Relationship Between Clinical Scapular Assessment and Scapula Resting Position, Shoulder Strength, and Baseball Pitching Kinematics and Kinetics

Abstract

Background: Scapular assessment is important in examining overhead athletes, but there is inconsistency in scapular clinical assessment and its relation to pathology. Purpose: To determine the relationship between clinical scapular assessment and biomechanical scapula resting position, shoulder strength, and pitching shoulder kinematics and kinetics. Study Design: Descriptive laboratory study. Methods: Two clinicians performed scapular assessments and graded the scapula as presence or absence of scapular dyskinesis. Shoulder external rotation (ER) and internal rotation (IR) strength were collected. The 3-dimensional biomechanics of the scapula resting position (upward/downward rotation, IR/ER, and anterior/posterior tilt) were assessed while participants stood at rest, and pitching kinematics (maximum shoulder ER, shoulder abduction, shoulder horizontal abduction, shoulder rotation velocity) and kinetics (maximum shoulder distraction force) were assessed when participants pitched off the portable pitching mound that was engineered to meet major league specifications. Results: A total of 33 high school baseball pitchers (age, 16.3 ± 1.2 years; height, 184.0 ± 6.9 cm; weight, 76.8 ± 20.8 kg; hand dominance: left, 9 [27%]; right, 24 [73%]; pitch velocity, 34.7 ± 2.3 m/s) participated in this study. Of them, 15 participants had scapular dyskinesis, and 18 had normal scapulothoracic rhythm. No differences were observed for upward/downward rotation or anterior/posterior tilt, shoulder ER, shoulder abduction, or shoulder distraction force, based on the presence of scapular dyskinesis. Pitchers with scapular dyskinesis demonstrated significantly greater scapular resting IR position (effect size [ES], 0.80; 95% CI, 0.06 to 1.54; P = .020), greater nondominant shoulder ER to IR strength ratio (ES, 0.49; 95% CI, –0.02 to 1.00; P = .018), and decreased shoulder rotation velocity (ES, 14.66; 95% CI: 12.06 to 17.25; P = .016). Pitchers with greater anterior tilt demonstrated greater shoulder rotation velocity ( r = –0.48; P = .006). Conclusion: Pitchers with scapular dyskinesis had greater scapular IR, greater nondominant shoulder ER to IR strength ratio, and reduced shoulder rotation velocity. Clinical Relevance: Scapular assessment may be more influenced by differential IR than upward rotation or anterior tilt. Scapular dyskinesis has no competitive performance advantage among amateur athletes. Greater understanding is needed to decipher the critical threshold between beneficial and maladaptive scapular movement patterns.