What Muscles Are Cut During a Reverse Total Shoulder Replacement?

The subscapularis is the primary muscle deliberately cut or released during a reverse total shoulder replacement (RTSA), and depending on the surgical approach, portions of the deltoid may also be detached or split to reach the joint. Beyond those two, no other muscles are routinely severed. The remaining rotator cuff tendons (supraspinatus and infraspinatus) are typically already torn or nonfunctional in patients who need this procedure, which is why a reverse design is chosen in the first place. But the full picture is more nuanced than a simple list of muscles, because the surgeon’s choice of approach, the decision of whether to repair the subscapularis afterward, and occasional releases of nearby structures all shape how much soft tissue is disrupted and how recovery unfolds.

Why the Reverse Design Changes the Surgical Equation

A reverse shoulder replacement flips the ball-and-socket anatomy: the ball goes on the shoulder blade and the socket goes on the upper arm bone. This switch was first popularized by Paul Grammont and is designed to shift the center of rotation inward, which increases the mechanical leverage of the deltoid muscle and allows it to power arm elevation even when the rotator cuff is destroyed.¹ Because the deltoid becomes the engine of the reconstructed shoulder, protecting it during surgery is a top priority. Every decision about which muscles to cut, split, or release is made with this reality in mind.

The Two Main Surgical Approaches and What They Do to Muscle

Surgeons reach the shoulder joint through one of two common routes, and each one handles muscle differently.

The Deltopectoral Approach

This is the more traditional route. The surgeon makes an incision along the front of the shoulder and works through the natural interval between the deltoid and the pectoralis major. The deltoid itself is not cut or split; it is retracted to the side. The subscapularis, which sits directly in front of the joint capsule, must be dealt with to expose the joint. This approach preserves deltoid continuity, which is a significant advantage for postoperative function.²

The Anterosuperior (Deltoid-Splitting) Approach

In this approach, the surgeon splits the deltoid muscle along its fibers, typically in the front-to-middle portion, to access the joint from above and in front. Sometimes the deltoid is partially detached from the acromion (the bony shelf at the top of the shoulder) to improve visibility.³ This gives the surgeon a more direct view of the glenoid (the socket side on the shoulder blade), which can make baseplate placement easier. The trade-off is that the deltoid sustains some disruption and must heal back together. The split is kept short to avoid injuring the axillary nerve, which runs across the deltoid a few centimeters below the acromion.

Neither approach requires cutting through the bulk of the deltoid. In the deltopectoral approach the deltoid is simply moved aside, and in the anterosuperior approach it is split along its grain rather than severed across its fibers. The distinction matters for recovery: splitting along fibers heals more reliably than cutting across them.

The Subscapularis Question

The subscapularis is the large rotator cuff muscle that covers the front of the shoulder joint. In a deltopectoral approach, it sits directly between the surgeon and the joint and has to be moved out of the way. How the surgeon handles it is one of the most debated decisions in reverse shoulder surgery. Three common techniques exist: tenotomy (cutting the tendon off the bone), a peel (stripping the tendon along with a thin layer of tissue from its attachment), and lesser tuberosity osteotomy, where a small chip of bone is lifted off with the tendon still attached.⁴

Each method has its rationale. Tenotomy is fast and gives excellent exposure but leaves the tendon disconnected unless it is repaired at the end. The peel preserves a bit more tissue continuity. The osteotomy keeps the tendon attached to bone, which in theory heals more reliably because bone-to-bone healing is biologically more robust than tendon-to-bone healing. In practice, surgeons choose based on bone quality, the condition of the subscapularis itself, and their own training.

Some surgeons now use a subscapularis-sparing technique, particularly through the anterosuperior approach. A recent randomized trial compared a sparing approach against tenotomy without repair in RTSA patients and found that outcomes differed enough to justify studying the question formally.⁵ The idea behind sparing is simple: if you do not cut the subscapularis, you do not have to worry about whether it heals.

Does It Matter Whether the Subscapularis Is Repaired?

After the implants are in place, surgeons who cut the subscapularis face a decision: repair it or leave it. This debate has generated a substantial body of research, and the answer is not as clear-cut as you might expect.

