The influence of asymmetric quadriceps loading on patellar tracking--an in vitro study.
BACKGROUND
In patients with anterior knee pain and patellar instability, a specific training of the quadriceps muscle - especially the vastus medialis - is often recommended, although the practicability is discussed controversially and the proof of a measurable clinical effect is difficult. Therefore, this in vitro study investigates the influence of asymmetric muscle loading on the motion of the human patella.


METHODS
Seven human knee specimens were tested in a specially developed knee simulator. During simulated weight-bearing knee flexion, the kinematics of tibia, femur and patella were measured using an ultrasound motion capture system. The quadriceps forces were controlled to achieve a constant ankle force over the whole flexion range which is assumed to represent almost physiological loading. Three different force distributions of the quadriceps were tested - a central, equally distributed load as well as mainly lateral and medial loads.


RESULTS
A significant influence of different quadriceps force distributions was found for patellar tilt around a proximodistal axis (up to 1.7°) and patellar rotation around an anteroposterior axis (up to 3.8°) with respect to the femur. Interestingly, the patellar mediolateral shift was influenced only marginally (<1.5mm).


CONCLUSIONS
Specific muscle training might help patients with patellofemoral pain and cartilage damage by a slight modification of the kinematics, but we could show that even highly asymmetric quadriceps loads only led to a small alteration of the mediolateral shift in case of a physiologic anatomy of the trochlear groove.
Biomechanics Research Laboratory, Department of Orthopaedic Surgery, University Hospital Tübingen, Hoppe-Seyler-Strasse 3, 72076 Tübingen, Germany. Andrea.Lorenz@med.uni-tuebingen.de
Andrea
A
Lorenz
Otto
O
Müller
Philipp
P
Kohler
Markus
M
Wünschel
Nikolaus
N
Wülker
Ulf G
UG
Leichtle
D005269:Femur / Q000502:physiology; D006801:Humans; D066298:In Vitro Techniques; D007593:Joint Instability / Q000503:physiopathology*; D007719:Knee Joint / Q000502:physiology*; D010329:Patella / Q000502:physiology*; D052097:Quadriceps Muscle / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology; D016474:Weight-Bearing / Q000502:physiology