Is it relevant to distinguish scapulothoracic abnormal motion (STAM) type in professional overhead athletes?

Background: Scapular dyskinesis, further characterized within the broader concept of scapulothoracic abnormal motion (STAM), is common in both symptomatic and asymptomatic overhead athletes. While STAM type 3 (winging) is a distinct pathological entity, types 1 and 2 remain less well defined and may represent sport-related adaptations rather than disease. The clinical relevance, prevalence, and sport-specific patterns of these conditions are still unclear. The objectives of this study were to: (1) evaluate the prevalence of STAM types 1 and 2 in the dominant and non-dominant shoulders of professional overhead athletes compared with a control population; (2) identify clinical consequences associated with STAM; (3) assess the impact of different overhead sports on STAM; and (4) explore the association between STAM and other shoulder conditions, such as glenohumeral internal rotation deficit (GIRD) and hyperlaxity. Methods: 45 professional in season overhead athletes (15 water polo, 16 basketball, and 14 CrossFit) were included in the study group. Control group consists in 21 volunteers with no or minimal shoulder involvement in sport activity. STAM type was diagnosed using clinical examination and the shoulder flexion resistance test. The shoulder passive range of movement, pain, hyperlaxity, GIRD, American Shoulder and Elbow Surgeons (ASES) score, and the Kerlan-Jobe score were also recorded. A statistical analysis was run to identify any differences in STAM between study and control groups, the clinical role of STAM types, any clinical factor associated to STAM, and the differences between the 3 selected types of overhead sports. Results: STAM type 1 was found more frequent in the dominant shoulder of athletes than in the control group (q = 0.045). No specific factor associated with scapular dyskinesis was identified in the univariate or multivariate regression analysis. However, STAM type 2 was associated with general joint hyperlaxity and the Beighton score (q = 0.04). A diagnosis of STAM type 1 or type 2 was not associated with higher pain scores, a higher GIRD rate, or lower Kerlan-Jobe or ASES scores. Conclusion: STAM type 1 was more common in the dominant shoulder of professional overhead athletes. In contrast, STAM type 2 was observed similarly in the dominant and non-dominant shoulders in both the study and control groups and was associated with generalized joint hyperlaxity. STAM types 1 and 2 were not associated with pain, GIRD, ASES score, or Kerlan-Jobe score in this cohort. These findings support epidemiologic differences between STAM subtypes, but do not establish causal mechanisms, distinct biological etiologies, or definite clinical relevance.