A systematic review looking at seven studies found that dislocation rates were low in both groups. Dislocations occurred in about 0.7% of patients whose subscapularis was repaired and about 1.5% of patients whose subscapularis was left unrepaired, a difference that did not reach statistical significance. The review did note a trend toward better range of motion and clinical scores in the repair group.⁶ A separate meta-analysis found significantly lower dislocation rates in the repair group, but also found that implant design played a big role: patients who had a lateralized center of rotation and no subscapularis repair still had low dislocation rates.⁷

The practical takeaway is that subscapularis repair seems to help, especially with older implant designs where the center of rotation is more medialized. With newer lateralized designs, the joint is inherently more stable and the subscapularis repair becomes less critical for preventing dislocation, though it may still contribute to strength and internal rotation.

The Conjoint Tendon and Why Some Surgeons Release It

The conjoint tendon is the shared tendon of the coracobrachialis and the short head of the biceps. It attaches to a bony projection called the coracoid process and runs down the front of the shoulder. In a deltopectoral approach, the conjoint tendon sits right alongside the surgical corridor and can become quite tight once the implants lengthen the arm slightly.

A recent randomized trial and cadaveric study investigated whether completely releasing the conjoint tendon during RTSA improves outcomes. The release group showed improved internal rotation and lower pain scores at one year compared to the control group.⁸ In the cadaveric portion, releasing the conjoint tendon reduced tension across the front of the joint and increased the shoulder’s internal rotation range. This is not a routine step in every RTSA, but it is becoming more common, particularly in patients who have limited internal rotation before surgery or in cases where the arm is being lengthened significantly.

What About the Pectoralis Major?

The pectoralis major is not routinely cut during a standard RTSA. However, there are specific situations where it gets deliberately detached and repurposed. When the subscapularis is completely irreparable and the shoulder is unstable after the reverse prosthesis is placed, some surgeons transfer the pectoralis major tendon to act as an anterior stabilizer. The technique involves detaching the tendon from its normal insertion on the upper arm bone, along with a strip of periosteum for better suture grip, and rerouting it to serve the function the subscapularis can no longer perform.⁹ Care is taken to leave about one to two centimeters of the lower attachment intact to protect the nerve that powers the muscle.¹⁰

This is a salvage procedure, not a first-line step. Most patients undergoing a primary reverse shoulder replacement will never have their pectoralis major touched. But if you are having a revision surgery for recurrent instability, it is something your surgeon might consider.

The Rotator Cuff Muscles That Are Already Gone

It is worth clarifying what does not get cut because it is already nonfunctional. The classic indication for RTSA is cuff tear arthropathy, a condition where massive, irreparable rotator cuff tears have led to arthritis. By the time surgery happens, the supraspinatus and infraspinatus are often retracted, atrophied, or replaced by fatty tissue. The surgeon does not need to cut them because they are no longer functioning as muscles in any meaningful way.

The teres minor is the one rotator cuff muscle that sometimes remains intact even in the setting of a massive tear, and its status has important implications. The teres minor provides external rotation and contributes to joint stability. A biomechanical study found that when the teres minor was torn in addition to the rest of the rotator cuff, it increased the abduction angle required under a given deltoid load, revealing the key role the teres minor plays in stabilizing the joint and powering external rotation after RTSA.¹¹ When the teres minor is also gone, surgeons sometimes turn to tendon transfers, rerouting the latissimus dorsi and teres major tendons to restore external rotation.¹² These transfers involve detaching those muscles from their original insertion and reattaching them in a new position. The latissimus dorsi and teres major are not cut as part of a standard RTSA; they are only rerouted in more complex cases where external rotation is severely deficient.

Protecting Nerves While Cutting Muscle

Muscles do not exist in isolation. Every muscle release or cut brings the surgeon closer to nerves that must not be damaged. The axillary nerve is the most vulnerable during RTSA. It wraps around the underside of the shoulder joint, and anatomic studies have measured its distance from key surgical landmarks: on average about 14 millimeters from the bottom of the glenoid rim and about 8 millimeters from the humeral shaft.¹³ Those distances are tight, especially in smaller patients. The axillary nerve powers the deltoid, so damaging it would undermine the entire premise of a reverse replacement. This is one reason the deltoid split in the anterosuperior approach is kept short and the surgeon works with retractors carefully positioned to protect the nerve.

The suprascapular nerve, which innervates the supraspinatus and infraspinatus, also runs close to the glenoid and can be stretched by hardware placement, though injury is less common because the muscles it serves are usually already nonfunctional in RTSA patients.

