Intramedullary fixation with screwed, conical stems--unsolicited results from animal experiments.
For the purpose of studying bone remodeling around prostheses, a segmental replacement for the goat tibia was designed, using a conical, screw-threaded, hydroxyapatite-coated stem for fixation. Eight goats were provided with the implant, seven of which loosened within 10 days post-operatively, displaying progressive radiolucency and gross rotational motion.  The eighth one also loosened radiographically, but developed a stabilizing callus bridge to prevent motion.  A second design of similar shape and coating, but lacking the screw threads, was designed and also applied in eight animals.  In this case, no loosening occurred in the first 6 weeks post-operatively.  It is concluded that the application of screwed intramedullary stems for prosthetic fixation is not a viable concept, because the threads prevent the stem from subsiding and restabilizing when minor initial interface stress-relaxation and remodeling has occurred.
Institute of Orthopaedics, University of Nijmegen, The Netherlands.
P J
PJ
van Loon
H
H
Weinans
R
R
Huiskes
K
K
de Groot
T J
TJ
Slooff
D000818:Animals; D016723:Bone Remodeling; D001863:Bone Screws; D005594:Fracture Fixation, Intramedullary / Q000379:methods; D006041:Goats; D008422:Materials Testing; D011474:Prosthesis Design; D011475:Prosthesis Failure; D011859:Radiography; D013314:Stress, Mechanical; D013977:Tibia / Q000000981:diagnostic imaging / Q000601:surgery*