The Journal of Bone and Joint Surgery, Vol 68, Issue 1 118-126, Copyright © 1986 by Journal of Bone and Joint Surgery, Inc
The effect of load alteration on the biological and biomechanical performance of a titanium fiber-metal segmental prosthesis
DA Heck, I Nakajima, PJ Kelly and EY Chao
The effect of overloading and underloading on tissue ingrowth into the
porous-coated titanium segmental prosthesis was studied in a canine femoral
model. The prosthesis has modular components that are connected by a
conical coupling joint. One of the dog's hind legs was immobilized and
suspended for three weeks using an external fixator to minimize loading and
prevent weight-bearing, while the contralateral leg was allowed to bear
weight freely, simulating an overloading situation. Five dogs reached the
final study period of twelve weeks without complication. There were no
significant differences between the non-weight-bearing and weight-bearing
sides on radiographic assessments. However, the immobilized side had
significantly higher stem-push-out strength and energy to failure. Bone
ingrowth was variable, and a fibrous layer was commonly demonstrated at the
prosthetic stem-bone interface. The orientation of the fibrous tissue was
more organized, in a penetrating pattern, on the immobilized side. The mean
concentration of titanium was insignificant in all tissue examined. Reduced
implant loading for the porous-coated segmental bone prosthesis during the
initial period of implantation was found to be beneficial as compared with
an overloading situation in achieving intramedullary fixation.