Does the pectoralis minor length influence acromiohumeral distance, shoulder pain-function, and range of movement?

Accepted Manuscript Does the pectoralis minor length influence acromiohumeral distance, shoulder painfunction and range of movement? S. Navarro-Ledesma, M. Fernandez-Sanchez, A. Luque-Suarez PII:

S1466-853X(18)30143-3

DOI:

10.1016/j.ptsp.2018.08.009

Reference:

YPTSP 941

To appear in:

Physical Therapy in Sport

Received Date: 8 May 2018 Revised Date:

22 July 2018

Accepted Date: 21 August 2018

Please cite this article as: Navarro-Ledesma, S., Fernandez-Sanchez, M., Luque-Suarez, A., Does the pectoralis minor length influence acromiohumeral distance, shoulder pain-function and range of movement?, Physical Therapy in Sports (2018), doi: 10.1016/j.ptsp.2018.08.009. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT TITLE PAGE

Does the pectoralis minor length influence acromiohumeral distance, shoulder

Navarro-Ledesma S*a,b; Fernandez-Sanchez Mc; Luque-Suarez Ab Department of Physiotherapy, University of Granada, Spain

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a

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pain-function and range of movement?

b

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Address: Av. de la Ilustración, 60, 18016 Urb. los Vergeles, Granada, España. Department of Physiotherapy, University of Malaga, Spain

Address: Facultad Ciencias de la Salud; Universidad de Malaga; Arquitecto Francisco Penalosa, 3; 29002 Malaga

Department of Nursing, Physiotherapy and Medicine, University of Almeria, Spain

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Address: Facultad Ciencias de la Salud; Universidad de Almería; Ctra de Sacramento S/N. 04120

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Almeria

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Corresponding author:

Santiago Navarro-Ledesma ([email protected]) Av. de la Ilustración, 60, 18016 Urb. los Vergeles, Granada, España

Word count: 3273

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Declarations of interest: none

ACCEPTED MANUSCRIPT TITLE PAGE

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shoulder pain-function and range of movement?

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Does the pectoralis minor length influence acromiohumeral distance,

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ABSTRACT Objective: To determine the association between pectoralis minor length (PML)

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and the acromiohumeral distance (AHD) in the symptomatic (S) and the asymptomatic (A) shoulder of subjects with chronic shoulder pain, and in shoulder free of pain controls (C). Furthermore, to analyze the relationship between PML

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and shoulder pain-function and range of movement (ROM) free of pain.

Setting: Primary care centres

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Design: A cross sectional study

Participants: A sample of fifty-four participants with chronic shoulder pain in their

pain.

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dominant arm was recruited, as well as fifty-four participants with shoulder free of

Main Outcome Measures: PML test and AHD measured by ultrasound.

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Results: There was a non statistical significant correlation between PML and AHD

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for all the groups at both 0º (S=0.03, p= 0.29; A=0.06, p= 0.66; C=-0.17, p= 0.29) and 60º (S=-0.10, p= 0.84 ; A=-0.18, p= 0.19; C=-0.03, p= 0.84) of shoulder elevation. Likewise, there was a non statistical significant correlation between PML and shoulder pain-function (0.09, p= 0.52), and ROM (-0.13, p= 0.35). Conclusions: PML is poorly associated with AHD, as well as with shoulder pain and mobility, in people with chronic shoulder pain. Other biomechanics alterations, as well as the presence of central/peripheral sensitization should be considered.

ACCEPTED MANUSCRIPT Keywords

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Shoulder pain; pectoralis muscles; ultrasonics; chronic pain

ACCEPTED MANUSCRIPT Highlights Pectoralis minor length is not associated with acromiohumeral distance at both rest position and 60 degrees of shoulder elevation, either symptomatic or

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asymptomatic populations.

length in chronic condition.

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Shoulder pain and range of movement are not explained by the pectoralis minor

In shoulder assessment, pectoralis minor length should not be considered as

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distinguishing factor in patients with chronic pain.

