What is the cause of secondary impingement in adolescent (high school) basketball players?

Cause of Secondary Impingement in High School Basketball Players

Secondary impingement in high school basketball players occurs when the humeral head fails to maintain proper centering in the glenoid fossa during overhead shooting and passing motions due to rotator cuff weakness combined with ligamentous laxity—not from structural anatomic abnormalities. 1, 2

Primary Biomechanical Mechanisms

The fundamental cause differs completely from adult primary impingement and involves a cascade of neuromuscular dysfunction rather than bony pathology:

Rotator Cuff Dysfunction

• Weakness in the rotator cuff muscles, particularly the external rotators and supraspinatus, fails to maintain proper humeral head positioning during the repetitive overhead movements required in basketball. 1, 2
• The rotator cuff undergoes repetitive eccentric stress during the acceleration and deceleration phases of shooting and passing motions, leading to progressive fatigue and inability to stabilize the glenohumeral joint. 2, 3

Scapular Dyskinesis

• Poor coordination of scapular movements during arm elevation is a primary contributor, with the scapula failing to properly rotate upward and tilt posteriorly during overhead movements. 2, 3
• This abnormal scapular positioning creates a functional narrowing of the subacromial space even without anatomic abnormalities. 2

Muscular Imbalance

• Weakened posterior shoulder musculature combined with overdeveloped anterior musculature creates pathologic biomechanics during the repetitive shooting motion. 2, 3
• This imbalance leads to abnormal humeral head translation and increased stress on the supraspinatus and external rotators during arm deceleration. 2, 3

Adolescent-Specific Vulnerabilities

High school athletes have unique anatomic factors that predispose them to secondary impingement:

Ligamentous Laxity

• Adolescents produce significantly more type III collagen in ligaments and tendons compared to adults, creating inherent tissue laxity that contributes to glenohumeral instability. 2
• This physiologic laxity, when combined with rotator cuff weakness, allows excessive humeral head translation during overhead activities. 1, 2

Open Growth Plates

• Epiphyseal plates remain open until late teens (proximal humerus: 17-18 years; glenoid: 16-18 years) and are weaker than surrounding joint capsules and ligaments, making the physis vulnerable to repetitive overhead stress. 2

Sport-Specific Contributing Factors

Basketball creates a perfect storm of risk factors for secondary impingement:

Training Volume

• Weekly training time exceeding 16 hours per week among 14- to 18-year-old youth has been correlated with injury risk. 4, 1
• The injury rate in basketball is greater in competition than practice, and tournaments with multiple games per day provide limited recovery time. 4, 1

Movement Patterns

• The repetitive overhead shooting motion subjects the rotator cuff to high eccentric loads during the acceleration phase, followed by posterior shoulder muscle fatigue during deceleration. 2, 3
• Basketball requires frequent overhead passing and shooting with inadequate rest between movements, leading to progressive neuromuscular fatigue. 1, 2

Critical Distinction from Primary Impingement

Secondary impingement is fundamentally different from the primary impingement seen in adults, which results from structural anatomic abnormalities causing compression of the rotator cuff against the anterolateral aspect of the acromion. 1, 3, 5

In contrast, secondary impingement in adolescent basketball players represents an instability pattern where the dynamic stabilizers (rotator cuff and scapular muscles) fail to maintain proper joint mechanics. 1, 2, 6

Progressive Pathophysiology

If the underlying causes remain unaddressed:

• Untreated impingement leads to tendon degeneration with potential progression to partial or full-thickness rotator cuff tears, resulting in permanent muscle atrophy and fatty infiltration over 5-10 years. 1, 2
• Undersurface (articular-side) rotator cuff tears from overuse become more common, resulting from atraumatic microinstability and weak rotator cuff muscles rather than degenerative changes. 2

Common Pitfall to Avoid

The most critical error is attributing shoulder pain in adolescent basketball players to structural/anatomic causes (as seen in adults) rather than recognizing the neuromuscular dysfunction and instability pattern that defines secondary impingement in this population. 1, 2, 5