In a typical year, surgeons in the US perform more than 270,000 rotator cuff surgeries, and more than 90% of these surgeries involve the supraspinatus tendon. Because the average cost of a rotator cuff repair is about $25,000, this translates into Americans spending almost 7 billion dollars annually for the surgical management of rotator cuff tears. What’s worse, because our population is aging and remaining active, these numbers are expected to increase in the next few years.
What makes the high surgical prevalence and astronomical expense so frustrating is the fact that studies going back more than 30 years have shown the majority of rotator cuff tears gradually improve over time, whether treated operatively or nonoperatively. In fact, research out of Germany and Norway confirms that partially torn supraspinatus tendons can regenerate following exercise intervention. Keep in mind that while even large partial tears of the supraspinatus can do well without surgery, massive full-thickness tears of the supraspinatus occasionally require surgical intervention, especially in young athletic patients. In most cases, surgery is recommended within the first 3 months following the development of initial symptoms, as the muscle quickly atrophies following complete tendon rupture.
In one of the few long-term studies comparing the effects of surgical versus non-surgical care for rotator cuff injuries, pain, and function at regular intervals over a five-year period in patients receiving operative versus nonoperative care for large rotator cuff tears. Interestingly, at the three-month mark, the surgically treated group had significantly worse outcomes as they reported more shoulder pain and disability than the nonsurgically treated group. However, by 15 months, the surgically treated group had less pain and greater function, which was also true at the two-year mark. It is important to note that there was an 80% probability that both groups would achieve a good outcome by 60 months, which is consistent with numerous studies showing good outcomes whether the patient receives surgery or not.
While the majority of orthopedic authorities continue to be baffled by the fact that most patients with supraspinatus tears get better without surgery, they shouldn’t be. In 1998, an anatomic study by Minagawa et al. confirmed that up to 50% of the posterior portions of the supraspinatus tendon interdigitate with the superior portions of the infraspinatus tendon. The shared common fibers create a strain-shielding effect in which infraspinatus can offload a damaged supraspinatus. The ability of infraspinatus to offload even a large tear of the supraspinatus was proven in a cadaveric study in 2009. This research emphasizes the importance of strengthening the infraspinatus when dealing with a supraspinatus tear, and also explains why supraspinatus and infraspinatus often tear at the same time.
Because massive full-thickness tears have better long-term outcomes with surgical repair, it is important to diagnose the degree of supraspinatus tearing with physical examination. The most common in-office test to identify supraspinatus tears is the Jobe test. This test is performed by having the patient resist abduction in the scapular plane (scaption) while the examiner notes pain and/or weakness. Unfortunately, the sensitivity/specificity of this test for diagnosing moderate full-thickness tears is poor, and many practitioners refer out for more accurate testing such as MRIs and/or diagnostic ultrasonography, which are often cost-prohibitive given the natural tendency for the majority of these injuries to resolve over time.
The easiest way to quantify the degree of supraspinatus tearing without expensive testing is with a simple in-office screening using a handheld dynamometer. This particular test was developed by researchers at Washington University, who performed diagnostic ultrasound on 237 subjects to determine the overall health of the supraspinatus tendon. Next, the researchers used a standard dynamometer to measure strength in the shoulder abductors and external rotators. The abduction strength score was then divided by the external rotation strength score and if the resultant ratio was greater than .86, the supraspinatus tendon was healthy. If the strength ratio was approximately .7, the subjects were more likely to have a moderate to significant full-thickness supraspinatus tear. Lastly, if the strength ratio fell below .48, the subject almost always had a massive full-thickness supraspinatus tear. I like this test because it takes about two minutes to perform, and supplies important information, not just for determining the extent of the tear (and hence whether or not to refer out for a second opinion regarding surgery), but also for evaluating the response to a rotator cuff strengthening program.
Handheld dynamometry can also be used to evaluate strength ratios between the shoulder internal and external rotators. Quantifying this ratio is invaluable as the weakness of the external rotators relative to the internal rotators is an extremely common cause of not just supraspinatus tears, but a wide range of shoulder injuries.