Abstract
The S-ROM stem is distally circular canal filling with thin sharp flutes which engage the endosteal cortex. The rotational stability produced by this is 37 Nm, which exceeds the service loads on the hip of 22 Nm. The distal canal fill prevents varus and valgus displacement. The porous-coated proximal sleeve provides resistance to vertical sink and also excludes the distal stem from the effective joint space.
The primary stem is straight and the long stem is bowed with a 15 degrees anteversion twist proximally. The neck comes in lengths from 30 to 46mm with varying offset. The sleeves come in variable size and geometry.
The stem choice in revision surgery is based on the Scoot Diamond Classification. Type 1 (this is going to be easy) is a primary stem. Type 2 (this is going to be difficult) implies diaphyseal bone loss and will require a long stem. Type 3 (Oh My God), implies more than 70mm of completely missing proximal femur and will require a structural allograft cemented to the sleeve.
Results
The follow-up is from 2 to 22 years. There were 119 primary stems. Revisions for aseptic loosening were zero. One stem was removed for late sepsis at nine years.
There were 262 long stem cases. Stem revision for aseptic loosening occurred in nine cases (3.7%). Four became loose because of inappropriate and obsolete techniques of allografting, one for non-union of a subtrochanteric osteotomy and four for failure of ingrowth into the sleeve. Four were revised for late sepsis. Structural allografts comprised seven cases. Three were revised at years 7, 11 and 16.
Conclusion
The revision rate for aseptic loosening in hip revision cases is acceptably low.
Other issues such as late polyethylene wear and dislocation continue to decrease.
