Beta-tricalcium phosphate plugs for press-fit fixation in ACL reconstruction--a mechanical analysis in bovine bone.
BACKGROUND
The goal of this study was to test fixation properties of microporous pure beta-tricalcium phosphate (TCP) plugs (porosity 40%) for press-fit fixation of the ACL graft using patellar tendons with and without bone blocks. We set out to establish whether it is possible, in this way, to obtain results comparable with those of interference screw fixation of bone-tendon-bone (BTB) grafts in terms of cyclic loading and load-to-failure.


METHODS
In a bovine model 30 ACL grafts were fixed in tibial drill holes, divided into three groups: 10 BTB grafts fixed with TCP press-fit plugs (7x25 mm), 10 pure patellar tendon grafts with TCP press-fit plugs (7x25 mm), and 10 BTB grafts with metal interference screws (7x25 mm). All grafts were tested by cyclic loading (50-200 N) and loaded until failure in a tensiometer.


RESULTS
Under cyclic loading one interference screw fixation failed. None of the TCP plug fixations failed. After 1500 cycles the displacement of the graft in the drill hole for BTB fixed with screws was 3.6+/-7.8 mm, for BTB/TCP plugs 1.6+/-3.4 mm, and for the pure tendon/TCP grafts 1.4+/-0.4 mm. Regarding cyclic loading the pure tendon/TCP system was significantly superior to BTB (p=0.007). The load-to-failure for the BTB/interference screw group was 908+/-539 N with a stiffness of 94+/-36 N/mm, 936+/-245 N for the BTB/TCP cylinder group with a stiffness of 98+/-12 N/mm, and 673+/-159 N for the pure tendon/TCP group with a stiffness of 117+/-9 N/mm. In terms of pull-out load the BTB/TCP system was significantly better than the pure tendon/TCP group (p=0.011). However, pure tendon/TCP grafts achieved significantly greater stiffness (p=0.002) than the BTB system.


CONCLUSIONS
Press-fit fixation with microporous pure beta-TCP plugs of BTB grafts or patellar tendon grafts without bone blocks for ACL reconstruction leads to primary stability comparable with that achieved by fixation with metal interference screws in case of BTB grafts.
Mayr
Hermann O
HO
Department of Orthopedic Surgery, OCM Clinic, Steinerstrasse 6, 81369 Munich, and Clinic for Orthopedic Surgery, Martin Luther University Halle-Wittenberg, Magdeburger Strasse 22, 06097 Halle (Saale), Germany. hermann.mayr@ocm-muenchen.de
Hube
Robert
R
Bernstein
Anke
A
Seibt
Alexander B
AB
Hein
Werner
W
von Eisenhart-Rothe
Ruediger
R
D000818:Animals; D016118:Anterior Cruciate Ligament / Q000601:surgery*; D001672:Biocompatible Materials / Q000494:pharmacology*; D001863:Bone Screws; D050376:Bone-Patellar Tendon-Bone Grafting; D002130:Calcium Phosphates / Q000494:pharmacology*; D002417:Cattle; D008422:Materials Testing; D023421:Models, Animal; D016474:Weight-Bearing
D001672:Biocompatible Materials; D002130:Calcium Phosphates; C485817:beta-tricalcium phosphate