This dynamic shoulder rotator cuff model is designed specifically to simulate shoulder dislocations and treatments but it can be used for a range of clinical education applications.

See here for video: https://youtu.be/GVXmNw9ABjo

In this model, the humerus is held in place by a series of elastic cords that simulate the pull of rotator cuff muscles and ligaments. Tension on the elastics can be adjusted to simulate variability in rotator cuff integrity and support around the glenohumeral joint.

The six anchor points between the scapular assembly and head of humerus represent the major components of the rotator cuff (subscapularis, infraspinatus, supraspinatus, teres minor, and approximations of the anterior and posterior glenohumeral ligaments)

Assembly requires six M6 barrel adjustors and approximately 1m of elastic cord or strap. Additionally, you may choose to use crimps to secure the ends of the elastic.

The M6 barrel adjustors are commonly used in bicycles to adjust cable tension of gear derailleurs. They can be purchased from a bike store or online.

This model shown uses two types of elastic, 1/4” (6mm) wide elastic band, and 1/8” (3mm) diameter elastic cord. While both will work fine, the cord is easier to work with during assembly.

Print the head and shaft of humerus as oriented. Print the scapular assembly as oriented but raise it above the surface of the bed approximately 3mm and build supports up to bottom surfaces and overhangs. It is important that the glenoid surface is oriented upwards so that it prints cleanly.

To assemble, begin by passing the first elastic through a small hole in the head of the humerus. Pull it out the large bottom hole and crimp or tie a knot so that the end does not pass back out through the hole. Next, thread the other end of the elastic through the appropriate hole in the scapular assembly and then through a barrel adjuster. Determine what length of elastic achieves the desirable amount of tension and trim the elastic to the appropriate length. Tie or crimp the end of the elastic so that it sits inside the end of the barrel adjuster. Repeat with each elastic. 

Once the elastics are in place, insert the shaft of the humerus into the bottom of the head of the humerus. The fit is intentionally tight, so you may have to gently file off the contact surfaces until you are able to insert it in securely.

This model was done in collaboration with Richmond Rescue in Vermont, USA, for use in their training programs. It is intended to support free and accessible open-source learning.

Reference files from:  "BodyParts3D, © The Database Center for Life Science licensed under CC Attribution-Share Alike 2.1 Japan".



Dynamic Shoulder Rotator Cuff Education Model

Do Not Print.stl

This 16-piece, full-sized anatomical model shows the position of the brachial plexus nerves relative to surrounding bones, muscles, and arteries. See here for video: https://youtu.be/Uol33HA0QOc 

The brachial plexus is a network of nerves in the shoulder that carries movement and sensory signals from the spinal cord to the arms and hands. This model is designed for use as a clinical education tool, specifically for ultrasound guided nerve blocks and anesthesia for surgery.

The model can be used upright or in supine. You can print either shoulder or both. Use different coloured filament to emphasis structures.

The “Brachial Plexus” includes all roots, trunks, divisions, cords and branches, as well as proximal portions of the suprascapular and long thoracic nerve. The phrenic nerve is included as well, not because it is a part of the brachial plexus, but because it is a structure to identify and avoid when doing nerve blocks or surgery in this area.

The main structural pieces are attached with magnets. To assemble both sides with magnets, you will need 36   1/4” x 1/8” (6mm x 3mm) cylindrical neodymium magnets. www.kjmagnetics.com is a good source of magnets. Pieces can be glued together for permanent attachment.

The roots of the brachial plexus and phrenic nerve are attached via insertion holes in the intervertebral foramen. The brachial plexus and subclavian/axillary artery are also held in place by the clavicle.

The following pieces form the structural base:

•	Spine Base 
•	Right and/or Left Scapula Rhomboid Base 
•	Sternum Rib Base 
•	Right and/or Left Clavicle

The follow pieces are non-structural. Print the pieces and sides that you need.:

•	Head of Humerus
•	Anterior Scalene
•	Brachial Plexus
•	Phrenic Nerve
•	Subclavian/Axillary Artery

This is an advanced print requiring knowledge in setting up supports and post-print cleanup.

The “Spine Base” and “Scapula Rhomboid Bases” should be printed as provided. The remaining files are in a “suggested orientation,” you may need to reorient and prepare them according to your preferences, equipment, and skill level. In general, try to orient outer surfaces upwards so that the surfaces in contact with support structures are less visible in the final model. 

For pieces with contoured bottom surfaces and hard-to-reach support areas, try raising the model a few millimeters off the build plate and using “tree supports.”

Here are considerations for assembly:
•	Before inserting magnets, clean out the magnet anchors with a 1/4” drill bit to remove any imperfections, allowing the magnets to sit properly.
•	Ensure that you insert magnets with polarity oriented to allow proper connections.
•	You may need to use glue to secure some of the magnets in place, especially if using the smaller metric sizes. CA glue works well.
•	Expect to do some post-print cleanup with sandpaper and files.

Every attempt has been made to maintain anatomical correctness; however, the following small modifications were necessary to optimize the files for 3D printing:
•	Magnet anchors have been added to allow insertion of magnets.
•	Some areas of bone have been thickened to support the magnet anchors and add strength
•	A portion of the posterior spine of the scapula has been enlarged to support the model in supine.
•	All neural structures have been thickened for strength and to facilitate printing.
•	The brachial plexus has been reshaped in some areas to allow for ease of printing and assembly. These alterations are within the range of normal anatomical variation. 
•	Anterior scalene is positioned slightly anterior to create more space in the interscalene triangle.
•	Groves have been added on the first ribs to facilitate proper positioning of the subclavian artery.

This project was done in collaboration with Eric Kramer and colleagues.

Eric Kramer is a nurse anesthesiologist and nurse practitioner with an interest in point of care ultrasound and ultrasound guided regional anesthesia. He is faculty for Nat

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Dynamic Shoulder Rotator Cuff Education Model

16-Piece Full Size Brachial Plexus Model