ACCEPTED MANUSCRIPT Does the pectoralis minor length influence acromiohumeral distance, shoulder pain-function and range of movement? Introduction

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Shoulder pain is one of the most common musculoskeletal conditions, with subacromial pain syndrome (SAPS) being the most frequent diagnostic label. (McCreesh, Crotty, & Lewis, 2013; Ratcliffe, Pickering, Mclean, & Lewis, 2014a) It

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is multifactorial, thus the exact cause remains controversial. (Wilk et al. 2009) It affects one in three adults, accounting for 1% of all general practitioner

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consultations in primary care(J. J. Luime, Koes, Miedem, Verhaar, & Burdorf, 2005), with a one-year prevalence between 7% and 27% in adults younger than 70 years.(J. Luime et al., 2004)

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The relationship between scapular positioning and shoulder pain has been widely investigated, however there is still inconsistent evidence to support this. (Ratcliffe, Pickering, Mclean, & Lewis, 2014b) The etiology has been attributed to both

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intrinsic and extrinsic mechanisms. The first are those related to histological

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changes within the tendons, alterations in biology, mechanical properties, morphology, and vascularity of the tendon.(Girish et al., 2011) The second include anatomical variants of the acromion, alterations in scapular or humeral kinematics, postural abnormalities, rotator cuff and scapular muscle performance deficits, and decreased extensibility of the pectoralis minor or posterior shoulder.(Seitz, McClure, Finucane, Boardman, & Michener, 2011) Within extrinsic factors, the role of the pectoralis minor length in shoulder conditions has been theorized. In this context, a shortened pectoralis minor alters the scapular positioning, which can

ACCEPTED MANUSCRIPT lead to a decrease in acromiohumeral distance (AHD), causing a subacromial impingement syndrome (SIS). (Borstad & Ludewig, 2005) The AHD has been defined as the shortest distance between the humeral head and the acromion

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process,(Hébert, Moffet, Dufour, & Moisan, 2003) and has been studied by ultrasound (US) in both asymptomatic(Luque-Suarez, Navarro-Ledesma, Petocz, Hancock, & Hush, 2013; Tanya Mackenzie, Lee Herrington, Lenard Funk, 2016)

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and symptomatic subjects. (Cholewinski, Kusz, Wojciechowski, Cielinski, & Zoladz, 2008; Savoie, Mercier, Desmeules, Frémont, & Roy, 2015) A relationship

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has been shown between AHD and both shoulder pain and function in patients suffering from acute SAPS, (Desmeules, Minville, Riederer, Côté, & Frémont, 2004) whereas no relationship has been found in chronic conditions. (Santiago Navarro-Ledesma et al., 2017) In a clinical setting, the AHD can be useful in the

position

when

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detection of shoulder dysfunction when a difference of 2.1mm is found at the rest comparing

the

symptomatic

and

the

asymptomatic

sides.(Cholewinski et al., 2008) Also, finding changes in AHD at 60 degrees of

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shoulder elevation may have clinical relevance, since differences between subjects with and without shoulder pain have been reported at this position. (S.

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Navarro-Ledesma & Luque-Suarez, 2018)

Different biomechanical factors have been studied in relation to AHD, e.g., scapular rotation, shoulder internal rotation, shoulder external rotation, total arc of shoulder rotation, and thoracic curve, with inconsistent findings. (Tanya Mackenzie, Lee Herrington, Lenard Funk, 2016) Further studies are necessary to increase knowledge in the field, and, especially, how these factors may influence AHD in presence of shoulder pain.(Mackenzie, Herrington, Horlsey, & Cools,

ACCEPTED MANUSCRIPT 2015a) One of these factors is the pectoralis minor length (PML). Previous studies have reported normative values on PML in the dominant and non-dominant side in both symptomatic and control populations.(Lewis & Valentine, 2007; Struyf et al.,

