Suprascapular Nerve Block Disrupts The Normal Pattern Of Scapular Kinematics

Sean McCullyDavid SuprakPeter Kosek

Andrew Karduna

Rotator Cuff Tears

• Incidence as high as 40% for people 40 years and older

• Disruption of motion between the scapula and humerus, may result in alterations in:

- muscle moment arms- compression of cuff tendons- joint stability

Pathology of Cuff Tears

• Majority start with supraspinatus tendon

• Next most commonly involved is the infraspinatus tendon

supraspinatus

infraspinatus

Models of Cuff Tear or Dysfunction

• Animal modelsinjection of collagenase (Soslowsky et al, 2002) injection of carrageenan (Tillander et al, 2001)

• Cadaver modelssurgical simulation of tears (Parsons et al., 2002)simulated paralysis (Sharkey et al., 1994)

• In-vivo modelsmuscle fatigue (Ebaugh et al., 2005)

Suprascapular Nerve

superior trunk of brachial plexus

passes through suprascapular notch

innervates supraspinatus and infraspinatus

Suprascapular Nerve Block

• Performed clinically for pain relief due to arthritis, frozen shoulder and operations

• Used in biomechanical studies of:

Strength

Colachis and Strohm, 1971; Howell et al, 1986; Kuhlman et al, 1992

Glenohumeral Kinematics

Howell et al, 1991

Purpose

Investigate the use a suprascapular nerve block as an model of dysfunction of the supraspinatus and infraspinatus.

Protocol

• 15 healthy subjects (mean age 26 years)

Baseline kinematics and force

Suprascapular nerve block

Repeat kinematics and force

KINEMATICS

• ISB recommendation (Wu et al, 2005)

Polhemus 3Space Fastrak

electronics unit

digitizer

sensors

transmitter

Scapular Tracker

sensor

Method Validation

bone sensor

skin sensor

Sensor Placement

humerus

scapula

thorax

transmitter

Scapular Rotations

Retraction/Protraction

Anterior/Posterior Tilting

Lateral/Medial Rotation

Clavicular Rotations

Retraction/ProtractionElevation/Depression

ISOMETRIC FORCE

• External rotation with arm at the side

• Data recorded with a load cell

• At this position, 75% of external rotation torque comes from infraspinatus and supraspinatus (Kuechle et al, 2000)

NERVE BLOCK

• 100 mg of lidocaine

• Injected into the suprascapular notch

• Nerve stimulator to confirm needle placement

• Data collection 10 minutes after injection

scapulartracker

needle

stimulationwire

lidocaineinjection

Subject Inclusion

• Threshold of 50% reduction in external rotation force (Colachis and Strohm, 1971)

4 subjects did not meet criterion

• Additional subject excluded due to inability to lift arm

• n=10 for statistical analysis

Results

• No effect on clavicular rotation

• No effect on scapular posterior tilting

• Significant effect for scapular internal rotation and upward rotation

Internal Rotation

10

15

20

25

30

35

40

0 20 40 60 80 100 120

Sca

pu

lar

Rot

atio

n [

deg

]

Humeral Elevation [deg]

External

Internal

**

* ** *pre-block

post-block

0

5

10

15

20

25

30

35

0 20 40 60 80 100 120

Sca

pu

lar

Rot

atio

n [

deg

]

Humeral Elevation [deg]

Downward

Upward

*

**

*

*

*

**

pre-block

post-block

Upward Rotation

0

1

2

3

4

5

6

7

0 20 40 60 80 100 120

Sca

pu

lar

Rot

atio

n [

deg

]

Humeral Elevation [deg]

Downward

Upward

*

**

**

*

*

*

increase in upward rotation

0

1

2

3

4

5

6

7

0 20 40 60 80 100 120S

cap

ula

r R

otat

ion

[d

eg]

Humeral Elevation [deg]

Downward

Upward

*

**

**

*

*

*

increase in upward rotation

Nerve Block

0

5

10

15

20

0 30 60 90 120 150

Incr

ease

in U

R [

deg

]

Arm Elevation [deg]

averaged from: Paletta, 1997 Yamaguchi, 2000 Mell, 2005

Cuff Tears0

3

6

9

20 40 60 80 100 120 140 160

Sca

pu

lar

Rot

atio

n [

deg

]

Humeral Elevation [deg]

Downward

Upward*

*

*

*

Fatigue

Discussion

• Results support use of model

• Although the supraspinatus and infraspinatus do not directly control the movement of the scapula, they appear to indirectly affect the scapulothoracic rhythm.

Limitations

• Assessment of successful block

• Proprioception

• Young subjects

What does this mean?

A) Results similar to cuff tears

Scapular changes due to tears are compensatory and represent an alternative method for arm elevation

What does this mean?

B) Results similar to fatigue

Scapular changes during to repetitive motion are due to fatigue of the rotator cuff muscles and may lead to cuff tears

What does this mean?

C) What is going on in the subacromial space?

increaseupward rotation