Scapular Dyskinesis

Anatomy and Biomechanics

Skeletal Attachment:

• AC joint & GH joint
• Sternoclavicular joint

Muscles

• Trapizius
• Serratus anterior
• Rhomboid muscles
• Levator scapulae
• Cuff muscles
• Pec. Minor and short head of biceps

Movements:

• Upward/downward rotation around a horizontal axis perpendicular to the plane of the scapula
• Internal/external rotation around vertical axis through the plane of the scapula
• Anterior/posterior tilt around a horizontal axis in the plane of the scapula

Coupling Movements of Scapula

• Retraction : external rotation, posterior tilt, upward rotation and medial translation
• Protraction : internal rotation, anterior tilt, downward rotation and lateral translation
• Shrug : upward translation, anterior tilt and internal rotation
• Coupling movements maintain glenoid as congruent socket, maximizing concavity compression and kinematics
• Scapula stabilized in retraction posture during arm elevation to achieve maximal activation of all muscles originating on the scapula

Stability and Mobility

• The clavicle acts as a strut
• This allows two translations to occur—upward/downward translation on the thoracic wall and retraction/protraction around the rounded thorax.
• When the humerus moves into elevation, clavicular elevation, retraction and posterior axial rotation occur at the sternoclavicular joint.
• while scapular internal rotation, upward rotation and posterior tilting occur at the acromioclavicular joint.
• AC joint – scapular posterior tilt.
• The upper and lower trapezius muscles in addition to the serratus anterior muscles have been shown to be the greatest contributors to scapular stability and mobility.
• The trapezius and serratus anterior muscle initiate upward rotation and posterior tilt of the scapula.
• Activation of the lower trapezius muscle plays an important role in the stability of the arm in the overhead position and in descent of the arm from a position of maximum elevation.
• The rhomboids assist the trapezius in stabilizing the scapula contributing to control of medial and lateral scapular translation.
• Latissimus dorsi and pectoralis minor : prime mover of arm.

Force couples:

• For scapular stabilization :

                                upper/ lower trapezius + serratus anterior paired with Rhomboid muscles

• For acromial elevation : lower trapezius + serratus anterior

                                paired with upper trapezius + rhomboid

At early movement

The upper and lower trapezius and serratus anterior muscles have long lever arms, being effective rotators and stabilizers.

• With higher arm elevation the upper trapezius moment arm is shorter, whereas the lower trapezius and serratus anterior moment arms remain long, continuing to rotate the scapula

• With maximum arm elevation, the lower trapezius maintains scapula position and the instant centre of rotation moves from the medial border of the spine to the acromioclavicular joint
• The levator scapulae functions to elevate the scapula and tilt the glenoid cavity inferiorly by rotating the scapula downward

Clinical features:

• Static : asymmetry prominence of scapulae resting position of protraction
• Dynamic :
  • medial border prominence
  • inferior angle prominence and/or early scapular elevation or shrugging on arm elevation
  • rapid downward rotation during arm lowering
  • Tenderness over coracoid

Causes:

• Bony : thoracic kyphosis
                 clavicle fractures – malunion shortening rotation

JSES,2018

• In the intervention limb group, the shoulder was passively and horizontally abducted at 150° of elevation for 5 minutes to stretch the pectoralis minor muscle
• Stretching for the pectoralis minor muscle increases external rotation and posterior tilt of the scapula during arm elevation

JOINT RELATED :

• AC joint dislocations : acromion displaced medially and inferiorly
• Leads to anterior tilt , internal rotation and loss of upward rotation – protraction scapula
• JOAS,2009 : Chronic type III AC dislocation causes scapular dyskinesis in 70.6% of patients. Of the latter, 58.3% have SICK scapula syndrome developed.

LATARJET

JSES,2015

• Scapular dyskinesis was found in 5 of 20 patients who underwent a Latarjet procedure.
• Dyskinesis may be related to the detachment of the pectoralis minor, and variation of the vector and the working length of the coracobrachialis and the short head of the biceps.

Clinical Evaluation

• Observation of static scapular position – rest , hands on both hips and 90deg abduction with full internal rotation
• Observation of scapular motion –
• Kibler’s four-type rating system, which required a single-forced choice among four categories, including three subtypes of dyskinesis: types
  • I (inferior angle prominence),
  • II (medial border prominence),
  • III (excessive superior border elevation) and
  • IV (symmetric and normal scapular motion).
• More specifically, weighted flexion was the motion that most commonly resulted in dyskinesis and a 3-kg load significantly reduced scapulothoracic motion through the range of 35°–45° of glenohumeral motion.

Scapula assistance test

• Scapula assistance test: the scapula is stabilized with one hand and the other hand ‘assists’ the scapula through its correct motion plane.
• The SAT evaluates scapular contributions to impingement and rotator cuff strength
• This procedure simulates the force-couple activity of the serratus anterior and lower trapezius muscles
  

  

Scapular retraction test

• Scapula retraction test: the examiner stabilizes the medial border of the scapula as the arm is elevated. Relief of impingement symptoms is a positive test.
• The SRT can be used for evaluation in cases of labral symptoms and rotator cuff strength.
  

  

Lateral scapular slide test

• Quantitative assessment of scapular stabilizer strength
• Lateral scapula slide test. (a) Initial position with arm at side. (b) Second position, arms on hips. (c) Third position with arms at 90 and internal rotation
• The threshold of abnormality is 1.5 cm and significant asymmetry is most commonly measured in the third position.
  

  

Scapula retraction test with resistance

• (a) The examiner performs a traditional ‘empty can’ test.
• (b) The examiner stabilizes the medial border of the scapula and repeats the test. If the impingement symptoms are relieved, the test is positive

Other tests

• Baylor square and double-square technique
• Measurement of the distance between the posterior border of the acromion and the table/wall
• Measurement of the pectoralis minor muscle length
• Measurement of scapular upward rotation

 Other investigations

• X ray
• EMG/NCVS
• Mri shoulder and c spine

Treatment :

Physical therapy

• To relieve the symptoms associated with inflexibility or trigger points and to re-establish muscle strength and activation patterns
• Surgery physiotherapy in Dyskinesis can often be caused by muscle inhibition created by soft tissue related pathology such as labral injury, internal impingement or rotator cuff pathology or hard tissue injury such as clavicle fractures and AC separations.
• Rehabilitation for scapular dyskinesis should start proximally and end distally.
• Core muscle strengthening : which the larger muscles of the lower extremity and trunk are utilized during the treatment of the scapula and shoulder
• Scapular protraction and retraction are facilitated by hip and trunk flexion and extension exercises.
• Lower trapezius and serratus strengthening (short lever, kinetic chain assisted exercises and finally long lever movements)
• Rotator cuff strengthening