Association of Pectoralis Minor Muscle Extensibility, Shoulder Mobility, and Duration of Manual Wheelchair Use

Accepted Manuscript Association of Pectoralis Minor Muscle Extensibility, Shoulder Mobility and Duration of Manual Wheelchair Use Margaret Finley, PT, PhD, David Ebaugh, PT, PhD PII:

S0003-9993(17)30263-0

DOI:

10.1016/j.apmr.2017.03.029

Reference:

YAPMR 56873

To appear in:

ARCHIVES OF PHYSICAL MEDICINE AND REHABILITATION

Received Date: 8 February 2017 Accepted Date: 31 March 2017

Please cite this article as: Finley M, Ebaugh D, Association of Pectoralis Minor Muscle Extensibility, Shoulder Mobility and Duration of Manual Wheelchair Use, ARCHIVES OF PHYSICAL MEDICINE AND REHABILITATION (2017), doi: 10.1016/j.apmr.2017.03.029. 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.

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Running Head: Pectoralis Minor, Arm Motion and Wheelchair Use

Authors: 1

[email protected]

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[email protected]

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Margaret Finley, PT, PhD

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Association of Pectoralis Minor Muscle Extensibility, Shoulder Mobility and Duration of Manual Wheelchair Use

David Ebaugh, PT, PhD

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Drexel University, Department of Physical Therapy and Rehabilitation Science Three Parkway Building, 1601 Cherry Street, Mail Stop 7-502, Philadelphia, PA 19102

Corresponding Author:

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Margaret A. Finley, PT, PhD Drexel University Dept of Physical Therapy & Rehabilitation Science Three Parkway Building 1601 Cherry Street, Mail Stop 7-502 Office 763 Philadelphia, PA 19102 267-359-5583 [email protected]

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Presentation of preliminary findings at the 40th Annual American Society of Biomechanics Conference, Raleigh, NC August 2016 Acknowledgements: This study was funded by an internal research funding grant from the College of Nursing and Health Professions, Drexel University Conflicts of Interest: None

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Abstract

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Objective: To assess the relationship of pectoralis minor muscle (PMm) length and ex-

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tensibility to shoulder pain, shoulder girdle motion, and duration of manual wheelchair

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(MWC) use and compare differences in muscle length, muscle extensibility, peak hu-

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meral elevation and pain among groups based on duration of wheelchair use.

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Design: Cross-sectional cohort study

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Setting: Laboratory setting

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Participants: Twenty-two individuals with SCI who used a MWC for daily community

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and home mobility (18 males, mean age 41.7 years, duration wheelchair use = 14.6

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years). Participants were stratified into groups based on duration of wheelchair use: < 5

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years (n=6), 5-15 years (n=8), >15 years (n=8).

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Interventions: Not applicable

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Main Outcome Measure(s): Clinical measures of PMm length and extensibility, shoul-

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der girdle motion, and shoulder pain (Wheelchair Users Shoulder Pain Index).

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Results: Significant, high correlations were found among duration of wheelchair use,

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passive PMm length, passive PMm extensibility and peak humerothoracic elevation.

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Moderate correlation of peak humerothoracic elevation to pain was found. Individuals

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with >15 years wheelchair use have reduced PMm extensibility and reduced peak hu-

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merothoracic elevation compared to those with < 5 years duration of use.

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Conclusions: This is the first investigation to identify the association of reduced PMm

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extensibility with reduced shoulder girdle mobility, pain, and duration of wheelchair use

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in individuals with SCI.

