title: Primary rotational stability of cylindrical and conical revision hip stems as a function of femoral bone defects: an in vitro comparison.
abstract: Bone stock losses in cementless femoral stem revisions compromise a stable fixation. The surgeon has to rely on his wealth of experience in deciding which stem shape to use. The aim of our study was to compare the primary rotational stability of cylindrical and conical revision hip stems subjected to femoral defects. Four current prostheses (two cylindrical, two conical) were implanted into four synthetic femora. Micro-motion was measured under torque application and femoral neck osteotomy and segmental AAOS Type I and III defects were simulated. The relative movements of all prostheses were significantly influenced by the extent of bone loss (p<0.01). Major differences were seen in fixation behavior (p<0.01). The main fixation area of conical stems is within the distal femoral isthmus, whereas cylindrical implants are dependent on proximal bone stock. In our study, cylindrical stems are advantageous for minor defects because they provide a proximal fixation. In cases of extensive substance loss, the conical implants showed lesser relative movements. These findings should be taken into account for clinical decisions.
authors.affiliation: Laboratory of Biomechanics and Implant Research, Department of Orthopaedic Surgery, University of Heidelberg, Schlierbacher Landstrasse 200a, 69118 Heidelberg, Germany.
authors.forename: Eike
authors.initials: E
authors.lastname: Jakubowitz
authors.forename: Rudi G
authors.initials: RG
authors.lastname: Bitsch
authors.forename: Christian
authors.initials: C
authors.lastname: Heisel
authors.forename: Christoph
authors.initials: C
authors.lastname: Lee
authors.forename: Jan P
authors.initials: JP
authors.lastname: Kretzer
authors.forename: Marc N
authors.initials: MN
authors.lastname: Thomsen
mesh_terms: D019544:Equipment Failure Analysis / Q000379:methods*; D005265:Femoral Neck Fractures / Q000503:physiopathology* / Q000601:surgery*; D005270:Femur Head / Q000503:physiopathology* / Q000601:surgery*; D006622:Hip Prosthesis; D006801:Humans; D009038:Motion; D011474:Prosthesis Design; D012399:Rotation