Tears of the rotator cuff are a very common reason for shoulder pain, weakness and poor motion. The rotator cuff is a group of deep muscles all around the shoulder joint. They provide stability and power to the joint, and unfortunately, they are prone to both injuries and wear with overuse and aging. Some of you outside the field of Medicine may know the names of each individual rotator cuff muscle: supraspinatus, infraspinatus, subscapularis, and teres minor. These muscles are intimately related to the so-called tendon of the long head of the biceps. Several aspects of rotator cuff disease have been discussed in our blog before (A Few Common Questions About Rotator Cuff Tears: How Do They Happen? Do They Heal? Do They Get Bigger? Why?, Acute Tears of the Rotator Cuff: Why seek Help Immediately?).
For years, shoulder surgeons were aware of the very common supraspinatus tears. On the contrary, tears of the subscapularis have been elusive: they commonly involve only a portion of the tendon, and they oftentimes start deep in the joint, where without the benefit of looking at the tendon form the inside (as done in arthroscopic surgery), they are difficult to identify.
So, what is the big deal? Well, … when subscapularis tears are missed at the time of surgical repair of the rotator cuff (which amazingly can happen!), the shoulder is seldom perfect after recovery. In fact, many times it hurts a lot and it feels weak. Luckily, over the last few years, shoulder experts have become more aware of these very common tears, and techniques have been developed to find subscapularis tears at the time of arthroscopic surgery: subscapularis tears are hidden and forgotten no more! However, if you have had cuff repair surgery and you are still struggling with your recovery, a missed tear of the subscapularis could be the reason. Come see us if that is the case, and we may be able to help you!
Brief anatomy of the subscapularis
It turns out that the subscapularis is the biggest of all the rotator cuff muscles. Its powerful muscle fibers cover the whole front of the shoulder blade (hence the name: “sub” = under; “scapula” = shoulder blade; “subscapularis” muscle = muscle under the shoulder blade) We abbreviate its name into “subscap” all the time! In reality, the “subscap” looks like two muscles joined together; the upper two thirds of its muscle fibers turn into tendon fibers to attach firmly to the region in the bone in the arm (humerus) known as lesser tuberosity. The top portion of the subscapularis has a stout, round, upper edge that many call “the rolled upper edge of the subscapularis”. The muscle fibers of the lower third connect almost directly to bone though very short tendon fibers: this fleshier portion of the lower subscapularis is termed by some “subscapularis minor”, since it mirrors the location of the “teres minor” at the back of the shoulder.
How not to miss a “subscap” tear…
Shoulder specialists may miss subscapularis tears when evaluating a patient with shoulder problems. Subscapularis tears may happen after a distinct injury, or they can be the consequence of wear and tear. The one injury that is known to cause subscapularis tears is a dislocation of the shoulder joint in patients over the age of 40 or 50. Shoulder specialists are particularly picky in their assessment of the subscapularis in these circumstances. However, degenerative wear of the subscapularis leading to tear is more insidious, and typically starts at the deep fibers of the upper portion of the tendon.
The hallmark of subscapularis tears (in addition to pain) is weakness in what shoulder specialists call internal rotation. Several maneuvers have been described to unmask weakness in internal rotation. The most common include the lift-off test, the belly-press test, and the bear hug test. In addition, most patients with subscapularis tears have too much rotation externally. The tendon of the long head of the biceps is very close to the subscapularis tendon, and not uncommonly patients with subscapularis tears will also complain of biceps pain.
Magnetic resonance imaging (or MRI) has become for many the best imaging study to assess the subscapularis. Large, complete tears are identified as a gap between the tendon fibers and the bone at the footprint of the lesser tuberosity. However, many subscapularis tears are hidden! The tendon tears in continuity…, like when you pull on two ends of chewing gum, and the gum becomes longer and thinner, but does not fully tear. In these circumstances, some MRI findings may hint to a subscapularis tear: the subscapularis tendon looks too long, the tendon of the long head of the biceps is out of place, or the muscle belly of the subscapularis has atrophy and is being replaced by fat (fatty infiltration).
In the end, some studies have shown that up to one third of subscapularis tendon tears do not show on MRI. In these shoulders, the diagnosis can only be confirmed at the time of surgery, when assessing the subscapularis tendon from the inside with an arthroscopic camera.
Currently, many shoulder experts recommend surgery for patients with painful, weak shoulders as a consequence of a subscapularis tear. In our hands, these repairs are performed arthroscopically: a camera is introduced into the shoulder, and additional small incisions called portals are used to pass instruments, anchors and sutures inside the joint and repair the tendon to bone. Arthroscopic repairs of the subscapularis can be technically challenging, and some surgeons prefer classic open techniques.
In our experience, patients who have shoulder pain and other symptoms as a consequence of subscapularis tearing really improve with arthroscopic repair of their tears. After surgery, most surgeons recommend use of a shoulder immobilizer for a few weeks (typically six), and most patients do not feel their best until they have completed physical therapy exercises for 4 to 6 months.
Beyond the fixable
Unfortunately, sometimes tears of the subscapularis are so bad that fixation will just not work: the whole muscle is off the bone, retracted, replaced with fat, and allows the humeral head to displace forward. In these circumstances, surgeons will recommend procedures to compensate for the torn, unfixable rotator cuff: either another tendon is transferred to compensate for the absent subscapularis, or the joint is replaced with an implant called reverse arthroplasty, stable enough to prevent further abnormal anterior displacement of the humeral head. Reverse shoulder arthroplasty is typically preferred for patients that have not only a subscapularis tear, but also arthritis and bad tears of other tendons, whereas transfer of a tendon (the latissimus dorsi is our choice) is preferred in younger patients with no arthritis and no other tendon tears.
If you want to learn more…, read our review article at JSES Open Access – Subscapularis Tears, Hidden and Forgotten No More!.