Biomechanical analysis of tibial strength after harvesting unicortical tibial grafts of two different lengths

Background: It is not known whether the use of the proximal tibia as a source of strut graft compromises the strength of the tibia. Our hypothesis was that unicortical proximal tibial grafts in two different sizes would not significantly decrease the torsional strength of the tibia. Materials and Methods: Ten matched pairs of human cadaver tibiae were stripped of all soft tissues. One tibia in each pair was randomly assigned to receive an osteotomy of 2 x 1.5 cm or 6 x 1.5 cm placed 1 cm dorsal to the tibial crest with the proximal graft edge 6 cm from the tibial plateau. Specimens were loaded at 720 N and in external rotational torque at 5 degrees per second to failure. Axial force or torque at failure were analyzed via T-test (p ≤ 0.05). Results: There was no significant difference in torque to failure between specimens with an osteotomy of 1.5 x 2 cm versus the matched intact specimens. Torque to failure for specimens with an osteotomy 1.5 x 6 cm was lower than that of the matched intact specimens (28.69 Nm ± 4.2 Nm versus 60.95 Nm ± 9.49 Nm; p = 0.01) and lower than that found in the 2-cm osteotomy group (p = 0.04). Conclusion: Torque to failure was significantly decreased with the larger 6-cm graft as compared with the intact tibia and with the graft 1.5 x 2 cm. The smaller graft did not result in a significant change in torsional strength of the tibia. Clinical Relevance: Though this study cannot be extrapolated directly to the clinical setting, the longer graft tested in this study may raise concerns regarding the strength of the tibia after graft removal.