Deltoid Tensioning and Its Consequences

Even though the deltoid is not cut in most approaches, the surgery changes its mechanical environment substantially. Placing the implants typically lengthens the arm, which stretches the deltoid. This increased tension is what helps the deltoid stabilize and move the joint after surgery. But there is a sweet spot. A study measuring deltoid lengthening found that the overall average increase was about 21 millimeters. Patients who developed acromial fractures or deltoid-related problems averaged about 29 millimeters of lengthening, while patients without complications averaged about 17 millimeters. Lengthening beyond roughly 26 millimeters appeared to be a risk factor for stress fractures of the acromion, deltoid tearing, or persistent deltoid pain.¹⁴

Acromial and scapular spine fractures are a recognized complication of RTSA. Strategies to prevent them include optimizing the patient’s bone health before surgery, carefully choosing screw lengths and positions in the glenoid, and avoiding excessive deltoid tension during implant placement.¹⁵ If the deltoid is over-stretched, it can fail at its weakest point, which is where it attaches to the acromion. So while the deltoid is technically preserved during surgery, the indirect mechanical stress placed on it is a serious consideration.

How Muscles Adapt After the Surgery

Understanding which muscles are cut is only half the picture. After RTSA, the remaining muscles reorganize how they work together. Electromyographic studies, which measure muscle activation during movement, show that the deltoid and the upper trapezius do the heavy lifting during open-chain exercises like lifting the arm against gravity. The other shoulder-girdle muscles, including the serratus anterior and the different parts of the trapezius, contribute variably depending on the exercise.¹⁶

Research into muscle synergy patterns, meaning the coordinated groupings of muscles that fire together during movement, found that patients with massive rotator cuff tears relied heavily on compensatory activity from the trapezius and serratus anterior even before surgery. After RTSA, those compensation patterns partially normalized. The similarity of postoperative synergy patterns to healthy shoulder patterns increased substantially, suggesting that the surgery restores a more natural coordination of muscle activity, not just raw strength.¹⁷ In other words, the muscles that were working overtime to compensate for the torn cuff got some relief once the prosthesis was in place and the deltoid could do its job more efficiently.

A Quick Reference of What Gets Cut, Split, or Released

To put all of this in one place:

Subscapularis: routinely cut (tenotomy, peel, or osteotomy) in the deltopectoral approach, sometimes spared in the anterosuperior approach. May or may not be repaired.
Deltoid: split along its fibers in the anterosuperior approach, sometimes partially detached from the acromion. Not cut in the deltopectoral approach.
Conjoint tendon: sometimes released to reduce anterior tightness and improve internal rotation, but not a routine step.
Pectoralis major: not cut in standard cases. Detached and transferred only in salvage situations involving irreparable subscapularis deficiency and instability.
Latissimus dorsi and teres major: not cut in standard cases. Transferred in complex cases where the teres minor is also absent and external rotation needs to be restored.
Supraspinatus and infraspinatus: usually already nonfunctional. Not deliberately cut.

What Patients Often Get Wrong

One of the most common misconceptions is that the deltoid is “destroyed” during a reverse shoulder replacement. In reality, the entire operation depends on the deltoid working well, and surgeons go to considerable lengths to protect it. The deltoid is the motor that drives the reconstructed shoulder. Cutting through it would be self-defeating. The confusion likely arises because the anterosuperior approach does split the deltoid, but a controlled split along the muscle fibers is very different from cutting across the muscle belly.

Another misconception is that the rotator cuff is “removed” during RTSA. The remnants of the rotator cuff tendons are cleaned up if they are in the way, but the goal is not to remove them. In patients with some remaining rotator cuff function, preserving whatever cuff tissue exists helps with rotation and stability. The reverse design compensates for the loss of the rotator cuff’s role in elevation and compression, but rotation, particularly external rotation, still benefits from intact posterior cuff tissue.

Finally, people sometimes assume that cutting the subscapularis means permanently losing internal rotation strength. While some internal rotation weakness is common after RTSA regardless of technique, modern implant positioning and rehabilitation protocols can often preserve functional internal rotation. The conjoint tendon release data mentioned earlier suggests that tight anterior structures may be a bigger barrier to internal rotation than the state of the subscapularis alone.