MMD I: Week 8 (Shoulder Biomechanics/SE and OMs)

Exam 3 content

The primary function of the shoulder complex is…

Placement of the hand to manipulate our environment

The only attachment point of the UE to the axial skeletion is through this joint…

The sternoclavicular joint

Describe the position of the scapula at rest

• Internally rotated 35-45°

• Upwardly rotated 5-10°

• Anteriorly tipped 10-15°

• Sits between T2-T7, 5-6 cm from SPs

Translatory scapular motions (couplings):

• Elevation/Depression

• Protraction/Retraction

• Elevation/Depression: SC depression/elevation + AC anterior/posterior tilt + AC IR

• Protraction/Retraction: SC protraction/retraction + AC IR/ER

What are the 4 passive restraints of the GH joint?

1. Bony geometry

2. Labrum

3. Capsule/Ligaments

4. Negative intra-articular pressure

Describe the bony geometry of the glenoid fossa:

• 5° superior tilt

• 6 -7° retroversion from scapular plane

  • Scapular plane is 30° from the frontal plane

Describe the bony geometry of the humeral head:

• ~1/2 sphere shape

• 30° retroverted

• Angle of inclination 130-150°

• 25-50% in contact with the glenoid

• Inferior surface of HH is in contact with the glenoid at rest

What is the function of the labrum? What attaches to it?

The funciton of the labrum is to increase surface area and add stability. Attachments:

• GH capsule

• All glenohumeral ligaments

• LH of the biceps tendon

Describe what happens to the GH joint capsule in the following positions: Rest.  Abduction + ER

Rest:

• Taut superiorly + Anterior/inferior slack

Abducted + Externally Rotated:

• Anterior capsule becomes taut = closed pack position

What is the weakest portion of the GH capsule?

The inferior portion, due to its folds to allow abduction

What is the open pack position for the GH joint?

30-40º scaption

What is the capsular patter for the GH joint?

Limitations in ER>ABD>IR>FLX

What are the functions of the superior GH ligament?

• Prevents inferior translation of the humerus - with the arm at the side (PRIMARY STABILIZER)

• Secondary: Limits EXT and ER

What are the components of the rotator interval capsule (RIC)?

• Joint capsule

• Coracohumeral ligament

• Superior glenohumeral ligament

What are the functions of the middle GH ligament?

• Limits ER in 45-75° ABD

• Limits ANTERIOR humeral translation between 0-60˚ ABD

• Resists INFERIOR humeral translation at rest

What are the functions of the inferior GH ligament?

• Pouch: Cradles the head; resists inferior translation

• Ant B: Limits ABD and ER; anterior/inferior translation

• Post B: Limits ABD and IR; posterior/inferior translation

Sulcus sign reflects pathology of the…

Superior GH ligament & loss of intra-articular negative pressure

Which ligament is primarily responsible for stabilizing the humerus for OH motions?

The inferior GH ligament

What is the vulnerable positon of the shoulder where dislocations typically happen?

Abducted and externally rotated (mainly limited by the AB of the IGHL and the MGHL)

What are the contents of the subacromial space?

• Supraspinatus tendon

• LH biceps

• Subacromial bursa

What can cause a reduction in the subacromial space, potentially leading to impingment?

“Anything that occupies space may limit motion.” Like:

• Hooked acromion

• AC joint degeneration

• GH instability

• Tight posterior capsule

• Lack of posterior tilting or upward scapular rotation

Elevation of humerus requires head to slide ______, while it rolls _______ on fossa. If not, will…

Elevation of humerus requires head to slide inferiorly, while it rolls superiorly on fossa. If not, will cause impingement on the coracoacromial arch

Center of rotation of the humeral head moves slightly superiorly during first ___ of elevation, then it stabilizes.

Center of rotation of the humeral head moves slightly superiorly during first 60°of elevation, then it stabilizes.

What is the purpose of the scapulohumeral rhythm?

• Distributes motion between several joints

• Increases stability by optimizing glenoid fossa orientation of humeral head

• Maintains optimal length-tension of GH muscles

Scapulohumeral rhythm has a GH:ST ratio of _____, which becomes constant after…

Scapulohumeral rhythm has a GH:ST ratio of 2:1, which becomes constant after 30° of abduction or 60° of flexion 

T/F: Upward rotation of the scapula can be influenced by the position of the thoracic spine

TRUE

During humeral elevation, normally the scapula should…

• Upwardly rotate

• Posteriorly tilt

• Externally rotate

What are the 3 main muscles responsible for upward rotation of the scapula?

1. Serratus anterior (largest moment arm)

2. Upper trap

3. Lower trap

Describe the activity of serratus anterior during upward rotation of the scapula:

SA active through the FULL ROM of both ABD and FLX

• Upper fibers: resist downward pull of gravity

• Mid/low fibers: stabilize medial border to the thorax and inferior scapular angle (preventing winging and tipping)

Describe the role of the muscles in the force couple for upward rotation:

First 30° of ABD:

• Superior fibers of SA and UT

Last 30° of ABD:

• Lower fibers of SA anf LT

Describe the role of the muscles in the force couple for abduction:

• The trapezius is more important in ABD (compared to UR)

• The middle trap functions primarily as a stabilizer

T/F: Complete shoulder FLEX is impossible with a denervated trapezius

FALSE. Complete shoulder FLEX is impossible with a denervated trapezius, but is weakened

T/F: With an intact trap & absent SA, active shoulder ABD is limited to about 75º

FALSE. The trap has a bigger role than the SA in this movement!!

