Purpose This study aimed to quantify the effect of interference screw insertion on
MPFL graft tension when securing the femoral attachment after patellar fixation. It
was hypothesized that interference screw insertion significantly increases graft tension.
Methods Ten fresh frozen human cadaveric femurs were utilized to compare graft tension
at three different preloading conditions (2 N, 5 N, 10 N) using a tensile testing
machine (Admet Inc., Norwood, MA). Each preloading condition was analyzed with varying
graft sizes (5-8 mm), tunnel diameters (7-9 mm), and interference screw sizes (7-9
mm). Non-parametric statistical analysis was utilized to compare testing conditions
among each other. Results Graft tension significantly increased after interference
screw insertion by 100% to 552%, with 2 N preload showing the greatest increase (p
< 0.001). Grafts with a larger diameter (7-8 mm) had a significantly greater increase
in tension than smaller grafts (5-6 mm), regardless of preloading conditions (p <
0.001). Interference screw size had no influence on graft tension (n.s.). A graft-tunnel
interference (tunnel diameter-graft diameter) fit of 0 mm and 1 mm significantly increased
graft tension for each preloading condition when compared to a slightly looser fit
of >= 2 mm (p < 0.05). Conclusion Femoral interference screw insertion significantly
increases graft tension in MPFL reconstruction even in low preloading conditions,
with graft size and graft-tunnel interference fit having a considerably effect on
graft tension. Surgeons should be aware of the inadvertent increases in graft tension
even in low preloading conditions to mitigate the risk of graft overtensioning.
