Background
Bone staples (BS) have been previously shown to be a viable modality for peripheral tendon graft fixation in knee surgery. However, soft tissue reactions might make implant removal necessary. Magnesium is a promising material for biodegradable orthopedic implants, with mechanical properties closely resembling human bone. The. purpose of the present study was to assess the primary stability of cortical fixation of tendon grafts in knee surgery comparing BS made of metal to a novel BS made of magnesium.
Methods
Primary stability of peripheral tendon graft fixation was assessed in a porcine model of MCL reconstruction (each n = 10), utilizing 8 mm wide Richards fixation staples (group Me1, Smith and Nephew, London, UK), 8 mm wide spiked ligament staples (group Me2, Arthrex, Naples, Florida), or magnesium staples (group Mg1, Medical Magnesium GmbH, Aachen, Germany). Primary stability was assessed using a uniaxial material testing machine (Instron, Norwood, MA). Cyclic loading at 50 N and 100 N was apllied for 500 cycles each, followed by a load to failure test. Statistical comparison was performed using the Kruskall-Wallis test.
Results
After 500 cycles at 50 N, elongation was 1.5 mm ±0.5 in the Me1 group, 1.9 mm ±0.5 in the Me2 group, and 1.8 mm ±0.4 in the Mg1 group. After 1000 cycles of loading (500 cycles at 50 and 500 cycles at 100 N), elongation was 3.6 mm ±0.9 in the Me1 group, 3.5 mm ±0.6 in the Me2 group, and 4.1 mm ±1.0 in the Mg1 group. No significant differences regarding elongation were found between the groups (p > 0.05).
Load to failure of the staples was 352 mm ±115 in the Me1 group, 373 mm ±77 in the Me2 group, and 449 mm ±92 in the Mg1 group. No significant differences regarding load to failure were found between the groups (p > 0.05). There was no significant difference observable between stiffness of the different fixation constructs.
Conclusion
BS made of magnesium display comparable biomechanical primary stability and may therefore be a possible alternative to classic metal BS.