Shoulder injuries in athletes

Glenohumeral joint instability is extremely common yet the defi nition and classifi cation of instability remains unclear. In order to fi nd the best ways to treat instability, the condition must be clearly defi ned and classifi ed. This is particularly important so that treatment studies can be compared or combined, which can only be done if the patient population under study is the same. The purpose of this paper was to review the problems with historical methods of defi ning and classifying instability and to introduce the FEDS system of classifying instability, which was developed to have content validity and found to have high interobserver and intraobserver agreement. Glenohumeral joint instability is extremely common. With regard to primary anterior shoulder dislocations, the incidence is between 8.2 and 23.9 per 100 000 person-years, with an estimated prevalence of 1.7%.1–3 Whereas these estimates seem high, they actually underestimate the true nature of instability, as they do not include subluxation events or instability in other directions. Despite the widespread nature of glenohumeral joint instability, the defi nition of this condition is not clear and there is no consensus on how this disorder should be classifi ed. Historically, the medical literature regarding instability has a number of fl aws. First, most studies in the literature are procedure-based and not condition-based. An example is the landmark 1980 paper by Neer and Foster4 on ‘multidirectional’ instability. In that study, the authors included patients with different features of instability—yet the patients had in common the same operation, an inferior capsular shift (table 1). When a paper is procedure based it may include a heterogenic population that will produce confusion both regarding the defi nition of the condition and whether the procedure described would be helpful for a particular patient in your offi ce. Instead, papers should be condition-based, in which a population of patients with a specifi c, well-defi ned constellation of features is collected and two treatments are compared. As a result of these historical problems, we do not have clear defi nitions for glenohumeral joint instability in the literature and papers tend to use a pot-pouri of descriptive terms (voluntary, traumatic unidirectional Bankart lesion treated with surgery, unidirectional, multidirectional, bidirectional, traumatic, atraumatic, microtraumatic, etc). This problem leads to heterogeneity in the literature making comparisons of different treatments diffi cult and meta-analyses nearly impossible. This confusion has been highlighted by McFarland et al,5 who compared four different classifi cation systems for patients with instability and found great variation, particularly with regard to multidirectional instability, leading the editors of the Journal of Bone and Joint Surgery to opine that the article by McFarland et al5 was a “...provocative call to action”, and “Until the criteria for diagnosis are clearly defi ned, investigators will be unable to contribute in a compelling way to understand the condition since they cannot know whether studies are comparing ‘apples and oranges’.”6 This confusion in how instability is defi ned was also demonstrated by Chahal et al,7 who found that physicians had poor agreement when asked to classify clinical scenarios of glenohumeral joint instability. These works provide evidence that we need better ways of defi ning and classifying glenohumeral joint instability. DEFINITIONS OF INSTABILITY Before a disorder is classifi ed, it must be defi ned very clearly. For example, does a pitcher with a dead-arm feeling when throwing have ‘instability’? Does a patient with a posterior labral tear with pain, but not sensation of the joint slipping or a feeling of looseness—have ‘instability’? Historically, many experts have offered different defi nitions for this common malady. In 1992, many of the North American shoulder experts met in Vail, Colorado, to help defi ne and determine the state of the art for many shoulder conditions.8 Interestingly, these experts offered a variety of defi nitions for glenohumeral joint instability (fi gure 1). In light of these different perspectives, how can a consensus be reached? The two common themes in these defi nitions are symptoms and translation. We know that many patients may have symptoms (especially pain) without instability. We also know that laxity exists in many Table 1 Features of Neer and Foster’s multidirectional instability population Feature No with symptom (N=40) for entire population