Q‐angle influences tibiofemoral and patellofemoral kinematics

Abstract

Numerous surgical procedures have been developed to correct patellar tracking and improve patellofemoral symptoms by altering the Q‐angle (the angle between the quadriceps load vector and the patellar tendon load vector). The influence of the Q‐angle on knee kinematics has yet to be specifically quantified, however. In vitro knee simulation was performed to relate the Q‐angle to tibiofemoral and patellofemoral kinematics. Six cadaver knees were tested by applying simulated hamstrings, quadriceps and hip loads to induce knee flexion. The knees were tested with a normal alignment, after increasing the Q‐angle and after decreasing the Q‐angle. Increasing the Q‐angle significantly shifted the patella laterally from 20° to 60° of knee flexion, tilted the patella medially from 20° to 80° of flexion, and rotated the patella medially from 20° to 50° of flexion. Decreasing the Q‐angle significantly tilted the patella laterally at 20° and from 50° to 80° of flexion, rotated the tibia externally from 30° to 60° of flexion, and increased the tibiofemoral varus orientation from 40° to 90° 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‐angle decrease may not shift the patella medially, but could increase the medial tibiofemoral contact pressure by increasing the varus orientation. © 2001 Orthopaedic Research Society. Punlished by Elsevier Science Ltd. All rights reserved.