A patient recently sent this limerick - surely worth sharing:

LIMERICK FOR SUBSCAPULARIS

This muscle is hidden from sight

It's working for you day and night

When you stumble and fall

And it won't work at all

Who knows if it can be put right?

Failure of the subscapularis after shoulder arthroplasty is a clinically important complication that can substantially compromise the comfort and function of the shoulder.

Take down and repair

Like most complications, subscapularis failure is better prevented than treated. Our approach includes takedown using a careful subscapularis peel, keeping the subjacent capsule intact to the tendon.

After the arthroplasty, the subscapularis tendon and subjacent capsule are repaired to the humerus using at least 6 sutures passed through secure drill holes at the margin of the humeral head cut.

The superior band of the subscapularis, also known as the upper rolled border, is the major strength of the subscapularis. The suture laced through it at the time of repair carries a disproportionately high percent of the total tendon load when the arm is externally rotated (see this link). We refer to this most important suture as the Mother Stitch.

This repair can be reinforced with a rotator interval plication.

During the first two months after shoulder arthroplasty, we are careful to have the patient stretch in flexion

but NOT in external rotation to avoid stressing the repair.

Diagnosing failure

Because post operative MRIs and sonograms after shoulder arthroplasty can be difficult to interpret, the diagnosis of subscapularis failure is often best made from

(1) history - force on the repaired tendon within the first two months after surgery resulting from

a fall on the arm,

a sudden or unexpected stretch in external rotation beyond the handshake position

a forceful internal rotation (e.g. while restraining a dog chasing a squirrel)

(2) physical exam

increased external rotation from what was recorded in the operating room at the close of the case

weakness of belly press with the arm out to the side

(3) radiographs

anterior subluxation of the humeral head on the glenoid seen on the axillary "truth" view of the left shoulder

Reconstruction

When diagnosed early after injury, the subscapularis can often be reconstructed with a hamstring allograft passed through drill holes in the lesser tuberosity laterally.

and through the residual tendon medially

Securing the graft back to the tuberosity reinforces the subscapularis attachment to the humerus

and restores stability to the joint.

Here's a variation of the method used in a case last week, this time on the right shoulder. The graft was first passed through the lower hole in the tuberosity, then up through the subscapularis tendon, then back down through the subscapularis tendon and then out the upper hole in the lesser tuberosity. In this case the graft was used to back up a standard repair of the subscapularis tendon to the humeral neck cut.

The two limbs of the graft passed through the lesser tuberosity were then tied to each other and secured with locking sutures.

An alternative to attempting reconstruction of a torn subscapularis is to consider a reverse total shoulder.

This option is discussed in this link.

An article on subscapularis failure was recently published:

Failure rates and outcomes after anatomic total shoulder arthroplasty are equivalent irrespective of subscapularis repair technique

They conducted a retrospective study of patients who underwent primary anatomic TSA with subscapularis tenotomy using either transosseous repair (TOR #=192) or direct primary tendon repair (PTR #=114) of a subscapularis tenotomy.

The "primary outcome studied was clinical subscapularis failure, defined as anterior subluxation of the glenohumeral joint as seen on axillary lateral radiographs with accompanying clinical decompensation, including pain and loss of active forward elevation and internal rotation.""Patients were not routinely screened by ultrasound or MRI to evaluate subscapularis integrity. Additionally, internal rotation strength testing was based on manual muscle testing. Clinical assessment of internal rotation strength is fairly subjective and limited because nearly all of the patients had 4/5 or 5/5 internal rotation strength." Substantial emphasis was placed on the patient's response to a question from the ASES score which asks about the ability to perform functional internal rotation activities such as putting on a bra or washing the back. Of note only 41.4% of the TOR group and 33.3% of the PTR group responded with “not difficult.”

Subscapularis failure was recognized in 13 patients (4.2% among the TOR group and 4.4% among the PTR group). Reoperation was performed in 18 patients. Subscapularis failures, complications not requiring surgery, and reoperations were not significantly different between the two groups.

Comment: In this retrospective study of an institutional database it appears that the patients in this series may not have been routinely and systematically examined for subscapularis failure, but rather the diagnosis was inferred from radiographs and from ASES scores. It is therefore possible that the rate of subscapularis failure was underestimated.

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