Does the Suprascapular Nerve Move within the Suprascapular Notch? Biomechanical Perspective Using the Finite Element Method

PURPOSE

We aimed to analyze changes in suprascapular nerve (SSN) position within the suprascapular notch during in vivo shoulder abduction.

MATERIALS AND METHODS

Three-dimensional models of the shoulder complex were constructed based on magnetic resonance imaging of the brachial plexus (BP-MR) in a patient diagnosed with SSN dysfunction but normal scapular movement. Using BP-MR in neutral position and computed tomography data on shoulder abduction, shoulder abduction was simulated as the transition between two positions of the shoulder complex with overlapping of a neutral and abducted scapula. SSN movement during abduction was evaluated using the finite element method. Contact stress on the SSN was measured in the presence and absence of the transverse scapular ligament (TSL).

RESULTS

In the neutral position, the SSN ran almost parallel to the front of the TSL until entering the suprascapular notch and slightly contacted the anterior-inferior border of the TSL. As shoulder abduction progressed, contact stress decreased due to gradual loss of contact with the TSL. In the TSL-free scapula, there was no contact stress on the SSN in the neutral position. Towards the end of shoulder abduction, contact stress increased again as the SSN began to contact the base of the suprascapular notch in both TSL conditions.

CONCLUSION

We identified changes in the position of the SSN path within the suprascapular notch during shoulder abduction. The SSN starts in contact with the TSL and moves toward the base of the suprascapular notch with secondary contact. These findings may provide rationale for TSL release in SSN entrapment.

How to assess scapular dyskinesis precisely: 3-dimensional wing computer tomography--a new diagnostic modality

BACKGROUND

Aberrations in scapular motion are believed to be associated with the presence of shoulder or elbow pathologies. There are many methods to evaluate scapular kinematics, but they have certain limitations. Nevertheless, it is believed that appropriate rehabilitation for each type of scapular dyskinesis is important.

METHODS

Eighty-nine athletes were videotaped and seven blinded observers categorized scapular dyskinesis into 4 types, which was followed by 3-dimensional (3D) wing computer tomography (CT). Four blinded examiners evaluated 5 angles [upward rotation (UR), internal rotation (IR), anterior tilting (AT), superior translation (ST), and protraction (PRO)] on the 3D wing CT. Inter-rater reliability (IRR) was calculated for both the methods. CT scan measurements were compared with the 4 observational types to establish the validity.

RESULTS

The IRR with observational assessment of scapular dyskinesis into 4 types was good, 0.780. The 3D wing CT analysis had a very high IRR, 0.972. There was a statistically significant correlation between observational assessment and 3D wing CT analysis. The UR angle, ST angle in type 3 scapular dyskinesis, and AT angle in type 1 scapular dyskinesis were increased as compared with those in the other types of scapular dyskinesis. All these measurements were made in the resting position of the scapula.

CONCLUSION

The 3D wing CT analysis allows precise quantification of a position associated with scapular dyskinesis. Therefore, 3D wing CT can be considered as an alternative method for assessing scapular dyskinesis.