Microporous pure beta-tricalcium phosphate implants for press-fit fixation of anterior cruciate ligament grafts: strength and healing in a sheep model.
OBJECTIVE
A sheep study was conducted to test a press-fit technique using microporous pure beta-tricalcium phosphate (beta-TCP) dowels for fixation of the anterior cruciate ligament (ACL) graft.


METHODS
Microporous (5 mum) cylindrical plugs of beta-TCP (diameter, 7 mm; length, 25 mm) with interconnecting pores were used. The material featured a novel configuration of structure and surface geometry. Implants were tested by use of press-fit fixation of ACL grafts with and without bone blocks in 42 sheep over a period of 24 weeks. Biomechanical, radiologic, histologic, and immunohistochemical evaluations were performed.


RESULTS
In load-to-failure tests at 6, 12, and 24 weeks after surgery, the intra-articular graft always failed, not the fixation. Grafts showed bony fixation in the tunnel at 6 weeks and primary healing at the junction of the tunnel and joint after 24 weeks. Tricalcium phosphate was resorbed and simultaneously replaced by bone. Remodeling was still incomplete at 24 weeks.


CONCLUSIONS
In the sheep model microporous beta-TCP implants used with press-fit fixation of ACL grafts permit early functional rehabilitation. After 6 weeks, the graft is fixed by woven bone or bony integration. Implanted microporous tricalcium phosphate is resorbed and replaced by bone.


CONCLUSIONS
In a sheep model we showed that primary healing of ACL grafts with resorption and bony replacement of the fixating implant can be achieved by means of press-fit fixation with pure beta-TCP.
Mayr
Hermann O
HO
Clinic for Orthopedic Surgery, Martin Luther University, Halle, Germany. hermann.mayr.ocm@gmx.de
Dietrich
Markwart
M
Fraedrich
Franz
F
Hube
Robert
R
Nerlich
Andreas
A
von Eisenhart-Rothe
Rüdiger
R
Hein
Werner
W
Bernstein
Anke
A
D000818:Animals; D016118:Anterior Cruciate Ligament / Q000601:surgery*; D001696:Biomechanical Phenomena; D001863:Bone Screws; D002102:Cadaver; D006801:Humans; D007719:Knee Joint / Q000601:surgery; D023421:Models, Animal; D019736:Prostheses and Implants; D019651:Plastic Surgery Procedures / Q000379:methods*; D012756:Sheep; D013977:Tibia / Q000601:surgery*