The ______ trap functions primarily as a stabilizer due to its line of pull

Middle

The dynamic stabilizers of the GH joint provide _____ of abduction strength and ____ of ER strength

The dynamic stabilizers of the GH joint provide 50% of abduction strength and 80% of ER strength

T/F: The ability to abduct is lost in the absence of the deltoid

FALSE. You can still abduct the arm but it will be a little weaker

T/F: The supraspinatus is active throughout elevation and in all scapular planes of rotation

TRUE

Which muscles are considered GH compressors?

• Supraspinatus (with the aid of gravity)

• Infraspinatus

• Teres Minor

• Subscapularis

• Deltoid (@ 90° of ABD)

• LH of the biceps (@ 90° of ABD/FLX)

Which muscles counteract the superior translation moment of the deltoid?

• Infraspinatus

• Teres minor

• Subscapularis

Prime movers for ER with a BIG role in deceleration forces

Infraspinatus and Teres Minor

Restricted scapular upward rotation results in loss of _______ tension and _______ active GH ROM

Restricted scapular upward rotation results in loss of deltoid tension and decreased active GH ROM

The deltoid is most efficient in the…

Scapular plane

What movement impairments can be seen with a deficit in upward rotators? What if SA/traps were paralyzed?

The middle and posterior deltoid would take over and downwardly rotate the scapula (opposite of what we want)

• In the complete loss of upward rotators, the arm can only raise 60-75°

What are the contributors to dynamic stability of the shoulder in the following positions: At rest, mid range, end range?

At rest:

• Negative intra-articular pressure

• Superior GHL

• Maybe also supraspinatus

Mid range:

• RTC and imuscular force couples

End range:

• Capsular ligaments

What does the patient specific functional scale measure? How is it scored?

• Measures up to 5 patient-selected activities — which MUST remain the same for reassessment

• Measured by “difficulty with activity” for 0-10 (higher numbers better)

Shoulder Pain and Disability Index (SPADI) Overview — (Items, completion time, scales, scoring, clinical application)

• 13 items (5 pain, 8 function)

• 5-8 min

• NPRS for pain & 10 pt (Likert) scale for function

• 0-100 (best to worst)***

  • Low scores=good (% of disability)

• MDC: 18 / MCID: 8-13

Simple Shoulder Test (SST) — (Items, completion time, scales, scoring, clinical application)

• 12 items (all function)

• <3 min

• Yes/no scale

• 0-12 (worst to best)

Disability of the Arm, Shoulder and Hand (DASH) — (Items, completion time, scales, scoring, clinical application)

• 30 items

  • 5 symptoms (pain, N/T, strength, stiffness)

  • 24 function

  • 1 sleep

•  5-8 min

• 5 pt Likert scale

• 0-100 (best to worst)***

  • Low scores=good (% of disability)

• MDC: 10.5 / MCID: 10.2

Quick DASH — (Items, completion time, scales, scoring, clinical application)

• 11 items

  • 2 symptoms (pain, N/T)

  • 8 function

  • 1 sleep

•  <3 min

• 5 pt Likert scale

• 0-100 (best to worst)***

  • Low scores=good (% of disability)

• MDC: 12.8 / MCID: 15.9

ASES Shoulder Score Overview — (Items, completion time, scales, scoring, clinical application)

• 11 items (1 pain, 10 function)

• <5 mins

• NPRS for pain & 4 pt scale (Likert) for ADLs

• 0-100 (worst → best)

• MDC: 9.4 / MCID: 6.4

Match the type of pain to the possible structure resposnible for it:

• Cramping, dull, aching →

• Dull, aching →

• Sharp, shooting →

• Sharp, burning, stinging, bright, lightning-like →

• Deep, nagging, dull →

• Sharp, severe, intolerable →

• Throbbing, pulsating, diffuse →

• Cramping, dull, aching → muscle

• Dull, aching → ligament, joint capsule

• Sharp, shooting → nerve root 

• Sharp, burning, stinging, bright, lightning-like → nerve

• Deep, nagging, dull → bone

• Sharp, severe, intolerable → fracture

• Throbbing, pulsating, diffuse → vascular

Frequency and pain nature

• Intermittent → Mechanical

• Constant, but varies w/ activity → Inflammatory & mechanical (related to movement & stress)

• Constant, but does not vary →  Acute disease or serious pathology

Match complaints to condition:

• Anterior/lateral pain with overhead activity

• Painful arc

• Pain lying on that side

External Impingement/Bursitis/Tendonitis

Match complaints to condition:

• Apprehension, pain with activity (ABD/ER)

• Dead arm feeling, performance loss

• Younger age (<35)

Instability/labral lesion

Match complaints to condition:

• Age 40+, pain and weakness

RCT/degeneration

Match complaints to condition:

• Fall onto that shoulder

• Pain laying on that shoulder

AC Sprain

Match complaints to condition:

• Poorly located, insidious onset, limited ROM

• Age > 45, female

Adhesive Capsulitis

Match complaints to condition:

• UE heaviness, numbness with prolonged postures and when lying on that sid

TOS/Cervical radiculopathy