Relationship of the subscapular nerves to the base of the coracoid

Subscapularis structural integrity and function after arthroscopic Latarjet procedure at a minimum 2-year follow-up

BACKGROUND

Subscapularis function after arthroscopic Bankart repair has been widely studied. However, data regarding subscapularis performance after arthroscopic Latarjet procedures are lacking. This study aimed to evaluate subscapularis clinical and radiologic performance after arthroscopic Latarjet procedures.

METHODS

We included 40 patients who underwent arthroscopic Latarjet procedure with a minimum 2-year follow-up. Clinical evaluation included Western Ontario Shoulder Instability Index and Rowe scores, specific subscapularis isokinetic study, and lift-off tests. Contralateral measurements were used for comparison. Computed tomographic evaluation included graft consolidation, muscle dimensions, and degree of fatty atrophy, calculated as the mean muscle attenuation (MMA).

RESULTS

There was a decrease of 8.3% of maximum internal rotation peak torque in the operated arm (P = .02). However, there was no significant difference in the agonist-antagonist ratio: 76.9% in the operated arm and 76% in the contralateral (P = .82). Lift-off strength test demonstrated a decrease in the first year but not at final follow-up (P = .38). There was a significant decrease in lift-off distance of 23% compared to the contralateral side (P < .001). Subscapularis MMA was diminished when compared to the infraspinatus/teres minor (P < .001) at the expense of its upper part (P = .03). Hyperlaxity and number of dislocation episodes were correlated to a lower MMA (P = .046 and P = .005).

CONCLUSION

Arthroscopic Latarjet procedures provide satisfactory clinical results. There seems to be a diminished subscapularis MMA depending on its superior half. Hyperlaxity and number of previous dislocations were correlated to a lower MMA. Although there was a decrease in the maximum internal rotation peak torque, we did not find any difference in the agonist-antagonist ratio or in the final lift-off strength between sides.

Anatomy of the Subscapularis: A Review

The subscapularis is the largest and most powerful muscle of the rotator cuff. Occupying the vast majority of the subscapular fossa, it is the only internal rotator of the rotator cuff. The subscapularis innervation is classically taught as a dual innervation of 1 upper subscapular and 1 lower subscapular nerve arising from the posterior cord of the brachial plexus. However, there is a large amount of research that suggests there is significant variance in the innervation of the muscle from multiple upper subscapular nerves to multiple lower subscapular nerves arising from various portions of the plexus. Although one of the main functions of the subscapularis is to internally rotate the humerus, there is substantial evidence that displays its importance in glenohumeral stability as well. The insertion of the subscapularis is both tendinous as well as muscular. The more superior tendinous portion inserts on the lesser tuberosity while the more muscular portion inserts inferior to the less tuberosity. The medial to lateral spread of the insertion is quite variable ranging from only on the lesser tuberosity to merging with fibers from the supraspinatus. Understanding the anatomy of the subscapularis improves subscapularis management during shoulder arthroplasty including techniques for takedown, release, and repair.

Characterization of an anatomic safe zone surrounding the lower subscapular nerve during an open deltopectoral approach

BACKGROUND

Due to anatomic variance in subscapular nerve innervation patterns, it is theorized that the dysfunction of the subscapularis could be the result of iatrogenic denervation during mobilization of the subscapularis while exposing the anterior glenohumeral joint in anterior surgical approaches. The purpose of this study was to describe innervation patterns of the subscapularis and to characterize a safe zone when conducting an anterior surgical approach.

METHODS

The study used 6 human cadaveric shoulder specimens (12 shoulders total). A deltopectoral approach was used to expose the axillary nerve back to the posterior cord of the brachial plexus and reveal the origins of the upper and lower subscapularis nerves. An anatomic safe zone was characterized by measuring distances from both the upper and lower subscapularis nerve insertions with respect to that of the lateral border of the conjoint tendon, the bicipital groove, superior border of the subscapularis, and the axillary nerve (for the lower subscapular nerve only) with the arm in 30° abduction.

RESULTS

The anatomic safe zone of the subscapular nerves medial to the conjoint tendon is less than 32 mm. In relation to the axillary nerve, the safe zone is less than 10 mm inferiorly and 15 mm medially.

CONCLUSIONS

This described safe zone with respect to the lateral border of the conjoint tendon and axillary nerve is aimed to provide guidance to reduce iatrogenic injury of the subscapular nerves during anterior shoulder exposure. Extra care should be undertaken while dissecting past this safe zone to prevent iatrogenic subscapular nerve injury.

Nerve supply of the subscapularis during anterior shoulder surgery: definition of a potential risk area

PURPOSE

The purpose of the study was to evaluate the position of the subscapular nerves relative to surgical landmarks during exposure and to analyze the pattern of innervation of the subscapularis to avoid injury during anterior shoulder surgery.

METHODS

20 embalmed human cadaveric shoulder specimens were used in the study. The muscular insertions of the subscapular nerves were marked and their closest branches to the musculotendinous junction and the coracoid process were measured in horizontal and vertical distances. In addition, the innervation pattern of each specimen was documented.

RESULTS

14/20 specimens showed an innervation of the subscapularis with an upper, middle and lower subscapular nerve branch. Even though the nerve branches were in average more than 2 cm medial to the musculotendinous junction, minimal distances of 1.1-1.3 cm were found. The mean vertical distance as measured from the medial base of the coracoid to the nerve innervation point into the muscle was 0.7 cm for the upper nerve branch, 2.2 cm for the middle nerve branch and 4.4 cm for the lower nerve branch.

CONCLUSIONS

The subscapularis has a variable nerve supply, which increases the risk of muscle denervation during open shoulder surgery. Dissection or release should be avoided at the anterior aspect of the subscapularis muscle more than 1 cm medial to the musculotendinous junction. In approaches with a horizontal incision of the subscapularis, splitting should be performed at a vertical distance of 3.2-3.6 cm to the coracoid base to avoid iatrogenic subscapular nerve injuries.