What Muscles Are Cut During a Total Shoulder Replacement?

The subscapularis is the main muscle that gets cut, peeled, or detached during a standard (anatomic) total shoulder replacement. This large, flat muscle sits on the front of your shoulder blade and covers the front of the joint, so the surgeon has to move it out of the way to reach the ball-and-socket joint inside. The deltoid, the big muscle that gives your shoulder its rounded shape, is typically split along its natural fiber lines but not cut through. How these muscles are handled, and how well they heal afterward, has a surprisingly large effect on how the shoulder works once you recover.

Why the Subscapularis Has to Move

Your shoulder joint is buried under layers of muscle, and the most common surgical route to it is the deltopectoral approach. This means the surgeon works through the natural gap between your deltoid and your pectoralis major (chest muscle). Neither of those muscles is cut in this approach; the surgeon slides between them. But once past that layer, the subscapularis is sitting right in front of the joint capsule, acting like a locked door. There is no way to see or work on the humeral head (the “ball” part of the joint) or the glenoid (the “socket”) without moving the subscapularis aside.

The deltopectoral approach preserves the deltoid and pectoralis origins while giving the surgeon a clear view of the humerus and access to the joint structures.¹ What changes from surgeon to surgeon is how they handle the subscapularis once they get to it. The three main options are tenotomy (cutting the tendon), a peel (lifting the tendon off the bone without cutting through its substance), and lesser tuberosity osteotomy (removing a thin wafer of bone with the tendon still attached). Each has trade-offs for healing, strength recovery, and complication risk.

Peel, Cut, or Osteotomy

With a subscapularis tenotomy, the surgeon cuts through the tendon itself near where it attaches to the humerus. A subscapularis peel does something slightly different: instead of cutting across the tendon fibers, the surgeon lifts the tendon off its bony attachment, keeping the tendon intact but freeing it from the bone. A lesser tuberosity osteotomy takes a thin chip of bone along with the tendon, so when it is time to reattach everything, the surgeon is putting bone back against bone rather than tendon back against bone. Bone-to-bone healing is generally more reliable.

From a biomechanical standpoint, lab testing has shown that the peel and the osteotomy produce similar initial fixation strength when repaired. The peel repair did show less variability in how much the repair gaps under load, which suggests it may be a bit more consistent, but neither technique clearly outperformed the other in terms of raw strength.² Clinical studies comparing the two in actual patients, though, paint a slightly different picture. In one study comparing outcomes of the two techniques, ultrasound imaging found abnormal subscapularis tendons only in the peel group (three attenuated and one ruptured), while all tendons in the osteotomy group looked normal. Those abnormal tendons in the peel group correlated with worse functional outcome scores.³

The debate is still active among shoulder surgeons. Each technique has experienced advocates, and the “best” method often comes down to the surgeon’s training and comfort level. What matters most from a patient perspective is that the subscapularis gets securely reattached and heals properly, regardless of which detachment method is used.

What Happens to the Deltoid

In the standard deltopectoral approach, the deltoid is not cut. The surgeon works through the interval between the deltoid and the pectoralis major, and the deltoid stays attached to the collarbone and shoulder blade throughout the procedure. It gets retracted (pulled to the side) to create working room, which puts some stress on it, but the muscle fibers themselves are left intact.

There is one notable exception. In the subscapularis-sparing rotator interval approach, which avoids touching the subscapularis entirely, the surgeon enters the shoulder from the top rather than the front. This requires splitting the anterolateral deltoid along its natural fiber boundary (called a raphe), then reattaching it at the end of surgery.⁴ The split follows the muscle’s natural grain rather than cutting across fibers, so it heals readily, but it is technically a disruption of the deltoid that does not happen with the standard deltopectoral route. Surgeons weigh whether the benefit of leaving the subscapularis untouched is worth the minor deltoid split.

Subscapularis-Sparing Techniques

Newer approaches have tried to sidestep the whole subscapularis problem by finding a way into the joint without detaching it at all. One such technique, the subscapularis-sparing windowed anterior technique, preserves both the subscapularis and the deltoid completely. Because the subscapularis is never taken down, patients can begin moving the shoulder earlier after surgery with no restrictions on internal rotation, which is the motion most affected when the subscapularis needs time to heal.⁵

These approaches are still gaining traction and are not yet the default at most centers. They require specialized training and tend to give the surgeon a smaller working window, which can make glenoid preparation (shaping the socket side) more technically demanding. But for patients worried about subscapularis healing or who need to return to activities faster, they represent a real alternative.

