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Biceps Instability

Biceps instability takes the form of either frank dislocation or more subtle subluxation. As noted previously, the primary restraining structures holding the LHB in the bicipital groove are the medial sling and subscapularis tendon. Habermayer and Walch divided LHB dislocations into extra-articular or intra-articular. The much less common extra-articular dislocations dislodge from the bicipital groove and travel over (anterior to) an intact subscapularis tendon.

According to Habermayer and Walch, as well as in our experience, these dislocations are extremely uncommon. More commonly a LHB dislocation from within the bicipital groove is associated with a partial or complete tear of the subscapularis tendon, allowing the LHB to dislocate posterior to the subscapularis. The medial sling remains attached to the superolateral border of the subscapularis tendon—even when that tendon retracts medially.

This arthroscopic anatomic landmark has been termed the “comma sign” . It is a critical arthroscopic finding because the comma easily guides the surgeon to the superolateral border of the subscapularis tendon thereby assisting in anatomic arthroscopic repair of the tendon back to the lesser tuberosity bone bed.

Biceps tendon subluxation can be a much more subtle diagnosis and we believe it is frequently missed even during arthroscopy. Again the critical anatomic components to prevent biceps subluxation are the medial sling and subscapularis tendon. In the early phases of biceps subluxation, the medial sling structures may remain largely intact while creating mechanical wear to the anteromedial portion of the LHB, which resides in the bicipital groove.

It is therefore quite important to thoroughly examine the anteromedial portion of the LHB by pulling the structure intra-articularly with a probe while visualizing “over the top.” This maneuver often requires a 70-degree arthroscope to adequately visualize these structures. As the pathology progresses, the medial sling becomes detached from its insertion on the superior aspect of the lesser tuberosity and the LHB begins to act as a knife cutting its way through the subscapularis tendon insertion, causing it to become detached from the lesser tuberosity.

Early findings of this phenomenon can only be seen with the 70 degree scope visualizing “over the top” to look down at the bone bed of the lesser tuberosity. The senior author has described this view with the 70-degree scope as the “aerial view”. Fraying may also be appreciated on the medial sling. This finding is termed a “pre-comma sign”.

As the humerus is internally and externally rotated the biceps tendon can be seen “breaking” posterior to the plane of the anterior border of the subscapularis. As a normal biceps tendon should remain anterior to the plane of the subscapularis, this “broken plane” phenomenon is a sure sign of early biceps instability. If not recognized, this will likely progress to LHB dislocation and complete tearing of the upper subscapularis insertion.

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