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Key Words: pectoralis minor, muscle extensibility, shoulder girdle, manual wheelchair

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use, spinal cord injury

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List of abbreviations

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ICC = intraclass correlation coefficient

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LCS = local coordinate systems

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MDC = minimal detectable change

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MWC = manual wheelchair

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PMm = Pectoralis minor muscle

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SCI = spinal cord injury

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WUSPI = Wheelchair Users Shoulder Pain Index

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The National Institute on Disability and Rehabilitation Research reported that nearly 1.7

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million people in the United Sates have disabilities that require use of a wheelchair, with

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1.5 million using a manual chair.1 In addition to wheelchair propulsion, manual wheel-

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chair (MWC) users depend on their upper extremities for transfers, pressure relief, and

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several other daily activities. Dependency on upper extremities for most activities of dai-

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ly living and mobility predisposes these individuals to overuse and is often associated

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with development of shoulder pain.2-4

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Level of spinal cord injury (SCI) and body mass index (BMI) are two potentially important factors for development of shoulder pain in individuals with a SCI. Conflicting

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evidence exists regarding injury level and prevalence of shoulder pain.5-7 Sinnott et al 7

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proposed that differences in trunk postural control in those with high (T2-T7) compared

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with low paraplegia (T8- T12) may contribute to shoulder pain. On the contrary, Ball-

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inger et al8 found that level of injury was associated with shoulder range of motion but

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not shoulder pain. BMI has been shown to be a strong predictor of shoulder pain one

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year following inpatient rehabilitation following SCI.9 Greater abnormalities on plain ra-

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diographs and ultrasound as well as clinical evaluation were found in individuals with

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long duration SCI with higher BMI. 10

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Reports of an association between shoulder pain and duration of SCI are incon-

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sistent. Shoulder pain is typically reported within one year of wheelchair use,9,11,12 with

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early onset of pain being predictive of persistent long term shoulder pain.9 Increased

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prevalence of shoulder pain is reported with duration of injury greater than 5 years4, in-

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creasing upwards to 75% in individuals 15-16 years post injury.3,12 On the contrary,

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shoulder pain was found equally prevalent among duration of injury groups based on

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five year intervals.5 Regardless of timing of onset, shoulder pain can create a devastat-

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ing loss of independence,8,11,13,14 activity and participation, all of which lead to a dimin-

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ished quality of life.15,16 The high incidence and rapidity with which shoulder pain devel-

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ops and progresses in this population emphasizes the need to identify factors that are

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associated with shoulder pain, and a management approach that focuses on early iden-

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tification of these factors prior to the onset of shoulder pain.

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Use of a wheelchair increases the need for overhead reaching in order to engage

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with various environments. During a typical 8-hour day, individuals who use a MWC

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spend upwards of five times the total time with the upper extremity in overhead posi-

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tions compared to individuals who do not use a MWC.17 Decreased independence

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with a reduction in activity and participation at 5-years following injury is

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associated with range of motion deficits. 1 8 Therefore, to ensure optimal in-

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dependence, assessing and maintaining shoulder mobility is crucial follow-

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ing SCI.

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The Alignment-Impairment model provides a conceptual framework for determin-

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ing the role that shoulder girdle alignment, neuromusculoskeletal impairments, and ab-

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errant shoulder girdle movements have in the development of shoulder pain and dys-

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function. According to this model, mal-alignments of the shoulder girdle cause neuro-

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musculoskeletal impairments which in turn lead to aberrant shoulder girdle movements.

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Collectively these changes lead to the development of shoulder pain and dysfunction.19-

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alignment due to persistent demands placed upon their shoulder girdle. Surprisingly,

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duration of wheelchair use and reduced shoulder adductor muscle strength are the only

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Individuals who use a MWC are at risk for development of altered shoulder girdle

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factors thus far that have been associated with the development of shoulder pain in

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MWC users.24 Activities of daily living, transfers, wheelchair positioning and propulsion

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place MWC users in sustained postures that place the shoulder girdle tissues at risk for

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impairment. Specifically, the aforementioned demands put the pectoralis minor muscle

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(PMm) in a shortened position thereby predisposing it to becoming shorter and stiffer

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with decreased extensibility.9,25 A shorter resting PMm length is associated with aber-

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rant shoulder girdle movements in a young healthy population.20,22 Although this finding

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is demonstrated in individuals who did not have complaints of shoulder pain, the aber-