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2014) Nevertheless, to the best of our knowledge, the level of association between PML and the AHD in patients with shoulder pain is still unknown. Only one study analyzing such a correlation in painfree sporty people exists.(Tanya

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Mackenzie, Lee Herrington, Lenard Funk, 2016)

The hypothesis of the present study is that because the pectoralis minor originates

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from ribs 3, 4, and 5, and attaches to the medial border of the coracoid process, the pectoralis minor would lead the scapula to rotate upwardly, internally, anteriorly tip, or descend in the case of shortening, contrary to what happens in painfree subjects. (Ludewig & Cook, 2000),(McClure, Michener, Sennett, &

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Karduna, 2001) This fact could be corroborated with a decreased AHD, function and ROM, and potentially greater shoulder pain, which means that a shortened pectoralis minor could be a potential mechanism of developing SAPS, requiring

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more attention in both shoulder assessment and treatment. Thus, increased knowledge about the relationship between the PML and the AHD in symptomatic,

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asymptomatic shoulders, and in shoulder painfree subjects, is needed.

Hence, the aim of this study is twofold: (i) to analyze the level of association between PML and AHD measured by US at 0° and 60° of shoulder elevation, in both the symptomatic and the asymptomatic shoulders, in patients with unilateral chronic shoulder pain, and in control subjects. (ii) To study the relationship between PML and shoulder pain-function, and ROM-free of pain in those with shoulder pain.

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METHOD

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Study design This was a cross-sectional, observational study, conducted according to the Declaration of Helsinki. Ethical approval was obtained from the Ethics Committee

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of the Health Care District where the primary care centres were located (PI9/012014). The study has been reported following the recommendations of

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STROBE statement for observational studies.

Setting

Sixty six participants presenting shoulder pain which lasted for more than three

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months were recruited from three different primary care centers. General practitioners carried out the recruitment. Research assistants then assessed participants for eligibility. If participants satisfied the inclusion criteria, they were

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studied. Three participants declined to participate, and 10 participants did not meet the inclusion criteria, therefore a sample comprised of 54 participants was

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assessed. Research assistants collected a consent form from every participant, and the confidential information collected from participants was password protected and stored.

During the first screening,

participants who presented any of the following

conditions were ineligible: 1) recent shoulder dislocation, systemic illnesses such as rheumatoid arthritis, and evidence of adhesive capsulitis as indicated by passive range of motion loss >50% in 2 planes of shoulder motion; 2) shoulder

ACCEPTED MANUSCRIPT pain that was deemed to be originating from any passive and/or neck movement or if there was a neurological impairment, osteoporosis, haemophilia and/or malignancies; 3) corticoid injections during the six months prior to the study and 4)

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analgesic-anti-inflammatory medication intake 48 hours prior to the assessment. Furthermore, other exclusion criteria had to be met: 5) men or women aged between 18 and 55 years; 6) no history of significant shoulder trauma, such as

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fracture or clinically-suspected full thickness cuff tear; 7) being involved in overhead sport activities. After that, the inclusion criteria defined to be part of the

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study had to present at least three of the following conditions: i) positive Neer test; ii) positive Hawkins-Kennedy test; iii) positive Jobe test; iv) painful arc present during flexion or abduction; v) pain during resisted lateral rotation and/or abduction (Bury, West, Chamorro-Moriana, & Littlewood, 2016; Michener, Walsworth, &

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Doukas, 2009) A sample of 54 participants with both shoulders free of pain over the last year was recruited. They were recruited from the same three primary care centres as the participants with shoulder pain. Furthermore, to participate in the

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study, they had to present: (i) a SPADI score ≤ 15 points, based on the minimal clinically detectable change for this tool.(Engebretsen K, Grotle M, Bautz-Holter E,

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Ekeberg OM, 2010); (ii) negative results for Neer test, Hawkins-Kennedy test Jobe test, Speed test and Gerber test; iii) no painful arc present during flexion or abduction; iv) no pain during resisted lateral rotation and/or abduction; (v) participants not enrolled in overhead physical activities.

