Q-angle influences tibiofemoral and patellofemoral kinematics

Numerous surgical procedures have been developed to correct patellar tracki ng and improve patellofemoral symptoms by altering the Q-angle (the angle b etween the quadriceps load vector and the patellar tendon load vector). The influence of the Q-angle on knee kinematics has vet to be specifically qua ntified, however. In vitro knee Simulation was performed to relate the Q-an gle to tibiofemoral and patellofemoral kinematics. Six cadaver knees were t ested by applying Simulated hamstrings, quadriceps and hip loads to induce knee flexion. The knees were tested with a normal alignment. after increasi ng the Q-angle and after decreasing the Q-angle. Increasing the Q-angle sig nificantly shifted the patella laterally from 20 degrees to 60 degrees of k nee flexion, tilted the patella medially from 20 degrees to 80 degrees of f lexion. and rotated the patella medially from 20 degrees to 50 degrees of f lexion. Decreasing the Q-angle significantly tilted the patella laterally a t 20 degrees and from 50 degrees to 80 degrees of flexion, rotated the tibi a externally from 30 degrees to 60 degrees of flexion. and increased the ti biofemoral varus orientation from 40 degrees to 90 degrees of flexion. The results show that an increase in the Q-angle could lead to lateral patellar dislocation or increased lateral patellofemoral contact pressures. A Q-ang le decrease may not shift the patella medially, but Could increase the medi al tibiofemoral contact pressure by increasing the varus orientation. (C) 2 001 Orthopaedic Research Society. Published by Elsevier Science Ltd. All ri ghts reserved.