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rant patterns were similar to those reported in individuals with shoulder pain secondary

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to subacromial impingement, rotator cuff disease, and glenohumeral instability 20,22,26

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Shoulder pain in MWC users is multifactorial. Numerous potential factors have

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been investigated to date. However, the relationship of PMm length on shoulder func-

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tion has not been investigated in MWC user. Therefore, the primary purpose of this

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study was to assess the relationship of PMm length and extensibility to shoulder pain,

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shoulder girdle mobility, and duration of MWC use. It was hypothesized that reduced

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PMm passive extensibility would be associated with longer duration of wheelchair use

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and reduced shoulder girdle motion. The secondary purpose was to assess differences

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in muscle length, muscle extensibility, peak humeral elevation and pain among groups

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based on duration of wheelchair use. We hypothesized that individuals with longest du-

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ration of MWC use would demonstrate the greatest impairments in muscle length, ex-

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tensibility, and shoulder girdle mobility and higher pain levels.

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Methods

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Study Design This study design was a cross-sectional cohort study with between group comparisons. The study was approved by the Institution Review Board at Drexel University

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All participants provided informed consent.

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Participants

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Twenty-two adult volunteers with SCI who used a MWC for community mobility participated in this study (males =18; mean age= 40.8±14.6years; duration of wheel-

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chair use = 13.8 ±12.2 year) between June 2015 and September 2016. Individuals were

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eligible for participation if they had a history of SCI and used a MWC for at least 75%

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community mobility. Exclusion criteria included signs and symptoms of cervical spine

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pathology, upper extremity radicular symptoms, preexisting neurological conditions oth-

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er than effects from the SCI, history of upper extremity fracture, dislocation or surgery,

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complications from other health conditions that could influence function, and women

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with known pregnancy. Participants completed a brief questionnaire to provide infor-

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mation on demographics of age and sex as well as details of their SCI, contextual fac-

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tors of wheelchair specifics, and daily activities. Participant weight and height was

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measured and BMI was calculated. Measures of shoulder pain, muscle length and

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shoulder girdle kinematics were collected. The order of study measures was random-

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ized to deter order effect.

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Study Measures

Pectoralis Minor Muscle Length: PMm length was defined as the distance between two bony landmarks; the coracoid process and inferior medial aspect of the 4th

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rib adjacent to the sternocostal junction. Initial landmark identification occurred with the

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participant supine where the landmarks were palpated and marked with a dark marker.

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Landmark location was reassessed while the participant was seated in their wheel-

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chair in their natural relaxed posture and any necessary adjustments in landmark loca-

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tion were made. In an attempt to minimize the influence of anterior chest wall soft tis-

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sue mass on PMm length measures we used a caliper (palpation meter, PALM) rather

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than a tape measure. All measurements were repeated twice.

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All PMm measures were obtained with the participants seated in their personal wheelchair. Resting PM muscle length was measured while participants were seated

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in a relaxed natural posture (ICC =0.92, MDC95 = 1.25cm). 27 Following resting

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measures, PMm length was measured during passively lengthened condition. Bony

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landmarks were re-palpated and remarked for measures taken in the lengthened

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condition. For the passively lengthened condition participants’ arms were placed in

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approximately 30° of flexion. While stabilizing the participant’s trunk, a clinician used

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the distal end of the participant’s humerus to push their shoulder in a superi-

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or/posterior direction until firm tissue resistance was encountered. 28 Two clinician

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investigators (MAF, DE) performed the passive lengthening technique which has

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been shown to have excellent inter-tester reliability (ICC =0.84, MDC95 = 2.05cm).27

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Pain: Wheelchair Users Shoulder Pain Index (WUSPI) is a 15-item, self-reported

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visual analog scale measure, developed to determine shoulder pain during functional

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activities in wheelchair users. The outcome has excellent test-retest reliability (ICC =

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0.99). The WUSPI score range is 0-150 with an adjusted performance score based on

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the total number of items completed. The minimal detectable change is 5.1 points.29,30

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Shoulder Girdle Kinematics: Three-dimensional kinematics of the trunk, scapu-

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la, and humerus were collected (at 100 Hz) with The MotionMonitor (Ascension

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TrakStar) long range electromagnetic transmitter system using the mini bird sensors.

