Deltoid Muscle Contribution to Shoulder Function
Condition: Nerve Injury; Nerve Palsy
Study type: Interventional

Summary: 
      There is only one study in the literature about the quantitative effect of M. deltoideus on
      the movement of the shoulder. Here, the author described a 35-80% loss of abduction power
      after selective blockade of the N. axillaris. Gerber, on the other hand, found a loss of
      abduction force of 73-86% after blockade of the suprascapular nerve. These results are partly
      contradictory, which is why the investigators think that further investigation is needed.

      For many questions in the field of shoulder orthopedics, this knowledge would provide an
      important additional basis for therapeutical decision-making. For example, in the treatment
      of rotator cuff ruptures but also in the implantation of both inverse and anatomical shoulder
      prostheses. Also, statements about different outcome prognoses could be made more precisely.

      Therefore, the investigators would like to perform muscle strength measurements of the
      deltoid muscle on 12 healthy volunteers on the dominant arm.

      Abduction, flexion, external rotation and internal rotation Mm. Infraspinatus, Supraspinatus
      and Subscapularis are tested respectively.

      The investigators plan to carry out the measurements three times before and after
      an-anaesthesiological nerve block of the axillary nerve thus inactivating the deltoid muscle
      (performed exclusively by an anesthesiologist specialized in regional anesthesia). The
      success of the nerve block is confirmed by needle electromyographies (EMG) by a neurologist
      specialized in electrophysiology. Using EMG neurogenic pathologies within the tested muscles
      are also ruled out.

      In order to exclude relevant rotator cuff pathologies the investigators will perform shoulder
      radiography in three planes and sonography of the rotator cuff before conducting the
      experiment described above.
    

Detailed description: 
      In order to exclude relevant rotator cuff pathologies the investigators will perform plain
      shoulder radiography in three planes and sonography of the rotator cuff before conducting the
      experiment described above.

      The force of abduction, flexion, external rotation and internal rotation is measured in a
      clinically standardized manner with a measuring device (IsoForceControl V1.1) and reported in
      Newton. These measurements are taken before and after the blockage of the axillary nerve,
      which is described below. Furthermore, before and after the blockade, an EMG of the rotator
      cuff and deltoid muscle will be performed in order to rule out neurogenic pathology and
      confirm the success of the nerve block.

      Anesthesia procedure:

      In the anesthesia induction area, standard monitoring (electrocardiography, blood oxygen
      saturation, non-invasive arterial pressure measurement) and peripheral venous access are
      attained and Ringer's solution will be connected to the venous access.

      Axillary nerve block block (AXNB):

      The AXNB is performed with the participant in the supine position using ultrasound with a 6-
      to 13-megahertz (MHz) linear probe.

      The anesthesiologist, wearing a facemask, cap, and sterile surgical gloves after surgical
      hand disinfection performs skin disinfection with a two-layer application of an alcoholic
      povidone-iodine solution. Three minutes later, the area of the puncture point will be
      surrounded with sterile drapes and the ultrasound probe will be covered with a sterile cover
      to allow sterile skin contact.

      The ultrasound probe is placed transversally in the infraclavicular region with the arm in
      90° abduction. The brachial plexus and its cords are identified l lateral to the brachial
      artery. The posterior cord is identified by ultrasound and is blocked - or, if the axillary
      nerve visible too - the axillary nerve is selectively blocked when it leaves the posterior
      cord and lies on the subscapular muscle accompanied by the posterior circumflex humeral
      artery. Using an in-plane technique, a short bevel needle (UPC 90, Te-mena) connected to a
      nerve stimulator with the setting 0.5 milliampere (mA) current intensity, 0.1 ms impulse
      duration and 2 Hz impulse frequency for dual guidance, will be advanced until its tip is
      positioned near the nerve without eliciting motor contractions. After careful negative (for
      blood) aspiration local anesthetic will be applied until the targeted neuronal structure is
      surrounded by the injected fluid.

      In the case of insufficient visualization of the nerve structures with this approach, the
      investigators will use a modified technique: the volunteer is placed in the sitting position,
      the shoulder in the neutral position but rotated 45° inward and the elbow flexed at 90° while
      the hand rested on the knees. Using an in-plane caudad-to-cephalad ultrasound probe placement
      parallel to the longitudinal axis of the shaft of the humerus and approximately 2cm below the
      postero-lateral part of the acromion on the dorsal side of the arm the investigators will
      identify the surgical neck and the shaft of the humerus and the cross section of the
      posterior circumflex humeral artery (PCHA), The axillary nerve is located cranially in close
      relation to the PCHA. The nerve will be blocked using the same material as mentioned
      above.All blocks will be performed by an anesthesiologist specialized in regional anesthesia
      (U.E. and J.A.) under standard monitoring in an anesthesia working area.

      Block success is evaluated assessing the degree of sensory block (cold test) over the
      distribution area of the axillary nerve every 5 min. The degree of motor block will be
      assessed by active abduction of the arm every 5 min. After a complete axillary nerve block is
      documented, the electrophysiological and strength tests will be performed.

      Peripheral venous line removal and participant ambulation will be performed after complete
      motor and sensory recovery of the hand and arm.

      All participants will be assessed for neurological status of the blocked extremity by the
      anaesthesiologist prior to discharge and 24h after the regional anaesthesia.

      A photo will be taken for documentation of the elevation function. Electromyographic studies
      will be performed by experienced neurologists certified in clinical neurophysiology (J.R. &
      M.S.). Needle EMG serves to verify the axillary block in all three portions of the deltoid
      muscle, to exclude pathology in the rotator cuff muscles and concomitant anaesthesia thereof.
      Assessment of possible spontaneous activity, recruitment pattern and motor unit potentials
      will be performed according to standard methods routinely applied in clinical
      neurophysiology. Patients on therapeutic anticoagulation will be excluded from needle
      electromyographic assessments.
    

Intervention name(s): Axillary nerve block for artificial deltoid muscle palsy
Intervention type(s): Procedure
Intervention description(s): Axillary nerve block block (AXNB):
The ultrasound probe is placed transversally in the infraclavicular region with the arm in 90° abduction. The brachial plexus and its cords are identified l lateral to the brachial artery. The posterior cord is identified by ultrasound and is blocked - or, if the axillary nerve visible too - the axillary nerve is selectively blocked when it leaves the posterior cord and lies on the subscapular muscle accompanied by the posterior circumflex humeral artery. Using an in-plane technique, a short bevel connected to a nerve stimulator with the setting 0.5 mA current intensity, 0.1 ms impulse duration and 2 Hz impulse frequency for dual guidance, will be advanced until its tip is positioned near the nerve without eliciting motor contractions. After careful negative (for blood) aspiration local anesthetic will be applied until the targeted neuronal structure is surrounded by the injected fluid.
Intervention model: Single Group Assignment
Masking: None (Open Label)
Primary purpose: Basic Science
Keywords: muscle function; rotator cuff