Ultrasound-detected pathologies cluster into groups with different clinical outcomes: data from 3000 community referrals for shoulder pain

This study has demonstrated, for the first time to our knowledge, clustering of ultrasound pathologies into four groups. These groups reported different treatments and to some extent had different age- and sex-adjusted outcomes at 2 years; however, owing to the low questionnaire completion rate, the longitudinal results need to be interpreted with caution.

Currently, there is limited evidence-based guidance on the role of imaging in the shoulder pain care pathway, and international guidance pre-dates the wide availability of ultrasound [23]. Though guidance for the diagnosis and management of many common painful musculoskeletal problems generally does not require imaging as part of routine care, the uncertainty in clinical evaluation, poor patient outcomes and increasing use of ultrasound support critical evaluation of the usefulness of a pathology-based classification. Researchers in a recent pragmatic randomised trial reported no evidence of difference in patient-perceived recovery between those with ultrasound-tailored treatment and usual-care groups [24]. Ultrasound-guided treatment was targeted at individual pathologies, and it would be interesting to see if outcomes would differ using our novel pathology-based classification.

The clinical validity of the pathology groups identified in this study require further evaluation in future studies. Conceivably, patients with just one pathology may respond differently to treatment compared with patients in whom the same pathology co-occurs with other pathologies. Although we did not attempt to examine the efficacy of different treatments, different patterns of treatment were reported. Group 1 was most likely to receive steroid injections. Steroid treatment may help with subacromial bursitis in the short term [25], which may explain the treatment in this group. Groups 1 and 2 may represent a spectrum; members of group 2 are older, and if we were to follow patients similar to those in group 1 over time, their patterns of shoulder pathology may eventually resemble those of group 2. Group 3 was the oldest group, confirming previous studies which have shown that RC tears increase with age [26]. Members of group 3 were less likely to receive steroid injections, even if they had concurrent bursitis, and they were more likely to undergo surgery. Steroid injections may impede tendon repair, and RC tears offer a surgical target, which may explain the variation in treatment. Group 3 also had the highest level of current pain and functional impairment. Surgical repair techniques of RC tears vary, and surgery has been shown to have conflicting results in improving outcomes in patients with shoulder pain [27–29]. Our data suggest that those who had surgery reported lower levels of pain and functional impairment. Group 4 was the youngest group, and a smaller proportion of these patients reported having surgery, because fewer had detectable pathologies present. Group 4 also had the lowest levels of pain and functional disability of all the groups.

Many (42%) in group 4 had no pathology; some of these patients may have improved at the time of their ultrasound scan. Another explanation is that other pathologies were present that ultrasound could not detect. Ultrasound is as sensitive and specific as magnetic resonance imaging (MRI) in detecting RC disorders [30], but further work is required to understand its sensitivity and specificity in detecting other pathologies, such as calcific tendinopathy. Furthermore, pathologies such as labral tears require MRI for identification [31, 32]. In addition, imaging-detected pathologies may not correlate with clinical findings. In the present study, 16% of patients without detectable pathology received steroid injections at the time of their scan; many reports documented that this was after discussion with the patient, and in some cases because clinical impingement was suspected even though this was not confirmed by the scan. A further explanation could be that the pain may be referred from other regions, such as the neck. The cause of chronic pain is multifactorial, and other features apart from imaging pathology play a role in characterising pain. Psychological factors such as fear avoidance, depression and poor quality of life can result in worse pain, function and perceived recovery outcomes [33, 34]. Ultrasound-detected pathologies have previously been reported in asymptomatic individuals, and further work is required to understand which factors result in the development and progression of symptoms in these individuals [14, 26, 27, 35].

Although we looked at associations between baseline pathologies and outcomes, the absence of baseline clinical data means we could not fully evaluate the predictive value of ultrasound. Previous attempts at identifying predictors of outcomes in people with shoulder pain have been made [36–40]. Pain characteristics such as worse baseline pain, duration of pain, concomitant psychological complaints, other concomitant musculoskeletal problems and repetitive shoulder action resulted in worse outcomes [37, 39–41]. Existing prognostic models to improve shoulder pain management have yet to be validated and assessed for clinical utility [39, 42]. There are very limited studies evaluating the prognostic role of ultrasound in shoulder pain: One suggested that the absence of subacromial bursa pathology may be a predictor of excellent outcomes at 3 weeks [36].

This study has a number of limitations. This study was undertaken in a single centre, though the sample size was large; the demographics of included patients seem similar to those of other large community cohorts [4, 43]. There was no control group, limiting our interpretation of pathologies and symptoms. Our local care pathway recommends that patients over the age of 65 years with shoulder pain undergo radiography of their shoulder, which may result in a channelling bias because patients with radiographic osteoarthritis may not undergo ultrasonography. In this study, local recommendations suggested that patients were referred for an ultrasound scan if they had moderate-severe pain and were not responding to physiotherapy, which could have led to selection bias in our cohort. However, it would seem that this group would likely be typical of patients with shoulder pain requiring investigation in potential future care pathways. Although the radiographers in this study followed a standardised method of performing ultrasonography of shoulders [44], standardised reporting of all pathologies was not routine, so if pathology was not documented, it was assumed absent. It is possible that some pathologies may not have been reported, especially if lesions that are considered more severe or clinically relevant are primarily reported. Group 3 had the highest level of glenohumeral osteoarthritis but a lower frequency of ACJ degeneration; the latter finding may be a result of non-standardised reporting, although it may also be an artefact introduced as a result of the groupings formed on the basis of LCA. A prospective study using standardised criteria for the different diagnostic labels is needed. This was a retrospective study, so we were unable to explore inter-reader reliability, especially in partial RC tears, where authors of a recent review showed that ultrasound has some difficulty in diagnosing this pathology [30]. Previous work has shown that, for most shoulder pathologies, the inter-rater reliability for two of the present sonographers was acceptable [17]. Impingement was assumed in all patients with complete RC tears. The patient questionnaire was retrospective, raising the possibility of recall bias. Only 33% completed the questionnaires; therefore, there is potential for selection bias. However, our work suggests that completers and non-completers were very similar in demographic characteristics and pathologic findings. Importantly, though we recorded symptoms around 2 years after an initial scan, we were unable to determine initial symptoms and subsequent changes. The prognostic value of a pathology-based classification needs to be established before consequent treatment pathways can be explored.