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(Innovative Sports Training, Inc., Chicago, IL). This system has a reported root mean

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square position accuracy of 0.07 inches/0.5 degrees at a 36 inch range with a resolu-

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tion of 0.03 inches/0.1degree.31 All kinematic measurers were based on the Interna-

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tional Society of Biomechanics recommendations.32 Sensors were placed on the

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most lateral portion of the acromion process, sternal notch of the manubrium, and

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humerus via a thermoplastic cuff placed just superior to the medial and lateral epi-

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condyles and secured with elastic Velcro straps.32 Participants performed three repe-

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titions of arm elevation, in self-selected plane of motion, with a verbally guided cycle

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time of 6 seconds (3 second up, 3 seconds down). Standardized instructions were

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provided with one to two practice trials performed to accommodate to the cycle tim-

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ing.

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Data Reduction

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The average for resting PMm length and passive PMm length trials were calculated. Extensibility is defined as the ability of a muscle to extend to an endpoint, and

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that stiffness is the change in tension per unit change in muscle length.33 For clinical

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application, the definition of extensibility applied in this study represents the ability of

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the muscle to elongate to an endpoint. PMm muscle extensibility (percent change) was

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determined by [(passive length – resting length)/resting length]*100.

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Kinematic data reduction was based on recommendations of the International Society of Biomechanics.32 Scapulothoracic data were collected as part of a larger

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study and are not reported here. Raw data were exported and humerothoracic plane

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and elevation were calculated in custom routines in Matlab (Mathworks, Natick, MA).

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Due to inability to transfer and sit safely for the kinematic collection, data on two partic-

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ipants were not collected.

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Data Analysis

Descriptive statistics of means, standard deviation or frequencies were deter-

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mined for demographics variables of age, sex, height, weight, BMI, and level of injury

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(high = SCI T6 and above, low = SCI T7 and below)7. Descriptive statistics were calcu-

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lated for WUSPI, resting PMm length, passive PMm length, PMm extensibility, plane of

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elevation and peak humerothoracic elevation. Data were examined and met paramet-

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ric assumptions. In order to identify potential covariates, multiple point biserial correla-

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tions were used to determine the association of BMI, injury level (high, low) and plane

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of elevation to peak elevation and PMm extensibility. Pearson correlations were used

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to determine associations (p≤0.05) of PMm length and extensibility, pain, peak eleva-

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tion, and duration of MWC use. Strength of association (correlation) was defined as r ≤

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0.30 as weak, r = 0.30-0.50 as moderate, r>0.50 as strong.34

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Based on previous studies3-5, participants were stratified on duration of MWC

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use; <5 years, 5-15 years and >15 years. Multiple ANOVAs (p≤0.05) were used to

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compare pain, peak humeral elevation, PMm length and extensibility, among the three

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groups. Bonferroni post hoc analyses were used to determine specific pair-wise differ-

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ences while controlling for Type I error. Effect sizes were calculated for between group

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measures using the equation: Cohen’s δ = (mean1 – mean2)/SDpooled. An effect size of

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0.2 was considered small, 0.5 medium and 0.8 a large effect.34

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Results

Demographic information is presented in Table 1. Across all participants mean resting PMm length was 16.49cm ± 1.98cm, passive PMm length was 20.05 ± 2.92cm,

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and PMm extensibility was 21.15%. Peak elevation was 139.66 ±14.77°. Peak eleva-

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tion was not associated with BMI (r=-0.16, p = 0.47), injury level (r=-0.23, p = 0.31) or

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plane of elevation (r = 0.12, p=0.57). PMm extensibility was not associated with BMI

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(r=-0.37, p = 0.20), injury level (r=-0.08, p = 0.73) or plane of elevation (r = 0.03,

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p=0.90). BMI was moderately associated with shoulder pain (r= 0.49, p =0.02).