Primary outcome Pectoralis minor length (PML)

ACCEPTED MANUSCRIPT The measurement of the PML has shown to have sufficient intra-rater reliability. (Lewis & Valentine, 2007; Struyf et al., 2014) It was carried out with the participant in the supine position. A small pillow was placed under the participant’s head for

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comfort. The participant’s arm was passively placed along the side of the body in the neutral position resting on the table. (Tanya Mackenzie, Lee Herrington, Lenard Funk, 2016). The resting muscle length is measured between the caudal

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edge of the 4th rib to the inferomedial aspect of the coracoid process with a sliding caliper (Figure 1). However, because of variability among subjects this

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measurement was best normalized creating a pectoralis minor index (PMI), which is calculated by dividing the resting muscle length measurement by the subject height and multiplying by 100.(Borstad & Ludewig, 2005) All measurements were carried out by a physiotherapist with more than 25 years of experience.

reliability.

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Furthermore, the mean of 3 measurements was taken to calculate the intrarater

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Secondary outcomes

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Acromiohumeral distance

The AHD was defined as the shortest linear distance between the most inferior aspect of the acromion and the adjacent humeral head (Figure 2).(Desmeules et al., 2004) A diagnostic ultrasound unit, Sonosite M-turbo (GE Healthcare, Wauwatosa, WI) with a 6–13MHz linear transducer was used to capture images in grey scale. Ultrasound images were obtained by a single examiner, who was a licensed physiotherapist with advanced training in musculoskeletal ultrasound imaging, and 5-years of experience. The acromiohumeral distance was measured

ACCEPTED MANUSCRIPT in rest position and at 60 degrees of shoulder abduction in the scapular plane, with the participant seated in an upright position. To guarantee 0 and 60 degrees of shoulder elevation, a hydro-goniometer was placed on the patient's arm. Patients

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were seated upright without back support, their feet flat on the ground. (Desmeules et al., 2004) The ultrasound transducer was placed on the most anterior aspect of the acromion edge, with the long axis of the transducer placed

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in the plane of the scapula and parallel to the flat surface of the acromion (Figure 3). The AHD was measured in centimetres, using the callipers on the ultrasounds’

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screen. Three measurements were taken in order to calculate the intrarater reliability, and the mean of the measurements were collected. An interval of one minute was provided between measurements. The ultrasound examiner was blind to all measurements (values were obscured by placing a shield on the ultrasound

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screen, and a research assistant registered the data), and was blind to the previous condition of each patient (shoulder function and pain severity) as well as to the affected side and hand dominant. All the ultrasound measurements were

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expressed in centimetres.

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Shoulder pain and disability index (SPADI) The Shoulder Pain and Disability Index (SPADI) is a self-administered questionnaire that consists of two scales, one for pain and the other for functional activities. SPADI total score fluctuates from 0 to 100, where 0 is the best and 100 is the worst. (Roach, Budiman-Mak, Songsiridej, & Lertratanakul, 1991) The SPADI has shown a good internal consistency with a Cronbach’s alpha of 0.95 for the total score, 0.92 for the pain subscale and 0.93 for the disability subscale as

ACCEPTED MANUSCRIPT well as the ability to detect change over time.(MacDermid, Solomon, & Prkachin, 2006) An adapted version of the SPADI was obtained following the International recommendations since English was not the native language for all the

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participants. (Wild et al., 2005)

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Active ROM-free of pain at shoulder elevation in the scapular plane

Active range of movement free of pain at shoulder elevation in the scapular plane

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was taken in standing position. A hydro-goniometer was placed on the patient's arm to determine the shoulder elevation where pain was arisen. Three measurements were taken at 1 min intervals, and the mean was calculated. ROM

Data analysis

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was expressed in degrees.

