Zweymüller Stem

The Zweymüller-type stem is a cementless straight stem with a rectangular cross-section and double taper design that was developed by Zweymüller et al. in 1979. The initial design had a collar on the proximal medial side of the stem. However, the collar was eliminated in 1983 when the design was changed because it caused insufficient bone contact at the distal part of the stem and interfered with the observation of the femoral bone marrow cavity during stem insertion and bone grafting into the marrow cavity. The distal portion of the stem, which had a groove structure on the inner and outer sides, was changed to a central ridge structure in 1985, and the ridge structure was later eliminated. The material of the stem in the initial design was a Ti6Al4 V alloy with a surface roughness of 1 μm by fine blasting; however, in 1985, the material was changed to a Ti6Al7Nb alloy with a surface roughness of 4–6 μm that was achieved using grit blasting to improve bone growth. Alloclassic (Zimmer Biomet) was improved in 1986 with a thinner neck and an offset stem; however, the basic concept and design were inherited from the initial design and are still currently being sold and used.