The Journal of Bone and Joint Surgery, Vol 75, Issue 7 976-987, Copyright © 1993 by Journal of Bone and Joint Surgery, Inc
Extramedullary porous coating to prevent diaphyseal osteolysis and radiolucent lines around proximal tibial replacements. A preliminary report
WG Ward, KS Johnston, FJ Dorey and JJ Eckardt
Division of Orthopaedic Surgery, University of California, Los Angeles School of Medicine 90024-6902.
Nineteen patients who had a primary malignant bone tumor of the proximal
end of the tibia were managed with wide resection and implantation of a
tibial endoprosthesis with cement, combined with a rotating-hinge knee
replacement. In the first ten patients, a ring of porous coating was
applied to the part of the tibial replacement that was just proximal to the
intramedullary portion of the stem, to encourage ingrowth of bridging bone.
No growth of bone into these porous rings occurred, and the rings were not
applied to the next nine endoprostheses. During the subsequent follow-up
period, progressive osteolysis (resorption of more than two millimeters of
the proximal end of the remaining tibial cortex) developed in only one
patient (who had a deep infection) in the group of ten patients who had a
porous ring, compared with five of the nine patients who did not have a
porous ring but in whom osteolysis developed. This difference was
significant (p < 0.001). In addition, the tibial osteolysis was
associated with the subsequent development of progressive periprosthetic
radiolucent lines at the bone-cement interfaces (p = 0.001). We postulated
that, in the patients who had an extramedullary porous ring, the
periprosthetic fibrous capsule that formed around the extramedullary
portion of all the implants became firmly adherent to the ring, thereby
sealing off the part of the capsule that was distal to the ring. The
particulate wear debris that was contained within the articular portion of
the capsule could not reach the distal tibial bone surrounding the
prosthetic stem, and debris-incited osteolysis, which leads to loosening,
did not develop. If this mechanism is confirmed, it could have important
implications for the design of implants that are used in joint replacement.
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