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The Statistical Package for the Social Sciences (version 23.0; SPSS Inc. Chicago, IL) was used to analyse the collected data. Normality of the variables was visually

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tested for a Gaussian distribution and additionally evaluated with a 1-sample Kolmogorov-Smirnov goodness-of-fit test. For the calculation of intrarater reliability of ultrasound measurements and PMI, the 3,1 model or a 2-way mixed consistency intraclass correlation coefficient (ICC) model was used. The mean and standard deviation (SD) of each subject’s characteristics, PMI and AHD were calculated.

ACCEPTED MANUSCRIPT A reliability coefficient less than 0.50 was an indication of “poor” reliability; “moderate” being between 0.50 and 0.75, “good” between 0.76 and 0.90; and “excellent” over 0.90. (Portney & Watkins, 2000) The Standard Error of

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Measurement (SEM) and the minimal detectable change with 95% confidence bounds (MDC95) were calculated.

To determine the correlations between PMI and AHD, PMI and SPADI and PMI

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and ROM-free of pain, a Pearson correlation coefficient was calculated for a normal data distribution, or a Spearman´s coefficient in the case of absence of

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normality. Weak correlation was defined as values between 0.3 and 0.5; between 0.5 and 0.7 correlation was considered moderate; strong was considered greater than 0.7.(Mukaka, 2012)

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RESULTS Sample characteristics

Sample characteristics are shown in Table 1. There were absence of differences

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between groups regarding age, gender, height, PMI and AHD measurements.

Control participants

46.39 (43.67-49.11)

46.42

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Patient participants

Age (yrs: CI)

(44.1

p

to 0.98

48.67)

Gender

Female

33

33

1

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21

Height

164,42

192,0)

55,69 (17,69-100)

2,66 (1,73 to 3,60)

N/A

N/A

N/A

6-9 months: 5 >9 months: 31

shoulder 10.80%

AHD 0° mean

(10.18- 10.85%

0.97 (0.93-1.00)

pain

of 91.43

0.68 (0.38-0.96)

%(9.7310.42%) 0.95

0.77

0.67

0.18

0.70) (40.00- N/A

Table 1: Sample characteristics; Mean (95% CI);

N/A (Non Applicable)

0.13

(0.63-

180.00)

p<0.05: statistically significant

p

(0.12)

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0.63 (0.60-0.66)

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Rom-free

(10.24- 10.07

11.46%)

0.96 (0.92-1.00)

AHD 60° mean

Control

shoulder

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11.43%)

Asymptomatic

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Symptomatic

PMI mean

– 0.36

168,65)

of 3-6 months: 18

symptoms

(150,0

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Chronicity

(160,20- 168,40

1

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SPADI (CI)

21

N/A

N/A

ACCEPTED MANUSCRIPT Correlation between PMI and AHD, PMI and SPADI, PMI and Rom-free of pain in symptomatic, asymptomatic shoulders and painfree controls There was absence of statistically significant correlations between all variables in

Asymptomatic shoulder

(r-values)

(r-values)

0.03

0.06

rest

p= 0.29

p= 0.66

position PMI and

-0.10

AHD at 60°

p= 0.84

PMI and SPADI

0.09

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at

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Symptomatic shouer

PMI and AHD

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the different groups. All correlations were less than weak (< 0.3). Control (r-values)

-0.17

p= 0.29

-0.18

-0.03

p= 0.19

p= 0.84

N/A

N/A

N/A

N/A

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p= 0.52 PMI and ROM-

p= 0.35

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free of pain

-0.13

Table 2: PMI and AHD mean (centimeters) and correlations in symptomatic,

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asymptomatic shoulders and in controls. p<0.05: statistically significant N/A (Non Applicable)

The intrarater reliability calculated in ultrasound measurements was excellent; ICC AHD 0°= 0.96 (0.13); ICC AHD 60°= 0.98 (0.37). The PMI also obtained excellent results regarding intrarater reliability; ICC=1 (2.01).

