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Primary stability of bone-patellar tendon-bone graft fixation with biodegradable pins
Andre Weimann1, Thore Zantop, Markus Rümmler
1Department of Orthopaedic Surgery, Christian-Albrechts-University Kiel, Kiel, Germany.
Purpose:
We evaluated the initial bone-patellar tendon-bone (BPTB) graft fixation strength of biodegradable pins compared with interference screws in anterior cruciate ligament reconstruction using bovine knees.
Type Of Study:
Biomechanical in vitro study.
Methods:
Ten BPTB grafts from human donors fixed with 2 biodegradable 2.7-mm pins (Rigid Fix; Ethicon, Mitek Division, Norderstedt, Germany) crossing the bone block perpendicular and 10 BPTB grafts fixed with conventional biodegradable interference screws (Absolute Absorbable Interference Screw; Innovasive Devices, Marlborough, MA) underwent ultimate single-cycle failure loading at a rate of 200 mm/min. The grafts were fixed to bovine tibia to simulate young human femoral bone density. Failure mode, displacement before failure, and ultimate failure load were tested with a testing machine. The pullout force was in line with the bone tunnel to simulate a worst case scenario.
Results:
The failure mode for cross pins was either fracture of the bone block (5 specimens) or fracture of the articular pin (5 specimens). The failure mode for interference screws was slippage past the screw in all specimens. In the single cycle loading test, the mean yield load for the biodegradable pins was 400.2 (+/- 122.4) N, maximum load, 524.6 (+/- 136.6) N, with a mean stiffness of 155.2 (+/- 32.4) N/mm. The yield load at failure for the interference screw was 402.7 (+/- 143.9) N, maximum load 515.7 (+/- 168.5) N with a mean stiffness of 168 (+/- 42) N/mm.
Conclusions:
Fixation of a BPTB graft with 2 biodegradable 2.7-mm pins (Rigid Fix) leads to primary stability that is comparable to fixation with biodegradable interference screws.