Biomechanics of medial unicondylar in combination with patellofemoral knee arthroplasty.
OBJECTIVE
Modular bicompartmental knee arthroplasty (BKA) for treatment of medio-patellofemoral osteoarthritis (OA) should allow for close to normal kinematics in comparison with unicondylar knee arthroplasty (UKA) and the native knee. There is so far no data to support this.


METHODS
Six fresh frozen full leg cadaver specimens were prepared and mounted in a kinematic rig with six degrees of freedom for the knee joint. Three motion patterns were applied with the native knee and after sequential implantation of medial UKA and patellofemoral joint replacement (PFJ): passive flexion-extension, open chain extension, and squatting. During the loaded motions, quadriceps and hamstrings muscle forces were applied. Infrared cameras continuously recorded the trajectories of marker frames rigidly attached to femur, tibia and patella. Prior computer tomography allowed identification of coordinate frames of the bones. Strains in the collateral ligaments were calculated from insertion site distances.


RESULTS
UKA led to a less adducted and internally rotated tibia and a more strained medial collateral ligament (MCL). Addition of a patellofemoral replacement led to a more posterior position of both femoral condyles, a more dorsally located tibiofemoral contact point and higher MCL strain with squatting.


CONCLUSIONS
In comparison to UKA modular BKA leads to a more dorsal tibial contact point, a medial femoral condyle being located more posteriorly, and more MCL strain. Mainly the changes to the trochlear anatomy as introduced by PFJ may account for these differences.
Department of Orthopaedics and Rheumatology, University Hospital Marburg, Germany. Electronic address: heyse@med.uni-marburg.de.
Thomas J
TJ
Heyse
Department of Orthopaedics and Rheumatology, University Hospital Marburg, Germany.
Bilal F
BF
El-Zayat
Smith & Nephew, Belgium.
Ronny
R
De Corte
Department of Orthopaedics, Katholieke Universiteit Leuven, Belgium.
Lennart
L
Scheys
Klinikum Großhadern, Orthopädische Klinik und Poliklinik, Labor für Biomechanik und Experimentelle Orthopädie, München, Germany.
Yan
Y
Chevalier
Department of Orthopaedics and Rheumatology, University Hospital Marburg, Germany.
Susanne
S
Fuchs-Winkelmann
Mechanical Engineering Technology TC, KU Leuven, Leuven, Belgium.
Luc
L
Labey
D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D001696:Biomechanical Phenomena; D002102:Cadaver; D005269:Femur / Q000601:surgery*; D006801:Humans; D007719:Knee Joint / Q000503:physiopathology / Q000601:surgery*; D020370:Osteoarthritis, Knee / Q000601:surgery*; D010329:Patella / Q000601:surgery*; D016059:Range of Motion, Articular / Q000502:physiology*; D013977:Tibia / Q000601:surgery*
Bicompartmental knee arthroplasty; Kinematics; Ligament strain; Modular