Do monocortical distal locking screws impair mechanical properties in opening wedge high tibial osteotomy with bone graft?-a sawbone biomechanical study.

Medial opening wedge high tibial osteotomy (MOWHTO) has gained popularity for treating patients with medial knee osteoarthritis. Bicortical screw fixation is conventionally preferred, but its mechanical advantage over monocortical fixation remains elusive clinically, and may have additional symptomatic hardware risks. Our study aimed to quantify mechanical differences between monocortical and bicortical distal screws construct in MOWHTO. Twenty artificial composite tibiae were used, with 10 specimens per arm. The first arm underwent MOWHTO with bicortical screw fixation throughout; the second arm incorporated two monocortical distal locking screws. Mechanical properties of specimens were evaluated with static compressive load-bearing till failure and cyclic fatigue strength testing. For quasi-static compression testing, monocortical specimens had a median ultimate load of 2.60 [interquartile range (IQR)=0.12] kN [mean ± standard deviation (SD) =2.59±0.15 kN], comparable to the bicortical group [median (IQR) =2.64 (0.46) kN, mean ± SD =2.56±0.33 kN]. Cyclic fatigue strength testing also demonstrated comparable maximal loads tolerated by both monocortical [median (IQR) =1.28 (0.08) kN, mean ± SD =1.33±0.12 kN] and bicortical [median (IQR) =1.28 (0.00) kN, mean ± SD =1.28±0.06 kN] specimens, as well as median number of cycles attained before failure. Mann-Whitney-U tests showed no statistically significant difference for all measured outcomes between monocortical and bicortical groups (P>0.05). Our study found monocortical fixation of the two distal-most screws in MOWHTO mechanically non-inferior to bicortical fixation. This supports monocortical fixation as an alternative technique for distal screw placement in MOWHTO.