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Significant, high, inverse correlations were found for duration of wheelchair use

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and PMm passive length, extensibility and peak elevation. PMm extensibility also had

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significant, high, inverse correlation with peak elevation. A significant moderate asso-

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ciation was found between peak elevation and pain. (Table 2)

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No difference among groups was found in resting PMm length; however, effect sizes were medium to large.(Table 3) Shoulder pain, per WUSPI, was not different

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among groups with a moderate effect (δ = 0.58) noted between the < 5 year group and

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the >15 year group. (Table 3) Significant differences were found among the three

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groups for PMm passive length (p=0.02, Table 4), extensibility (p=0.01, Table 4) and

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peak elevation (p= 0.001, Figure1).

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Discussion The primary objective of this investigation was to determine the relationship of

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PMm length and extensibility to shoulder pain, shoulder mobility and duration of MWC

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use in individuals with SCI. The hypothesis was partially supported in that findings of

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reduced PMm passive length and extensibility were strongly associated with increased

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duration of wheelchair use as well as a reduction in peak humerothoracic elevation. Ad-

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ditionally, in addressing the secondary objective, greater deficits in PMm extensibility

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and peak elevation were found in individuals with more than 15 years of wheelchair use.

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Our findings of reduced PMm extensibility with a reduction in peak elevation with

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the group with the longest duration of wheelchair use are in conjunction with the align-

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ment-impairment model. Following a SCI, individuals perform almost all daily activities

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in a seated position. It has been reported that on average a MWC user is in the wheel-

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chair for 8.3±3.3 hours per day35 and perform 14-18 transfers/day36. The typical position

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of the trunk during wheelchair propulsion, working at a desk, or performing manual

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tasks is 30° of forward flexion.17 Seated transfers and weight relief maneuvers place the

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trunk in flexion with scapular internal rotation and anterior tilt.36,37 Prolonged postures

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that bring the origin and insertion of the PMm close together create an environment for

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decreased length with decreased extensibility.38-40 High frequency, and prolonged dura-

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tion of these postures, places the PMm in a shortened position, which in turn may lead

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to an increased stiffness, or reduced ability to lengthen (decreased extensibility). Indi-

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viduals with longer than 15 years of wheelchair use demonstrated nearly 10% reduction

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in passive extensibility compared with individuals in the first 5 years of wheelchair use.

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Furthermore, although not statistically significant, a large effect size was reflected in the

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6% reduction in extensibility found between those with less than five years of wheelchair

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use, and the group with 10-15 years. This supports the need for further study with larger

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sample sizes as the progressive reduction across duration of use indicates the loss of

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muscle extensibility begins early.

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Our previous study determined resting PMm length, passive PMm length, and passive PMm extensibility values in healthy, young adults.27 A secondary, post hoc

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analysis compared the healthy, able-bodied sample (n=34) to the current group of indi-

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viduals with SCI (n=22) across all muscle length measures. Although the sample with

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SCI were older (p<0.001), there was no difference (p=0.72) in the resting muscle length

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between the groups. However, 21% passive extensibility in those with SCI was signifi-

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cantly less (p<0.001) than 29.4% in the healthy sample. Irrespective of duration of

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wheelchair use or resting PMm length, those with SCI who use a MWC have reduced

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muscle extensibility compared to able-bodied adults.

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Contrary to our hypothesis, a lack of significant association was found with resting PMm length to humeral motion, pain, or duration of wheelchair use. No significant

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difference was found in resting PMm length among the duration of use groups. Previ-

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ous literature has inferred that a “short” resting PMm length was tight, or has reduced

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extensibility.20,41-43 However, the ability to which the muscle could be lengthened was

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not investigated. Our finding of no difference in resting muscle length with significant

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reduction in muscle extensibility in MWC users with SCI suggests that muscle extensi-

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bility may be a more appropriate factor leading to reduced and/or aberrant movement.