ACCEPTED MANUSCRIPT Discussion This study aimed to investigate the level of association between PML and AHD in patients suffering from unilateral chronic shoulder pain. This relationship was also

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analyzed in the contralateral asymptomatic shoulder and in control subjects in order to compare whether the PMI and AHD behave similarly. Furthermore, the level of association between PMI and shoulder pain-function, and ROM-free of

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pain were studied. This study represents the first approach in this line, showing a less than weak correlation between AHD and PMI in both the symptomatic and the

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asymptomatic shoulders, and in control subjects. Moreover, the PMI was less than weak correlated with shoulder pain-function and ROM.

The results obtained are contrary to Mackenzie et al(Tanya Mackenzie, Lee Herrington, Lenard Funk, 2016), who found that painfree male participants

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showed a weak positive correlation between PMI and AHD at rest position. This may be explained because of differences in participants; while our study was carried out in patients with unilateral chronic shoulder pain, without being involved

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in any overhead sport activity, Mackenzie et al studied a sport population. (Tanya

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Mackenzie, Lee Herrington, Lenard Funk, 2016) Prior studies in sports populations have shown

a different scapular behavior even in the absence of

pain.(Hosseinimehr, Anbarian, Norasteh, Fardmal, & Khosravi, 2015) To the best of our knowledge, there are no more studies analyzing this relationship. On the other hand, participants from the present study showed mean PMI values of 10.80 in the symptomatic shoulder, 10.85 in the asymptomatic shoulder, and 10.07 in control participants, which are close to previous studies. In participants with shoulder pain, mean values of 9.66 in the symptomatic side and 9.64 in the

ACCEPTED MANUSCRIPT asymptomatic have been reported, while values of 9.17 have been shown in participants free of pain. (Struyf et al., 2014) However, Borstad et al found more reduced values for PMI (7.42).(Borstad & Ludewig, 2005) These values are in line

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with a study carried out in a population of adolescent tennis players, showing values of 7.1 (0.4) in males and 6.9 (0.9) in females. (Cools et al., 2010) Differences with Borstad et al. could be attributed to differences in sample

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characteristics. First, they studied painfree subjects. Second, PML was measured in a standing position,(Borstad & Ludewig, 2005) whereas we decided to use a

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supine position to avoid postural influences, following accepted literature(Cools et al., 2010; Struyf et al., 2014). Third, the mean age of 46 years in participants from the present study, who had chronic symptoms, versus painfree people with a mean age of 28.6 years in Borstad et al.

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Regarding the second aim of this study, there was a less than weak correlation between PMI and AHD at both 0 and 60° of shoulder elevation in scapular plane in all groups. There are no studies analyzing the level of association between PMI

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and AHD during arm elevation in patients with shoulder pain. It is hypothetised that a smaller PMI can increase the anterior tilt and, thus, decrease the AHD and

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ROM, causing a possible mechanism for SIS. For this reason, and because passive tension from the pectoralis minor can influence scapular tipping, the relationship between PMI and ROM was also assessed, again showing an absence of correlation at both rest position and 60 degrees of shoulder elevation. Only Borstad et al. studied this in painfree people with and without shortened pectoralis minor, showing an anteriorly tipped position of the scapula at 60 degrees of shoulder elevation in those with a shortened pectoralis minor, but

ACCEPTED MANUSCRIPT without measuring the AHD.(Borstad & Ludewig, 2005) In this regard, AHD has been shown to be decreased at 60° of shoulder elevation in those with shoulder pain when compared to controls.(S. Navarro-Ledesma & Luque-Suarez, 2018)

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Rosa et al. suggested the possibility that neuromuscular mechanisms other than PML are related to shoulder pain and disability.(Rosa, Borstad, Pogetti, & Camargo, 2016) After a pectoralis minor stretching protocol in participants with

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and without shoulder pain, they obtained an absence of differences in pectoralis length, but found an improvement in pain-disability in those with pain. However,

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they did not study the level of association between variables.

