This narrative review examines glenohumeral radial mismatch, the difference in radii of curvature between the humeral head and glenoid components in anatomic total shoulder arthroplasty. It synthesizes native anatomy, biomechanical models, and clinical outcomes to define how much mismatch optimizes kinematics without compromising the glenoid.
When you set humeral head and glenoid sizing in an anatomic TSA, you are choosing radial mismatch, and the target is roughly 4 to 8 mm. The mental model: too conforming, and the humeral head translates until it edge-loads the glenoid rim, driving delamination. Too little conformity, and contact pressures and micromotion climb, threatening the cement-bone interface.
Understand the rocking-horse phenomenon. Eccentric loading levers force through the peg or keel and lifts the opposite side of the component, and this is worsened by rotator cuff deficiency and glenoid retroversion beyond 10 degrees.
A practical pitfall to avoid: do not manipulate mismatch to compensate for a poorly balanced or malpositioned glenoid, since conformity contributes only about 3% to dislocation resistance. Also remember that radiolucent lines rise with mismatch but have not been shown to change Constant scores or revision rates, so lucency alone does not equal clinical failure.
This narrative review examines glenohumeral radial mismatch, the difference in radii of curvature between the humeral head and glenoid components in anatomic total shoulder arthroplasty. It synthesizes native anatomy, biomechanical models, and clinical outcomes to define how much mismatch optimizes kinematics without compromising the glenoid.
When you set humeral head and glenoid sizing in an anatomic TSA, you are choosing radial mismatch, and the target is roughly 4 to 8 mm. The mental model: too conforming, and the humeral head translates until it edge-loads the glenoid rim, driving delamination. Too little conformity, and contact pressures and micromotion climb, threatening the cement-bone interface.
Understand the rocking-horse phenomenon. Eccentric loading levers force through the peg or keel and lifts the opposite side of the component, and this is worsened by rotator cuff deficiency and glenoid retroversion beyond 10 degrees.
A practical pitfall to avoid: do not manipulate mismatch to compensate for a poorly balanced or malpositioned glenoid, since conformity contributes only about 3% to dislocation resistance. Also remember that radiolucent lines rise with mismatch but have not been shown to change Constant scores or revision rates, so lucency alone does not equal clinical failure.