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It should be noted that a large effect size was found in resting length differences be-

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tween the less than 5 year group and those with greater 15 years of use. This indi-

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cates that with extended duration of MWC use there may be a shortening of the rest-

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ing length along with a reduction in muscle extensibility.

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Humeral elevation is a critical motion for individuals who use a MWC. In a typical day, wheelchair users reach overhead (above 90°) five times more often than able-

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bodied controls.17 A loss of humeral mobility can lead to decreased activity and partici-

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pation17,18 and as in previous studies8,18 was associated with shoulder pain. Concomi-

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tant to reduced PMm extensibility, the current study found reduced peak elevation be-

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tween the longest duration group and those with less than five years, and 5-15 years of

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wheelchair use. Inflexibility of shoulder girdle soft tissues has been purported to contrib-

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ute to secondary impingement in individuals with SCI.44,45 This is the first study to inves-

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tigate the role of the PMm extensibility on shoulder girdle motion and pain. Although

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pain was not associated with reduced PMm length or extensibility, it was correlated to

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reduced peak humerothoracic elevation, similar to previous investigations.8 The associ-

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ation of reduced extensibility and humerothoracic elevation with prolonged MWC use

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provides insight into possible mechanisms of shoulder dysfunction. Periodic clinical as-

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sessments of PMm extensibility with early intervention to mitigate the development of

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movement impairment and shoulder pain is warranted.

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Limitations

The cross-sectional nature of this project has inherent limitations such that the

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sample may not be representative of the population of individuals with SCI who use

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MWC for mobility. A longitudinal design would provide a more decisive conclusion re-

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garding changes over time, potentially allowing for determination of causation. The

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small sample size and distribution among duration of use groups may have led to Type

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II error in numerous measures. Additionally, a duration group at initial injury is needed to

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provide important information regarding baseline status of individuals sustaining a SCI.

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Conclusions

Shoulder dysfunction is a highly common source of devastating activity limitations

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and participation restrictions in individuals with SCI who use a MWC. Numerous factors

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have previously been associated with the development of shoulder impairments. This is

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the first investigation to identify the association of reduced PMm extensibility with re-

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duced humerothoracic mobility and duration wheelchair use. These findings provide a

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foundation for the importance of early identification and intervention to potentially miti-

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gate this debilitating problem.

