Gap between the fragment and the tibia affects the stability of tibial tubercle osteotomy: A finite element study

Tibial tubercle osteotomy (TTO)is commonly performed in cases of complicated juxta-articular trauma or revision total knee arthroplasty. However, strategies for firmly fixing the resulting osteotomy bone fragment are not sufficiently understood. This study aims to investigate the effect of the location of the gap between the fragment and the tibia and with various fixed screw configurations on TTO stability, contact force on the fragment, and bone stress by using the finite element method. A TTO model with a 1-mm gap, either above or below the fragment, was developed. Furthermore, five screw configurations, including two parallel horizontal screws placed at 20- and 30-mm intervals, two parallel downward screws, two trapezoid screws, and two divergent screws, were used. A vertically upward 1600-N force was applied on the tibial tubercle to mimic a worst-case condition. Placing the fragment close to the superior cutting plane (above the gap)yielded greater stability and less stress on the bone than did placing it close to the inferior cutting plane. The superior cutting plane of the tibia generated the largest contact force on the superior plane of the fragment for static balance under loading. Additionally, among all screw configurations, the configuration involving two parallel downward screws resulted in the highest stability but also the greatest stress on the cortical bone. The fragment obtains a solid barrier and support from the tibia immediately after surgery to against the patellar tension force when the fragment is close to the superior cutting plane of the tibia.