Use of Ultrasound in Detection Of Rotator Cuff Tears
Musculoskeletal (MSK) injuries are one of the most common pain conditions seen in clinical practice. In 2004, it was estimated that MSK injuries accounted for $510 billion in direct medical costs and an addition $339 billion in lost time and productivity. 1 The Bureau of Labor Statistics recently reported that 387,800 employees missed work due to MSK disorders in 2011.
Shoulder pain represents a significant portion of MSK injuries and typically ranks in the top three MSK complaints seen in physician offices. In 2006 there were over 7.5 million physician visits for shoulder pain and current estimates are that 440 million work days were lost specifically because of shoulder pain and rotator cuff injury.2 Rotator cuff injuries, in particular, can be painful and debilitating, leading to chronic disability and job loss. In the manufacturing sector where upper extremity motion and cumulative trauma is more likely, the incidence (new cases) of shoulder pain is greater than in the general population.
Clearly, higher vigilance needs to be considered for workplace shoulder injuries, which would include a surveillance approach for those workers with existing injury. The goal in this type of monitoring initiative would be the prevention of further trauma via early and noninvasive interventions.
The use of diagnostic ultrasound (DUS) could figure prominently in this type of preventive and/or early intervention program—and already does with some larger employers. It is within this context of collective pain, disability, and cost generated by shoulder injury management that we review the value of DUS.
The use of DUS as an imaging source to help guide the diagnostic process in shoulder evaluation has grown exponentially in the last few years. Instead of being the cheaper alternative to the “gold standard” magnetic resonance imaging (MRI), current evidence supports the use of DUS as an accurate primary imaging test for MSK lesions. Indeed, both MRI and DUS are excellent tests for assisting in the diagnosis of rotator cuff tears (RCT) of the shoulder.3 However, the addition of a contrast agent with MRI probably tips the accuracy rate and diagnostic precision slightly in favor of MRI. So why use DUS? DUS has the advantage of demonstrated cost-effectiveness, ease of use, and patient compliance.
Prevalence of RCT
Why focus attention on prevalence? Prevalence is usually defined by the number of people with the disease over the number of people at risk, and determined at a single point in time. Much has been written about RCT prevalence with seemingly very different values being reported in the literature. It is evident that the reported prevalence in a study is dependent on the actual population under investigation. The various point estimates reported in the literature reflect the varied subsets of population groupings that are available to investigators. For example, the prevalence of symptomatic RCTs is expected to be greater in a population of men working on an assembly line and over the age of 45 years than their younger counterparts under 30 years of age, reflecting a relative disparity attributable to a single risk factor. Presumably, the physiologic status of a human tendon is a culmination of factors that include wear and tear, genetic factors, nutritional status, and overall health of the persons MSK system, to name but a few.
There are other risk factors that have been associated with a higher than normal risk for rotator cuff tearing, including repetitive work, heavy work, age- related rotator cuff delamination (rotator cuff disease), gender, postural dysfunction, acromial hooking (Bigliani scale), frailty/deconditioning, and metabolic disease.4 Preoperative diagnosis of a RCT will depend on several key factors, including the capabilities of the diagnostic tool and the experience/skill of the interpreter. As a result, the literature reports varying diagnostic accuracy indicis while using DUS to detect RCTs and is even stratified them, in some cases, based on professional category such as radiologist, orthopedic surgeon, chiropractor, podiatrist, physical therapist, and physiatrist. The practitioner performance reporting actually serves several important functions:
- Reports practional-specific accuracy rates (competency)
- Identifies a specific practitioner group capability (capacity)
- Assists in validating professional groups’ claim to a test or technology (utility)
- Provides useful data for professional policy makers in lobbying for expanding profession-specific scope of practice.
Rationale for Testing
The general assumption that all RCTs lead to pain and dysfunction has been challenged repeatedly. We now understand that not everything that appears “damaged or abnormal” is symptomatic. In cases where we have a partial tendon tear through non-traumatic processes, as in age-related rotator cuff delamination, it is entirely feasible and very likely “probable” that there is little if any pain—even when exertions are placed on the shoulder. We would expect very poor mobility and strength- generating capabilities in this shoulder, but not necessarily pain.
By contrast, a more acute and less severe condition such as a strain could conceivably generate significantly more pain signals, leading to weakness through reflex joint inhibition as a result of pain and swelling. The message then becomes that we must all be careful with the assumptions that are made on the relationship between what we see versus what patients are reporting as symptoms.
All this preamble is not to downgrade the value of a diagnostic test; rather it is to help clarify why there is so much variation in how validity indicis are reported in reference to the ultrasonography detection of RCTs in the shoulder. After all, is there any aspect of a diagnostic test that impacts its usefulness more than the ability of that test to accurately detect the lesion of interest? Cost, availability, patient acceptance, feasibility, and other factors are certainly important, but at the end of the day, if the test suffers from poor intrinsic measurement capabilities such as reliability and validity, then the utility of that test becomes compromised.
A shoulder is examined for various reasons such as pain, weakness, deformity, swelling, and/or motion deficits. Sometimes only one of these is present, other times all are present. The reason why clinicians do not rely solely on images to establish a diagnosis is that shoulder pain, weakness, or range of motion (ROM) deficits are not attributes that can necessarily be captured in a picture. We cannot see pain nor do we have a universally accepted and agreed upon method to objectively measure pain.