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Lysack C, Komanecky M, Kabel A, Cross K, Neufeld S. Environmental factors and their role in community integration after spinal cord injury. Can J Occup Ther. 2007;74 Spec No.:243-254. Tate DG, Kalpakjian CZ, Forchheimer MB. Quality of life issues in individuals with spinal cord injury. Arch Phys Med Rehabil. Dec 2002;83(12 Suppl 2):S1825. Requejo PS, Mulroy SJ, Haubert LL, Newsam CJ, Gronley JK, Perry J. Evidence-based strategies to preserve shoulder function in manual wheelchair users with spinal cord injury. Topics Spinal Cord Injury Rehabilitation. 2008;13(4):86-119. Eriks-Hoogland I, de Groot S, Snoek G, Stucki G, Post M, van der Woude L. Association of Shoulder Problems in Persons With Spinal Cord Injury at Discharge From Inpatient Rehabilitation With Activities and Participation 5 Years Later. Arch Phys Med Rehabil. Jan 2016;97(1):84-91. Borstad JD. Resting position variables at the shoulder: evidence to support a posture-impairment association. Phys Ther. Apr 2006;86(4):549-557. Borstad JD, Ludewig PM. The effect of long versus short pectoralis minor resting length on scapular kinematics in healthy individuals. J Orthop Sports Phys Ther. Apr 2005;35(4):227-238. Hebert LJ, Moffet H, McFadyen BJ, Dionne CE. Scapular behavior in shoulder impingement syndrome. Arch Phys Med Rehabil. Jan 2002;83(1):60-69. Ludewig PM, Cook TM. Alterations in shoulder kinematics and associated muscle activity in people with symptoms of shoulder impingement. Phys Ther. Mar 2000;80(3):276-291. Lukasiewicz AC, McClure P, Michener L, Pratt N, Sennett B. Comparison of 3dimensional scapular position and orientation between subjects with and without shoulder impingement. J Orthop Sports Phys Ther. Oct 1999;29(10):574-583; discussion 584-576. Mulroy SJ, Hatchett P, Eberly VJ, Lighthall Haubert L, Conners S, Requejo PS. Shoulder Strength and Physical Activity Predictors of Shoulder Pain in People With Paraplegia From Spinal Injury: Prospective Cohort Study. Phys Ther. Jul 2015;95(7):1027-1038. Miyahara M, Sleivert GG, Gerrard DF. The relationship of strength and muscle balance to shoulder pain and impingement syndrome in elite quadriplegic wheelchair rugby players. Int J Sports Med. Apr 1998;19(3):210-214. Kibler WB, Ludewig PM, McClure P, Uhl TL, Sciascia A. Scapular Summit 2009: introduction. July 16, 2009, Lexington, Kentucky. J Orthop Sports Phys Ther. Nov 2009;39(11):A1-A13. Finley M, Goodstadt N, Soler D, Somerville K, Friedman Z, Ebaugh D. Reliability and validity of a novel technique for active and passive pectoralis minor muscle length measures. Brazilian Journal of Physical Therapy. 2016;in press. Muraki T, Aoki M, Izumi T, Fujii M, Hidaka E, Miyamoto S. Lengthening of the pectoralis minor muscle during passive shoulder motions and stretching techniques: a cadaveric biomechanical study. Phys Ther. Apr 2009;89(4):333341.

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Curtis KA, Roach KE, Applegate EB, et al. Reliability and validity of the Wheelchair User's Shoulder Pain Index (WUSPI). Paraplegia. Oct 1995;33(10):595-601. Curtis KA, Roach KE, Applegate EB, et al. Development of the Wheelchair User's Shoulder Pain Index (WUSPI). Paraplegia. May 1995;33(5):290-293. Accuracy and resolution manual. 2014; www.themotionmonitor.com. Accessed January 15,2014. Wu G, van der Helm FC, Veeger HE, et al. ISB recommendation on definitions of joint coordinate systems of various joints for the reporting of human joint motion-Part II: shoulder, elbow, wrist and hand. J Biomech. May 2005;38(5):981-992. Weppler CH, Magnusson SP. Increasing muscle extensibility: a matter of increasing length or modifying sensation? Phys Ther. Mar 2010;90(3):438-449. Cohen J. Statistical Power Analysis for the Behavioral Sciences 32nd ed. Hillsdale, NJ: Lawrence Erlbaum Associates; 1988. Tolerico ML, Ding D, Cooper RA, et al. Assessing mobility characteristics and activity levels of manual wheelchair users. J Rehabil Res Dev. 2007;44(4):561571. Finley MA, McQuade KJ, Rodgers MM. Scapular kinematics during transfers in manual wheelchair users with and without shoulder impingement. Clin Biomech (Bristol, Avon). Jan 2005;20(1):32-40. Nawoczenski DA, Clobes SM, Gore SL, et al. Three-dimensional shoulder kinematics during a pressure relief technique and wheelchair transfer. Arch Phys Med Rehabil. Sep 2003;84(9):1293-1300. Kendall F, McCreary E, Provance P, Rodgers M, Romani W. Muscles: Testing and Function, with Posture and Pain 5th ed. Baltimore: Lippincott, Williams & Wilkins; 2005. Page P. Current concepts in muscle stretching for exercise and rehabilitation. Int J Sports Phys Ther. Feb 2012;7(1):109-119. Sahrman S. Movement impairment syndromes of the shoudler girdle. Diagnosis and Treatment of Movement Impairment Syndromes. St Loius: Mosby; 2002:193261. Rosa DP, Borstad JD, Pires ED, Camargo PR. Reliability of measuring pectoralis minor muscle resting length in subjects with and without signs of shoulder impingement. Braz J Phys Ther. Mar 15 2016;20(2):176-183. Rosa DP, Borstad JD, Pogetti LS, Camargo PR. Effects of a stretching protocol for the pectoralis minor on muscle length, function, and scapular kinematics in individuals with and without shoulder pain. J Hand Ther. Oct 18 2016. Williams JG, Laudner KG, McLoda T. The acute effects of two passive stretch maneuvers on pectoralis minor length and scapular kinematics among collegiate swimmers. Int J Sports Phys Ther. Feb 2013;8(1):25-33. Burnham RS, May L, Nelson E, Steadward R, Reid DC. Shoulder pain in wheelchair athletes. The role of muscle imbalance. Am J Sports Med. Mar-Apr 1993;21(2):238-242. Curtis KA, Tyner TM, Zachary L, et al. Effect of a standard exercise protocol on shoulder pain in long-term wheelchair users. Spinal Cord. Jun 1999;37(6):421429.