How Well the Subscapularis Heals After Reattachment

After the implants are in place, the surgeon reattaches the subscapularis using sutures, sometimes anchored through drill holes in the bone or around the implant stem itself. The good news is that healing rates are generally high. In one study of 60 shoulders where the subscapularis was peeled and then repaired using a stem-based technique, ultrasound showed the tendon had healed intact in about 92% of cases. Roughly 5% were attenuated (thinned but intact), and about 3% had torn.⁶

Those numbers sound reassuring, but “healed on imaging” does not always mean “functioning normally.” Functional testing tells a more complicated story. In one early study that carefully tested subscapularis strength after total shoulder replacement, about two-thirds of patients showed abnormal results on both the lift-off and belly-press tests, which are standard clinical ways of checking subscapularis function. Of patients with an abnormal lift-off test, 92% reported reduced function in daily activities like tucking in a shirt.⁷ The researchers concluded that even with careful repair, return of full subscapularis function is not guaranteed.

A more recent study showed better functional results, with most patients passing the lift-off and belly-press tests after a tendon-to-tendon repair.⁸ Surgical techniques and repair methods have improved, so the gap between structural healing and functional recovery has likely narrowed over time. Still, subscapularis function after total shoulder replacement is something surgeons actively monitor.

When the Subscapularis Repair Fails

A failed subscapularis repair is one of the more serious complications after anatomic total shoulder replacement. If the tendon does not heal or tears again later, the front of the shoulder loses its primary stabilizer. The consequences include the humeral head drifting forward (anterior instability), accelerated loosening of the glenoid component, and decreased overall function.⁹

Early signs of subscapularis insufficiency include difficulty with internal rotation activities (reaching behind your back, tucking in your shirt, hooking a bra), weakness when pressing your hand against your belly, and a feeling that the shoulder is loose or unstable in the front. In severe cases, the shoulder can partially dislocate. Management options range from physical therapy to strengthen surrounding muscles, to revision surgery that may involve converting to a reverse shoulder replacement, which relies less on the subscapularis for stability.

How Reverse Shoulder Replacement Changes Things

A reverse total shoulder replacement flips the anatomy: the ball goes on the socket side and the socket goes on the arm side. This design was created specifically for people whose rotator cuff muscles are too damaged or atrophied to support a standard replacement. Because the reverse design shifts the mechanical workload away from the rotator cuff and onto the deltoid, the surgical handling of muscles changes in important ways.

In a reverse replacement, the subscapularis may still be detached to get into the joint, but if the tendon is already torn or the muscle is severely atrophied (which is common in patients who need reverse replacements), the surgeon may not repair it at all. The prosthesis is designed to function without a working subscapularis, relying instead on the implant geometry and the deltoid to keep the joint stable. Where a reverse replacement also cannot fully compensate, however, is active external rotation. When both the infraspinatus and teres minor muscles are absent or atrophied, the reverse prosthesis alone cannot restore the ability to rotate the arm outward.¹⁰ In those situations, surgeons sometimes transfer a tendon from another muscle (like the latissimus dorsi) to restore external rotation.

The Deltoid’s Expanded Role After Reverse Replacement

After a reverse shoulder replacement, the deltoid becomes the engine that drives nearly all arm movement. The design of the prosthesis increases the deltoid’s mechanical advantage by lengthening its moment arm, essentially giving it more leverage to lift and move the arm. One modeling study found the reverse design increased the deltoid’s moment arm by about 42%, compensating for the dysfunctional rotator cuff.¹¹

The middle portion of the deltoid appears to be the workhorse. Muscle activation studies using surface electrodes have shown that the middle deltoid is the primary contributor to shoulder function after reverse replacement, showing significant involvement in all shoulder motions and increasing its activation over time as the patient adapts.¹² The anterior and lateral parts of the deltoid contribute more at the beginning of arm elevation, while the posterior deltoid plays a larger role at higher angles.¹³

This is why protecting the deltoid during a reverse shoulder replacement is absolutely critical. Any damage to the deltoid or to the axillary nerve that powers it can be devastating for the outcome. It also explains why rehabilitation after a reverse replacement focuses heavily on deltoid strengthening once the initial healing phase passes.

