The Normal Pattern of Three Dimensional Scapular Kinematics

doutfanaticalMechanics

Nov 14, 2013 (3 years and 8 months ago)

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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


Glen
o
humeral 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/Protraction

Elevation/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

scapular

tracker

needle

stimulation

wire

lidocaine

injection

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
Scapular Rotation [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
Scapular Rotation [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
Scapular Rotation [deg]
Humeral Elevation [deg]
Downward
Upward
*
*
*
*
*
*
*
*
increase in
upward rotation
0
1
2
3
4
5
6
7
0
20
40
60
80
100
120
Scapular Rotation [deg]
Humeral Elevation [deg]
Downward
Upward
*
*
*
*
*
*
*
*
increase in
upward rotation
Nerve Block

0
5
10
15
20
0
30
60
90
120
150
Increase in UR [deg]
Arm Elevation [deg]
averaged from:
Paletta, 1997
Yamaguchi, 2000
Mell, 2005
Cuff Tears

0
3
6
9
20
40
60
80
100
120
140
160
Scapular Rotation [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?

increase

upward

rotation