Shoulder Brace on Muscle Activation and Scapular Kinematics in Patients With Shoulder Impingement Syndrome and Rounded Shoulder Posture

Background:

Rounded shoulder posture (RSP), associated with altered scapular kinematics and imbalance of muscle activation, is one of potential risks for shoulder impingement syndrome (SIS) due to alignment deviation of scapula. Evidence showed shoulder brace improved degree of RSP by postural correction. However, it is unknown whether shoulder brace with different characteristics (tension and direction) is optimal for muscle activation and scapular kinematics in patients with SIS and RSP.

Objective:

There are 4 objectives for the present study: (1) to investigate the relationships among degree of RSP, scapular kinematics and muscle activation in SIS patients with RSP; (2) to compare the effect of shoulder brace on degree of RSP, muscle balance ratios (Upper trapezius/Lower trapezius, Upper trapezius/ Serratus anterior) and scapular kinematics (upward/downward rotation, anterior/posterior tilt, external/internal rotation) during arm movements; (3) to compare the effect of two tensions of brace strap (self-comfortable and forced tension) in symptomatic impingement patients with RSP; (4) to compare the effect of two types of direction of strap (paraspinal muscle and diagonal orientation) in symptomatic impingement patients with RSP.

Design:

Patients with SIS and RSP will be recruited in this study. Participants will be randomly assigned into 2 groups (self-comfortable following forced tension and forced following self-comfortable tension groups) with 2 directions of strap in each tension wearing shoulder brace. Each patient has the assessment 2 times with 1-week interval. Pectoralis minor, acromial distance, scapular index and shoulder angle will be used to assess degree of RSP. Three-dimensional electromagnetic motion analysis and electromyography muscle activity will be used to record the scapular kinematic, absolute muscle activation and muscular balance ratios during arm movements with or without shoulder brace.

Main outcome measures:

Scapula kinematic (upward/downward rotation, anterior/posterior tilt, external/internal rotation), absolute muscle activation (Upper trapezius, Middle Trapezius, Lower trapezius, Serratus anterior) and muscle balance ratios (Upper trapezius/Lower trapezius, Upper trapezius/Serratus anterior) are main outcomes of the study.

Participants will be recruited from outpatient clinic in National Taiwan University Hospital (NTUH) and also through general announcements in social media. Subjects will be undergoing physical examinations for eligibility by a physical therapist. Thoracic kyphosis angle, one inclinometer over 1st and 2nd thoracic spines, and another inclinometer over the 12th thoracic and 1st lumbar spines in relaxed standing with adopting a natural posture of the subject, is calculated by the summation of the angle recorded by two inclinometers. Participants will sign a consent form approved by the National Taiwan University Hospital institutional review boards. Participant characteristics will be collected by the assessor including age, gender, height, weight, dominant side, involved side, VAS (Visual Analogue Scale) pain intensity during arm movements, symptom duration and shoulder function. Shoulder function will be assessed by Flexilevel Scale of Shoulder Function (FLEX-SF), a self-administered questionnaire. The questionnaire was commonly used in shoulder pain patients to assess shoulder function with sufficient psychometric properties. Lower FLEX-SF score represents limited function.

Subjects will be randomly assigned into 2 groups (self-comfortable following forced tension and forced following self-comfortable tension groups) with 2 directions of strap in each tension wearing shoulder brace. Each subject has the assessment 2 times with 1-week interval. At the first, each subject will be assessed on PMI, SI, AD and SA with and without shoulder brace in resting position. Then the surface EMG electrodes and FASTRAK kinematic sensors will be attached to the subjects. Surface EMG electrodes will be placed on upper trapezius, middle trapezius, lower trapezius and serratus anterior of involved shoulder. Three electromagnetic sensors will be attached to the sternum, the flat bony surface of the acromion and the distal humerus via Velcro straps.

Then subject will be tested wearing shoulder brace with two tensions of strap (self- comfortable/ forced) under two directions of strap (paraspinal muscle/ diagonal orientation). Strap is applied from mid-level of thoracic spinal process to mid-point of clavicle on the tested side and then pulled downward diagonally back to the thoracic spinal process and then applied the same way in the other side. In general, strap had a cross on mid-thorax and ran through mid-point of clavicle and axillary two sides. For the strap tension, length of strap will be adjusted with buckles relative to original length of figure 8 by the experimenter. Self- comfortable tension of strap will be adjusted by subject's feedback with comfortable feeling as "please feel postural correction by shoulder brace without tight pressure". Accordingly, the self-comfortable tension of strap will be increased till forced tension of strap using buckles. Direction of strap will change bilaterally as upper part of shoulder brace is fixed at 2 points of shoulder brace .

Then subjects will be tested and familiarized with the arm movement with and without shoulder brace. To ensure that each subject perform arm movements at a standard speed, a metronome will be set as one beat per second. Subjects will be asked to elevate and lower arm by following three beats, respectively. Each subject will do task three times with or without shoulder brace in each session. After one week from the first assessment, each subject will be assessed again under another condition of strap tension according to their assignment groups.

Maximum voluntary isometric contraction (MVIC) of the subject will be collected after the testing session to prevent fatigue of the scapular muscles. The MVIC for upper trapezius muscle will be measured during resisted shoulder flexion. The subjects will be seated with shoulder flexion 90 degrees and resistance will be applied on the distal arm. For measuring MVIC of middle trapezius muscle, the subjects will lie prone with testing arm at 90 degrees of abduction. For measuring MVIC of lower trapezius muscle, the subjects will lie prone with testing arm at 120 degrees of abduction in line with muscle fibers. Resistances will be applied to against further elevation. For measuring MVIC of serratus anterior muscle, the subjects will be seated with arm elevated at 135 degrees. Resistances will be applied to distal upper arm against further elevation. The MVICs will be collected for 5 seconds for 3 trials, with a 1- minute rest interval between each trial.

Eligibility Criteria:
Inclusion Criteria:

* At least 2 of the following 5 impingement signs

  1. Neer's impingement test;
  2. Hawkins-Kennedy impingement test;
  3. Empty can test;
  4. External resisted test;
  5. Pain during rotator cuff palpation
* Acromial distance higher than 2.6 cm.

Exclusion Criteria:

* History of shoulder dislocation, fracture, shoulder surgery, or direct contact injury to the neck or upper extremities within the past 3 months
* Glenohumeral joint instability (apprehension test or sulcus sign)
* Neurological disorders (thoracic outlet syndrome or pectoralis minor syndrome)
* Pain (VAS\>5) during the experimental tasks
* Excessive thoracic kyphosis higher than 50 degrees