians and trainers alike have endorsed these programs, largely on the basis of conceptual theory and anecdotal experience. The notion that an unstable scapula is related to shoulder dysfunction and pathology is well accepted, but is it accurate? The aim of this perspective article is to challenge the concept of scapular stabilization through the application of biomechanical and motor control constructs. The objectives are to critically examine current beliefs about scapular stabilization, to discuss definitions of stabilization and stability in the context of the scapulothoracic region, and to evaluate key evidence regarding scapular stabilization and scapular dyskinesia. Several new approaches that may affect the understanding of normal and atypical scapula motion are explored. Finally, a historical analogy is presented and future research and clinical directions are suggested. The aims are to lead readers to the essential concepts implied on scapular stabilization, to increase the critical thought process in rehabilitation practice, and to suggest some open topics to be explored in future research.

Effects of a stretching protocol for the pectoralis minor on muscle length, function, and scapular kinematics in individuals with and without shoulder pain

Study Design: Parallel‐group intervention with repeated measures. Introduction: Shortening of the pectoralis minor (PM) may contribute to alterations in scapular kinematics. Purpose of the Study: To evaluate the effects of a stretching protocol on function, muscle length, and scapular kinematics in subjects with and without shoulder pain. Methods: A sample of 25 patients with shoulder pain and 25 healthy subjects with PM tightness performed a daily stretching protocol for 6 weeks. Outcome measures included Disabilities of the Arm, Shoulder, and Hand questionnaire, PM length, and scapular kinematics. Results: Disabilities of the Arm, Shoulder, and Hand scores decreased (P < .05) in the patient group at post‐intervention. No differences (P > .05) were found for PM length in both groups. Scapular anterior tilt increased (P < .05) at 90° of flexion in the healthy group. Discussion: This study demonstrated that a daily home stretching protocol significantly decreases pain and improves function in subjects with shoulder pain. The mechanism responsible for these improvements does not appear directly related to PM muscle length or scapula kinematics, suggesting that other neuromuscular mechanisms are involved. Conclusion: The PM stretching protocol did not change the PM length or scapular kinematics in subjects with or without shoulder pain. However, pain and function of the upper limbs improved in patients with shoulder pain. Level of Evidence: 2b.