Suprascapular Nerve Block Disrupts The Normal Pattern Of Scapular Kinematics

1. Suprascapular Nerve Block Disrupts The Normal Pattern Of Scapular Kinematics Sean McCully David Suprak Peter Kosek Andrew Karduna

2. 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

3. supraspinatus infraspinatus Pathology of Cuff Tears • Majority start with supraspinatus tendon • Next most commonly involved is the infraspinatus tendon

4. 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)

5. Suprascapular Nerve superior trunk of brachial plexus passes through suprascapular notch innervates supraspinatus and infraspinatus

6. 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

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

9. Protocol • 15 healthy subjects (mean age 26 years) Baseline kinematics and force Suprascapular nerve block Repeat kinematics and force

10. KINEMATICS • ISB recommendation (Wu et al, 2005)

11. transmitter electronics unit sensors digitizer Polhemus 3Space Fastrak

12. sensor Scapular Tracker

13. Method Validation skin sensor bone sensor

14. thorax scapula transmitter humerus Sensor Placement

15. Scapular Rotations Retraction/Protraction Anterior/Posterior Tilting Lateral/Medial Rotation

16. Clavicular Rotations Elevation/Depression Retraction/Protraction

17. 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)

18. NERVE BLOCK • 100 mg of lidocaine • Injected into the suprascapular notch • Nerve stimulator to confirm needle placement • Data collection 10 minutes after injection

20. stimulation wire needle lidocaine injection scapular tracker

21. 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

22. Results • No effect on clavicular rotation • No effect on scapular posterior tilting • Significant effect for scapular internal rotation and upward rotation

23. Internal Rotation

24. Upward Rotation

26. Nerve Block Fatigue Cuff Tears

27. 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.

28. Limitations • Assessment of successful block • Proprioception • Young subjects

29. 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

30. 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

31. What does this mean? C) What is going on in the subacromial space? increase upward rotation