Transcript The Normal Pattern of Three Dimensional Scapular Kinematics

Suprascapular Nerve Block Disrupts The Normal
Pattern Of Scapular Kinematics
Sean McCully
David Suprak
Peter 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 models
injection of collagenase (Soslowsky et al, 2002)
injection of carrageenan (Tillander et al, 2001)
•
Cadaver models
surgical simulation of tears (Parsons et al., 2002)
simulated paralysis (Sharkey et al., 1994)
•
In-vivo models
muscle 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
transmitter
electronics
unit
sensors
digitizer
Scapular Tracker
sensor
Method Validation
skin sensor
bone sensor
Sensor Placement
thorax
scapula
transmitter
humerus
Scapular Rotations
Retraction/Protraction
Anterior/Posterior Tilting
Lateral/Medial Rotation
Clavicular Rotations
Elevation/Depression
Retraction/Protraction
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
stimulation
wire
lidocaine
injection
needle
scapular
tracker
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
Scapular Rotation [deg]
Internal 40
External
pre-block
35
*
*
*
*
*
*
30
25
post-block
20
15
10
0
20
40
60
80
Humeral Elevation [deg]
100
120
Upward Rotation
Scapular Rotation [deg]
Upward 35
30
post-block
*
*
*
25
20
*
*
*
15
*
10
*
5
Downward 0
pre-block
0
20
40
60
80
Humeral Elevation [deg]
100
120
Upward
Scapular Rotation [deg]
7
*
*
*
*
6
increase in
upward rotation
*
*
*
5
*
4
3
2
1
Downward 0
0
20
40
60
80
Humeral Elevation [deg]
100
120
Upward
Scapular Rotation [deg]
7
*
*
increase in
upward rotation
*
*
*
6
*
*
5
*
4
3
2
Nerve Block
1
Downward 0
0
20
40
60
80
100
120
Humeral Elevation [deg]
9
20
*
averaged from:
Paletta, 1997
Yamaguchi, 2000
Mell, 2005
*
*
Increase in UR [deg]
Scapular Rotation [deg]
Upward
6
*
3
Downward 0
Fatigue
20
40
60
80
100
120
Humeral Elevation [deg]
140
160
15
10
5
Cuff Tears
0
0
30
60
90
Arm Elevation [deg]
120
150
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?
increase
upward
rotation