Post on 15-Jan-2016
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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