"Modes of Failure" of Cemented Stem-type Femoral Components
Gruen, McNeice and Amstutz
CORR 1979
Seven Gruen zones
1 - proximal lateral 1/3
2 - central lateral 1/3
3 - distal lateral 1/3
4 - tip
5 - distal medial 1/3
6 - central medial 1/3
7 - proximal medial 1/3
Modes of Failure
I. Pistoning
Ia. stem pistons in cement (punch-out crack)
Ib. cement pistons in bone (halo)
II. Medial Midstem Pivot - medial migration of proximal stem, lateral migration of tip
III. Calcar Pivot - medial-lateral toggle of tip (windshield)
IV. Cantilever Bending - loss of proximal support, tip is fixed