Biomechanical study of a Poly-L-Lactide (PLLA) sternal pin in sternal closure after cardiothoracic surgery

Background. Stainless steel wiring is currently the standard method of median sternotomy closure but it has been reported that sufficient stiffness is not obtained by the method in anterior-posterior and cranial-caudal directions. A bioabsorbable Poly-L-Lactide (PLLA) sternal pin has been developed as an additive material for sternal closure. We biomechanically examined the effectiveness of a PLLA sternal pin in the two directions by using the sternum of a juvenile pig. Methods. Juvenile pigs 14-17 kg weight were used. After the sternum was extirpated it was cut into two pieces at the midline. In a wire fixation group the pieces were fixed by two stainless wires. In a wire and intrasternal fixation group a hole was drilled into the bone marrow and a PLLA sternal pin for an infant was set into the hole. Then the both sides of the wired sternum were fixed tightly at the testing machine and the shear stress was forced into the one side. The shear stress was forced in anterior-posterior and cranial-caudal directions. Results. In an anterior-posterior direction, the stiffness was 13.84 ± 1.84 (N/mm) in a wire and intrasternal fixation group and 7.00 ± 2.71 (N/mm) in a wire fixation group (p = 0.0002). In a cranial-caudal direction it was 10.61 ± 4.88 (N/mm) and 4.38 ± 2.12 (N/mm), respectively (p = 0.03). Conclusions. The use of a PLLA sternal pin as an additive material to steel wiring was effective in preventing the displacement of the sternum in both directions. Our data showed that closure technique using a sternal pin would provide adequate fixation.