With regard to the association between PMI and pain-function measured through the SPADI, our results did not show significant findings. To our knowledge, there are no studies investigating this association. The “less than weak” correlation (very

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small) may be explained as the PMI does not completely assess the state of the pectoralis minor since the intrinsic properties, which indicate the stiffness of the soft tissue, and whose changes may influence pain perception and shoulder ROM,

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were not measured. Hence, more studies which evaluate the properties of the pectoralis minor with tools like ultrasound elastography for the intrinsic properties,

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(Brandenburg et al., 2015) and pain pressure thresholds, are needed. Additionally, there is some evidence on the role that central/peripheral sensitization may play on chronic shoulder pain.(Sanchis, Lluch, Nijs, Struyf, & Kangasperko, 2015) Likewise, recent systematic reviews have shown the influence that, in one hand, psychological factors(Martinez-Calderon, Meeus, et al., 2018) and, on the other hand, pain beliefs, may have in the prognosis of chronic shoulder pain. (MartinezCalderon, Struyf, Meeus, & Luque-Suarez, 2018) Thus, chronic shoulder pain

ACCEPTED MANUSCRIPT should be considered as a multifactorial condition, not only influenced by biomechanic/tissue factors, but also by other different mechanisms. Some aspects of this study must be highlighted. This study is the first analyzing

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the relationship between PMI and AHD at 0 and 60 degrees of shoulder elevation measured by US, in both symptomatic and asymptomatic shoulders in patients with chronic shoulder pain, and in controls. Since there is only one study which

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analyzes this in painfree male subjects,(Tanya Mackenzie, Lee Herrington, Lenard Funk, 2016) this present study will allow a better understanding of the role of PMI

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and its influence on AHD, shoulder pain-function and ROM-free of pain. Other strength is that similarities in demographic characteristics were presented when the sample was recruited. Furthermore, extensive exclusion criteria was carried out by assessing the integrity of both shoulders to avoid participants with any

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shoulder condition or partial-full rotator cuff tears either symptomatic or asymptomatic.(Wiener & Seitz, 1993) Additionally, intrarater reliability in both PMI and AHD measurements were calculated which showed excellent results.

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In addition, some limitations should be recognized. Shoulder pain is multifactorial.

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As the PMI only assesses part of this condition, another intrinsic factors in shoulder pain need to be considered and included to better explain this condition. (Mackenzie, Herrington, Horlsey, & Cools, 2015b) Quality and flexibility of the tissue were not evaluated, as they have been investigated in others musculoskeletal disorders.(Docking, Rosengarten, Daffy, & Cook, 2015; Pozzi et al., 2017) Thus, the real influence of the pectoralis minor on AHD, shoulder painfunction and ROM is not fully explained. Moreover, the interrater reliability of PMI

ACCEPTED MANUSCRIPT and AHD was not calculated and the sample size is small, thus, our results must be interpreted with caution. New techniques are appearing to quantify the quality and flexibility of soft tissues, the

small

associations

obtained

in

the

present

study

could

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so

change.(Brandenburg et al., 2015) However, this is still challenging in musculoskeletal disorders. For now, clinicians can assess the pectoralis minor

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quality through flexibility,(Borstad & Ludewig, 2005) but more studies combining both flexibility tests and analysis of the quantified soft tissue quality, and elasticity

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are necessary. Furthermore, more research is needed to determine whether an increase in the PMI after a physiotherapy treatment could be clinically significant

Conclusion

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for populations with shoulder pain.

Pectoralis minor length is not a distinguishing factor in shoulder assessment when

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a chronic condition exists, and it seems not to play a key role in pain perception and ROM. Hence, other factors such as the intrinsic properties of the tissue or

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central/peripheral sensitization should be considered.

