The anatomic basis for the concept of lateralized femoral stems - A frontal plane radiographic study of the proximal femur

We determined the range of sizes for a system of monoblock femoral prosthes es that would provide adequate (a term defined in the text) fill in the fro ntal plane and restore femoral offset and leg length. We performed an anato mic study, based on measurements in 200 anteroposterior pelvic radiographs. If diaphyseal filling implants are to be used, 9 sizes are sufficient to o btain excellent canal filling and restoration of femoral offset in >80% of cases, assuming that the level of neck osteotomy can vary over a l-cn range . When using metaphyseal filling implants, only a limited adjustment can be obtained from the level of neck osteotomy. A system limited to 8 sizes app roximates the anatomy of the femoral canal with satisfactory precision in 7 3% of cases. If such a system is provided with only a single neck shaft ang le for each stem size, it does not allow restoration of the biomechanical c enter of the hip in >67% of cases. A system of 8 sizes of 1 neck/shaft angl e and a 22-mm modular head restores the anatomy in only 49% of cases. Appro ximating the frontal anatomy of 85% of femora with an implant filling the m etaphysis requires at least 15 sizes distributed in 3 metaphyseal configura tions, each supplied with 2 different neck shaft angles.