Why the Condition of Your Muscles Before Surgery Matters

The muscles that are not cut during surgery can still profoundly affect your outcome. Fatty infiltration, where muscle tissue is gradually replaced by fat, is common in patients with long-standing rotator cuff tears who eventually need shoulder replacement. This fatty replacement makes muscles weaker and less able to contribute to shoulder motion even after a new joint is installed.

The teres minor, a small muscle on the back of the shoulder blade responsible for external rotation, turns out to be especially important. In reverse total shoulder replacement, patients with severe fatty infiltration of the teres minor had significantly worse outcomes than patients whose teres minor was still in reasonable shape. One study found that the group with healthier teres minor muscles gained an average of nine degrees of external rotation after surgery, while the group with severe fatty infiltration actually lost an average of seven degrees.¹⁴ A systematic review confirmed these findings and also found that fatty infiltration of the infraspinatus negatively affected forward elevation and external rotation after reverse replacement.¹⁵

Fatty infiltration and muscle atrophy are also risk factors for worse outcomes after anatomic total shoulder replacement.¹⁶ This is one reason surgeons evaluate rotator cuff muscle quality on preoperative imaging: it helps determine whether an anatomic or reverse replacement is the better choice, and it sets realistic expectations for how much function the patient can regain.

Rehabilitation and Protecting the Repair

If your subscapularis was detached and repaired, the early weeks after surgery revolve around letting that repair heal without putting too much strain on it. Rehabilitation follows a phased approach designed to avoid premature stress on the healing tendon while still preventing the shoulder from getting excessively stiff.¹⁷ In practical terms, this usually means wearing a sling for four to six weeks, doing only passive or assisted range-of-motion exercises during that period, and avoiding active internal rotation (the motion the subscapularis controls) until the tendon has had time to knit back together.

The specific restrictions depend on how the subscapularis was handled. With a subscapularis-sparing approach, the restrictions are lighter and the progression faster because there is no tendon repair that needs protection. With a peel or osteotomy repair, most surgeons will limit external rotation for the first six weeks to avoid pulling the repair apart, and will hold off on resisted internal rotation exercises for three months or more. After a reverse replacement where the subscapularis was not repaired, restrictions center more on deltoid recovery and avoiding certain positions that could dislocate the prosthesis, such as extreme internal rotation combined with extension (reaching behind your back).

Active strengthening typically begins around six to eight weeks for the deltoid and periscapular muscles, and later for the rotator cuff if it was repaired. Full recovery to maximal strength and function generally takes six months to a year, with continued improvement possible beyond that as muscles adapt to the new joint mechanics. Patience during this phase matters. Pushing too hard too early risks disrupting the subscapularis repair, while being overly cautious can lead to stiffness and weakness that is difficult to reverse later.

Other Muscles That Can Be Affected Indirectly

Though the subscapularis is the only muscle routinely detached, other soft tissues around the shoulder are affected by the surgery. The long head of the biceps tendon runs through the joint and is frequently either tenotomized (cut and left to retract) or tenodesis’d (cut and reattached lower on the humerus) during shoulder replacement. In subscapularis-sparing approaches, biceps tenodesis is a standard step because the rotator interval through which the surgeon enters contains the biceps tendon.⁴ Most patients tolerate biceps tenotomy or tenodesis well, though some notice a cosmetic change (the “Popeye” bulge in the upper arm) or mild cramping with heavy lifting.

The joint capsule itself, while not a muscle, is cut open to access the joint and may be partially removed. The coracoacromial ligament, which arches over the top of the rotator cuff, is sometimes released during surgery. In reverse replacements, releasing this ligament can affect stability because it acts as a secondary restraint against upward migration of the humeral head. Nerves running near the surgical field, particularly the axillary nerve (which powers the deltoid) and the musculocutaneous nerve (which powers the biceps and brachialis), are at risk of stretch injury during retraction. Nerve injuries are uncommon but worth being aware of, especially because temporary deltoid weakness from an axillary nerve stretch can slow early recovery and mimic a failed repair.