References Borstad, J. D., & Ludewig, P. M. (2005). The effect of long versus short pectoralis minor resting length on scapular kinematics in healthy individuals. The

ACCEPTED MANUSCRIPT Journal of Orthopaedic and Sports Physical Therapy, 35(4), 227–38. http://doi.org/10.2519/jospt.2005.35.4.227 Brandenburg, J. E., Eby, S. F., Song, P., Zhao, H., Brault, J. S., Chen, S., & An,

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K.-N. (2015). Ultrasound Elastography: The New Frontier in Direct Measurement of Muscle Stiffness. Arch Phys Med Rehabil, 95(11), 2207– 2219. http://doi.org/10.1016/j.apmr.2014.07.007.Ultrasound

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Bury, J., West, M., Chamorro-Moriana, G., & Littlewood, C. (2016). Effectiveness of scapula-focused approaches in patients with rotator cuff related shoulder

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Cholewinski, J. J., Kusz, D. J., Wojciechowski, P., Cielinski, L. S., & Zoladz, M. P.

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(2008). Ultrasound measurement of rotator cuff thickness and acromiohumeral distance in the diagnosis of subacromial impingement syndrome of the shoulder. Knee Surgery, Sports Traumatology, Arthroscopy : Official

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Age (yrs: CI)

Patient participants

Control participants

46.39 (43.67-49.11)

46.42

(44.1

to

p 0.98

48.67)

33

33

Male

21

21

Height

164,42 168,65)

SPADI (CI)

– 0.36

192,0)

55,69 (17,69-100) of 3-6 months: 18

symptoms

(150,0

6-9 months: 5

2,66 (1,73 to 3,60)

N/A

N/A

N/A

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Chronicity

1

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(160,20- 168,40

1

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Female

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Gender

>9 months: 31

shoulder

shoulder

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Asymptomatic

10,80%

(10,18- 10,85%

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PMI mean

Symptomatic

11,43%)

AHD 0° mean

0,96 (0,92-1,00)

Control

(10,24- 10,07

11,46%)

p

0.13

%(9,7310,42%)

0,97 (0,93-1,00)

0,95

0.77

(0,12) AHD 60° mean

0,63 (0,60-0,66)

0.68 (0.38-0.96)

0.67 (0.630.70)

0.18

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of 91,43

(40,00- N/A

N/A

N/A

180,00)

Table 1: Sample characteristics; Mean (95% CI); p<0.05: statistically significant

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N/A (Non Applicable)

ACCEPTED MANUSCRIPT Asymptomatic

shoulder

shoulder

Correlation between

0.03

0.06

-0.17

PMI and

p= 0.29

p= 0.66

p= 0.29

Correlation between

-0.10

-0.18

PMI and

p= 0.84

p= 0.19

Correlation between

0.09

N/A

PMI and SPADI

p= 0.52

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AHD at 60° GH abduction

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AHD at rest position

Correlation between PMI and -0.13 ROM-free of pain

N/A

Control

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Symptomatic

-0.03

p= 0.84

N/A

N/A

p= 0.35

Table 2: PMI and AHD mean (centimeters) and correlations in symptomatic,

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asymptomatic shoulders and in healthy controls.

p<0.05: statistically significant

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N/A (Non Applicable)

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Figure 1: Pectoral minor length measurement

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Figure 2: AHD landmarks and measurement

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Figure 3: Transductor position

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ACCEPTED MANUSCRIPT Highlights

Pectoralis minor length is not associated with acromiohumeral distance at both rest position and 60 degrees of shoulder elevation, either symptomatic or asymptomatic populations.

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Shoulder pain and range of movement are not explained by the pectoralis minor length in chronic condition.

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distinguishing factor in patients with chronic pain.

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In shoulder assessment, pectoralis minor length should not be considered as

ACCEPTED MANUSCRIPT Ethical Approval

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This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors

ACCEPTED MANUSCRIPT CONFLICT OF INTEREST FILE Conflict of Interest “None declared” Ethical Approval

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This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors Funding

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“None”