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Figure Legend

442

Figure 1

444

Peak humerothoracic elevation (in degrees) by duration of wheelchair use groups:

445

< 5 years: solid; 5-15 years grey thatched; > 15 years black checkerboard

446

*indicates significant difference between groups

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Table 1: Participant demographic information (mean ± standard deviation)

41.68 ±14.62

Gender

Male = 18 C5-T6 = 11 Female = 4 T7-L5 = 11

Height (cm)

Weight (kg)

BMI

177.50 ± 8.59

80.06 ± 15.51

25.12 ± 6.76

BMI = body mass index [(weight/ height^2)*100]

14.63 ± 12.36

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WUSPI = Wheelchair User Shoulder Pain Index

Duration wheelchair WUSPI use (max = (years) 150)

RI PT

Age (years)

Level of injury

25.45 ± 25.02

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Table 2: Pearson Correlations Peak Humeral Duration elevation wheelchair use 0.064

Passive Pectoralis Minor length

0.255

Peak Humeral elevation Duration wheelchair use WUSPI = Wheelchair Users Shoulder Pain Index

M AN U

*. Correlation is significant at the 0.05 level (2-tailed).

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**. Correlation is significant at the 0.01 level (2-tailed).

0.093

-0.534*

-0.033

-0.601**

-0.399

-0.572**

-0.438*

SC

0.547**

Passive extensibility

-0.319

RI PT

Resting Pectoralis Minor length

WUSPI

0.145

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Table 3: Effect size (Cohen’s δ) between duration groups

< 5 years vs. 5-15 years

0.03

Pectoralis minor resting length 0.76*

5-15 years vs. >15 years

0.45

0.43

< 5 years vs. > 15 years

0.58*

1.04

†

†

Pectoralis minor passive length † 1.01 0.71* 1.69

†

Peak humeral elevation

1.00

0.66*

0.69*

2.04

†

1.95

2.18

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Cohen’s δ *0.5 = moderate effect size ; 0.8 = large effect size34

Pectoralis minor extensibility

RI PT

WUSPI

†

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Table 4: Pectoralis minor muscle length measures (means ± sd)

2

PMm Passive (cm)

PMm extensibility (%change) 22.53 ± 2.65* < 5 years (n=6) 17.78 ± 2.16 26.92 ± 4.32
5-15 years (n=8) 16.38 ± 1.48 19.98 ± 2.40 20.99 ± 6.11 18.28 ± 2.43* >15 years (n= 8) 15.63 ± 1.98 16.98 ± 4.55
PMm = pectoralis minor muscle; * group difference, p=0.01;
group difference, p = 0.01

RI PT

PMm Resting (cm)

3

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Figure 1: Peak humerothoracic elevation by duration groups 180

p=0.03 p=0.001

RI PT

140 120 100 80 60 40 20 0 <5 years

5-15 years

>15 years

M AN U

2

SC

Humeral elevation (degrees)

160

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1