Abstract
Proper placement of the prosthetic components is believed to be an important factor
in successful total knee arthroplasty (TKA). Implant positioning errors have been
associated with postoperative pain, suboptimal function, and inferior patient-reported
outcome measures. The purpose of this study was to investigate the biomechanical effects
of femoral component malrotation on quadriceps function and normal ambulation. For
the investigation, publicly available data were used to create a validated forward-dynamic,
patient-specific computer model. The incorporated data included medical imaging, gait
laboratory measurements, knee loading information, electromyographic data, strength
testing, and information from the surgical procedure. The ideal femoral component
rotation was set to the surgical transepicondylar axis and walking simulations were
subsequently performed with increasing degrees of internal and external rotation of
the femoral component. The muscle force outputs were then recorded for the quadriceps
musculature as a whole, as well as for the individual constituent muscles. The quadriceps
work requirements during walking were then calculated for the different rotational
simulations. The highest forces generated by the quadriceps were seen during single-limb
stance phase as increasing degrees of femoral internal rotation produced proportional
increases in quadriceps force requirements. The individual muscles of the quadriceps
displayed different sensitivities to the rotational variations introduced into the
simulations with the vastus lateralis showing the greatest changes with rotational
positioning. Increasing degrees of internal rotation of femoral component were also
seen to demand increasing quadriceps work to support normal ambulation. In conclusion,
internal malrotation of the femoral component during TKA produces a mechanically disadvantaged
state which is characterized by greater required quadriceps forces (especially the
vastus lateralis) and greater quadriceps work to support normal ambulation.
Keywords knee arthroplasty - biomechanics - kinematics - quadriceps function - component rotation
