23.6 Humeral Head

• The humeral head is part of a “sphere” which is variable

• Articular surface covers 25-30%

• Thus, there is limited intrinsic stability

• Intrinsic stability also depends on the glenoid and humeral cartilage and their congruency (ie the conformance of convect to concave surface)

Kempf 1999[@Kempf1999]

• Congruency

• If the radii are the same, congruency ratio is 1

  • Contact surface is maximized (9% of patience)

  • Stresses are limited

• If the humeral head radius of curvature is less than the glenoid, congruency ratio is less than 1

  • Present in 90% of patience

  • Favors mobility over stabilty

• Humeral head with a larger radius is rate

  • May be selected for hemi-arthroplasty for stability

---