Biomechanical evaluation of a medial-only fixation strategy for Takeuchi type 2 lateral hinge fractures in medial open wedge high tibial osteotomy.

BACKGROUND

Medial opening wedge high tibial osteotomy (MOWHTO) is a standard treatment for knee osteoarthritis. However, lateral hinge fractures occur in 19-25% of cases, with Type 2 fractures causing significant instability. While lateral plating is recommended, it requires an additional incision. This study investigated whether medial-only fixation using a 4.5 mm cortical screw inserted into the Tomofix plate's oval hole could provide sufficient stability for Type 2 hinge fractures.

METHODS

Twelve fresh pig knees underwent MOWHTO with a 6 mm opening. They were divided into two groups: Group I (intact lateral hinge) and Group F (induced Type 2 hinge fracture fixed with a medial 4.5 mm cortical screw in the Tomofix oval hole). Specimens were subjected to 2,000 cycles of axial loading (up to 800 N), representing early postoperative partial weight-bearing conditions. Displacement during cycling, and changes in the anterior gap (AG), posterior gap (PG), and posterior tibial slope (PTS) were measured.

RESULTS

Group F exhibited significantly greater displacement during cyclic loading compared to Group I (p = 0.0029), indicating significantly greater construct displacement. There were no statistically significant differences between the groups regarding changes in AG (p = 0.15), PG (p = 0.53), or PTS (p = 0.22).

CONCLUSIONS

Fixation with a 4.5 mm cortical screw in the Tomofix oval hole did not restore stability comparable to an intact lateral hinge for Type 2 lateral hinge fractures during an ex vivo porcine MOWHTO model.